How do you build a speed control for a brushless motor??

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canidoit

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Apr 6, 2009
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Is building a speed control for a remote control car motor as simple as adding a potentiometer between the + line going to a set of batteries from the motor?

What I am trying to do is build a motorized system for a camera slider:
BMD_Moco-e1358184266539.jpg

[remote control car motor] <-- [speed control] <-- [7.2 volt battery pack or 4 X 1.5v AA batteries]

Does anyone have any suggestions for a motor that already has a strong power but does not spin fast, I am connecting a pulley direct to the motor so there are no gears to slow down the revolution??

If the motor runs on 7.2 volts at 10,000 rpm, they say that lowering the voltage will slow down the revolution. Will this minimize the motors lifespan and I can not picture lowering the volts enough to get the RPM I need.

Any help appreciated!
 
R/C car motor is brushless now? News to me.

> lowering the volts enough to get the RPM I need.

Which is WHAT? 9000RPM? 100RPM? 1RPM? 1 Turn per day?

And how big is your pulley?

And what happened to the gearbox that was ON the car motor to gear-down to the wheels? Compact prime movers "always" turn faster than vehicle wheels. My Honda is geared-down 4:1 at 50MPH. That may be faster than you want your camera, and the explosion-engine is only turning 2,500RPM which is a bunch slower than your motor. Also the Honda has 28 inch "pulleys" (tires) and your unspecified pulley may be smaller. IIRC a slot-car is geared 8:1 and still goes too fast to see.
 
Sounds like you need to pull some old office equipment and tape players apart to get some motors to play around with and get an understanding of how they work and what they do.

Brushless Motor: Nope, wont work. Brushless motors have drive electronics to drive them. They are almost like miniature 3 phase motors, and the drive electronics takes your DC power, and creates three phase AC sinusoidal signals that drive the motors windings and pull the armature around. The speed is dependent on the frequency of the output of the driver

http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

Brushed DC motor - yes - speed is affected by voltage, but not to the extent that it will be in any way useful for your application. To put it simple, long before you lower the voltage to get the speed you want, there would not be enough power to make the motor spin, let alone do anything useful. Experimentation required.

There are two ways to do this on the budget of a hobbyist.....

1. Small DC motor with a high gear reduction already built in. For example....... http://www.jaycar.com.au/productView.asp?ID=YG2732&form=CAT2&SUBCATID=983#1

2. Stepper motors - but you do not just hook them to a battery with a pot. Research and experimentation required.

Cheers,

T


 
Thanks people for the replies!

I think I am getting somewhere.

I found some items on ebay.

So I plan to get the following:
12v DC 120rpm motor: 
http://www.ebay.com/itm/IN-UK-Electrical-Machine-Shaft-Torque-120RPM-DC12V-Geared-Motor-for-Auto-Shutter-/140932949028?pt=LH_DefaultDomain_0&hash=item20d0422424

Reversing Switch PWM Speed Controller:
http://www.ebay.com/itm/Adjustable-DC-Motor-Speed-PWM-Controller-10V-12V-24V-30V-Reversing-Switch-120W-/321166067425?pt=LH_DefaultDomain_0&hash=item4ac6fd46e1

It sais there that the controller can run on 10-30 volts and that its rated current is 3amps and maximum 4amps.

Now I plan to get this power pack that uses 10 X AA batteries to give 12 volts:
http://www.ebay.com/itm/12V-10AA-Battery-Pack-for-LCD-Video-Monitors-/200989639725?pt=LH_DefaultDomain_0&hash=item2ecbea842d

How does the amps work on the battery pack?? So if there are 10 X AA batteries installed that are various in ampage from 1800 to 2600, does that mean the amps on the power pack is 1800mah when connected to my controller or 2600 or something else?? Will this battery pack idea work??

Also do batteries run out quicker when running a motor than a video monitor that the power pack is made for??

Also if you notice that something is not going to work in my plan, please advise :)
Thanks
 
Also, someone told me that if my circuit runs at 5amps/12v dc and I connect a 10amp 12 volt battery to it. It is OK, as long as I connect a 5amp fuse between the battery and my circuit. My circuit will only take up no more than 5amps from the battery?

Is this right, because I remember that the more amperage you have on your battery, the longer your battery will last. So if I decide to get this battery pack:
http://www.ebay.com.au/itm/New-DC-12V-Portable-9800mAh-Li-ion-Super-Rechargeable-Battery-Pack-2-/230755241536?pt=AU_Electronics_Batteries_Chargers&hash=item35ba158e40&_uhb=1

Which sais it has 9800mah and my controller can only take 4amps max. If I connect the battery to my controller, it should be OK as long as it has a 4amp fuse in between?? Is that right??

Also, if a motor struggles to turn, does that mean, it tries to use more amps, which then may cause the controller to push past 4amps from the battery??

Thanks!

 
Brushless dc-motors are not good candidates for running slow - they have zero momentum close to zero rpm.

I'd recommend an Arduino, a stepper shield, and a stepmotor.

Alternatively a digital "limitless" servo, hooked up to a simple servo tester.

Jakob E.
 
Perhaps an old dot matrix printer?

How fancy do you want to get.. a stepper motor can control each step... THere are many crude speed controls.

JR

PS: back in the '70s we needed to speed control a cassette deck motor so added a tachometer to it, but that was not a cheap solution.
 

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