Thursday, July 30, 2009

44> Going, Going… Gone.

PML Flightlink has been purchased. “Who’s that?” You ask. Well, according to a yet-to-be-updated Wikipedia entry under “Wheel Motors”, it is “a UK based company that currently designs and builds the highest power density electric wheel motors in the world.”
The problem is that it appears that the new owners have discontinued the “E-Wheel” series of wheel motors, opting instead to offer custom engineered products only. That, by itself, is not such a big problem since a fleet of PRT vehicles with multiple motors/wheels each would represent a pretty big order, but now it’s pretty hard to design a system, since they took the spec sheet away. Luckily I happen to have a copy of the specs right here.

These motors were specifically made for small electric vehicles, with oversize tapered (automotive type) bearings and waterproof housings. They were designed to be run on batteries, and have regenerative braking. To those more familiar with “horsepower” it is the stated wattage divided by 746. Torque, in “foot-pounds” equals the stated Nm rating times 1.356.

These were extremely powerful motors for their size and weight. They came with standard bolt patterns so off-the-shelf wheels would fit. Anyway the present company is still in the business of wheel motors for full size vehicle conversions, since eliminating the motor, transmission, differential, etc. frees up a lot of space for batteries. They have built a 640 hp Mini Cooper, among other projects. Anyway, it was largely these amazing torque/weight numbers that made me so in love with wheel motor technology. I wish someone from the LIM (linear induction motor) camp would explain how their system could possibly compete with these kinds of numbers, since I know there are plenty of LIM believers out there.

Also speaking of LIMS, I don’t understand how they can, on one hand, describe their reaction plate being comprised of aluminum or copper over steel, and then say that steel alone will do. Why would they add it if it didn’t matter? And, assuming it does matter, how much does it matter? And I can’t help but wonder, are there actual designs out there which put the LIMS in the vehicle, or are the current designs calling for LIMS all along the track? And if they do put it in the vehicle, are they water-cooled or what?


Anonymous said...

A little thing that worries me about in-wheel motors is that several manufacturers have experimented with them (in particular Volvo and Mitsubishi), and have not produced anything using in-wheel designs yet. Indeed, Mitsubishi showed concept cars with in-wheel motors under the MIEV label, but in the end released a production version that did not have in-wheel motors. Have they come across some problem (e.g., durability/reliability) that we don't know about?

Dan said...

Dan the Blogger Responds-

That's a good question, Anonymous. I'll give my best guess...

One “motor in the wheel” approach that does not qualify as a "wheel motor" is the Michelin unit I pictured in my April 25th post. As is shown, the wheel is very complex, including suspension and brakes. It's ready for the potholes and slippery streets of everyday driving. I have also heard rumors about handling problems with the mega-horsepower conversions that PML was doing. I heard that there was way too much weight in the front (steering) wheels, and I can certainly believe it, if they were trying to get 160 hp out of each wheel of a Mini Cooper. The point here is that there’s a lot of engineering between a car’s wheels and the car’s frame, and it is all easy for a driver to perceive and compare. “Sports car” performance took lifetimes to achieve and is the benchmark your examples have to compete with. That’s a very big challenge.

Anyway wheel motors, without the steering, suspension or friction brakes are pure simplicity. Their cousins, drum motors, power conveyor belts around the world. Their baby sisters, muffin fans, cool my computer. Ceiling fans have motors that revolve around a stationary axle as well. Motor wheels are widely used in Asia to motorize bicycles. The fact is that they are pretty much anywhere you need more torque and less RPMs without gears, chains or belts. Because it is more of a concept than anything else, I would seriously doubt that any difficulties couldn’t be overcome. Wheel Motor simply means the axle part is stationary and the rest revolves around it, instead of the other way around. Any type of motor – AC, DC, 3 phase, induction, stepper, brushless, etc. can be rewired in this way, from what I see…after all, all you need to do stick the shaft of a motor in a vise, turn it on and voila! Wheel motor. (A split second later a very twisted power cord has been ripped out of the wall and is whipping everything in sight) The point is that any motor can be called a wheel motor as long as its shaft is hollowed to accept the wires, so that they don’t wind up. (OK, that’s a bit of a simplification, but not by much)