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 Post subject: Motor build
PostPosted: Jan Fri 24, 2020 5:57 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20610
Location: Warner Robins, GA
Several years ago I stumbled upon this kit

I got it then immediately proceeded to improve it by using a pair of bearings and a shaft.

Using a DC supply I had to watch the speed as if I got it going fast enough it would throw a magnet across the room.

Eventually I wanted to use two coils for more torque so I found a couple pre-built coils which have a threaded iron rod that the coil form is mounted on and that improved torque and speed, but did require a higher operating voltage. Around that time I secured the magnets using better glue.

Maybe a couple years ago I wanted to improve it further after seeing their later kits which use neodymium magnets so I took a new unused rotor, prepared it like the first one and installed four small neodymium magnets only this time I used 5 minute epoxy and used enough to build up the area to the same height as the rotor end caps to ensure the magnets would stay in place no matter how fast the rotor spins.

I then used a small drill bit and a file to get the rotor as balanced as possible.

I actually have faster speed which is somewhat limited by the rotor not being perfectly balanced.

At over 20Vdc on the motor, the waveform on the coils starts having a higher duty cycle and the motor doesn't increase its speed any. Now that could be either because the rotor isn't balanced enough or there is too little torque to increase the speed any so the higher voltage maybe makes the coils stay on longer perhaps. I on;y have gone as high as 30Vdc as I don't want to exceed the input voltage maximum of the 7805 regulator powering the hall effect sensor.

Here's the circuit

Simple motor circuit.png
Simple motor circuit.png [ 9.92 KiB | Viewed 738 times ]

I want to build a couple more of different designs.

One I want to have 8 magnets.

The other I want to have two rotors of four magnets with one rotor having the magnets at a 45 degree offset from the other magnets.

I want both to be controlled by the hall effect sensor, but I also want them to where I can use a function generator to control the speed so that the speed isn't voltage dependent.

The problem I'm running into is that I have no way to actually make the necessary rotors and have them be very nearly perfectly balanced and because of that I haven't done anything at all.

Also if I use a function generator I would need to alter the circuit to use an NPN transistor unless I can find a low cost function generator that can put out a negative pulse.

Now for this type of circuit would a power MOSFET with a low on resistance be any better.

Also would I be able to modify the original circuit to use a power MOSFET?

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