Potentiometer (Pot)

Article in progress, edit as needed:

From: http://www.endless-sphere.com/forums/viewtopic.php?p=527196#p527196

Some problems with pot throttles:

--requires gears (or friction rollers) to convert rotary motion around the handlebar into a different range of rotary motion for the pot's knob/shaft, or into linear motion for a sliding pot. (unless you do what I did once and put the pot INSIDE the handlebar end, and connect it's knob/shaft to the end cap of the throttle grip body ;))

--inexpensive pots are not sealed, and their resistance is easily affected (sometimes permanently) by humidity or water intrusion. Sealed pots are enough more expensive that typically they wouldn't be used by most throttle makers (though they should be).

--dust and dirt can also get into such unsealed pots, which will get in the contacts and grind away at the surfaces, changing the resistance unevenly and even breaking the connection entirely eventually. (ever have a "crackly" volume knob? taht's why)

--They're bigger and bulkier than hall sensors + magnets, which can be placed in various configurations in the throttle grip or mounting body.

--hall sensors + magnets are probably cheaper by some significant margin than even unsealed pots, but mostly they are more reliable in environments that pots can't handle for very long. Since most manufacturers don't seal the hall *leads* or any of the wire ends, then corrosion and/or conduction across the leads happens when they get wet inside, and that is a flaw, but it is the same problem you might have with a pot, depending on the controller's throttle input design, and the current flow vs voltage sensitivity of things.

There are a number of *advantages* to pots, too, most especially that if your controller is designed to take advantage of the full-voltage-range-swing you can get much finer control. Plus if you are gearing it anyway, you can use a pot with a lot of range and gear it so you have a lot of twist available on the throttle grip, so you can more finely tune your speed.

It can be pretty coarse and "jumpy" with hall throttles, partly because of the much more limited voltage output range of them, depending on how they designed the mechanical body of the throttle and where the magnets are in relation to the hall, as well as the magnet strength.

Determining wiring for the throttle:

http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=48238&p=709960#p709960

[quote="amberwolf"]If by pot you mean a resistive trhottle like the Magura, you could search on Magura and find a lot of posts discussing it (and a few about wiring).

But basically it is a resistor, from one of the wires to one of the others. Then there is a tap wire in the middle that allows the rotation of the throttle to change the resistance from taht wire to each of the others.

In most ebike use, it's being used as a variable voltage divider, putting a voltage across teh two main leads, and tapping off taht voltage on the middle wire.

To determine which wire is which, you use your meter on Ohms, usually in the 20K range.

1--Red lead on any wire, black lead on another.

2--Turn the throttle and see if reading changes.

3--If not, then you have foudn the two main wires.

4--Move red lead to the remaining wire.

5--Turn throttle and see if reading changes.

6--If reading goes up in value, then the black lead is on the Ground wire, and the red lead had been on the Positive wire, and is now on the Throttle Signal wire.

7--If it goes down, then black is on Positive and Red was on Ground.

8--If step 2 reading changes, then refer to step 6&7 for results.[/quote]

http://www.endless-sphere.com/forums/viewtopic.php?p=709998#p709998 [quote="amberwolf"]That part I dunno for sure, as they vary.

But if you measure from controller's battery negative to each of the three throttle wires, you'll find one has 0V. Then another has around 5V, and another should have less, or none, but might flicker around. The 5V will be power to the throttle, 0V ground, and the lesser V the signal, most likely. So assuming you measured yours that way already, the higher V is power and the lower is signal input.

Here's a catch, though: If you use a resistive throttle on a typical ebike controller, it will have a pretty big "dead zone" at the start and end, and a fairly narrow range in the middle that actually controls the motor speed. Most ebike controllers these days expect a hall throttle, which might output 0.9-1.4V at it's bottom end (off) and 3.5-4.5V at it's top end (WOT).

But a resistive throttle outputs from 0V to whatever voltage is at it's top (5V in this case).

So if the controller expects say 1.4V-3.5V for it's input, then the entire part of the throttle rotation for 0-1.4V is "wasted motion", then from 1.4V-3.5V it will increase speed, then no further increase from 3.5V-5V. Some controllers even have a protection so that if the throttle output goes over it's expected high end, it shuts off the controller--so the motor will stop powering the bike after you twist the throttle past that point.

If you look up "Magura" and maybe "voltage" or "voltage divider" in the forum search, you'll find a number of ways people have worked around this issue. (if you do find them, you are welcome to add links to them to the wiki article for pot throttles, for future questioners).[/quote]