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Thread: Variable speed / variable direction electric motor drive

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    Default Variable speed / variable direction electric motor drive



    Hi, i'm new to this forum in search of a solution to a problem i have. What i am looking for is a way to control a small electric motor so that it has variable speed and variable direction based on the amount of pressure you apply to a switch and the direction of the switch. Would anyone know if this is possible? and perhaps point me in the right direction? I have been trying to read and do my own research on this but most of it is over my head as my background is not in electronics but video. Basically what i am looking to replicate is the way a zoom leaver works on a digital camera or a forward/reverse leaver works with a RC car... so the further you push the switch/lever the faster the zoom works or the faster the car travels.

    Any ideas would be appreciated. Thanks



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    Senior Member Reschs's Avatar
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    Several projects in Silicon Chip magazine that would do the job.
    I suggest you look up Oatley Electronics as they do most of these kits.

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    Hi, thanks for your message, has helped me think more about the project and the things i need to work out. I've been reading more online and looking at kits on a lot of sites, but by the sound of it i need a Bidirectional Motor Speed Controller? does this sound correct. Also what is the difference between Bidirectional and Bipolar (they sound the same to me).
    Do you think any of these kits would work:



    I found this video of a guy doing something similar, except i don't need the computer control, just a switch to control speed / direction:
    [ame=http://www.youtube.com/watch?v=Y7KLs0H0haQ]YouTube - ‪My DIY Follow Focus - Foco motorizado‬‏[/ame]


    Quote Originally Posted by Reschs View Post
    Several projects in Silicon Chip magazine that would do the job.
    I suggest you look up Oatley Electronics as they do most of these kits.

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    Senior Member beer4life's Avatar
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    Wink Motor control.

    G'Day Cobber,
    What you need are ' servo controller ' in a google search.
    That search will give a plethora of sites for your edification.
    There are a myriad of applications in robotics and commercial situations.
    Don't be put off with reference to PC control. Can be simple one chip design to very complex.
    Most servo motors are ' Stepping Motors ' with various poles and can F/R or stop in specific positions.

    Kindest Regards, " The Druid ".


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    Quote Originally Posted by pixxelpusher View Post
    What i am looking for is a way to control a small electric motor so that it has variable speed and variable direction based on the amount of pressure you apply to a switch and the direction of the switch. Would anyone know if this is possible? and perhaps point me in the right direction? Basically what i am looking to replicate is the way a zoom leaver works on a digital camera or a forward/reverse leaver works with a RC car... so the further you push the switch/lever the faster the zoom works or the faster the car travels.

    Any ideas would be appreciated. Thanks
    Radio control equipment used in radio controlled cars, aircraft etc., uses pulse width modulation techniques.

    Without specific information of what you wish to do, i.e. precisely what you wish to control, it is not possible to provide the advice, which you require.

    There are many things to consider, including the amount of torque required.

    Tell us what the equipment is, including a model number.

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    Hi beer4life and tristen, thanks for your comments, it's all helping me work out exactly what i need even to just begin making a plan of attack.

    I do understand that there is a lot of things to think about, i've written out pages of notes, and i'm not sure exactly what specific information you may need to help me out but i'll try explaining again with links.

    I have a dslr camera (sony nex 5: ) with an old manual minolta lens on it (). As it's a manual focus lens i'd like to be able to turn the focus on the lens with an electronic switch. This will either be done with a gear attached to the lens (like in the video above) or with the motor butted up against the lens with a rubber wheel on it. The entire rig will be mounted on a steadicam like a Hauge MMC ().

    So the functionality i am looking for is to be able to push a switch (mounted on the handle) "up" and make the motor turn slowly turning the focus, and as i push the switch further the motor will turn faster. When i release the switch it will snap back to the middle starting position and the motor will immediately stop. When i push the switch "down" the motor will go in the opposite direction, again slowly at first but then faster as i push further.

    I guess my main problem is I haven't really known where to start. But i've tried to make a list of the things i need to know first before i start purchasing parts and prototyping, these are: what kind of motor do i need to turn the focus on the lens, what kind of electronic controller do i need to use to run the motor both forwards and reverse at different speeds, what kind of switch can i use to interface with the electronics and what kind of battery do i need to power it.

    I've also tried to set a goal of keeping it as cheap and light as possible (due to it being just a hobby project and the handheld rig it will be on). You can buy professional equipment but it's in the thousands.

    Thanks for the advice on servo controllers!! I have no idea what a servo is or a stepping motor but i will start researching that direction over the weekend.

    Cheers.

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    Quote Originally Posted by pixxelpusher View Post
    I have been trying to read and do my own research on this but most of it is over my head as my background is not in electronics but video.Thanks
    Having read from your post #6 regarding what you wish to accomplish, and in light of what you have said concerning your own lack of electronics expertise, I think that you will have great difficulty in constructing such a device, even with help from members of this forum. Even the simple assembly of a "kit" requires experience in soldering and fault finding techniques if it fails to work.

    I don"t want to discourage you, but we need to be realistic about it.

    You would be far better advised to seek the services of a local electronics expert/service contractor/repairer or perhaps a local radio club.

  8. The Following User Says Thank You to tristen For This Useful Post:

    beer4life (11-06-11)

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    Pixxelpusher,

    If you wish to pursue this yourself, try a Google search using terms along the lines of DIY motorised camera lens focusing.

    See the thread at and similar. The article describes the use of a CD mechanism stepper motor, which will give a jerky movement. This will be all right if your application will tolerate it. If not, a linear servo type of mechanism will allow smoother operation.
    Another thing to consider is vibration of the motor and gear train.

    One of the older train speed controllers, which utilised variable pulse-width techniques and coupled to a suitable dc electric motor would achieve what your YouTube video displays.
    Try to duplicate the mechanics used in the video.
    Last edited by tristen; 11-06-11 at 10:12 PM.

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    Senior Member watchdog's Avatar
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    Cool

    Read up on NE555 ICs (specifically) pulse width modulation. The electronic part is fairly easy even for a layman. The hard part will be the mechanical side. You do realise that you are trying to re-invent the wheel. You can buy motorised lens's at a reasonable price.
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    how many turns is the lens or deg?
    you may need stops either end to prevent damage
    a 4-20 controler with a servo may do what you need

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    Hi, thanks for all the info, i've had a massive working week and haven't had time to follow up on any of the ideas but i will look into what's been written over the next few weeks and come back with any questions i have. Thanks again guys.

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