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Small stepper motor & controller advice please

 
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johan



Joined: 06 Sep 2011
Posts: 1004

PostPosted: Wed Apr 04, 2012 1:18 am    Post subject: Small stepper motor & controller advice please Reply with quote

Hello,

Some of you will have seen Elf's fabulous contraption at http://www.photomacrography.net/forum/viewtopic.php?t=16540 - and my repurposed boat lamp holder designed to achieve something similar.

But I need a little help please, or would appreciate being pointed in the right direction, regarding a electro mechanical part that I think would be a really nice addition, namely a small motor and controller to rotate a needle that a specimen would be mounted on.

Can I ask, has anyone done this before, and what were the problems/ gotchas that I'll need to be aware if?

I think I need a stepper motor (type of motor good at rotating slowly incrementally) and a very basic turn clockwise or turn anticlockwise controller, does that sound about right? I don't suppose there's any way to disassemble a no longer loved child's remote control toy to achieve this, with a potentiometer added to slow down what would normally be a wheel motor?

Many thanks for your help!
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ChrisR
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Joined: 14 Mar 2009
Posts: 8394
Location: Near London, UK

PostPosted: Wed Apr 04, 2012 2:53 pm    Post subject: Reply with quote

You can get small stepper motors


but I think radio-controlled-model servos would be easier to get working, and good enough. They have the advantage of using feedback, so they just keep trying until they reach your desired position, whereas a stepper can lose steps and not move at all. Their (steppers)torque can be very low too.
Servos are driven with a repeated variable-length pulse which is easy enough to arrange from something like 555 timer chips. A multi-turn pot would probably be best for the hand-control but a "joy stick" would be more intuitive. Of course you have the option of remote operation with an actual radio control kit. You can take the transmitters apart to use different knobs etc. Whole transmitter + receiver + servos kits seem to be cheap for 2 channels, jumping a lot to 6, which is a bit annoying.

Analogue servos are easier, digital ones are more precise.

I once investigated this a bit, and asked Futaba what the resolution on their servos was. They didn't know - or they weren't saying ! Confused
If you found you didn't have enough though, you could just use two - coarse and fine movements.
As you probably know there's a range of connection methods to join your servo to your model. Bendy rods in bendy tubes, are popular.
If you google for "servo tester" you should find some simple circuits to make them go.
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johan



Joined: 06 Sep 2011
Posts: 1004

PostPosted: Wed Apr 04, 2012 3:15 pm    Post subject: Reply with quote

Thank you very much Chris. Most appreciated. A fun little project!
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