Update 15.11.13

Update 15.11.13

Since the last update, I have finished machining all the parts for the magnetic coupling on the propeller side. For machining the slots in the ring that holds the magnets, the institute for product development and materials (IPM) at NTNU kindly let me use their workshop. I had to use a rotary table to index the slots, and this is not available at the workshop I mainly use.

Milling the tabs that will connect to the clutch grooves on the inner hub of the propeller. These tabs will transmit torque from the coupling to the propeller and ensure that the propeller is mounted concentric.

The magnet ring holder and the inner hub of the propeller. The tabs on the magnet ring holder will be inserted into the grooves in the inner hub.

Milling the slots in the magnet ring. I would rather have used an indexing head, but it was inavailable at the moment. It took a lot of measurements to get the part concentric with the rotary table. I cut the full 2.5mm in one pass with 700 rpm and a slow feed rate. The magnets were just a bit larger than the 10mm endmill I used, so I had to file the slots some to get the magnets in there.

The finished magnet ring with magnets in place. After milling the slots, I cut the ring in a lathe using a parting tool. The magnets are very powerful and tend to pick up all chips and metal particles laying around.

The next part I machined was the tapered ring that covers the magnet ring in the magnet holder. This was also machined from delrin (POM). 

How everything fits together. The voids between the magnets and the holder will be filled with epoxy upon final assembly, potting the magnet ring and thus eliminating water contact and subsequent corrosion to the steel ring.

The fully assembled propeller with the magnetic coupling attachment.

I have also made some progress in modeling the scooter. Since last update I have modeled the motor and inside magetic coupling. I have also designed the struts that will hold the shroud to the tailcone. The next challenge is the throttle. I have some ideas for this, but I'm not fully satisfied with my solution yet.

I plan on using a linear hall effect sensor in the throttle housing to controll the speed. As the handle is twisted, two magnets are tangentially moved in relation to the sensor. The magnets are placed 90 degrees apart with opposite poles facing up. Twisting the throttle will vary the magnetic field around the sensor, yielding a change in output voltage that is directed to the motor controller.

Any input on this design would be greatly appreciated!