# Let's Talk Pot Boxes!



## LithiumaniacsEVRacing (Oct 9, 2010)

I am told that running two separate pot boxes to two Zillas can some create two different signals because the difference in pot box designs. What has been explained to me is the controllers/motors may be working sometimes evenly, sometimes one harder than the other, and sometimes one "fighting" the other. If this is the case than creating one pot box that sends two even signals may help performance. What are your thoughts?


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## piotrsko (Dec 9, 2007)

two precision pots, indexed such that they both have the same voltage levels at the same time can be acquired and set up and even ganged to the same lever. 

I cannot see how the controllers would "fight", only that one MIGHT have slightly somewhat less watts to the motor which would mean to you that one motor is putting out perhaps 2 -3 hp less. Not really an issue on Siamesed motors. definitely wouldn't shave more than .001 second in the quarter. 

Might be a problem on dual systems that drive two different wheels but I gave up rocket science when I blew up the rocket site.


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## LithiumaniacsEVRacing (Oct 9, 2010)

I have spoken with two engineers who tell me using two different pot boxes, even though they work simultaneously, the controllers and motors are not getting their full potential because the pot boxes are not that precise. Another words one pot box will differ from the other in it's signal, this causes one motor to work harder than the other. When this happens one motor is "carrying" the dead weight on the other until the other kicks in and gives it's force. Netgain says this is bad for the motors, and I am losing valuable HP and torque. The perfect fix is a pot box that that sends an even signal to each controller, these would create the same HP and Torque at the same time. It would gain more than just a few hp's, it would gain and also reduce the lag from the motor not equal. 

I have contacted a few for estimates on building me this "special" pot box, if anyone is interested in the project please email me at:

[email protected] 



piotrsko said:


> two precision pots, indexed such that they both have the same voltage levels at the same time can be acquired and set up and even ganged to the same lever.
> 
> I cannot see how the controllers would "fight", only that one MIGHT have slightly somewhat less watts to the motor which would mean to you that one motor is putting out perhaps 2 -3 hp less. Not really an issue on Siamesed motors. definitely wouldn't shave more than .001 second in the quarter.
> 
> Might be a problem on dual systems that drive two different wheels but I gave up rocket science when I blew up the rocket site.


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## DawidvC (Feb 14, 2010)

LithiumaniacsEVRacing said:


> I have spoken with two engineers who tell me using two different pot boxes, even though they work simultaneously, the controllers and motors are not getting their full potential because the pot boxes are not that precise.


It is quite common for pots to be specced at 10% variance, which means that as you move the wiper, the resistance changes between 2 identical pots will differ. Wirewound pots are a little bit better, but they tend to give a step-like response compared to carbon-track pots. Getting pots (and pot-boxes) with better specs will be expensive.

Dawid


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## alexcrouse (Mar 16, 2009)

DawidvC said:


> It is quite common for pots to be specced at 10% variance, which means that as you move the wiper, the resistance changes between 2 identical pots will differ. Wirewound pots are a little bit better, but they tend to give a step-like response compared to carbon-track pots. Getting pots (and pot-boxes) with better specs will be expensive.
> 
> Dawid



As far as your step-like response, you are very correct. But remember, all of these pots are hooked to analog to digital converters, typically 8-bit. That means that there are 256 (2^8) steps in the throttle, no matter how good your pot is.

Matching the pots to 2.5% or better should be PLENTY accurate.


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## rwaudio (May 22, 2008)

I'm not sure if it's practical here, but in audio some people will use a quad pot with two of the sections in parallel for each channel. That way you can mix and match to try and get the best match channel/channel as a volume control. Use a quad 10k pot if you want to end up with a dual 5k pot. There is a massive range in quality though and outside of an expensive audio pot I'm not sure if Quads are common.


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## Guest (Aug 18, 2011)

Then the answer must be to use on good quality TPS to feed both controllers at the same time. It is only feeding a voltage difference and nothing else. Should be no problem for one to feed both. 

Simple, problem solved. 

Have you tried to run both off one TPS yet? Have you tried to run both on separate TPS yet? 

You really need to experiment. Under low power it should be no issue to test. Most of us only have one controller and one motor.


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## alexcrouse (Mar 16, 2009)

gottdi said:


> Then the answer must be to use on good quality TPS to feed both controllers at the same time. It is only feeding a voltage difference and nothing else. Should be no problem for one to feed both.
> 
> Simple, problem solved.
> 
> ...



That's a good point. Don't use a 5k signal, use a 5 VOLT signal. They should both read the same ADC value, and behave identically.


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## Salty EV (Jun 8, 2009)

Ron, in regards to the motors fighting each other, I don't think it should matter in drag racing under WOT. In normal driving or partial throttle then yes this is a concern, say for instance 1 POT is giving 30% throttle feedback but the other 1 is giving 32%. But under WOT if you check the reading from the POT's, the voltage reading on both should be enough to trigger 100% throttle. I seem to remember on my Alltrax controller there being a setting about the throttle range, and after a certain value it would be 100%, so you actually have a tiny bit of pedal movement at the end that does not give really do anything other then guarenteeing both POT's can get to 100%. And 100% is all that should matter if your drag racing, if your lifting thats a different problem


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## LithiumaniacsEVRacing (Oct 9, 2010)

Thank you guys, good input.


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