# Controlling the controller



## tchapin (Feb 2, 2011)

I am running a 0 to 5k pot (0k = off, 5k = full go) to an alltrax controller to handle my brushed e-tek motor in my Ford 8n tractor conversion. The conversion is a clucth-less one. The pot is controlled by the original hand throttle. I would like to hook up a pot to the original clutch peddle to give the tractor a more original feel for the controls. I want to be able to have the hand throttle set at (let’s say 2.5k or half throttle) and be able to active the original clutch pedal to slow the tractor to a stop (0k). 
This kind of control is needed when hooking up trailers, running the lift with one hand and the steering with the other hand. It would be handy for the foot to control the motor.
How can I accomplish this action?
I know I can’t just put another 0 to 5k pot in line with the first one. Do I need to also put in a couple of double pole micro switches to “disconnect” the one pot and bring the other “on-line”?


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## Ziggythewiz (May 16, 2010)

Do you want another pot or just an off switch on the clutch pedal?


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## tchapin (Feb 2, 2011)

ideally, i would like it to work like a clutch where the tractor would slow down to a stop. So i guess a pot over a switch would be better. The switch would make for a jerky setup.


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## Ziggythewiz (May 16, 2010)

Your current pot is a 0 > 5k ... you just need one that's 5 > 0 k in parallel for the clutch. it will nominally be at 5k and act as a pass-through for the regular pot, while also reducing the max value in half, and when pressed will bring it down to 0 slowing you to a stop.


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## tchapin (Feb 2, 2011)

"act as a pass-through for the regular pot, while also reducing the max value in half, and when pressed will bring it down to 0" 

Do you mean that if the current pot was set at 2.5k (half throttle), going thru the "clutch" pot would reduce it in half or 1.25k (1/4 throttle) so i would need a 10k pot for the original one?


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## Ziggythewiz (May 16, 2010)

If the current pot is at 2.5k and the clutch one were at 5k the parallel result would be 1.67 k (1/R = 1/R1 + 1/R2)

If both were at 5k the result is 2.5k, which is what you said you wanted. If you wanted the full resistance to still reach 5k you'd need something at least a little more complicated.


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## tchapin (Feb 2, 2011)

Sorry for not being clear. This is the first, i have messed much with pot boxes and controllers.

the current setup works fine on a pot running 0-5k. The 5k gives me full range of speeds from full throttle to zero. this is all hooked to the original hand throttle lever that when put in a possition, it stays there. This functions the same as the original gas motor would.

I want to a a way to override the first pot with something connected to the original foot clutch peddle so i can set the speed with the hand throttle hooked to the first pot. Then when both hands a busy, I can still slow the tractor down to zero from whatever the hand throttle pot is set at with a push of the foot peddle. When the foot peddle is released the tractor speeds up to the setting of the hand throttle. This would function similar to the original clutch setup.


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## ga2500ev (Apr 20, 2008)

tchapin said:


> "act as a pass-through for the regular pot, while also reducing the max value in half, and when pressed will bring it down to 0"
> 
> Do you mean that if the current pot was set at 2.5k (half throttle), going thru the "clutch" pot would reduce it in half or 1.25k (1/4 throttle) so i would need a 10k pot for the original one?


Not exactly. It would only be half when both pots are equal. The formula you need is the parallel resistance formula:

Rparallel = (R1 * R2)/(R1 + R2)

Note that two resistors of any type in parallel will have a parallel resistance than smaller/equal than either of the two original resistors. So you are correct that if the current pot is 2.5k and the foot pot is 5k, then the current resistance is:

Rp = (5k * 2.5k)/(5K+2.5K) = 12500/7500 = 1666 ohms.

The problem is that the foot pot will affect the hand pot even if you are not using the foot pedal. First you are correct that the two pots would have to be 10K each in order to get the full 5K range. So consider if the foot pot remains 10K through the throttle range of the hand pot. Take the two end points and the middle:

(10K * 10K)/(10K + 10K) = 5K (ok for full on)
(10K * 0)/(10k + 0) = 0 (ok for full off)
(10K *5K)/(10K + 5K) = 3.3K (definitely not centered anymore at 1/2 hand throttle)

It may not be a big deal since the hand pot can sweep through the entire 5K range as long as the foot pot is at 10K. An advantage is that the foot pot can only make the motor spin slower than the hand throttle since it's at maximum when released. BTW to get the original 2.5K center the hand pot has to be at 3.3K when the foot pot is released.

I attached a quick graph I created showing the plot of the hand pot with the foot pot fixed. It's a skewed linear plot over the range.

ga2500ev


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## Ziggythewiz (May 16, 2010)

tchapin said:


> I want to a a way to override the first pot with something connected to the original foot clutch peddle so i can set the speed with the hand throttle hooked to the first pot. Then when both hands a busy, I can still slow the tractor down to zero from whatever the hand throttle pot is set at with a push of the foot peddle. When the foot peddle is released the tractor speeds up to the setting of the hand throttle. This would function similar to the original clutch setup.


Yes, that's how it would work as I suggested. The only difference is that if you want a full range (0-5k) input to controller you'd need both pots to be 10ks (or a 0-50k for the clutch would get you close) or add some other switching circuitry.


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## frodus (Apr 12, 2008)

Have you thought about calling Alltrax at all? They're great with customer service and probably already have a solution for you.

IIRC, the throttle is relative to pack negative, so there may be something you can do easily there, but you might need to ask them.


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