Jon Elson <[EMAIL PROTECTED]> wrote:
> You need a lot more voltage supplying the H bridge. At 55% duty
> cycle, you are getting 12 * 0.55 = 6.6 V at the motor. I am a
> little surprised the motor doesn't start to turn before this, it
> must have a lot of friction. Have you measured the motor
> current just before it starts to turn? That would be
> interesting to know.
It's a cheap used motor from the local surplus place, so maybe it's
been abused. The manufacturer's specs say:
Friction Torque: 0.35 oz * in
Rotor inertia: 0.00014 oz * in * s^2
I dont know how to think about these numbers, really, or how they compare
to other motors.
I don't have an oscilloscope, just a cheap multimeter, so I don't think
I can accurately measure the current just at spinup time.
> Umm, 1.6 Oz-In continuous torque? What kind of machine are you
> planning on making with this? You might be able to run an
> etch-a-sketch with it if you provide sufficient belt reduction,
> but you couldn't even drive that directly! Do you know how
> LITTLE 1.6 Oz-In is? The Bridgeport guys use 640 Oz-In motors
> and up.
I know it's tiny, but I'm not planning to run a bridgeport with it. ;-)
I believe Chris Radek is running X and Z on his Sherline lathe using
motors not much bigger (maybe around 2.5 oz*in continuous torque) with
3:1 belt reduction.
I can easily stop the (thin) motor shaft with my fingers, but it puts
up a pretty good fight. Stall torque is a whopping 7.4 oz*in.
For me so far this is a chance to play with EMC and start learning the
principles of motion control. If/when this gets applied to building a
machine, I may well have to buy bigger motors & drivers & power supply,
and I'm ok with that.
--
Sebastian Kuzminsky
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