Permanent Magnet Starter Motor

Let's Make Robots Projects Showcase
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I found homepages.which.net/~paul.hills/ … rters.html a while ago.
Until then, I had thought that starter motors were a no-go, because one couldn’t reverse them.

It wasn’t until yesterday that I realized that my brother was a mechanic (ok, yea, that’s dumb) and that he could get me one easily.

He ripped the starter out his Ford Probe parts car and gave it to me (::plop::).
I then hooked up his car battery to the motor, to make sure that it worked.

(By the way, if anybody’s planning on trying it, you hook the black jumper onto the motor’s frame, the other side of the black jumper onto the negative battery terminal, the red jumper onto the large bolt sticking out of the solenoid, and the other side of the red jumper onto the positive battery terminal. Then you start the motor by taking a large gauge wire and bridge the positive terminal to the smaller terminal on the solenoid. This activates a 12V relay which allows the motor to draw current.)

And, boy does she roar!

So, I ripped it appart and cleaned it up real shiney with an inordinant amount of free cans of brake cleaner (another perk of a mechanic in the family).
Then, I layed it out on some newspaper and dried it with a hair dryer, and took the picture below (I didn’t include the solenoid in the pic, because I don’t need it):

x10.putfile.com/3/6313061062-thumb.jpg

To my great dismay, I looked closely at the motor housing, and found permanent magnets instead of field coils/pole shoes.
The starter that the guy who made the above site took appart was a field series motor.

Does anyone know if a permanent magnet starter can be modified for reverse?
And how that would be done?

Is there any reason not to use a PM motor in a robot?

Are they about as strong as field series starters?

I sent an email to the guy who made that site, but I’m not sure if that’s still an active email account.
I figured that a couple hundred heads were better than one.

:smiley:

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PM motors tend to be more efficiant the field series. So if your going to throw that in a bot your better off with the PM I think. Also the reason why they say you can run one in reverse is because of motor timing. One way to check if the motor has timing is to look at the brush hoods and the PMs. If they line up totally symetrical then the motor isnt timed and will should be fine in reverse. The motor you got looks like a good one. Just make sure you clean the comm. very well, maybe even cut it.

A timed motor can run in reverse, its just that it when it does it has horrible effiiciancy and can create a lot of heat and in some cases destroy itself.

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Thanks, Topher!

So that means that all I’ll have to do connect the positive terminal to the frame and the negative terminal to the Vin on the motor (the exact reverse of what is normally done).

The odd modifications on the site only concern field series motors, then?

Dan Albert (the head of South Jersey Robotics Group) sent me this link, which seems to agree with what you said.
injoy-1.com/catal_1.htm
Apparently, they sell a Ford starter motor that is quite happy to go in both directions.

By the way, I scrupulously cleaned the commutator, as well as the brushes, the reduction gears, the output shaft, …, and even the bolts and nuts, hehe. Brake cleaner, borax, a water rinse, and a hair dryer, totally owns auto grease.

After I finish my homework (homework is meant to keep young people from taking over the world; that’s why all the President, kings, czars, and etc. are all old people) I’ll start modifying the mechanical parts of the motor.

I’ll need to figure out how to weld the shaft into the out-position.
Then I’m going to hack appart the unnecessary pieces of the shroud.
Then I’ll replace the bronze “bearing” with a ball bearing.
And then I’ll lube everying with a lithium grease and then slap it back together.

I’ll keep everyone updated, but it’ll be a while before I get anything done (I have to get my brother to show me how to weld, hehe.)

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Yes homework is designed to keep people like us form taking over. Its the man tryen to keep us down.

Anyways if you have one, tig weld the shaft. Mig welding might not hold up depending on the power your putting threw it.

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I though starter motorsa were a no go because they are designed for extremely high load / current draw, but for very a short duty cycle. A motor designed to be run for only 5 seconds shouldn’t be able to operate for 10 or 20 minutes at a time, even if the load is reduced. Just my $0.02 worth. Wonder why the keyboard doesn’t have a “cents” character. :stuck_out_tongue:

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I suppose that it comes down to relying upon the safety factors.
I’m not saying that I won’t have to replace these motors every once in a while, but since they’re free…
Even if I have to start buying them, they’re only about 20 bucks from my local junkyard.

Of course, it takes a bit of time to prepare them, but that shouldn’t take long after I get the first done.
And, since any dc motor probably won’t last long under the same sort of abuse, I’d rather build my first bot out of cheap ones.

The only real annoyance is the high amp draw, but a bit of modification reduces that.
Hopefully, I’ll find a NimH or NiCd (blegh!) cell the size of a Lead-Acid battery, and that’ll solve the last of my problems.

Has anyone found any of those?

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Your right they do. Still doesnt mean you cant use one tho. You could easily rewind the motor with more windings and/or use hard brushes and softer springs. You could also increase the amount of magnet poles for more torq, less rpm. What really matters is laminations and overal size of the motor as well as the comm. Windings, brushes, bearings, and all can easily be changed. I used to use CD-ROM and Floppy motors and modify them to power my RC helicopters. Worked great and the only real cost was $2 for the magnet wire.