How does a brush DC motor stop?

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noobster
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How does a brush DC motor stop?

I don't know but I can guess that to stop a dc motor you would cut the input current and run the produced power from the motor from the continuing rotation through a resister. Though if the resister were to have too many ohms wouldn't it act like a open circuit and not work? I'm confused.

antiscab
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Re: How does a brush DC motor stop?

what is the application for this motor?
what type of motor is this? (PM, series, shunt, sepex, compound?)

if road going, mechanical breaks are ususally the answer :)

if not, than a resistor and a capacitor could be used, or if you can wait, just let the motors (and loads?) internal friction cause the motor to stop.

Matt

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noobster
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Re: How does a brush DC motor stop?

It was for a pm motor. It's for this ongoing idea I have for a planetary cvt. By limiting the speed of the planets you can change your gear ratio. I wikipedia'ed dynamic braking after posting and it confirmed my fears, that the energy is wasted as heat or can be used to charge the battery like regenerative braking. My idea was that I could control the primary more rpm and to a lesser extent load making for a more efficient overall drivetrain. But the energy wasted as heat from the dynamic brake would probably be more than I'd save by running the primary motor at the proper rpm. It's either this, a servo actuated belt cvt or a pw50 gearbox.

go green

spinningmagnets
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Re: How does a brush DC motor stop?

When you stop applying power to the motor, it will free-wheel a while, and will slow down and stop from friction.

If your controller configures it to regen, you are then applying a load to the motor, and your vehicle slowing down will spin the motor until it comes to a stop.

When you release the trigger on a portable circular saw, the blade can spin for a very long time because it acts like a flywheel, so many of them are required to have an actual brake that applies when there is no power going to the motor.

You should study how a car differential works, perhaps find a Google animation. During cruise, both tires get some input, but when theres a big difference in traction, one tire spins, and the other just rolls along.

This is good for a common car turning a sharp corner, but in slippery snow and rain conditions, The Limited Slip Diff (LSD) can make sure that both tires get some power. These are also popular for performance cars, so when stepping on the accelerator, both tires get power for taking off.

Some have a self actuating viscous LSD (fluid activated) to help tranfer extra power to wheels that start spinning in slippery conditions.

I think this may prove useful for you in developing a CVT from a planetary gear. You can get some cheap used planetary gear sets from an automatic transmission re-builder.

If the 3 planets are attached to a side plate, and the operator can adjust how much that plate spins in relation to the pinion and ring gear (like a caliper on the side plate like its a disc brake?) it could perform like an infinitely variable trans? I'm sure there must be a more clever way to get some free junk to work well, sound like fun and I wish you luck.

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