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Introduction.     (by John Self.)

I read Jan Cack’s description of his KISS PMM and was interested in the possibilities of his design – an elegant solution, using epicyclic sun and planet gears to remove as much of the fatal magnetic lock positions as possible, but mechanically challenging. His CAD drawings were also very helpful in establishing the most favourable number of rotors (8)and stators (10). That, and Nick Rasmussen’s inspiring magnetic flux and 3D simulations convinced me that it was worth trying to make one.

It was interesting working out the design: much frantic sketching and measuring on paper, and thinking while driving to and from work. Also, making a cardboard model just to figure out the minimum gap between the sun and planet magnets so as to avoid clash, and the rough dimensions of the sun magnet holders. I’ve made them with a slotted hole to allow for set up.

To keep the costs down, I chose to make the sun and planet wheels out of MDF without running to the expense of cutting gear teeth – just relying on friction. Risky, I know, because there's the potential for the planets to slip out of register, but I'll mount the planet wheels against the sun with a fair amount of friction. I reasoned that it was worth taking that risk because I was trying to save costs while I overcame my scepticism and the possibility that it wouldn’t work - let’s face it, the odds are against me. I'm treating this as a proof principle exercise, the ‘A’ model. Having said all that, if the motor shows the slightest inclination to work, and even if it destroys itself in the process, it’ll be worth pushing on with the ‘B’ model,

Progress

·         I have had a local engineering firm turn some simple ‘top-hat’ bearings out of brass, to be used between the base plate and the sun and planet wheels. Not ball bearings, but they spin freely enough for the test.

·         I have made the base plate (400 x 400mm) out of MDF and marked it out ready for drilling the sun and planet bearing holes.

·         A wood turner friend has done an excellent job making the sun and planets in the required profile, and also making the sun magnet holders. The sun has 240mm diameter and the planets 60mm, maintaining Jan Cack’s design ratio of 4:1.

·         I now have the special order planet magnets (50 x 20 x 5mm) with the north and south poles on the faces rather than the ends, and I've also got the sun magnets
(22 x 10 x 10mm) with north and south poles traditionally on the ends.

·         The design of the planet magnet fixing has caused me a bit of sweat, but now I've cracked it by using slotted pillars, and I'll use the same engineering firm to turn them out of brass too.

Pictures

Sun and planets and holders

Bearings and fixing bolt

Sun wheel and bearing


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