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Thread: Perseverance Mars Lander

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    I was looking for a meme that closely resembled how I thought about all this Mars stuff...




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    ...they won't be able to fire guns indoors? That would render the US sourced P.D. useless.
    However a bullet shot outside from a normal 0.22 calibre rifle aimed up at 30-45˚ angle could reach well over 100km range and easily hit a dome and pierce it or other random targets.
    Last edited by Uncle Fester; 24-02-21 at 10:38 PM.
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    very interesting what can happen as normal in our lives but on the moon or mars the differences become almost impossible what we know involves the atmosphere and gravity and its hard to get ones head around that when its not there , I wonder what effect it would have on the hidden things like emotions and ethics ???

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    Quote Originally Posted by hinekadon View Post
    very interesting what can happen as normal in our lives but on the moon or mars the differences become almost impossible what we know involves the atmosphere and gravity and its hard to get ones head around that when its not there , I wonder what effect it would have on the hidden things like emotions and ethics ???

    Everything will be about staying alive and surviving and that will only work when everybody works perfectly together.
    So the ethic is: You behave properly or we all die.
    This might eventually lead to a kind dictatorship but initially the colony is a team of flexible and highly skilled people who all know what to do without being commanded too much.
    The main emotion will be a feeling of success that we lived another day and maybe missing something from home like fresh air, water and good food.
    As everyday is an achievement, people should stay in a reasonably good mood.
    I know this feeling when I am 'roughing it' in the bush.
    I feel quite satisfied with achieving basic things that we normally take for granted.
    And some of these things are going to be an incredible achievement on Mars.


    Of course a lot will change dramatically when the colonists can start to procreate.
    Last edited by Uncle Fester; 25-02-21 at 09:34 PM.
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    Quote Originally Posted by Uncle Fester View Post
    Dry ice is quite soft, I can crumble it with my hands.
    Earth dry ice. Not Mars dry ice. There's just a slight difference there.

    BTW I think it is time the stop sending these awkward rovers and just send a bunch of Boston Dynamics "Spots".
    You forgot - power hungry. The advantage of a rover is power efficiency.
    But in general, spot offers no advantages for Mars exploration.

    [qoute]
    Unlike what Trash claims, it sure got there but the lander crashed due to an engine failure in the last seconds before touchdown.
    [/quote]
    I didn't say it was impossible or it had not happened. It's just harder to land there and not because it has anything to do with landing sites.
    It has everything to do with orbital mechanics and the energy required to just get to the landing phase.

    If you approach mars equatorially, you can take advantage of Mars's orbital velocity and subtract that from your spacecraft's velocity for a fuel saving on an orbital insertion. If you try to do that in a polar orbit you do not have that saving so even the orbital approach has to be different which is another fuel consideration.
    Of course you can go for a direct entry which is common, again it requires the right approach and burn. Once in the atmosphere everything is the same except for the approach speeds and angle but those are still able to be factored in. The cost is really about the fuel. Small lander it's not a lot of difference, but a big lander the cost goes up in multiples. At the end of the day they are already picking the low hanging fruit first for life anyway.

    Quote Originally Posted by lsemmens View Post
    There must be an atmosphere on the moon,
    There is an atmosphere but not a lot of it.
    I can't remember the composition. Hydrogen and Helium make up most of it. Pressure is about 2e-12 torr which is what I call a "damn hard vacuum"
    My pumps go down to 1e-7. Which "suck a balling ball through 10ft of garden hose" kind a vacuum.

    Quote Originally Posted by Uncle Fester View Post
    However a bullet shot outside from a normal 0.22 calibre rifle aimed up at 30-45˚ angle could reach well over 100km range and easily hit a dome and pierce it or other random targets.
    I'm kind of surprised it's not further than that, but I suppose it's just a .22. Have you crunched some numbers to see if it is correct?

    I can't help myself, I have to crunch the numbers for fun anyway.
    .22 is about 500m/s and Mars gravity about 3.7m/s/s. which means it's 135 to apogee if shot straight up.
    s=ut+1/2at^2 == 500 - (0.5 * 3.7 * 135^2) = ~34km altitude.

    For 45 degrees we use 354m/s. which gives us 95.5 seconds to apogee at 17km and 191 seconds flight time.
    We'll ignore air friction. 191s x 354m = ~68km.

