Converting servos 360 degree continuous rotation

[SmallHaul]

Some people have asked me about converting servos to 360 degree continuous rotation so, I thought I would give explaining it a shot.

Think of a servo as a 200:1 gearbox that has a potentiometer (pot) that turns with the final output shaft and the shaft has a physical "stop" on it so that it can only rotate 180 degrees or so and there is an electronic speed control that is regulated by the position of the pot.

Now to convert the servo so that it runs continuously to be a winch or to drive a wheel You need to do 3 things.

1) Remove the physical stop that prevents the servo from rotating continuously. On metal gear servos there is usually a metal pin stuck in the output gear that needs to be pulled out or cut off. Most servos with plastic gears just have a little plastic nub that needs to be cut off.

2) Eliminate the physical connection between the pot and the output gear. Some servos are easy to do this because they have a little clip inside the output gear that the pot shaft sits in that moves it. On a servo with a clip you just push the clip out through the bottom and that step is done. Some mini & micro servos are more difficult though because the pot shaft is what the main output gear actually rides on. So, in this case the end of the pot shaft will be keyed. You just need to cut the keyed end off but, MAKE SURE you don't let the shaft get hot enough to melt or damage the pot or its mount! Make sure the servos runs smoothly before final assembly to make sure you didn't cause the gears to bind at all when you cut the pot shaft.

3) Lock the pot into one position. power the servo up and set your trim on your radio to neutral then rotate the pot until the servo motor stops turning. Then glue the pot shaft so that it won't move.

Here is a link to pictures that might explain it better:

http://www.societyofrobots.com/actua...ifyservo.shtml

If you have any old or week servos laying around take them apart and convert them for practice.

Good luck!

[Waterboy]

thanks scott! great tip

[muddin98jeeptj]

could the servo be used as a winch by doing that ????????????

[SmallHaul]

Originally Posted by muddin98jeeptj

could the servo be used as a winch by doing that ????????????

Yes, all of my dump trucks use a modified servo used as a winch to raise & lower the dump bed.

[holycaveman]

Cool vid!!

Yes servo's actually make much better and stronger winches than the winches you can buy.


You can mount the servo most anywhere, then use brake line to feed the winch cable through. You can even bend the brake line around objects in your truck, to route the cable to the front of your bumper or rear.


Also servo winches will walk abit. So its best to place a power on/off switch located on your truck somewhere. So when you use it, just flip the power switch on, then work the winch from your radio.

If you use a 3 pos switch and a y harness on your truck, you can work two winches (front and rear) by the same channel on your radio. So basically only a 3 channel radio is needed for two winches, steer, and throttle. Or by the same standards, a 2 channel radio can be used for a winch and steer and throttle.

Sorry, getting off track LOL

[Tanqueray]

quick question, but how many ounces are you using as servos for winching?

[SmallHaul]

The servos used on my tonka dump trucks are 40oz (torque) servos and the ones on my crane are 200oz servos.

[madman1983]

Thanks scott, you were very helpful

[sgtsteve]

I realize this is an old thread but I wanted to give a shout out to a new product that takes care of all the work that goes into making a servo winch along with some really high quality parts. Check them out.

http://www.scale4x4rc.org/forums/showthread.php?t=67056

[peeprox]

I've forgotten the specifics, but I know that if you're ok with a soldering iron you can replace the potentiometer with two resistors so long as they're the same resistance, both from the central leg of the pot, one to each outer leg. A pot changes the resistance between the two outer legs in relation to the center, so by replacing it with two resistors of the same value you get something that fools the board into thinking the pot is perfectly true, and will result in no 'walking'. It's the cleaner and more reliable solution, and saves you from messing around with getting the pot perfectly center and trying to stop it from being keyed to the final drive of the servo by removing it completely.

[lilbandit85]

hey does anyone have advice on how to pull the final gear off the pot when converting metal gear servos?

[braq]

Originally Posted by peeprox

I've forgotten the specifics, but I know that if you're ok with a soldering iron you can replace the potentiometer with two resistors so long as they're the same resistance, both from the central leg of the pot, one to each outer leg. A pot changes the resistance between the two outer legs in relation to the center, so by replacing it with two resistors of the same value you get something that fools the board into thinking the pot is perfectly true, and will result in no 'walking'. It's the cleaner and more reliable solution, and saves you from messing around with getting the pot perfectly center and trying to stop it from being keyed to the final drive of the servo by removing it completely.

Hi,

I have found that with the two resistors you actually have to stick very close to the total value of the original potentionmeter, which typically is 4.7K Ohms. So a pair of 2.2K Ohm Resistors did work well, but 2.7K send the motor controller into madness.
The creeping or walking is actually a feature of the servo in it's original design to show as little deviation from the desired position as possible. You can only get rid of it by either:
i) trimming
ii) increase the deadband of the controller > either change the programm code or if it relies on an external capacitor increase it's value (take a 0.1uF Cap and try out in parallel to the existing caps on the board)

Glueing the pot, or replacing it with two resistors does not widen the deadband of the servo controller circuit (!)

cheers

braq