getting motor (DC) down to 2 RPM

LCGarage

Hey, this is my first post. Just got the discovery kit and have been enjoying it tremendously.
I also bought the HB-25 motor controller to drive a DC gear motor.
My application has the motor turning in one direction until a limit switch is hit, then waits for me to push a button, then goes in reverse until another limit switch is hit.

The problem is with the 12VDC gear motor (50in-lbs) I have does not have enough torque for the load.
I took a 24VDC motor out of one of my kids elec vehicle toys (this motor is at least 10X bigger than the 12VDC gear motor)...that works but spins too fast. I can slow it down, but lose the torque.

I do have this which may be choppy, but give enough of a pulse to move, then delay, so with the load may give just a few rpms:
DO
PULSOUT HB25, 750 + 50 'Motor 1 Forward Slowing
PAUSE 100
PULSOUT HB25, 750 ' Stop Motor 1
PAUSE 1000
LOOP

I am·trying to find another higher torque gear motor....
Is there any way to get that 24VDC motor (form kids elec vehicle) down to 2rpm and still have some torque?
Any other Ideas on what I can do with the program PBasic?
Maybe a stepper motor?

I' ll post some pic latter
Thanks!
-Grant

Leon

No, they simply aren't designed to run that slow. You need one with a gearbox, or a stepper motor.

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Leon Heller
Amateur radio callsign: G1HSM

Martin_H

Besides slowing down the rotation a gearbox will also increase the motor's torque.· You could probably even get away with a smaller motor.· Most toys use this approach, so you might be able to get a gearbox out of a broken toy or use a Lego gearbox.

Post Edited (Martin_H) : 7/11/2010 10:58:43 AM GMT

APSpijkerman

have you considered using a servo ?
A servo has a build in gear box, so it can have a lot of torque, and as it
has a build in driver .. you only need one pin to control it.
And you can specify the angle at which it has to be, a draw back is that
the angle you can put it in is limited. Unless you modify it to be
just a motor with gear by removing the electronics and endstops.
Which also might be convinient for you as you can use the servo horn
to control end switches.

What i used when i needed to turn something very slow was the motor
from an old CDrom drive. It is a brushless motor meaning you have to
make a 3 phase signal to drive it. Which took like 6 transistors and 6 diodes
but it can run at very very slow rpms, and you can glue a CD on it to drive things.

LCGarage

Ok thanks for the quick feed back. Yes I am seeing the torque limitation of a slow dc motor first hand.
Thanks for the help. I did promise some pictures...

Here is the 50 in-lb motor and gear reduction assy


This is the 1st doner vehicle a Razor Chopper


Out of this came a 24V (250W) DC motor THAT has a lot of torque, but not at low speed. This is the motor and my test setup


Now here are the·2nd doner vehicles a couple of electric kids vehicles. Saw these in a dumpster a few days ago, grabbed them this morning


Out of these came·DC motors·with some gear reduction...these are the ones I'm working with now


Thanks again for the inputs!
-Grant




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Basic Discovery Kit (newbie)