Two servos on one drive?

[protman16]

Group,

Is it possible to use two motors on the same drive? I am thinking of using two motors in a 2:1 timing belt reduction to a ballscrew with the encoder feedback from the screw to the drive. So essentially the drive would see the motors as one large motor. Has this been done before?

Protman16

[Al_The_Man]

You may get away with it with steppers due to the synchronized stepping, but not with servo's due to variation in motor performance, Systems that use two motors, as in either side of a Gantry X axis, use two motors, both with encoders and one encoder is slaved to the other. Galil and Acroloop cards have commands specifically for this.
Al.

[protman16]

Al_The_Man,

Realizing that the two motors have slightly different performance, wouldn't they balance each other somewhat? How much of difference is there in two identical motors? If they share a common timing belt and the encoder is coupled to the screw, or any other point in transmission chain, I don't see drive would have difficulty controlling them.
I thought that steppers would have more difficulty due to alignment of shafts in relation to step position of each motor.


Protman16

[daedalus]

are you talking about 2 motors attached to seperate ballscrews, or two mounted back to back driving one ballscrew. If its the latter, i have a similar setup on one of the robots at work, and it works pretty well.

[protman16]

Originally Posted by daedalus are you talking about 2 motors attached to seperate ballscrews, or two mounted back to back driving one ballscrew. If its the latter, i have a similar setup on one of the robots at work, and it works pretty well.

Two motors connected to the same screw using 1 timing belt. This would be similar to what your robot has.

[NC Cams]

Will it work? Probably but that depends on the motors and your expectations.

HOWEVER, motors of the exact same design don't always perform exactly the same with respect to either torque or RPM. Should one or the other lead or lag in performance, there may be some moderated/mild "conflict" between the two. Moreover, they won't always share the work and the belt will encounter the conflict.

Although they SHOULD act as one big motor, they may not. As long as you plan for that contingency, the situation should not provide any surprises. However, always be prepared for surprises.

There is this thing involving the perverse nature of inanimate objects that always jumps up to bite you sooner or later when avante garde approaches are taken.

[joejared]

Originally Posted by protman16 Group, Is it possible to use two motors on the same drive? I am thinking of using two motors in a 2:1 timing belt reduction to a ballscrew with the encoder feedback from the screw to the drive. So essentially the drive would see the motors as one large motor. Has this been done before? Protman16

You might want to consider a U-Shaped configuration using a chain belt and 6 pulleys. I have a drawing of my MicroMill router online that uses wire rope, which is less expensive, to allow one lead screw to be off to the side, keeping the area below the router clear, while not pinching the axis. Have a look at the "Router" at http://www.oretek.com/dxf/index2.html . Also, if price is an issue, I've found that the best vendor cost wise is http://www.a-m-c.com/content/prods/prodsmain.html . Glentek used to charge a minimum of $635.00 for repair of their amplifiers, and I found a comparible amplifier from AMC that cost less than that new. I did the math.