"paralleling" servos

[bartles]

I am building a small dragline and have decided to use servos from my rc helicopter days for power. The contemplated arrangement would have two servo's each with a pinion, both driving a larger gear to power the hoists. These servos would be converted to continuous rotational capability of course.

I am a little concerned about this arrangement because of the possibility of balancing the power between each servo motor. Granted we are not starting a construction company with high usage hours expected but I don't want to have to deal with burnt motors all the time.

Opinions and advise are welcomed as always.

[Espeefan]

You should be able parallel two servos quite easily, and they really shouldn't have a problem sharing the load, but if you plan to convert the servos to continuous rotation, sometimes you can run into problems getting the motor to hold position at neutral stick. If you can get the potentiometer centered perfectly there will be no problems, but I do know that servos converted this way like to drift a little bit - correctable with a little radio trim adjustment. If you have two servos that are drifting opposite ways, they might be fighting each other at neutral, just a little. That's about the only concern I would have. It may not even be a big enough problem to worry about, but if there is a lot of drifting going on, both servos will fight one another and draw some current, possibly getting warm/hot. You'll have to play with a pair of servos and see what kind of results you get!

[savage_basher]

normally the best way i find with the continuous mod is to replace the potentiometer with two 2.5k resistors.

its much more reliable than centering the pot and gluing it as over time evn very small vibrations from the servo operating can cause the pot to move such a miniscule amount that its enough to start the dreaded drifting.

tony

[bartles]

Thanks for the help!!!

[Rvjimd]

Tony,

Do you have a picture of a servo using the resistor mod? I was going to try that, and a picture would help me.

Bart,

Any pictures or detail on your progress with the dragline and the parallel servos?

Thanks

Jim

[bartles]

I just started fabrication of the carbody, and the drums are finished. When I get the drums mounted I take some photos and pass them along. I have spent a lot of time making working drawings from scaling up from a parts manual. I just received the slip ring so the building will speed up for sure. Work related travel is messing with my play time, but next week will get things going for sure.

I have never done anything like this so my work progress is slow, but it is a lot of fun for sure.

Originally Posted by Rvjimd

Tony,

Do you have a picture of a servo using the resistor mod? I was going to try that, and a picture would help me.

Bart,

Any pictures or detail on your progress with the dragline and the parallel servos?

Thanks

Jim

[savage_basher]

Originally Posted by Rvjimd

Tony,

Do you have a picture of a servo using the resistor mod? I was going to try that, and a picture would help me.

Bart,

Any pictures or detail on your progress with the dragline and the parallel servos?

Thanks

Jim

if you desolder the potentiometer and resolder the pair of joined resistors in its place




just need to solder one pair of the resistors leads together, the joined pair will go to the centre solder point where the pot used to go.

anything between 2.2k to 3.5k have been used with sucessfull results, you just have to make sure they are both the same value.


tony

[Rvjimd]

Tony,

Thanks! That is perfect, going to try that and see if it solves my drifting servos on my little dragline.

Jim