Fly-by-wire throttles - two potentiometers?

jonescg

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Seems as good a place as any to post...

I'm looking for an electronic throttle for a car conversion I'm working on. Looks like many late model vehicles (and all electric vehicles :wink: ) use a dual potentiometer system. That is, instead of the usual 3-wire pot (5 V, analog wiper and ground) you see 6 wires.

This from the internet:
APPS pedal connector.gif

So how should I wire this up to a typical inverter/controller? Both 5 V, wipers and grounds in parallel? :?
 
AFAIK, these are usually designed so that each pot reads in reverse of the other, so that when one is all the way "on", the other is fully "off". This is protection against a faulty pot, so the controller reads both of them at the same time, and if either one doesn't read the opposite of what the other does, the controller would shutdown to prevent potential hazardous operation.

If you're wiring up the one youve got to a controller that doesn't have dual pot inputs, you can only wire up one of them--the second doesn't do you any good as it's output should be opposing that of the first. Just make sure it's the one that reads in the direction you need it to. ;)
 
Thanks Mike, I figured I would only need one of them.

Of all the weird redundancy measures... Surely a couple of 200 ohm resistors on either end of the pot would create a safe buffer and protect against accidental WOT or chopped?
 
Apparently it's a common method of failure protection; I've read of it here on ES a few times as well as on DIYEC; haven't personally run into one.

It's simple enough to implement in the throttle and in the controller during the design process of those, I'd guess.

I haven't worked out a schematic and PCB, but I have pondered before what it would take to add it to a controller that doesn't have it. Should be simple: could be done with an op-amp circuit that "flips" the voltage from one of the throttles, and a comparator of the two. The comparator output goes to the KSI or other enable circuit of the controller, so it disables it if the comparator detects a difference between the two throttle pots.

The voltage of either comparator input can be used to drive the throttle signal input of the controller.
 
BTW, one thing that the dual pot would protect against where the inline resistors won't is loss of ground between throttle and controller. I've experienced that, and it can cause full WOT or only partial throttle, without actually having any throttle action at all, because of the way a hall sensor works along with the internal resistances of the controller circuits.
 
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