Designing a brushless AC motor for Formula Student


by Frosteh
Tags: brushless, designing, formula, motor, student
Frosteh
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#1
Feb19-12, 02:28 PM
P: 8
I am on a Formula Student team and we have decided to design our own brushless AC motor. Our main issue is how we will cool the motor, since we want to keep weight down while also increasing power output. We will be making the rotor from forged Titanium (Ti6Al4V) and the housing from forged 7075-T6 aluminum. We want to use water (or a water/ethylene glycol mix) to cool the aluminum housing which will be cooling the magnets and coils. The main concern is that somehow the polarity of water will affect the workings of the magnets and reduce our power output. Is this an issue? Our other idea was to circulate mineral oil (like the stuff used in transformers) around the coils directly to cool them. Which would be a better method and do we have anything to worry about if we use water/EG to cool it?

Second, we are wondering about winding the magnets. If we want a higher power to weight ratio, should we use smaller gauge wire and more winds, or larger gauge wire and few winds around the magnet?
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xxChrisxx
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#2
Feb20-12, 05:28 AM
P: 2,032
Don't really know about cooling brushless motors, but.

Formula Student team
rotor from forged Titanium (Ti6Al4V)
housing from forged 7075-T6 aluminum.
You must be bloody well funded.
Has anyone costed this?
Frosteh
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#3
Feb20-12, 06:33 PM
P: 8
Quote Quote by xxChrisxx View Post
You must be bloody well funded.
Has anyone costed this?
We're actually broke as ****. My dad's company forges structural pieces for Boeing's planes and is being generous to donate the blocks we need. Not pressed into the shapes yet, as tooling costs would be roughly $200k, but we have the tools to machine aluminum and titanium. If this were priced out, though, it would be damn expensive, that's for sure.

xxChrisxx
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#4
Feb21-12, 01:12 AM
P: 2,032

Designing a brushless AC motor for Formula Student


Buy one. From steel.

Thats part of engineering. There are about a million brushless motors out there. There will be one that fits your needs, and if someone has a catalogue part thats works perfectly well. You dont design a bespoke one yourself. As one offs cost an absolute fortune.

If you agree to slap a sponsor sticker on you may even get it free.
Frosteh
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#5
Feb21-12, 01:47 AM
P: 8
Quote Quote by xxChrisxx View Post
Buy one. From steel.

Thats part of engineering. There are about a million brushless motors out there. There will be one that fits your needs, and if someone has a catalogue part thats works perfectly well. You dont design a bespoke one yourself. As one offs cost an absolute fortune.

If you agree to slap a sponsor sticker on you may even get it free.
While there are tons of brushless motors, very few have the specs we're looking for. The best fit for our application is the YASA-750, which costs $11k. They've already said they won't sponsor us. The motor we're going to use needs to be less than 10kg, output ~35kW, and fit our budget. Since we have the CNC mills and tools to mill the parts, and the metal is donated, it's much cheaper and more effective for use to design and build our own. Motors are quite cheap, considering they are basically metal, magnets, and copper wire.
xxChrisxx
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#6
Feb21-12, 02:45 AM
P: 2,032
So is this a pure electric formula, or some kind of hybrid?

Not having something available (at a sensible price) is a pretty good reason for building it yourself. It's good that you have invesigated buying a motor first.
You see it all the time with students, they think they have to design everything and don't consider buying stuff out.

Sorry I couldn't help with the motor or cooling question.
Frosteh
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#7
Feb21-12, 02:50 AM
P: 8
Quote Quote by xxChrisxx View Post
So is this a pure electric formula?

Not having something availalbe is a pretty good reason for building it yourself.
Indeed. We actually have two cars: one running a 4 banger (not sure which motor, since I'm not working on that car) that we'll run this year, and the electric one which will be complete next year.
OldEngr63
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#8
Feb29-12, 05:18 PM
P: 343
I would suggest that you better get someone who knows what they are doing to work on the electromagnetic design of this motor. Without that, you could easily wind up with a lot of machined pieces wrapped in wire that produce little or no power. Remember that this all has to function with your power supply. There are lots of concerns ab out getting the maximum current to flow (to produce maximum torque), which involves a lot of electrical considerations. You also have to worry about just where the heat will be generated and how you can get it out.
jim hardy
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#9
Feb29-12, 07:39 PM
Sci Advisor
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P: 3,139
If Dad's got connections at Boeing...
perhaps see what he can find out about aircraft generators like the first four here:

they're lightweight rotating machines on same order of magnitude you're contemplating.....

http://www.ips-llc.com/products.htm

if you could find one on surplus market to study..


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