Can drive motor affect steering servo?

[sparkycuda]

I had my PH350 off-road dump truck driving around the basement for the first time last night. But, whenever the truck is above about 1/3 throttle, the steering servo gets a mind of its own and goes to the left. Sometimes it cycles from center to left and back. Whenever the drive motor is off or at very low speed, steering works perfectly. I have an 85T crawler motor and using Taser 15 ESC. Steering is Hitec HG-645MG servo. Radio is Spektrum DX6i. I mounted the servo parallel to and about 1/4" from the motor body - a very clean setup - but is the EMF from the motor causing the problem with the servo? I'm new to the R/C stuff, so I may have made a basic boo-boo.

Any help would be greatly appreciated. Thanks!

Ken

[ihbuilder]

Ken I had the same prob on the Mack .It was worse when loaded . I installed an external BEC . that solved the issue . I also had the same issue in my 5900 heavy haul tractor with a 75t motor , I also put an external BEC in that too .

[Stuff]

could possibly be a power drain issue? if you pick up the truck and try going full throttle will it still spaz out?

[sparkycuda]

I appreciate the help! Pulled red wire from ESC/BEC lead to Rx, then added a battery to run the servos & Rx. Problem FIXED! So now off to the hobbyshop for an external BEC, and I get to leave the steering servo in its original location.

Thanks!

Ken

[RCP57]

Come on Ken, where is the video?????? I love this build and need an update!

[Stuff]

glad to hear you got it fixed!

[Espeefan]

Yes, we need to see some video! Please? Or at least some updated pictures in your build thread! I love this build.

Glad you figured out your steering glitches. Like the others said, an external BEC, for a heavy model like yours, is a big help. Sometimes you can still get some EMF back feeding, but these days it's not such a problem. We have 2.4 giga-hertz radios, and many motors have built in snubbers/capacitors, to stop the EMF problems.

[sparkycuda]

W_E_L_L H_E_X_X!!!!!!!!!!!!!!!

Installed the external BEC and now the problem is NOT FIXED!!! Steering pulls left if throttle is above about 1/3. Works perfectly otherwise. Maybe I was too quick when I used the separate battery and thought it worked OK. Will retest and see what happens.

So back to the drawing board....

I'm going to try something I read in a Physics article about shielding magnets from electrical components. Basically it involves using an iron-based shield between the motor and servo. Simple to make and try. I'll see what happens.

I'll try to get a video up in the next several days. Wanting to finish the cab mounts so it looks like a truck.

Ken

[doodlebug]

Maybe you could try some of those "chokes" from radio shack, and wrap the servo leads?
Play around?
Cheer's, Neil.

[Espeefan]

Sorry to hear that didn't help solve your problems, Ken. The next thing I would try is to solder some capacitors to the motor. At least two. One from the negative terminal to the motor can, and one from the positive terminal to the motor can. You can use anything from .001 uF to .1uF. Make sure they are the ceramic type capacitors. I've run up to three capacitors as well. If you use a third, it goes between the positive and negative motor terminals, in addition to the others already mentioned. It's a little old school, but it might be worth a shot!

[sparkycuda]

Nathan & Neil, thanks for the suggestions. I'll try both the chokes and capacitors. The motor is an Integy V11 and is supposed to already have the capacitors but it's worth a try. Relocated the steering servo last night and it seemed to make a small change. The servo does not pull to the left when the motor runs above 1/3, it just won't return to center when you quit steering. Kill the motor, steering re-centers and away you go. Or, if I just creep along at slow speed, steering works properly. And I thought the electronics was going to be the easy part! I'll keep trying.
Thanks to everyone for the help!

Ken

[WhiteWolf McBride]

I agree with the 'choke' idea, aka, a ferrite core.

You often see then on monitor power cables and the like, its that bulge in the data cord. You can get clip-on two-part ones, or simple ring-shaped ones, but feeding a servo cable to wrap it around the ring a few times may be hard. You may also want to run the power feeds to the drive motor thru a core as well... 2 or three wraps of the power line minimum.

Bit I agree, its probably a electrical/magnetic feedback issue. With a separate battery supply, there is less direct path for the feedback in the wiring. Thats why it spikes when the RPM is cranked.

WhiteWolf

[sparkycuda]

Tried the easier "fix" first and added a Radio Shack snap-on ferrite core choke on the steering servo lead. The servo uses a large, twisted wire bundle and could only install one bundle through it - not wrapped as discussed. Guess what? The truck steers perfectly now! Even moved the servo back to its original position - still good! Then I tried using the ESC-BEC instead of separate battery - not good - the servo dithers on its own, but not in relation to motor speed. So tomorrow I install the external BEC and we'll see if is okay.

Thanks to everyone for suggestions. Now to finish the cab mount and see about a video.

Ken

[WhiteWolf McBride]

Sparky,

Glad to see ya got it solved. Give us some pics if ya get the chaance, we may need to use thre thread to help others, and a good set of reference pics would be a benefit, eh?


WhiteWolf,
off to try for the first full night's sleep in a week...