DIYbanter - View Single Post - Help please w/ electromagnetic slip clutch

Cydrome Leader

wrote:
Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning . Anywhere from 0 to 40 inch pounds. I
have been looking at magnetic particle clutches and brakes, eddy
current brakes, and disc type clutches and brakes. The magnetic
particle brakes would seem to be a good solution except that the ones
I have seen that can provide enough drag have too much drag when not
energized and have too large a diameter. About 3 inches diameter by
about 3.5 inches long is the space the clutch or brake must fit in. I
am considering rolling my own devices but am not sure how I would do
it. Maybe some sort of generator feeding a resistive load. By varying
the field strength the resistance to rotation would increase. Whatever
the solution is the resistance to rotation must be linear to the
current that actuates the device. That's one of the reasons I like the
magnetic particle barkes.
Thanks,
Eric

handhwheel speeds are usually slow. gear or belt drive up to a DC motor
and short it out with some type of bridge recitfier (for use in
both directions) constant current setup. Even a cheapo
hacked LM317 might work if you can adjust it with whatever your controls
are. Hell, maybe just PWM it if you're using a computer. A single triac
might pull this off.

If you want it to feel nice, use coreless motors as they don't cog as
much. Yaskawa "Minertia" type servo motors are good too as they don't cog
and feel REAL smooth when run backwards.