JRK Setup and Pots Issues

[frankrizzo2]

I'm having some issues with getting the feedback correctly setup for the pots in the Jrk utility. I've been at this for a few weeks now trying different mounting methods for the pots and I'm coming up with the same jittery feedback from the pots. First I mounted the pots directly to the back of the motor shaft for a 1:1 ratio and was able to get one side to be fairly stable with the right PID settings but the other side was still jittery with the same settings. I've been through about 10 pots hoping I would get one that would be more accurate. The pots i was using were from Radio Shack and they have a %20 tolerance. I tried 5k,10k and had the best luck with their 50k for some reason. I just received some 10k cermet pots with a %5 tolerance and mounted them with gears at a 1:1 ratio and figured with the lower tolerance that it would be more accurate and jitter free but I'm still have the same issues. I've spent hours trying different PID settings and have searched high and low on the forums to find the answers but I've gotten to the point that it's time to ask the experts for some help. Has anyone had issues with using unshielded hobby wire for wiring pots or should I be using shielded cables? I'm up for any suggestions that someone might have. Thanks

[Erwan960]

No problem for me with PPC 27, precision potentiometer of high quality.
http://www.megatron.fr/composants/posit ... ique_f.php

First try with gears (lack of precision, perfect alignment required...) :


Then with "silent bloc" (perfect result) :


Final result :

[Bruceaust]

I have had problems in the past. but now use shielded cable. Also try keeping the feedback cables (very low current 0-5v) away from the motor cables (very high current Pulse Width Modulation). Using shielded cable will certainly reduce the possibility of stray interference - so it is always good practice and is easy to try and see if it helps solve your problem.

[frankrizzo2]

Thanks for the pics and suggestions. I will try to use some different cable from the JRKs to the pots tonight. I've got some cat6 cable at home so I'll try that first and go from there. Here is a few pics so you can see what I'm working with and what I've done so far. I'm using Spectral Cermet Pots but maybe I need to go for even more precision. Because of the orientation of the motors I can only go up to a little over 1 Inch for gear size.

[prodigy]

Nice looking sim.
What motors are those?

[frankrizzo2]

Thanks! It was a lot of figuring and work but it was a blast to build! The software has a little learning curve to it though. I got the motors off eBay from a Canadian seller. They are pretty powerful. They run at 180 rpms and had no problem pushing a friend of mine around and he's over 220 lbs. I just wish I could get the motors to quit shaking when I'm using them. Maybe I'm missing something in setting up the feedback in the jrk utility.

[prodigy]

I don't know why you have jitter problems, I remember that I didn't have that kind of problem and I was using some cheap 5K pots with JRK's.
Are they shaking while you're standing still - not driving?
Can you make a small video?

[frankrizzo2]

Yeah they are shaking when I move them with the set target function in the jrk utility when I'm trying to set my midpoint for the motors. That's why I'm wondering if the wires on the pots are picking up interference from the power wires on the motors. I'm going to try a few things when I get home tonight. This is the first time I've had to ask for help on any forums. I usually can find the answer or figure it out on my own but its been too many late nights and trial and error. I'll try to make up a video to show plus I would like to post my entire project once I am finished and its working properly. This is an amazing forum with a lot of very talented people. Thanks to everyone for sharing your ideas and projects.

[Bruceaust]

Just a thought; are you using the JRK Plugin? ---- its fantastic. (We must thank the developer of this great add on!)
It makes a huge difference to the smoothness.

Cat5 cable will help a bit but the only way to shield from interference is to use shielded cable. Also, when using shielded cable you should only attach the shield at one end.

[frankrizzo2]

I am using the JRK plugin(it comes with the newest x-sim software right?), which seems to be really great and I'm sure I'll love it once I get my issues worked out with my sim hardware. I didn't have a chance to mess with anything last night so I'll have to try some things tonight. The more that I think about it though, it's got to be something with the potentiometer wiring causing interference. I thought at one time that it could be my usb cables causing the problems but i switched them out with some shorter radio shack cables and had the same issues. I am also using the usb ports on the back of the computer and the JRK's are on com ports 3 and 5. Is there anything specific that I should be looking for in a shielded cable? Basically we have a radio shack and a couple computer stores here so that is where I'm going to start looking today. Also, what should I attach the shielded end to? Do I ground it to my sim somewhere? Once again, thank you for your help and I will post my findings as soon as I make some progress on this.