Telescope controller circuit

[SimonFB]

Hi, I just signed up to see if anyone can help me with a circuit to control a couple of stepper motor to motorize my dobsonian telescope.
I know just enough about electronics to be a danger to myself, so designing my own circuit is not going to end well.

There are many projects out there, but none quite what I want. I'm looking to build something like the one in this YouTube video but with a little extra control.

Here is what little I do know.
I expect to use 2x Nema 17 stepper motors (for 3D printers) for the movement, they seem to be the most prevelent in other projects, and the whole telescope arrangement weighs about 20kg, apparently they can cope with that.
It does not need to move very fast - 360 degress of movement in 24 hours when tracking, but faster when finding a target.
Two directional movement - Azimuth for side to side and Altitude for elevation.

The controls I'd like to have are:
Three way rokkor switch for modes auto, manual, and off.
Rotary dials for auto mode that can be used to pre-set the desired speed, which is then applied when auto mode is selected on the rokkor switch.
Joystick or sticks for manual mode that can be used for moving on demand (as in the youtube video) at varying speed, each axis independent of the other.

I'd like to keep it as simple as possible (obviously) and I don't know what is required to control stepper motors, is it just voltage or does it require digital signals from a computing device - many projects seem to use Arduino or Pi units?






Thanks for any help or ideas
Simon.

[Reschs]

There was a similar project in Silicon Chip Magazine in last few years.

[wotnot]

I'd like to keep it as simple as possible (obviously) and I don't know what is required to control stepper motors, is it just voltage or does it require digital signals from a computing device - many projects seem to use Arduino or Pi units?

Typically one uses a H-bridge to control stepper motors --

Your biggest trouble would be the reduction gearing -- each 'step' will move the scope 'x' degrees ; you want as fine movement control as you can get...ie; 1 'step' = 100th of a degree ; any of a myriad of arduino like projects out there will do for control ; getting the gear reduction right will be your biggest challenge

[hinekadon]

there are a multitude or dish controllers that are easy to build and reliable ?

[SimonFB]

Typically one uses a H-bridge to control stepper motors --

Your biggest trouble would be the reduction gearing -- each 'step' will move the scope 'x' degrees ; you want as fine movement control as you can get...ie; 1 'step' = 100th of a degree ; any of a myriad of arduino like projects out there will do for control ; getting the gear reduction right will be your biggest challenge

Thanks wotnot,
I'm thinking the gearing won't be an issue, the circumferance of the baseplate is over 1.6 metres (1633 mm). Geared around the edge at say, 2mm per tooth, that gives me 816 teeth for 360 degrees of rotation, or 2.27 teeth per degree.
If I put a 10 tooth gear on the motor, then one revolution is about 4 degrees of rotation? With 200 steps per revolution that's 1/50th of a degree per step?

So, I am guessthing that I do need processing board of some description, e.g. an Arduino, I was hoping it was something I could do with discreet components.

I'll go look up some Arduino projects - and eBay prices.

Thanks again

[wotnot]

Thanks wotnot,
I'm thinking the gearing won't be an issue, the circumferance of the baseplate is over 1.6 metres (1633 mm). Geared around the edge at say, 2mm per tooth, that gives me 816 teeth for 360 degrees of rotation, or 2.27 teeth per degree.
If I put a 10 tooth gear on the motor, then one revolution is about 4 degrees of rotation? With 200 steps per revolution that's 1/50th of a degree per step?

So, I am guessthing that I do need processing board of some description, e.g. an Arduino, I was hoping it was something I could do with discreet components.

I'll go look up some Arduino projects - and eBay prices.

Thanks again

You can do it with discrete components, for example google the string '555 stepper motor controller circuit' ..however, when looking at component count/cost and complexity, a microcontroller based solution probably wins =)

[SimonFB]

OK, micro controller it is.
Just been looking at eBay, the Arduino is pretty cheap - but which one to get?
There are Nano's, Uno's, R3's, Mega's, Micros, etc.

Think I'll order a kit and have a play before trying this project, but would be greatful for suggestions on a resonable kit, and the right sort of board for this project.

[wotnot]

M'kay... relative to what you want to do, a Nano is enough, This boils down to how much hardware DIY/soldering you want to get involved with.

For example, if you get a Mega/Uno, you can buy 'shields' that plug straight in...ie; ..and you can stack these to get more than one motor controlled.