    Turns out it's less. But that is an average .22 velocity I just picked.
    Of course we can go magnum, hornet or my personal fave, wildcat

    Now did somebody say spot?
    Last edited by trash; 25-02-21 at 09:31 PM.
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    Quote Originally Posted by trash View Post

    You forgot - power hungry. The advantage of a rover is power efficiency.
    But in general, spot offers no advantages for Mars exploration.
    The rover only seems efficient because it is slow but it is also very heavy, so I will question the efficiency to work load ratio here.

    Spot's base weighs 32.5kg (on Earth), lets say 50kg with arm and gun (to fire holes in the ice )
    20 spots could do a hell of a lot more than a single rover and without having to be extremely careful before you consider even moving the rover a single meter. Pretty sure Spot can crawl out of small but unexpected deep craters that would bog or tip over the rover and losing a few spots won't really matter.

    I did say we need to drop a power pack to charge the Spots, better in nuclear form especially for polar expeditions.
    Spot (or two Spots) could also carry expansion battery packs with foldable solar panels to distant locations to increase the accessible range.
    Essentially they would become the first inhabitants and workers.

    Oh did I mention cost: 2.2Billion for the rover. Spot costs $74K, probably cheaper by the dozen. Plenty left for batteries, transceivers, mining tools, test equipment and drones.


    EDIT: just when I was thinking about contacting JPL and Boston dynamics I did a duckduckgo search and :



    I am always too late

    Happened last time when I contacted them with a suggestion to install wipers on the solar panels of the Opportunity rover, kind of like those fine brushes you use to clean vinyl records that self clean themselves when they pass over an edge.
    I was told the idea had merit but I had contacted them TOO LATE to allow for any further additions.
    Opportunity DID fail likely due to dust eventually covering the panels but it lasted way longer than expected as the wind managed to keep them clean which was unexpected at that time.
    Maybe with my wipers it could still be active today.
    Last edited by Uncle Fester; 25-02-21 at 10:53 PM.
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    interesting thread very good participants intelligent conversation well done , I wish all threads were this good

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    Quote Originally Posted by hinekadon View Post
    interesting thread very good participants intelligent conversation well done , I wish all threads were this good
    Hey! You forgot about me! I'm not that intelligent!
    I'm out of my mind, but feel free to leave a message...

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    Thumbs up generally

    I was generalising still a quality thread in my opinion

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    Quote Originally Posted by hinekadon View Post
    I was generalising still a quality thread in my opinion
    I dunno...we started talking about Mars Exploration and ended up talking about guns......

    Then again, Perseverance IS American...
    The fact that there's a highway to hell and a stairway to heaven says a lot about the anticipated traffic flow.

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    Hang onto your hat Hink, we're going to keep you amused for a while yet.

    Quote Originally Posted by Uncle Fester View Post
    The rover only seems efficient because it is slow
    No, it's efficient because it has wheels. Wheels are way more efficient than legs.
    Consider the energy used to walk compared to riding a bike which carries the extra overhead of the bike's weight.

    but it is also very heavy, so I will question the efficiency to work load ratio here.
    Did I say wheels? Overcoming the friction of the axel for a truck takes a lot less energy than moving a leg capable of supporting the same weight.
    Hehe... you're pushing shit uphill with a pointy stick, if you put wheels on it..... it ain't going to look as weird as legs either.

    20 spots could do a hell of a lot more than a single rover and without having to be extremely careful before you consider even moving the rover a single meter. Pretty sure Spot can crawl out of small but unexpected deep craters that would bog or tip over the rover and losing a few spots won't really matter.

    I did say we need to drop a power pack to charge the Spots, better in nuclear form especially for polar expeditions.
    Spot (or two Spots) could also carry expansion battery packs with foldable solar panels to distant locations to increase the accessible range.
    Essentially they would become the first inhabitants and workers.
    pull that spot over to the side of the Martian autobahn !

    20 spots... Lets start at the bottom.
    Perseverance produces ~110W/hr it uses about half of that

    Spot uses 400W/hr four times what Perseverance produces. x 20 = 8kW/hr or 192kW/day consumption.
    2000 times as much power.
    Where do you think you're going to get that from? The sun? Lets do those numbers.
    So a day on Mars is about the same as Earth, so you can assume that because there is no cloudy weather on Mars you'll get 5 hours of useful sunlight.
    But the sun is 1/4 the brightness, so that means four times as many panels.

    Spots have a run time of 90 minutes, and two hours to charge which means in 6 hours of useful sunlight you get two runs of 90 minutes.
    600Whr capacity charge 2 hours = 300W per spot x 20 spots = 6000W of solar. x4 to compensate for Mars sunlight means you need 24kW of solar panels on the ground.
    You know how those spots weigh 32kg each, their support panels alone weigh a tonne. Did you forget the cost of the fuel to get them into space and then onto the surface, then unpack them all and ..... I think you just engineered yourself into a corner.

