On 18 Feb 2016 20:57:16 GMT, "DoN. Nichols"
wrote:

On 2016-02-18, wrote:
On Fri, 12 Feb 2016 16:39:36 -0800 (PST), whit3rd
wrote:

On Friday, February 12, 2016 at 3:45:34 PM UTC-8, wrote:
On Fri, 12 Feb 2016 16:26:54 -0500, "Steve W."
wrote:

How about using DC to brake an AC servo? Higher the voltage the more
resistance to motion.

How would that work? How are AC servos made? I'll look online.

Most AC motors (the ones without brushes) will brake if you feed 'em
some DC. Steppers (but they cog), shaded-pole, or hysteresis types,
all have a rotor without driven windings, and DC on the stator makes
them into brakes.
I thoughty they only braked while spinning and once stopped there is
no braking force.

That is true for AC motors. For steppers, since they have a
permanent magnet rotor, the braking continues, but things are a bit
rough until it gets to a stop. Perhaps sense the speed, and when it
comes close enough to a stop, switch from AC motor to stepper. (Make
things biggern than you want. :-)

I ordered some MR fluid and will try making my own
magnetorheological brake.

Have fun with that -- and let us know how it goes.

Good Luck,
DoN.
I'm looking forward to finding out myself. I looked online for small
quantities but couldn't find any. Looked on ebay with no luck and then
a couple days later some showed up. It sounds like the perfect stuff
for my needs.
Eric