Designing a Linear Drive Motor for an Educational Toy

[dragonqi]

Hello,
I am seeking assistance with a design project for my engineering design class. We are tasked with developing an educational toy and then assembling a working prototype. Our group decided to develop a small scale electromagnetic roller coaster (Yes we are quite ambitious for a group of freshmen). The conceptual design we have so far is a small electromagnet attached to a hall sensor, a transistor, and a 6V power supply. We have assembled a small carriage to carry the circuitry.

The electromagnet is composed of a 1/2" long by 1/4" thick bolt wrapped with thinly insulated copper wire. It is positioned off the front off the cart and the hall sensor is positioned off of the back. We have a central thrust track composed of alternating NSNS permanent magnets. The permanent magnets are 1/16" thick by 1/8" diameter Neodyium magnets.

Our working theory is that the hall sensor enters the permanent magnet's field and turns on. This completes the circuit and activates the electromagnet which pulls itself towards the next magnet. This moves the sensor out of the magnetic field, turning it and the electromagnet off. inertia keeps the cart moving forward until it enters into the next magnetic field which activates the electromagnet (with its poles flipped). The cycle repeats until the cart reaches the end of the track, where there are no magnets, and comes to a stop.

We have run into a few problems with our EM not being strong enough to pull the cart to the next magnet and the poles not flipping when the magnet is re-activated. Also, heat has become a bit of an issue. I was wondering if anyone here might have any insight for a bunch of overly ambitious freshmen lol.

Thanks,
Dragon

 

[berkeman]

Our working theory is that the hall sensor enters the permanent magnet's field and turns on.

Hall sensors do not turn On and Off. Their resistance changes in a magnetic field, which you can sense with an external bias circuit attached. That is probably not what you are intending for this part of your vehicle to do.

Instead, you may be wanting to use the external magnetic field to flip a switch to alternate the polarity of the field that you generate with your electromagnet. It may take a more complicated arrangement of the permanent magnets, and it may take more than one electromagnet on your vehicle, but it seems like it could be made to work.

One problem is that most "magnetic switches" (use a Google search) respond the same for both polarities of the external field. When you are searching for them, add some extra search terms into see if you can find some that are "double-throw" for the two different polarities of magnetic field.

Good luck!