Throttle pot adjustment idea
Discussion
I had a thought, while mulling over the thorny old subject of adjusting the throttle pot positions.
Instead of having to physically move the pots to get the required reading at idle (or at end stop), would it not be better if they had an electronic adjustment?
I'm thinking about another potentiometer (a variable resistor) - probably a little pcb-mounted trimmer or even a multi-turn, which would be connected across the usual pots and would adjust the voltage being presented to the ECU.
I havn't quite got the exact connection method straight in my mind, but it should be an easy mod.
Any thoughts?
Andy.
Instead of having to physically move the pots to get the required reading at idle (or at end stop), would it not be better if they had an electronic adjustment?
I'm thinking about another potentiometer (a variable resistor) - probably a little pcb-mounted trimmer or even a multi-turn, which would be connected across the usual pots and would adjust the voltage being presented to the ECU.
I havn't quite got the exact connection method straight in my mind, but it should be an easy mod.
Any thoughts?
Andy.
Not that I'm aware of.
I assume that the throttle pot is just that, a potentiometer. So I guess one pin is 12v, one is -ve and the other (the wiper) is the output.
In which case I think you could put a high value pot across it, and at that new pot's centre of travel the output would be the same.
Must think about this. It would make the setting up of the pots a lot easier and more accurate.
A.
I assume that the throttle pot is just that, a potentiometer. So I guess one pin is 12v, one is -ve and the other (the wiper) is the output.
In which case I think you could put a high value pot across it, and at that new pot's centre of travel the output would be the same.
Must think about this. It would make the setting up of the pots a lot easier and more accurate.
A.
I like that idea! My throttle pots are very sensitive to tiny movements and anything that would help setting them up would be great. I am trying to think of any reason it wouldn't work - but havn't come up with anything yet.
I may just have a rummage in my bits b ox and see if I can lash up a test rig one evening.
Nice one!
I may just have a rummage in my bits b ox and see if I can lash up a test rig one evening.
Nice one!
alinton said:
Not that I'm aware of.
I assume that the throttle pot is just that, a potentiometer. So I guess one pin is 12v, one is -ve and the other (the wiper) is the output.
In which case I think you could put a high value pot across it, and at that new pot's centre of travel the output would be the same.
Wouldn't putting another resistor in parallel only be able to decrease the resistance, or am I missing something?I assume that the throttle pot is just that, a potentiometer. So I guess one pin is 12v, one is -ve and the other (the wiper) is the output.
In which case I think you could put a high value pot across it, and at that new pot's centre of travel the output would be the same.
You could have another in series and choose them such that the net effect is zero at their centres? Sounds like a nice idea though, could have the 4 pots mounted inside the cabin somewhere
Does the reistance go up or down as the throttles are opened I wonder.
Well I havn't measured the value of the throttle pot, but let's say its 5k.
If you were to put a 100k pot across that, pin to pin, the resultant resistance would be 4.76k. So not much change.
The wiper output of the main pot would be similar with the new pot at its centre, but if you wurzelled the new pot a little you'd move the output up or down a little.
I'm thinking a couple of new cables connected in parallel with the existing ones, running to a small watertight box, and the new pots mounted in it with two little holes through which they could be adjusted.
I'll see if I can rig up a little test jig. Gotta change a pot soon anyway.
A.
If you were to put a 100k pot across that, pin to pin, the resultant resistance would be 4.76k. So not much change.
The wiper output of the main pot would be similar with the new pot at its centre, but if you wurzelled the new pot a little you'd move the output up or down a little.
I'm thinking a couple of new cables connected in parallel with the existing ones, running to a small watertight box, and the new pots mounted in it with two little holes through which they could be adjusted.
I'll see if I can rig up a little test jig. Gotta change a pot soon anyway.
A.
alinton said:
Well I havn't measured the value of the throttle pot, but let's say its 5k.
If you were to put a 100k pot across that, pin to pin, the resultant resistance would be 4.76k. So not much change.
The wiper output of the main pot would be similar with the new pot at its centre, but if you wurzelled the new pot a little you'd move the output up or down a little.
I'm thinking a couple of new cables connected in parallel with the existing ones, running to a small watertight box, and the new pots mounted in it with two little holes through which they could be adjusted.
I'll see if I can rig up a little test jig. Gotta change a pot soon anyway.
A.
I agree that twiddling the wurzel would move the resistance up and down, but you could only get back to 5k (with trim pot set to infinite resistance/not connected), you wouldn't be able to trim it the other way.If you were to put a 100k pot across that, pin to pin, the resultant resistance would be 4.76k. So not much change.
The wiper output of the main pot would be similar with the new pot at its centre, but if you wurzelled the new pot a little you'd move the output up or down a little.
I'm thinking a couple of new cables connected in parallel with the existing ones, running to a small watertight box, and the new pots mounted in it with two little holes through which they could be adjusted.
I'll see if I can rig up a little test jig. Gotta change a pot soon anyway.
A.
You could adjust the main pots initially, to have a little too much resistance, to ensure that the trim pot can always reduce overall resistance to get back into trim, but that would only line up the trim at closed throttle (or wherever you choose to line it up) and it would be out elsewhere in the sweep. Adding a constant resistor in parallel will always cause this problem (constant from the point of view of any given trim pot setting). If the main pot gave linear resistance with angle, which it doesn't of course, you could use a series resistor.
Having said that, the error becomes less as the main pot's resistance (m) goes down (because 1/R = 1/m + 1/t, where t is the trim resistance: you want 1/m to be large compared with 1/t). This is why I asked if the resistance goes up or down as the throttles increase - assuming you set the trim at idle, if the resistance goes down you may be ok, but if it goes up then the error will magnify and the ECU will never see WOT...
Yeeeessssss. Hmmmm. OK, an op-amp then. Stock pot connects to the +ve input, op-amp has a pot around the feedback loop, and that's the one you adjust.
The output would then linearly follow the input, but just be offset by the feedback resistor.
Cheap and cheerful, an old 741 would do, I think you get them free with cornflakes these days.
What ya think, FP?
A.
The output would then linearly follow the input, but just be offset by the feedback resistor.
Cheap and cheerful, an old 741 would do, I think you get them free with cornflakes these days.
What ya think, FP?
A.
I think you might be in danger of blowing your ECU I believe voltage increases as the throttle is opened. There is only 1 voltage measured so no fancy dual output.
The limits in the ECU are such that if the voltage goes outside the expected range the value defaults to the limit value so the voltage used by the ECU never goes outside the range.
The limits can be changed but I don't think it would help with the pot adjustment since its just the upper and lower extremes.
There is a 2d map converting voltage to throttle site could be shifted on the X axis to achieve the equivalent of a trim pot but we had no success altering this and it would be even more hassle changing it than twiddling with the pots.
The limits in the ECU are such that if the voltage goes outside the expected range the value defaults to the limit value so the voltage used by the ECU never goes outside the range.
The limits can be changed but I don't think it would help with the pot adjustment since its just the upper and lower extremes.
There is a 2d map converting voltage to throttle site could be shifted on the X axis to achieve the equivalent of a trim pot but we had no success altering this and it would be even more hassle changing it than twiddling with the pots.
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