Replacing standard pot with plunger type on mobility scooter setup

[Adman]

Hi,
First post, so apologies if I don't get terminology quite right, I'm sure you'll let me know!
I am making a mini landrover for my son using a donor mobility scooter for the motor, speed control and controllers. My query is to do with the throttle pot. It is a standard round pot which is used for forward and reverse ie standstill is halfway round, turn to left is reverse and turn to the right is accelerate. Hope that makes sense so far. I want to convert this to a plunger type pot for acceleration and reverse (reverse will use a switch on the dash). The controller knows when the pot is not centered as it doesn't work.
Is this even possible? Could someone recommend a solution please.
Thanks in advance

 

[duke37]

Electronic organs used to use rotary potentiometers for volume control driven by levers or rack and pinion. These wore out or got noisy and then light sensitive resistors were used in a light tight box with a variable flap between thr resistor and a bulb.

The system you have probably produces a voltage of one polarity for one direction and the opposite polarity for the other direction. This should be fairly easy to make with perhaps a relay to change polarity for reverse. Some information on the original circuit would be needed.

 

[Adman]

Thanks for the reply, I'll contact the manufacturer to see if I can get a circuit diagram.
Thanks
Adam

 

[jpanhalt]

I would consider mounting an arm (e.g., servo arm) to the shaft of the pot and then using a linkage to convert the up and down motion of a throttle pedal to rotary motion of the pot like this:



You can get the parts at a local hobby shop. Here's a link to Servo City so you know what to ask for: https://www.servocity.com/html/servos___accessories.html

John

 

[Adman]

Thanks for that. I had thought about a lever but wasn't sure how I could get the reverse to work using the same lever.

I have contacted the manufacturer to see if they can give me anything regarding the circuit diagrams so watch this space.

 

[jpanhalt]

I am not quite sure what you mean by the "same lever." I would not have the same action, e.g., pushing forward, control both directions.

In many tractors, a single throttle lever is pivoted in the center. Pressing forward goes forward, back is reverse. My tractor has two levers side by side. The single lever is a little easier to use. The same linkage idea could be used -- just attach a pushrod to both sides of the wheel 180° apart.

John

Edit: On further inspection, two push rods won't be able to do any more than a single pushrod with center/off at 90°.

 

[mursal]

Kubota use this pedal arrangement Click

If you make a center pivot with a neutral position. The neutral position could be a simple ball bearing sitting in a slit cut out of the shaft. A spring behind the ball bearing will give resistance to movement. Link the pot to the center shaft with an adjustable lever (as above) so that you can set the neutral point on the pot.

Cars have drive by wire accelerator pedals with built in pots, most have two pots, one increasing in resistance as the pedal in pushed, the other reducing in resistance. You may be able to use one of these for forward and another pedal for reverse?

 

[shumifan50]

Depending on the resistance and wattage of the resistor, you could buy one from the link below. They are sliding resistors.
The problem I would foresee with the round pot will be rotating it 270 degrees without exerting undue force on the shaft of the pot.

Check the resistance and wattage of the existing pot.

Sliding potentiometers here


You could even put 4 fixed resistors in series (1/4 of existing resistor) and then depending on a gear lever switch, connect each one, depending on the gear selected, to the output through the sliding resistor. I am bad at drawing diagrams so here goes a description:

Low gear: connects through 3 of the fixed resistors and then the sliding resistor to the output.
2nd gear: connects through 2 of the fixed resistors and then the slider to the output.
and so on.
It means each 'gear' position will control one quarter of the total speed.

 

[mursal]

Another idea 5 minutes in, though as mentioned above the movement may not be quite enough.

Let us know how you get on .........

 

[Adman]

Thanks for all the suggestions. If I can't get circuit diagrams from the manufacturer, I think I'll go for the lever setup as shown in the last YouTube clip. The current pot setup called a wigwag setup on mobility scooters only registers about 30 degrees each side of neutral, anything past this, it stays at full forward or reverse.
It's becoming very complicated to undertake someone I thought was simple! The last resort for me is to use the current pot mounted to a pedal which pushes the pot into forward position only and then have a huge amp for/rev switch on the motor some thing like this:

http://www.ebay.co.uk/itm/181142799135

I think this should work, would you agree?

 

[duke37]

You could switch the motor but a small switch to change the ends of the pot should do the same thing.
You could measure the resistance of the pot and replace with a new one with the mechanical setup you require.

 

[Adman]

Ok, I think I'm getting somewhere. I have done as you said duke and put a dash mounted rocker switch to change from forward to reverse which works! That is an achievement in itself for me as it took ages to figure the wiring on the switch - tut, I hear most of you say!
I could just use the rotary pot now to mount to a lever to act as the throttle, but I have an idea which I wouldn't mind running past you guys. I already have a plunger pot 5k ohm that nicely fits in to my throttle pedal which I originally planned to use as the throttle. As the neutral position on the current pot is 2.5k ish, could I wire in a 2,5k resistor with the plunger pot so the computer thinks it is neutral, then when the plunger is applied this should increase the speed... Would that work, hope I have explained it well enough.

 

[duke37]

Try it but don't exceed warp level three

 

[shumifan50]

It depends how the pot is wired. If it has three wires connected to it, one on each end and one on the wiper, then it won't work. If it only has two wires connected to it it will sort of work. It might be better to just use half the travel of the plunger by limiting the pedal travel, centring it when it is fully released. You could amplify the amount of travel on the pedal with a lever or by connecting the the plunger to the pedal very close to the pivot of the pedal.