With a Nano, you'll be doing all your own hardwiring between microcontroller & driver board.

When it comes to stepper motor control for this, you'll want a driver board/module that can do 'micro-stepping'...ie;

A lot of the time, I just use a Nano for simple projects, because they're small and easy to fit in a small project box.

A Mega is basically a Nano/Uno with heaps more I/O, hardware UARTs, and more program memory (most shields for Uno fit/work with Mega)

Typically you'll get more accuracy/control over the stepper motors, using a driver with it's own dedicated PWM generator circuit built-in

[SimonFB]

That's awesome info, thanks.
I'm thinking the Uno and using shields (my soldering skills are iffy) and, as a learning project, being able to dissassemble and reassemble various versions it is probably a good idea.
I have my eye on this kit.

I will still need to shields and drivers and suitable motors, but it should give me enough to experiment with. The last time I programmed a microcontoller was in the early 90's, using assembly language

[wotnot]

You can still bitbang arduino hardware with ASM, however it's hardly worth it these days -> check 'ruggedcircuits' comment here

That's not a bad kit ; it has all the bits and pieces you need to get into this scene.

Wrt suitable stepper motors, I've got some interesting assemblies here (salvaged from various devices)...ie; iirc this is 5:1 gear reduction with belt drive pulley hub



You'll also need to take into account the torque needed to move the mount... I've got some fancy units here ;



That's a big one (motor is 55mm dia. x 50mm length) with opto encoder disc on the back.

I keep threatening (myself =) to list these on ebay, but if you PM me we might be able to sort something out =)

[Reschs]

Look at DIYODE MAGAZINE as they did exactly what you need as a project complete with software.

[SimonFB]

Look at DIYODE MAGAZINE as they did exactly what you need as a project complete with software.

Thanks, I'll take a look for that.

[wotnot]

Good treatise on this -->

[SimonFB]

Finally got round to getting my Arduino kit, gees I should have got one of these a long time ago, so easy to work with.
2 hours after never having ever seem one and I have a joystick and and two pots giving me readings on their status that I can use to control a device with.
Did run a quick trial with the stepper motor in the kit using the supplied stepper controller, but there is also an H-bridge in the kit to play with and code up.



Now to get some proper stepper motors, NEMA 17's seems to be the way people usually go.
I know I am a long time between posts, but I will get back with progress when there is some more.

[fandtm666]

once setup with the stepper drivers and the nema motor you need to set the step

1:200
1:400

and mine go all the way up to 3200, this also determines the speed that
it rotates at.

you then need to calibrate this in the software to make sure that when you say 20mm it rotates
enough to move 20mm.Also i suggest using shielded cable considering that your requirements
would require minuscule movements and steppers and drivers suffer from ef noise and can miss steps.

Mine is a laser and cnc setup but the drivers and nemas are the same plus all mine is shielded with ferrite
cores on all cables.

[hinekadon]

how much power does it take to start movement ?
on my dish I have 200/1 gearboxes on frequency drives they have 300w 3phase motors and chain driven elevation with rotary optos at 3600pulses per rev on both rotation this feeds into a allenbradley plc that counts the pulses and hunts to get its self correct the drives are setup to start slow and then increase in steps every 5 seconds to full speed and dymamic breaking with dc injection which stops the motors dead but this may be a little big for you as it weighs over three tons and is 4.5 meters in diameter?

[trash]

Arudino's are a curse on Astronomy.

I have a telescope I had to repair. I giggle at which telescope this is. One of my guys built the controllers for it. It used TWO (count them) ardunios.
This is a colossal amount of processing power to drive a Dec/RA telescope. I repaired it good. I replaced the two arduinos with four diodes, two mercury switches and a relay.
I'm a serious risc assembler programmer and to date my best program has used three lines of code to complete a complex task. The new record is now zero.

If you're using stepper motors then just buy some cheap chinese microsteppers like this one.


You can get them cheaper than amazon from bangood or aliexpress.
They will do all the stepping hard work leaving your microcontroller code to say "left and right".
If you're ok with a little bit of code or just good with timers then you can get it to track sidereal time.
If you're running az/el then you'll need a bit more processing power.

Depending on where you are you should be able to find a local astronomy club that members will probably had done what you are trying to do.
In NSW, Port Macquarie and Tamworth clubs are very active. (also check out facebook).