Electromagnetic/DC motor gurus...

[Howard]

Originally posted by: Eli

Originally posted by: Howard
School project. We'll be using retinal dynos to measure the RPM.

Bah! How ghey.

At least invest in a vibration tachometer so you can take accurate measurments.

How much voltage will you be working with?

Do you have to make your own armature and electromagnet from scratch?

6V or 9V. We get bonus marks for making it run with 6V.

EDIT: Yes, everything from scratch. I plan on using using a big U-bolt as the core, with those plates welded onto nuts that are screwed on. 24/26/28 gauge magnet wiring, aluminum shaft, etc.

 

[Eli]

Originally posted by: Howard

Originally posted by: Eli

Originally posted by: Howard
School project. We'll be using retinal dynos to measure the RPM.

Bah! How ghey.

At least invest in a vibration tachometer so you can take accurate measurments.

How much voltage will you be working with?

Do you have to make your own armature and electromagnet from scratch?

6V or 9V. We get bonus marks for making it run with 6V.

EDIT: Yes, everything from scratch. I plan on using using a big U-bolt as the core, with those plates welded onto nuts that are screwed on. 24/26/28 gauge magnet wiring, aluminum shaft, etc.

Interesting. I wish we had projects like this when I was in school.

It shouldn't be hard to get one to run on 6V. You just have to be conservative with your windings...

So the ultimate goal is the fastest motor on 6V? Hmmm.

A U bolt as the core of the stator electromagnet? U bolts aren't typically square, are they?

 

[Howard]

Originally posted by: Eli

Originally posted by: Howard

Originally posted by: Eli

Originally posted by: Howard
School project. We'll be using retinal dynos to measure the RPM.

Bah! How ghey.

At least invest in a vibration tachometer so you can take accurate measurments.

How much voltage will you be working with?

Do you have to make your own armature and electromagnet from scratch?

6V or 9V. We get bonus marks for making it run with 6V.

EDIT: Yes, everything from scratch. I plan on using using a big U-bolt as the core, with those plates welded onto nuts that are screwed on. 24/26/28 gauge magnet wiring, aluminum shaft, etc.

Interesting. I wish we had projects like this when I was in school.

It shouldn't be hard to get one to run on 6V. You just have to be conservative with your windings...

So the ultimate goal is the fastest motor on 6V? Hmmm.

A U bolt as the core of the stator electromagnet? U bolts aren't typically square, are they?

No, they're not. They're round. But I wanted a U-bolt and my dad asked me if it could be square, so I just tossed out the question.

What do you mean by conservative winding? More turns = stronger, right?

Yes, that is the ultimate goal.

 

[Howard]

Got any ideas for an inexpensive/free low-friction lubrication?

 

[Eli]

Originally posted by: Howard

Originally posted by: Eli

Originally posted by: Howard

Originally posted by: Eli

Originally posted by: Howard
School project. We'll be using retinal dynos to measure the RPM.

Bah! How ghey.

At least invest in a vibration tachometer so you can take accurate measurments.

How much voltage will you be working with?

Do you have to make your own armature and electromagnet from scratch?

6V or 9V. We get bonus marks for making it run with 6V.

EDIT: Yes, everything from scratch. I plan on using using a big U-bolt as the core, with those plates welded onto nuts that are screwed on. 24/26/28 gauge magnet wiring, aluminum shaft, etc.

Interesting. I wish we had projects like this when I was in school.

It shouldn't be hard to get one to run on 6V. You just have to be conservative with your windings...

So the ultimate goal is the fastest motor on 6V? Hmmm.

A U bolt as the core of the stator electromagnet? U bolts aren't typically square, are they?

No, they're not. They're round. But I wanted a U-bolt and my dad asked me if it could be square, so I just tossed out the question.

What do you mean by conservative winding? More turns = stronger, right?

Yes, that is the ultimate goal.

Maybe I'm totally wrong, as I'm no electronics expert.. but I think it's a tradeoff. More windings will be stronger.. to a point, then you start running out of voltage to push the current through.

 

[Howard]

V = IR

More voltage = more current for the same resistance (length of copper)

More turns = stronger field for the same current

More turns = more resistance

I don't know the best balance.

 

[Eli]

Originally posted by: Howard
Got any ideas for an inexpensive/free low-friction lubrication?

Hmm. What kind of bearings are you going to be using? Just plain bushings?

Maybe some spray on graphite lube(meant for chains).. might be kinda expensive though.

3-in-1 oil would probably work. It's nice and thin, so you wouldn't run into viscosity resistance..

 

[Eli]

Originally posted by: Howard
V = IR

More voltage = more current for the same resistance (length of copper)

More turns = stronger field for the same current

More turns = more resistance

I don't know the best balance.

Yeah. I would do some heavy electromagnetism research. I am sure you can find some stuff on different core materials, windings, etc. Maybe you can even find a electromagnetism forum.

You should ask your teacher if you can build a tesla coil instead of a motor. Scare the sh!t out of your classmates.

"Hold my hand"

 

[Howard]

Originally posted by: Eli

Originally posted by: Howard
Got any ideas for an inexpensive/free low-friction lubrication?

Hmm. What kind of bearings are you going to be using? Just plain bushings?

Maybe some spray on graphite lube(meant for chains).. might be kinda expensive though.

3-in-1 oil would probably work. It's nice and thin, so you wouldn't run into viscosity resistance..

Probably not even bushings. Maybe paperclip arm supports =)

 

[Howard]

Tesla coils are dangerous. If it blew up I'd probably be suspended.