    Space is not easy. It's hard. Spot is deigned to work on Earth. In space he's a dead dog.
    The first Martian dust storm and you have a lot of dead hardware not withstanding nasty wear and tear and no servicing. Spot is also not space hardend.

    So lets to the mythbusters thing and see if we can't engineer the fuuk out of spot.
    We're going to probably just go with a fission reactor. The three that jump to mind are RORsat, Topaz and SNAP. You might like to consider their electric power supply, their weight and the cost and factor that up and then work out how much to put it on Mars. Suddenly that "little" fission reactor is not so little.
    And again you have to scale it for the task. And still, the range is limited to the proximity of the supply. 4kph with 45min range is 3km radius.
    You just cannot plunk these things down like road flaps on Mars, even the small ones.

    Oh did I mention cost: 2.2Billion for the rover. Spot costs $74K, probably cheaper by the dozen. Plenty left for batteries, transceivers, mining tools, test equipment and drones.
    Lets say a nice round figure like $2.7 Billion USD. And it's srvice life design is 2 years.
    I'm going to be lazy here because I already know the planetary society did a summary of this large spend.


    EDIT: just when I was thinking about contacting JPL and Boston dynamics I did a duckduckgo search and :
    Yes, that is a much more suitable task for them. What do you think it will cost to build a Mars Spot?
    The speed of travel is an advantage and a disadvantage. That on the fly processing power comes at a cost.
    The tradeoff will be between idle running power and continually moving in a race against time.

    Exploring caves on Mars will be not unlike snorkeling on Earth. How long can you hold your breath and swim under water out and back coving as much distance as possible. You're going to want to see Boston Dynamics do this on earth first. Start from a location outside of the cave, charge, go in and come out , recharge and go back in. You might start to see this one dimension form of exploration is rather limited. You'd think a quad copter can do that job cheaper. $74k for spot and $300 buck for a drone. Oh hang on, then why do you think it cost $85 million for a Mars RC Helicopter?
    Lets face it, you know as well as I do that $74k is gunna scale

    At the end of the day you engineer the best solution possible for the task to be performed with constraints on cost, size and weight. And in space there are no second chances. Every action is you last chance. Spots will surely find an application, but exploring Mars, nope it's just not their gig.


    Maybe with my wipers it could still be active today.
    There are a few issues there. The first is you assume they will work. That's extra weight, power and point of failure.
    You might imagine if a small rover is buried, wipers are not going to help. On a big rover, big panels you need big wipers.
    But this is a game you can play at home. Buy yourself a solar cell and build a cleaning system powered by the solar cell so it can clean itself when you throw fine dirt on it. Amusing how impractical this is on Earth, now imagine those scaled costs for Mars. Limit your power by four and keep the weight to a minimum.
    It might just be simpler to fold them up and hibernate.

    Solar panels are cheap, simple, a little heavy, limited by sunlight and a bit clumsy in terms of spacecraft power supplies.
    The bottom line is that wipers are probably just not practical.

    As Rovers get bigger, so does their demand for power. RTG's are smaller, but low power with limited lifespans.
    They behave a bit like pocket sized 24 hour solar panels. With batteries you bank the power budget to a point.

    Fission reactors are heavier but offer more power but also need more shielding for their operation and are limited by their fuel.
    Each has advantages and disadvantages. The Juno mission is a good example of where they weighed up these options and went with Solar for one reason more than others. There wasn't enough fuel available.
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    But, but, but?
    Traditional Mars rovers are limited mostly to flat surfaces, but many scientifically interesting Martian regions are only reachable by crossing very rough terrain or descending below ground. Walking robot "dogs" are well-suited for such challenges — even if they fall down, they can get back up again.
    "Toppling does not mean mission failure," the scientists said during the presentation. "Using recovery algorithms, the robot can self-right from a multitude of falls."
    A Mars Dog would also be roughly 12 times lighter than current rovers and would be capable of traveling much faster, reaching normal walking speeds of 3 mph (5 km/h) during terrestrial tests. To put that into perspective, the Curiosity rover rolls along the Martian surface at about 0.09 mph (0.14 km/h), the researchers reported.
    From Festers link =
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    Trash, I think you need to learn to think a bit outside of the box.

    BTW the active time for the Opportunity rover was expected to last only 90 days:
    So anything that could significantly increase that time using something as simple as wipers, which could be done with very light weight materials would have been worth it.
    It came as a surprise for all that the Mars winds did the job instead.



    Some of the major issues I have in your argumentation for a rover is the lack of speed and limited coverage area, wheels are only good on a road or relatively even surfaces.
    One Spot can cover more in a single hour than the rover in a day, possibly a lot more.
    Then you are also fully ignoring that gravity on Mars is roughly 1/3 of ours which significantly reduces the power Spot consumes there(it weighs less). I won't say 3 time less because it still has to deal with the same inertia as on Earth but 50% less would be realistic.
    I have no info about Perseverance but Curiosity moves 1.68km in 12 hours. Spot moves 10km in 2 hours and still has 1hour reserve.
    Hence they ARE significantly more efficient.

    So that 90 minutes would look more like 3 hours on one charge and then let it charge over the strongest sun period for the rest of the day, means a smaller panel. Foldable Solar panels don't weigh much. As mentioned earlier Spot could carry it's panel to a more distant location and work from there.
    Spot can clean them or fold them up before the dust storm.
    Spot can crawl itself out of a pile of dust after or while there is a dust storm.
    Already too much dead (rover) hardware lying around on Mars.

    Modifying Spot for space is not going to cost anything near 2.7 billion and after that it is a production item for many future missions and they are obviously not going to be sent individually in large supportive FedEX boxes in styrofoam but all crouched and strapped down to a platform with a self releasing mechanism "Ready To Go", that is not a great engineering feat.
    Anyhow despite your almost unfathomable pessimism they are on it.

    You really ARE scared of Spot, aren't you
    Last edited by Uncle Fester; 02-03-21 at 10:22 PM.
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    Just want to clarify again that it is rather pointless to search for traces of life on any open surface on Mars or even a meter deep in the ground due to perchlorates found wide spread which has been demonstrated to have been created with the help of strong UV radiation due to lack of an Ozon layer on Mars.

    Caves are protected from UV light and likely may contain very little perchlorate or none at all and life would have survived much longer inside them, maybe exist even in some microbial form today. Water could also to be trapped in some subterranean form inside as well.

    Caves also provide very useful shelter for future manned missions and colonisation.

    And then there are these

    Bring on the Spots to sniff out those caves and tubes ASAP !
    Last edited by Uncle Fester; 02-03-21 at 08:17 PM.
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    Bluddy Hell Trash! You are letting facts get in the way of good story!!!!!
    I'm out of my mind, but feel free to leave a message...

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    Quote Originally Posted by lsemmens View Post
    Bluddy Hell Trash! You are letting facts get in the way of good story!!!!!

    Facts that ignore other facts will always be fiction until reality judges.
    Last edited by Uncle Fester; 02-03-21 at 10:19 PM.
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    Quote Originally Posted by Uncle Fester View Post
    Trash, I think you need to learn to think a bit outside of the box.
    The problem with thinking outside of the box is you tend to ignore what's inside the box and why.
    What you're saying is "Take a risk". Ok.. it also often means to try something different.
    Well they certainly did that with the skycrane. I wouldn't have thought of that.

    Thinking outside the box. Nope. RTG is in the box. It cost more but has less dust issues.

    Some of the major issues I have in your argumentation for a rover is the lack of speed
    So impatient. What's your rush, not a lot changes on Mars in a human lifespan.

    and limited coverage area,
    Everything is limited. But lets compare. Spirit traveled about 8km on Mars, Curiosity about 20km and Oportunity about 45km.

    Spot (the earth version can operate for 90 minutes at 4kph. That's 6km out and dead.
    Or 3km radius if you go out and return to recharge.

    wheels are only good on a road or relatively even surfaces.
    That's a good generalisation but as you might have noticed, Mars is relatively rough depending on the scale you look at it and it doesn't consider the size of the wheels. Of course you might also be overestimating the ability of legs. We tend to consider that kind of engineering with respect to steps.
    Imagine a planet of steps, what does a good robot use to get around?

    One Spot can cover more in a single hour than the rover in a day, possibly a lot more.
    That is definitely true. But we know you're well aware of that tradeoff with speed. You can deal from the bottom of the deck, it's not like we don't know you're doing it If speed is the advantage, then a probe is designed for speed. If speed is not a critical consideration then how fast you finish a game of golf does not improve your score. Though personally the sooner golfers got the hell off my landing runways the better.

    Then you are also fully ignoring that gravity on Mars is roughly 1/3 of ours which significantly reduces the power Spot consumes there.
    Hence they ARE more efficient.
    You know I can tell when you just make shit up. I mean come on... have you not read Tytower's posts and seen my use of my modified scientology E-meter. (their pathetic version of a lie detector) I call mine the B-meter.

