On Mon, Jul 12, 2010 at 10:41 PM, RussellMc wrote: > desired braking profile. Electrically applied force =A0braking also > entirely feasible. *IF* blade can be adequately coupled to hub then > the hub could be braked allowing far more controlled design of brake > ie doesn't have to friction couple to a blade surface. Existing hubs > are usually friction afaik which almost certainly would not be good > enough. I once developed an electric-powered helicopter (in graduate school for my thesis). It was one of the now-common four-rotor designs. The rotors were all fixed pitch propellers - two of them off-the-shelf and the other two custom made for us by APC to be pusher versions of the first two. This allowed positive net thrust production with the props counter-rotating in pairs. I digress... The relevant part of this to the braking discussion is this: the motor was about 1 HP, 30000+ RPM top speed (high performance expensive hobby electric motor) and was coupled to the 18-inch diameter, about 200 gram propeller via a 6:1 reinforced timing belt drive reduction. Once while it was spinning in a test stand at hover speed (4200 RPM), I decided to see what happened when I instantaneously commanded 0 RPM. The controller I had designed would not reverse the sign of the PWM but it would short the motor. As soon as I hit the enter key on the datalogging/command PC, the prop came to an instant complete stop, accompanied by a loud thud/twang. No damage to motor, prop, timing belt, or pulleys. The delay between command and full stop was totally imperceptible to my brain. It was probably not as fast as this SawSafe unit, but it couldn't have taken more than a few 10s of milliseconds to stop the prop. It really is amazing what electric motors can do! Sean > > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Russell > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist