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RC Model Servo Motors

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IntraWinding

Fri Jul 13 2012, 10:49PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Anyone know about RC model servo motors?

I've started a project to remotely rotate a potentiometer with a low cost servo motor (wow,are they cheap! See eBay).

I assumed servo motors would rotate through at least the range of angles of a pot (say 300Â°) but it seems 90Â° is the norm.

Are there low cost servos out there that fit my needs?

Patrick

Fri Jul 13 2012, 11:38PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i know alot about all types of servos.
the turnigy ones from china are as cheap as rocks, but failure prone.

there are special servos and programmable servos, but theyre not cheap, and you need a special device to program them.

i would reccomend getting a mid cost one and then using a gear, wheel, or push rod to extend your effective rotating angle at the cost of resolution. 300/90 = 3.3 so your hunting and settling would be sacrificed.

a robotics source and spec web site :

and

tobias

Sat Jul 14 2012, 01:32AM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Some people would mod them. You can try. Open and first of all measure the resistance of the pot used as position reference. Break or cut the pin that acts as a mechanical stop. This would allow it to give full turns if it was not for the pot.

Check the range of this pot. If you are lucky enough it will allow way more then 90deg.. now you have to compensate for the resistance at both ends. I would try to solder tiny smd resistors between the pot leg and pcb or something not-pretty like that.

If the servo is so cheap I think it is worth trying!

Patrick

Sat Jul 14 2012, 02:09AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

he wants to attach a RC servo to a Pot, how about changing the resistence of this pot, (not the servo pot) ... this way you could use a 300k pot at 90 degrees, instead of a 100k pot at 300 degrees.

Ash Small

Sat Jul 14 2012, 07:36AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Any reason why you can't use a cheap stepper motor and gear driven pot instead?

Would this not give greater sensitivity/control?

Patrick

Sat Jul 14 2012, 08:07AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ash Small wrote ...

Any reason why you can't use a cheap stepper motor and gear driven pot instead?

Would this not give greater sensitivity/control?

yes, in fact if you have all the pieces, that might be easier and better.

lightlinked

Sat Jul 14 2012, 11:05PM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
Location:
Posts: 115

alot of servos will swing 180 if you give it the full 1ms - 2 ms pulse range. you could also add gears or timing belt/ pully to get more rotation.
can you just replace the analog pot with a digital pot? or swap the pot for a motorized one? what is this pot on/doing?

IntraWinding

Mon Jul 16 2012, 07:45PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Thanks for the input folks.

I'm remotely turning a volume control that has about 300 degrees rotation.

I like the idea of adding resistors either side of the servo feedback pot to fool the contol circuit into turning further. Plus, if the original pot has limited rotation range I guess I can replace that too!

Patrick

Mon Jul 16 2012, 07:59PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

IntraWinding wrote ...

Thanks for the input folks.

I'm remotely turning a volume control that has about 300 degrees rotation.

I like the idea of adding resistors either side of the servo feedback pot to fool the contol circuit into turning further. Plus, if the original pot has limited rotation range I guess I can replace that too!

just one last point, most pots are "keyed" to the position of the output splined gear, and hae mechanical stops you may have to grind out.

Steve Conner

Tue Jul 17 2012, 07:42AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Do you know that you can buy ready-made motorised audio volume pots?

They have a quiet low-speed motor, and a slipper clutch so you can also work the volume control by hand without the grinding noises and stiff feel you get when turning a servo by hand.

The one thing they lack is position feedback. The application gets round that by just having "volume up" and "volume down" buttons on the remote. If you try to drive the pot past its end stops, the clutch just slips.

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