How to fine control a brushless dc motor

[delir66]

Hi, I'm building a pottery wheel for my wife.

Since it needs to reverse direction and have a nice control over rpm, I decided to pick a diy electric scooter motor.

It operates at 48v and comes with a controller.

It has three wires for speed control
-5v
-gnd
-signal.

The problem is that if I use a 100k pot, motor starts spinning when 1.4v and will get to max revolutions at 3.4v. With this 2v range, the potentiometer is not really ideal, as it will change suddenly rpm with the slighlest touch.
I need something that is more accurate and have a longer travel. I would like to use a lever to change rpms...

I tried with a Hall effect sensor, but again the distance from 0rpm to 600rm (full) is too small to be controlled....

I thought that something like an adjustment pot would do, but something difficult to manipulate, need the actuator to be a lever/pedal....

Only idea left is pinting gears for the potentiometer, but that's something i'd like to avoid....

Thanks!

[stj]

Re: How to fine control a brushless dc motor

100k?
try a 4k7 or 5k pot with the 5v and ground on the outer pins
5k is the usual size for analog inputs like that.

[delir66]

Re: How to fine control a brushless dc motor

Thanks for your reply.

No, that doesn't seem to do the trick.
Really not an expert, but unsure if this is a regular analog input. The thing is that it has a really defined start/max rpm)stop voltages. Starts spinning at lowest rpm when 1,30v and maxes at 3,40v (600rpm), if 3,50v will stop.
Looking for a 0 to 250 rpm working range, so my voltage is between 1,35v and 1,60v aproximately.

I attached my laboratory supply and giving that voltage straight to the signal cable, no pots.... With the fine knob from the suply I can get the aproximate range I want.

Thought about building an resistor switch that gives 1.30, 1.40, 1.50, etc.. but I think easiest will have a cheap DAC connected to the pwm of an Arduino, so I can get a power supply that operates from 1,35v to 1,60v in a full pot turn, if that makes sense...

Thanks!

[redwire]

Re: How to fine control a brushless dc motor

For safety, a scooter motor control board has a lot of "deadband" for the throttle. You don't want the throttle stuck... so they waste a lot of the 5V range.
Can you post a picture of the board?
You can make a restricted range potentiometer to give the 2V span but it still is a bit delicate.