    Lets start with the most basic of physics. F=ma. To accelerate a mass on Earth requires the same energy on Mars. You'll notice Gravity has nothing to do with it.
    And if you think the friction is different.... again. The dirt and bearing also have the same friction as on Earth as Mars.

    You legged robot might use less force to lift itself in lower gravity, but that overhead still exists while a wheeled robot does not have to lift itself to move.
    That overhead lessens as the robots climb and you don't get a free lunch on the decent. Wheels get that

    You might consider backing this argument up a bit and asking why the Earth bound spot doesn't use wheels?
    Well the main reason is it looks cool. It also opens up consideration for legged robot applications we might not have considered.
    So while legged robots might not be practical on Mars, what we learn from them on Earth can then be applied to the best applications in space either in part or whole.


    So that 90 minutes would look more like 3 hours on one charge
    Your premise on efficiency was wrong. Your robot died because you miscalculated something. At least you made that mistake on Earth and not on Mars

    means a smaller panel.
    Nope. You have the rover in front of the dog. Your charging time doesn't change even if you did have a more efficient robot.
    Who do you think you're fooling here? You get more range for the same power or the same range for less power. Not BOTH.
    Pick one, do you want longer range or a smaller battery?

    Foldable Solar panels don't weigh much. As mentioned earlier Spot could carry it's panel to a more distant location and work from there.
    Riiight. So now you're losing that speed advantage (if it actually was one).
    But it is an interesting thought experiment.
    If you have a short range robot that is detatched from it's prime clumsy power source but also capable of moving it.
    So thinking about it, if it is capable of moving it's power source, what is the advantage of disconnecting from it?
    Taking it with you is an advantage because you don't have to go back to recover it. Reconnaissance might be a reason, I'm not sure if it is an advantage in it's own right. Access to a restricted space not possible with the power supply would be an advantage.

    Spot can clean them or fold them up before the dust storm.
    That seems feasible. How do you propose it cleans them? On earth we use Meth addicts at traffic lights to clean sheets of glass. The key ingredient in that equation is not Meth, Coin or even a Squidgee. It's water. Without water Meth addicts can become very unpredictable.

    Spot can crawl itself out of a pile of dust after or while there is a dust storm.
    Oh, the B-meter started moving again. That is an assumption and a shortcut to failure.
    Have you seen something that is not a robot climb out of an engulfing material?
    Do you think there might be a better strategy than wasting limited power?


    Already too much dead (rover) hardware lying around on Mars.
    What are you implying here? That failure is unacceptable? That equipment should last forever? That sending robots to Mas is bad?

    Modifying Spot for space is not going to cost anything near 2.7 billion
    That is true, because that is for the entire mission.
    That also includes what my customers would call "stuff". You know, cheap stuff like spectrometers, cameras, space grade radiation hardened components and a couple of jaycar 555 timers.

    Anyhow despite your almost unfathomable pessimism they are on it.
    You might be mistaking my high engineering standards for a high bar you think it is impossible to get over.
    It's better to be on Earth making mistakes and wishing your robot was on Mars than having your robot on Mars wishing you'd made the mistakes on Earth.
    It's not pessimism, it's just rationalism of reality. Sometimes you can't just do whatever you like and instead have to chose from the best set of limited set of options. And doing something cool does not mean it is the best thing to do. Though sometimes, you might send a Tesla to Mars rather than a cheap block of concerete because it does the same job and is cool.

    You really ARE scared of Spot, aren't you
    Oh fvck yeah... those things are killing machines. They need to be removed from this planet and put on another of their own where they can fight it out for my amusement with no hope of building their own spacecraft and looking for new things to kill.
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    Quote Originally Posted by trash View Post
    You know I can tell when you just make shit up. I mean come on... have you not read Tytower's posts and seen my use of my modified scientology E-meter. (their pathetic version of a lie detector) I call mine the B-meter.
    Oh dear, you always like to show off with your BS-meter but now you just fell deep down a rabbit hole lava tube with your following comments:

    Lets start with the most basic of physics. F=ma.
    OK, 7th grade Physics, you got that right.

    To accelerate a mass on Earth requires the same energy on Mars. You'll notice Gravity has nothing to do with it.
    Incorrect!

    Gravity in this case has a hell of a lot to do with it.
    We have both established that Spot is not a little wagon with wheels on a smooth flat track that is typically used for high school year 7 experiments to demonstrate F = ma, which in that case merely deals with inertia and friction. Then little Fester did something naughty to annoy his teacher and tilted the tracks upwards.

