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Posted by Eriswerks on August 1, 2006, 5:00 pm
Please log in for more thread options slow_mac_modem@yahoo.com wrote:
> How about using linear actuators to drive a robot arm instead of
> stepper motors or servos? The big 340+ oz/inch servos cost a fortune
> and are incapable of lifting a measly five pounds with an 18 inch arm
> length.
>
> 12V actuators are down to $59 on feeBay and that's less than the price
> of the large servos.
>
> Of course an actuator would weigh a lot more than a servo but so what -
> they lift 300 pounds. Heck, you could jack up your car with it.
>
> Caveats I see is actuators are a lot slower and eat current. Full
> extension on an actuator is maybe 45 secs and they can draw 5 amps but
> I suspect that lighter loads would not consume so much.
>
> Any thoughts on this infallible idea?
>
> Pokey.
I'm dealing with this problem too, in trying to make a robot arm.
Servos just aren't strong enough, even the expensive ones. As far as
getting position feedback on the arm, I would suggest measuring the
actual position of the output arm rather than trying to measure
something in the geartrain and calculate the position. If your
home-made parts are in the same range of precision mine are (which is
to say, poor), then it's hard to get good feedback by calculating where
the arm *should* be. A potentiometer on the axis of rotation works, or
you might go for a resistive "bend sensor," as seen in those old
Nintendo Power Gloves.
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> stepper motors or servos? The big 340+ oz/inch servos cost a fortune
> and are incapable of lifting a measly five pounds with an 18 inch arm
> length.
>
> 12V actuators are down to $59 on feeBay and that's less than the price
> of the large servos.
>
> Of course an actuator would weigh a lot more than a servo but so what -
> they lift 300 pounds. Heck, you could jack up your car with it.
>
> Caveats I see is actuators are a lot slower and eat current. Full
> extension on an actuator is maybe 45 secs and they can draw 5 amps but
> I suspect that lighter loads would not consume so much.
>
> Any thoughts on this infallible idea?
>
> Pokey.
>