Servos as speed controllers and cheapo 9g gear motors!

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Strobe111
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Servos as speed controllers and cheapo 9g gear motors!

Post by Strobe111 » Wed Dec 05, 2012 9:06 pm

Hi all! I was thinking about using servos as speed controllers using microswitches. Would this work? Also, are these cheap gear motors good enough for drive?

1) http://www.ebay.co.uk/itm/6V-540RPM-Tor ... 4ab8b3b4f5

OR

2) http://www.ebay.co.uk/itm/6V-300RPM-Tor ... 4d01aa77da

OR

3) http://www.ebay.co.uk/itm/6V-100RPM-Tor ... 337784ddb1

Or are they all junk/not suited for this purpose.

I hope the links will be of use anyway to anyone!
Cheers in advance!
A cheapy robot is a happy robot!

razerdave
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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by razerdave » Wed Dec 05, 2012 9:46 pm

Numbers 1 and 2 are the better option for antweight purposes.

You say use servo boards and microswitches ? If you are using servo boards as motor controllers, you do not need microswitches. Whole servos are used to click microswitches that operate big relays. Its how a lot of heavyweights (and some early featherweights) used to be controlled.

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earthwormjim
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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by earthwormjim » Thu Dec 06, 2012 11:07 am

Dave is on the money.You can just remove the circuit board inside the servo,and use that to drive the motor.where the board connects to the tiny motor inside the servo,just connect them to the gear motor,and Bob's your uncle,cheap speed controllers.They are not perfect,but they work.You cant put big voltages through them,but some can handle 2s no problem,AFAIK??

You could use servo's and micro switches,but you would have no proportional speed control,and would be completely undrivable,by my reckoning?? Would be fun to try it though!
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Strobe111
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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by Strobe111 » Thu Dec 06, 2012 7:22 pm

Cheers everyone, how would I remove the servo boards and wire them to the motors though? I am quite a new person to robot combat so please bear with me! :D
A cheapy robot is a happy robot!

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BeligerAnt
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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by BeligerAnt » Thu Dec 06, 2012 8:20 pm

You need the control boards from standard-size servos (around 35-45g) to drive the gearmotors. The boards from smaller servos won't be up to the job.

Dismantle the servo carefully, remove the 4 screws in the bottom and pull the top and bottom covers off. The top cover houses the gearbox so you will probably get showered in small plastic gears :) No matter, you don't need them anyway ;)
The centre section houses the control board, motor and feedback potentiometer. These are the important bits that you need. The motor is usually soldered directly to the circuit board, and may be screwed to the case by a tiny screw. The potentiometer is usually just clipped in place and should push out. It may be soldered directly to the board or be on wires.
Next you need to unsolder the motor from the board. You can replace the potentiometer with two fixed value resistors or glue the potentiometer shaft in its centre position to stop it moving.

More details and lots of pictures in my step-by-step guide to building a basic robot:
http://homepage.ntlworld.com/g0xan/robo ... iagram.htm
Gary, Team BeligerAnt

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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by Andrew_Hibberd » Fri Dec 07, 2012 12:06 am

A really nice guide
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Strobe111
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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by Strobe111 » Fri Dec 07, 2012 8:08 pm

Would I be able to use SG90 servo boards if I run them at 4.8v?
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ajw
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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by ajw » Fri Dec 07, 2012 8:50 pm

I've used SG90 boards driving those chinese 540RPM gearmotors you list in your first post in the past off a 6V battery. They work, but the lifespan of the boards is questionable since they already run pretty warm with the smaller motor in the stock SG90. I've had one board fail in the last few months but that is with minimal use. If you've got the space I'd go with Gary's standard servo board suggestion.

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BeligerAnt
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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by BeligerAnt » Sun Dec 09, 2012 4:07 pm

The thing to understand is that servo boards are not designed to drive the servo motors anything like continuously. So although some micro servos (Park HPFX) use 12mm motors very similar to the gearmotors, it's well worth going to the next size of board (designed to drove a bigger motor) so that it is slightly under-run and therefore likely to last longer, especially if running directly off 7.4V (nearer 8.4V when fully charged!)

So the boards you have will work, so if you're strapped for cash and/or impatient you can use them for a while, but it would be best to replace them with bigger boards when they die.
Gary, Team BeligerAnt

PJ-27
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Re: Servos as speed controllers and cheapo 9g gear motors!

Post by PJ-27 » Wed Jan 02, 2013 6:12 pm

I was planning on doing a similar thing, use the servo boards from large Servos to control gearmotors but I found with the hack I did on those Micro servos that the trimming constantly had to be reset.

Is there a way to stop this?

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