    To keep Spot's body above the ground it's legs need to constantly counteract the acceleration of 9.81ms^-2 on Earth, even if it looks like it is moving perfectly lateral.
    Even when it is not moving, energy is required to maintain that height.
    It may be possible to lock up the legs when it is stationary using worm gears in the DOFs but that would make it slow and far less agile than you see it
    in operation, so I doubt they use worm gears.
    Another possibility is closing valves in a hydraulic system but AFAIK Spot uses electrical servo motors for the DOFs.

    However the mechanics of a leg or robotic arm here is a lot different than lets say hovering a drone that weighs 32kg where 400W would be way to weak.
    Regenerative force and friction from the geared down motors help to counteract the force of gravity and I assume that Spot is so sophisticated that it can use this kind of regenerative braking in the DOFs while it is walking to charge the battery in short bursts with each step where the mechanics allow for that.

    But remove power from the all the DOF servos and Spot will immediately go limp and collapse because of gravity.

    On Mars Spot has to counter act only 3.72ms^-2. That makes a huge difference for this kind of movement.
    While it is climbing up on rocks the power consumption will only marginally increase while it also has to deal with the inertia of raising it's body but only at a relatively low speed.

    Neil Armstrong's steps on the Moon where not just ' a giant leap for mankind' he could literally do giant leaps as he only weighed 1/6 of his weight on Earth.
    Humans are slightly better designed than Spot as they can keep their legs fully stretched while they are standing and only a small amount of energy is then required to keep balance.
    Spot's legs are always flexed ready to prance. Despite this energy hungry state I assume that is the preferred condition for Spot's abilities, but maybe they might modify that for the space version.
    I would think keeping stretched out legs would be better than having the Spots crouch in the dust every time they go idle for shorter periods of time.

    And if you think the friction is different.... again. The dirt and bearing also have the same friction as on Earth as Mars.
    Incorrect!

    Bearing:
    A vehicle weighs roughly 3 time less on Mars than on Earth
    Therefore the load on the bearings of that vehicle on Mars is roughly 3 times less. This applies of course to the Rover just as much as to Spot's DOFs.
    Everybody knows if you put too much load on a bearing it can get so hot that it will seize up.
    It might come as a surprise to you but the balls in a ball bearing deform under load. This deformation energy is transferred to heat.

    Dirt:
    When a wheel sinks into loose dirt it does so because of it's weight. The higher the weight the deeper it's wheel or foot will sink in and therefore
    the more dirt it has to displace while it moves and that will require a lot more energy.


    Conclusion:
    Spot can indeed run with less power on Mars, possibly even built lighter as it can get away with smaller powered DOFs and achieve a better range on a single charge rather than two charges each day, allowing it to spend more time each day to replace that single charge with a smaller panel.
    Last edited by Uncle Fester; 03-03-21 at 05:44 PM.
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    Quote Originally Posted by Uncle Fester View Post
    Gravity in this case has a hell of a lot to do with it.
    Gravity has nothing to do with mass.
    Lets keep it simple for you.
    If you have a 100kg train on rails and apply 100N to it you will accelerate it at 1m^-2.
    If you take the same setup to Mars it's still 100kg mass and applying 100N to it accelerates it at .... 1m^-2.
    Gravity has NOTHING to do with it.


    We have both established that Spot is not a little wagon with wheels on a smooth flat track that is typically used for high school year 7 experiments to demonstrate F = ma, which in that case merely deals with inertia and friction. Then little Fester did something naughty to annoy his teacher and tilted the tracks upwards.
    The reason for the simple experiment is to demonstrate this exact point. To give you a basic understanding which I think the young Fester missed out on when he put his fingers on the scale so to speak.

    So lets start with like for like. If you're going to compare apples and oranges, then you need to understand the advantages and disadvantages of both by understanding the most basic of physics.

    So lets start with you tilting the tack up.
    If we do this on both Earth and Mars, NOW gravity as a vector comes into consideration.
    So as you climb a hill it requires more acceleration on Earth to climb and less on Mars.
    But remember Fester, you have your fingers on the scale. Now you'll take them off.
    Now the cart/train is rolling down the other side of the hill. That acceleration is now not subtractive, but additive.
    So as you climb over a hill, it costs more energy on Earth and less on Mars. But you get more energy on the downhill.
    So unless Mars has some kind of weird spatial asymmetry where it has more up than down, you have a net sum gain of zero.

