Frequent motor direction changes

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Arthur Sadler (Arfdog)
Member
Username: Arfdog

Post Number: 1
Registered: 7-2008
Posted on Wednesday, July 30, 2008 - 9:14 am:    Edit Post    Move Post (Moderator/Admin Only)

Hi,
I'd like to know how quickly I can expect to decelerate a 12V-150W feathergold motor from full speed CW down to 0rpm, and up to full speed CCW.
My application requires the motor to drive a piston with a 'sawing' motion, but I need to be able to vary the stroke length.
I plan to use a linear toothed shaft, driven by a sprocket on motor shaft.
How could I calculate how many cycles per minute I might expect to achieve?
Thanks.
Admin (Admin)
Board Administrator
Username: Admin

Post Number: 836
Registered: 10-2004
Posted on Thursday, July 31, 2008 - 6:57 am:    Edit Post    Move Post (Moderator/Admin Only)

Arthur,

There is no practical way to calculate this and depends on load and acceleration. Regardless, is very likely to run hotter as it is see repeated starting currents. Have you considered using a simple mechanical reciprocating motion?
Arthur (Arfdog)
Member
Username: Arfdog

Post Number: 2
Registered: 7-2008
Posted on Thursday, July 31, 2008 - 7:56 am:    Edit Post    Move Post (Moderator/Admin Only)

Hi Admin,
The problem with using reciprocating motion is that the stroke length would be fixed, and I need it to be variable. Think along the lines of the motor moving a 2kg linear shaft to and fro by up to 10 inches, as it it were printer head.
The maximum number of turns the motor would have to make in either direction is 5 turns before stopping.
I require a maximum cycle time of 10ms from begin to end and back (5 turns CW, 5 CCW) and I guess this is just hopelessly too fast to be possible anyway..
Admin (Admin)
Board Administrator
Username: Admin

Post Number: 838
Registered: 10-2004
Posted on Friday, August 1, 2008 - 12:59 pm:    Edit Post    Move Post (Moderator/Admin Only)

Arthur,

I cannot see anyway in which a standard brushed motor could quickly and accurately turn 5 turns CW and then 5 turns CCW. It even sounds too much of a challenge for a stepper motor with a 2kg mass but may be worth exploring. Linear actuators would be too slow. High speed pneumatics would likely take 20mS + for a full cycle but you would need to work out some way of having a variable mechanical stop for the variable travel. It's a tough one to solve.

Regards

Paul