Making a 5k joystick work

a member of our teams father has found some very nice joysticks in the dumpster where he works. they have 5k pots on them and the biggest range we can get out of them is from 1.7k-2.7k. our programers tell us that the range they will give us will be to small to be accurate. I was wondering if these could work and if so how.

Thanks
Ben Van Selous

Your programmers are correct. The IFI Operator Interface wants 100k pots, and the 5k ones will give you only a few counts at the extreme end of the range.

The joysticks can be made to work by keeping the mechanical assembly but replacing the 5k pots.

Hey, is it legal then use other joysticks? We found some nice ones but did not know if it was legal

Yes you can use any joysticks that work for you. The 100k pot item is what the OI is designed for any other thing will give you limited range.

well one solution to the origional question of how would be to change the 5k pot out for a 100k pot.
you can get the 100k pots at radioshack.

good luck

Wait, are you sure about that? As I understand the OI and the analog inputs on the RC, they measure the voltage on signal pins with respect to +5 and ground. The wiper on the pot still goes from one side of the resistive material to the other, and thus runs from 0 to +5 in 270º of rotation, regardless of the actual resistance. The only difference that I can think of is that the 5k pots would draw 20x the current of the 100k pots, and that’s why IFI suggests 100k. Judging by Alan’s reputation, he knows what he’s talking about, so I’m hesitant to disagree, lest I look like a fool. Have I completely lost my mind?

(If my understanding is indeed correct, then my theory is that the joystick is not moving the pot through its full range of motion, hence the limited range of readings. Changing the pot wouldn’t help, unless you found one with a smaller range of motion. Of course, if I’m wrong, this is all moot anyway.)

Alan and Biff are incorrect.

There is another reason why 5k pots won’t work, though. There is circuitry in the OI to detect when the joysticks are unplugged. This circuitry depends on 100k pots. It is necessary so that when you unplug the joysticks, the robot doesn’t fly backwards.

Once again, are you sure? This is merely speculation, but I would think that the circuitry would detect when the current flow through a particular potentiometer is below .05mA (5V / 100kohm), so it would know when the joystick is unplugged. A 5k pot would draw more current, and I can’t imagine that the circuitry is designed to send a signal of 127 to the RC when there is most definitely something plugged into the port. I wouldn’t be surprised if a 250k pot didn’t work, but a 5k? I disbelieve.

That is true of the RC analog inputs. However, it is not how the joystick inputs on the OI work.

The OI measures the resistance between +5 and the joystick input pin, using an internal resistor to ground to complete the voltage divider. It is designed specifically for a 100k variable resistor. There is no ground connection to the other end of the joystick pot.

The “disconnected” detector merely notices that the sensed voltage is at ground. A 5k pot will result in that voltage being very near 5 volts, so it won’t trigger that problem.

One more thing to consider, maybe those joystick were in the trash for a good reason.