    If you climb a hill on Mars, lets say 100m with 100kg then on Earth is is 100,000Nm and on Mars it is about 30,000Nm.
    It doesn't matter if you robot has wheels or legs. It's the same physics on both planets.

    Even when it is not moving, energy is required to maintain that height.
    I have been working with this assumption because brakes usually don't use any energy. You can apply them and release them expending energy but that is trivial and I don't think we need to consider that in the energy budget.

    But remove power from the all the DOF servos and Spot will immediately go limp and collapse because of gravity.
    Again, I don't see that as a disadvantage and spot can sit or stand with no energy expendature as far as I'm concerned, you'd engineer those advantages.


    On Mars Spot has to counter act only 3.72ms^-2. That makes a huge difference for this kind of movement.
    While it is climbing up on rocks the power consumption will only marginally increase while it also has to deal with the inertia of raising it's body but only at a relatively low speed.
    That is correct. There is less energy required to climb. (you're notice that is the same for rover).

    Neil Armstrong's steps on the Moon where not just ' a giant leap for mankind' he could literally do giant leaps as he only weighed 1/6 of his weight on Earth.
    Not sure if you know but they had a lot of trouble walking. It was more a function of the spacesuit than gravity. They had to learn how to move and they found that skipping was the easiest way to get around. But giant leaps is a bit of an overstatement. If you learned anything from the physics lesson above (the one you didn't understand at school) there is some physics here to pay attention to. Lets say Neil Armstrong weighed 80kg on Earth. The same as his spacesuit.
    Total 160kg. On the moon with his suit on he weighed 28kg. So easy for him to jump. But if he's he's moving he still has 160kg of mass to propel and stop.
    So moving at speed on the moon can be dangerous. The same with the ISS when they are moving heavy loads around. They weigh zero but they still have a big mass and big momentum. That's why they move things very slowly. It's easy to get moving but hard to stop if you are not prepared to counter that momentum.

    Just as a side note, if your inside on the moon with no spacesuit and you could jump unobstructed. Jump as high was you can you're going to hit the ground with the same impact as you would on Earth for the same effort. Slightly more dangerous, because of your considerably longer time of flight you risk losing your attitude and hitting the ground with something other than the souls of your feet. It would be like (on earth) spinning around and making yourself dizzy and then jumping as high as you can. There's a good chance you're going to hurt when you hit the ground.


    OK, so lets just assume for this sentence that wheels are the ducks nuts. They are the best tool for the job. Is there a role that legs have an advantage.
    Yes they do and it is for climbing. When spot is moving it expends energy lifting each of it's legs. So this is added to the energy required to move forward.
    Since gravity is less on Mars lifting each leg uses less energy than it does on Earth for spot to walk. It doesn't change the energy used to move forward.
    So a slight disadvantage. But when it comes to climbing there is a clear advantage because that energy is less of a loss because the vector of motion total is up (with less down) so now there is almost parity with wheels. And the mechanical advantage that legs can climb steeps easier than proportional wheels.

    Now if we consider the down slope. A leg only has to be lifted a short distance and lowered a longer distance. If we assume it picks up an energy gain or rather a negative energy loss then that should even out. But as we say in physics, there is no free lunch. Now spot has to do something about that mass coming down the slope. On Rover it is brakes or regenerative braking or reverse acceleration. On spot you have pretty much the same options. On Earth you'd just roll in neutral and run out the kinetic energy as momentum. Spot can't really do that. It's the equivalent of a fat person running down a hill and getting to the bottom, they can't stop running, their momentum is carried. If they stopped moving their legs they'd face plant. Spot could just do that to stop and it wouldn't hurt.
    I'm just not sure if it makes sense for a robot to run out that inertia too.
    Reality is of course that rolling unbraked down a hill is not something a Mars rover would ever do and it would be just as silly to let a Mars Spot do it.

    If there was to be a Mars, Moon or even Venus spot, you'd find that slow walking or stepping would be the mode of operation. Running. There's just no practical application for that speed.

    Therefore the load on the bearings of that vehicle on Mars is roughly 3 times less. This applies of course to the Rover just as much as to Spot's DOFs.
    Everybody knows if you put too much load on a bearing it can get so hot that it will seize up.
    It might come as a surprise to you but the balls in a ball bearing deform under load. This deformation energy is transferred to heat.
    You might not have noticed, but bearings work the same at 0g 0.5g 1g and 2g.
    Fans don't spin faster on the ISS because their bearings have less friction because of zero gravity.
    You're confusing two different things and it also explains why you think gravity has an effect on friction. It doesn't.