I blew a fuse in science lab once. I placed a bunch of staples (glued together, like how they come from the package) into a socket. I got a friend to push it in, and everything just went dark.

 

[Eli]

Originally posted by: Howard
Tesla coils are dangerous. If it blew up I'd probably be suspended.

I blew a fuse in science lab once. I placed a bunch of staples (glued together, like how they come from the package) into a socket. I got a friend to push it in, and everything just went dark.

Tesla coils aren't dangerous.. Where did you hear that?

I mean, sure.. a very large one would be dangerous.. but.. lol. There is nothing to blow up with a tesla coil, it's just coils of wire and some simple electronics.

If it's just paperclip supports.. 3-in-1 oil will be fine.. anything really, WD-40...

 

[PowerEngineer]

I think you should consider having each of the three windings extend all the way through to the other side of the rotor, making it a six pole armature rather than a three pole one (or drop the number of windings to two or one for fewer poles). You'll also need to double the number of commutator "bars" to provide for field reversal for each winding. The orientation of the commutator bars needs to be set such that the rotor's field is counter to the stator's field (i.e. N to N and S to S) just past dead center. If you're still looking for materials, large iron nails make reasonably good core iron. The iron in motors and transformers is laminated in order to limit eddy currents (which contribute to unwanted heating and reduce effeicency). The "pick axe" shape is intended to better spread the flux being produced in the motor's rotor (flux goes where there's iron much like electricity goes where there's copper); the aim is to even out the flux densities in the stator iron.

Good luck!

 

[Howard]

A 6-pole would definitely be too complicated. How would you go about building a 6-pole armature?

 

[LordMorpheus]

It would be easy to go with a four . . . i fergit what they are called, but replace the 3 coil part with a four coil, it will make it so that you can have it running with only two split ring commutators. As it is now, you would need three. The beuty of even number coil electric motors is that you can run two coils off of one split ringer. Using the three coil design, you each coil will need its polarity reversed at different times. This means that you need a split ringer for each coil.

So, in conclusion, it will work, but it is inefficient and a wast as it is. Add another coil, get more power, a more continuos torque output, and make it easier to build and run.

Trust me on this.

edit: on seeing your wiring diagram, if you plug it all up correctly, yes, it will spin, but it will not ever be able to output as much torque using that diagram as it would be able to otherwise, here is why(yah!):

you know that force, mag feild, current will always be perpendicular, correct, so you get the most power of of the motor when the pole of the armature is in the plane of the magnetic feild due to the horshoe magnet (the current is flowing perpinduclar to the pole . . its going around it in a coil). But, using your commutator, none of your poles will have current in them when they could provide the most torque. this is bad and needs fixing.

 

[KMurphy]

Originally posted by: Howard
V = IR

More voltage = more current for the same resistance (length of copper)

More turns = stronger field for the same current

More turns = more resistance

I don't know the best balance.

More voltage = less current
More turns = more mass = more wk^2
You want low mass and low resistance for your project. How much available current will you have from your 6V source? We can size the wire for windings with that information.

 

[KMurphy]

You may want to register and post your question here:
http://www.eng-tips.com/gthreadminder.cfm/lev2/11/lev3/47/pid/237
There is a lot of practical experience at this site for all engineering disciplines.

 

[PowerEngineer]

Yes, I agree that a six pole design would be too complicated (but I didn't know how you came up with three poles in the first place)

A four pole design with two windings will be complicated enough; a two pole design with one winding would be much easier to build.

If the object is to maximize RPM, then you'll want to keep the rotor diameter as small as possible to minimize windage. On the other hand, if you're trying to maximize torque then you'll want a larger rotor where the replusive force is applied against a larger "lever" to the shaft.

You can produce the same magnetic field strength with 6 VDC as you can with 9 VDC. What matters is the number of turns, the current, and the flux carrying capacity of your core. Example: a 90-turn coil with 9 VDC will have only 75% of the field strength of two 60-turn coils connected in parallel (NOT series) with 6 VDC. The important thing is to be sure you have a high capacity six volt supply like a bunch of lattern batteries, not some little AA ones. You don't want your voltage to drop as you draw lost more current with those coils in parallel.

Other things to watch out for: you already know that the "bearings" and lubrication will be important, solid contact between the brushes and commutator is a must, and minimize the air gap between the rotor and the stator (the size of the air gap has a huge impact on the flux carrying capacity of your core circuit).

Good Luck!

 

[Howard]

Originally posted by: LordMorpheus
It would be easy to go with a four . . . i fergit what they are called, but replace the 3 coil part with a four coil, it will make it so that you can have it running with only two split ring commutators. As it is now, you would need three. The beuty of even number coil electric motors is that you can run two coils off of one split ringer. Using the three coil design, you each coil will need its polarity reversed at different times. This means that you need a split ringer for each coil.

So, in conclusion, it will work, but it is inefficient and a wast as it is. Add another coil, get more power, a more continuos torque output, and make it easier to build and run.

Trust me on this.

edit: on seeing your wiring diagram, if you plug it all up correctly, yes, it will spin, but it will not ever be able to output as much torque using that diagram as it would be able to otherwise, here is why(yah!):

you know that force, mag feild, current will always be perpendicular, correct, so you get the most power of of the motor when the pole of the armature is in the plane of the magnetic feild due to the horshoe magnet (the current is flowing perpinduclar to the pole . . its going around it in a coil). But, using your commutator, none of your poles will have current in them when they could provide the most torque. this is bad and needs fixing.

The poles do have current in them when they're perpendicular to the field.

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