speed control for wiper motor (BBQ Rotisserie)

[chothers]

I'm disigning a BBQ rotisserie and the type of motor I plan to use is
a windshield wiper motor. The problem I'm having is that the motor
turns to quickly in low speed!

I don't know what make and model of wiper motor I have, but I think
the specs are something like this...

High Speed
- 106 RPM, 12VDC, 4 Amps

Low Speed
- 41 RPM, 12 VDC, .91 Amps

I could simply gear it down, and have all the parts to do that, but I
would much rather have a variable speed motor.

I'm having trouble finding the correct parts to create the speed
control.

Do I need something like a Potentiometer?

 

[petrus bitbyter]

I'm disigning a BBQ rotisserie and the type of motor I plan to use is
a windshield wiper motor. The problem I'm having is that the motor
turns to quickly in low speed!

I don't know what make and model of wiper motor I have, but I think
the specs are something like this...

High Speed
- 106 RPM, 12VDC, 4 Amps

Low Speed
- 41 RPM, 12 VDC, .91 Amps

I could simply gear it down, and have all the parts to do that, but I
would much rather have a variable speed motor.

I'm having trouble finding the correct parts to create the speed
control.

Do I need something like a Potentiometer?

Standard mehod to control a DC motor is PWM. You need a puls generator with
variable pulswidth. A 555 timer will do this job. The pulses are used to
switch a power transistor that controls the motor.

petrus

 

[Jim Thompson]

I'm disigning a BBQ rotisserie and the type of motor I plan to use is
a windshield wiper motor. The problem I'm having is that the motor
turns to quickly in low speed!

I don't know what make and model of wiper motor I have, but I think
the specs are something like this...

High Speed
- 106 RPM, 12VDC, 4 Amps

Low Speed
- 41 RPM, 12 VDC, .91 Amps

I could simply gear it down, and have all the parts to do that, but I
would much rather have a variable speed motor.

I'm having trouble finding the correct parts to create the speed
control.

Do I need something like a Potentiometer?

I doubt that you'll have enough torque without gearing down a
higher-speed motor.

I think I'd start with a stepper.

I have a little hand-turned rotisserie that holds a dozen
shish-kabobs. It's a pain-in-the-butt to turn a little increment at a
time. Maybe I'll play with automating that.

Anyone know where I might obtain the equivalent of speedometer cable,
but high-temperature-capable?

...Jim Thompson

 

[Zak]

I'm having trouble finding the correct parts to create the speed
control.

Do I need something like a Potentiometer?

It is best to reduce the voltage. A low voltage power supply would work
best, and should be enough. Wiper motors are strong, and the reduced
torque at lower voltage will still be enough.

For a 'you can find it in your garage' solution, you can wire a car
lightbulb in series. Lower wattage will mean slower rotation.

Now if you'd like to do it 'right' you could use a constant voltage and
mke this higher asthe current goes up. This is to compensate for
theinternal resistance. If done right, you can get the motor to ren
really slow with acceptable force.

You need an op-amp, some resistors, a potentioneter to set the speed and
a potentiometer for the stability control, and some transistors to
manage the current.


Thomas

 

[Jim Thompson]

[snip]

Now if you'd like to do it 'right' you could use a constant voltage and
mke this higher asthe current goes up. This is to compensate for
theinternal resistance. If done right, you can get the motor to ren
really slow with acceptable force.

You need an op-amp, some resistors, a potentioneter to set the speed and
a potentiometer for the stability control, and some transistors to
manage the current.


Thomas

See "MotorDriver-Simple.pdf" on the S.E.D/Schematics Page of my
website. The amplifier must be able to support the current
requirements of the motor.

...Jim Thompson

 

[Joerg]

Ok, hold the tomatoes, but can I make a low tech suggestion?

A few years ago I have seen a cheap rotisserie "motor" that was simply
wound up like an old alarm clock. Just imagine what would happen to Jim's
shish-kabobs if the power goes out, or in the case of batteries the old
ones were accidentally left in there and the rotisserie grinds to a halt.

Personally I prefer the human feedback version. Hand turns the meat, eyes
provide the feedback, and loop stabilization is performed with a nice
cold bottle of Corona. An even higher phase margin can be achieved by
substituting the Corona with a Margarita. Top shelf, of course.

Cheers, Joerg.

 

[Jim Thompson]

Ok, hold the tomatoes, but can I make a low tech suggestion?

A few years ago I have seen a cheap rotisserie "motor" that was simply
wound up like an old alarm clock. Just imagine what would happen to Jim's
shish-kabobs if the power goes out, or in the case of batteries the old
ones were accidentally left in there and the rotisserie grinds to a halt.

Personally I prefer the human feedback version. Hand turns the meat, eyes
provide the feedback, and loop stabilization is performed with a nice
cold bottle of Corona. An even higher phase margin can be achieved by
substituting the Corona with a Margarita. Top shelf, of course.

Cheers, Joerg.

I wouldn't mind a wind-up (1) if it existed and (2) would run for at
least 30 minutes... I like to do my Halibut kabobs over a slow fire.

Too much "phase margin" results in burnt meat ;-)

...Jim Thompson

 

[Joerg]

Jim, I am not sure but I believe these are the ones you have to crank and then
they trundle for a long time:

http://www.fufgirarrosti.it/catalog/product_info.php?cPath=24_25&products_id=31

Then when the wheels slow down a little bell rings and you have to crank
again. Since it's Italian I guess some red wine in hand is acceptable while
cranking. Even when it doesn't go on the food. Ok, these are very high end.
You can also get them "electrified".

The one I was referring to was small and cost under $20, I believe it came
from a Canadian camping gear outlet. A couple was using it on a campground and
even though that thing was thoroughly dented up it ran for at least 20
minutes.

Regards, Joerg.

 

[Jim Thompson]

Jim, I am not sure but I believe these are the ones you have to crank and then
they trundle for a long time:

http://www.fufgirarrosti.it/catalog/product_info.php?cPath=24_25&products_id=31

Then when the wheels slow down a little bell rings and you have to crank
again. Since it's Italian I guess some red wine in hand is acceptable while
cranking. Even when it doesn't go on the food. Ok, these are very high end.
You can also get them "electrified".

The one I was referring to was small and cost under $20, I believe it came
from a Canadian camping gear outlet. A couple was using it on a campground and
even though that thing was thoroughly dented up it ran for at least 20
minutes.

Regards, Joerg.

Thanks, Joerg! We have a camping outfitter about five miles away.
I'll look there.

...Jim Thompson

 

[Dave Cole]

I doubt that you'll have enough torque without gearing down a
higher-speed motor.

I think I'd start with a stepper.

I have a little hand-turned rotisserie that holds a dozen
shish-kabobs. It's a pain-in-the-butt to turn a little increment at a
time. Maybe I'll play with automating that.

Anyone know where I might obtain the equivalent of speedometer cable,
but high-temperature-capable?

...Jim Thompson

Look at surplus outfits for the remote-tuning cables used in the old airborn
ADF and comm radios when they were suitcase-sized toob units mounted below
decks w/ small cockpit control heads. Seems like these cables were pretty
tough.
HTH
Dave Cole