    Why your confused is because you do not understand the aspects of friction and a coefficient of friction.
    Bearings by their very nature has a very low coefficient of friction. So low that you're arguing about what engineers call "A bees dick difference".
    So small it is negligible.

    So lets put your finger back on the scale and this time I'm going to put my finger on the scale and push that bastard down hard.
    Lets use our train on rails. But this time with no wheels. Now gravity has a big influence on the coefficient and as a result the friction between the train and the rails has a different curve on Mars than it does on Earth. In this case gravity has a big enough influence.

    When a wheel sinks into loose dirt it does so because of it's weight. The higher the weight the deeper it's wheel or foot will sink in and therefore
    the more dirt it has to displace while it moves and that will require a lot more energy.
    You're trying have it both ways here fester. So in terms of wheels, you're now saying their more efficient on Mars because of the lower gravity?
    You're working my side of the street their buddy. But you might not have noticed, Rover does not propel itself forward by throwing dirt out the back nor by displacing it on the ground. Now you might not have noticed this until now but us engineers are pretty magical people. When it comes to wheels we have made them in a few different sizes and it's rather interesting how different size wheels behave on different hardness surfaces. We sometimes even choose a tyre that is appropriate for a specific task.
    And what's really interesting is that when it comes to building spot, we can do the same thing for legs. We can make Spot a dachshund or a greyhound to suit the task. And just like Rover, Spot's feet can sink into a surface depending on its hardness. Is it hard to walk on wet beach sand or dry beach sand? Is it hard to ride I bicycle on hard beach sand or soft beach sand?
    Same same but different.
    And engineers have a solution for traveling over dry beach sand. They make the contact surface area bigger. They give spot big feet and they give rover fat tyres.

    Spot can indeed run with less power on Mars
    Oh I'm going to have to bring you back down to Earth on this one.
    SPOT can't use less power on Earth than Rover, what makes you think it's going to use less on Mars?
    1/3rd Gravity. This is very easy to simulate. Compare a 100kg spot and 100kg rover on Earth and then a 30kg spot and a 30kg rover on Earth.
    There's your answer.


    So it looks like Spot is barking up the wrong tree here. Really, wheels or legs makes no difference to me. We use what is best.
    We could just put six legs on Rover and make him spider rover (or ant rover - spiders have 8 legs). So why not do that?
    Well really it is just more simple engineering. Legs have more points of failure in that case. more motors, more moving parts and not advantage for the risk.
    That is the main reason why legs aren't used.

    The problem spot has is not that it has legs. It's the power consumption period. There is no using the lighter gravity of Mars as an excuse for BS engineering.
    In order to get Spot to Mars you have to prove it's going to work and at the moment Spot's first hurdle is it's own power consumption.
    Really what would demonstrate spot is up to the task of Mars is to have it walk 10km in the Australian outback, but do it using only solar power from a discharged start. Then repeat the exercise with a quarter the solar energy (or less). When that happens, spot has a chance on Mars.
    Last edited by trash; 05-03-21 at 11:50 PM.
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    Trash, we are mostly talking past each other.

    You stay stubbornly fixated on mass and inertia.
    I am always referring to WEIGHT and gravity because that is what it is here all about, so don't go on about the friction of bearings on a friggen space station but yeah they will probably never wear out unless the space station is rotating creating artificial gravity and constant load on bearings located towards the outer perimeter.

    I never said Spot is more efficient than a rover in terms of the way it moves. Of course wheels are more efficient and I can't make that more clear than I wrote in my last post.
    Spot is more efficient in terms of speed and therefore the distance it can cover on a day to day basis also considering the type of terrain it can cover and that is what it is on Mars all about. You are not going to find anything interesting in the flat desert.

    Also when it comes to the comparisons it is incorrect to cheat.

    Of course I can implement features to REDUCE the depth wheels or feet sink into sand, we all know that, but that does not distract from the fact that gravity still plays a vital role here that is different and more beneficial on Mars than on Earth.
    Same goes for Neil Armstrong's suit. Imagine how hard it was for him to walk with that heavy weight on EARTH !

    As for jumping upwards on the moon, you can add a forwards vector in that jump that will propel you significantly further than it would on Earth as you stay up longer, same applies for running. Spot can't run, only skips ropes for now but you might not have seen Cheetah, how far do you think these leaps will get him on Mars or the Moon, he won't be faster but can save a lot of energy:



    How about having these nine fellas chasing after you with some sharp toothed grabber attachments

    Last edited by Uncle Fester; 06-03-21 at 04:32 PM.
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