Re: Belt tensioners on toothed belts

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet" <thom@...> wrote:

>
> I just finished helping a customer with a servo driven plasma table
> and I was surprised to see spring loaded idler wheels on swing arms
> (like the old reel-to-reel tape drives) being used to tension the
> belts on the toothed pulleys. The tension mechanism was a coil spring
> and was not very taunt so that when the motors changed direction the
> belt would bow out or in, depending on the direction. Seems to me the
> flexing of the belt would introduce some errors. Do any of you have
> any experience with a design of this type? Seems like a way to move
> the motor to maintain belt tension would be a better approach. I
> guess if the belt tension was strong enough it might be a better
> solution (?)
>
> I do know that in this circumstance it ended in disaster. The pivot
> arm became loose and the arm got cocked at an angle. It was okay with
> the axis running in one direction but it acted almost as a brake in
> the other direction and since the motors were large it just ran until
> the fuse blew (about 30 msec after the servo drive blew!).
>
> Tom Caudle

I would expect everything to be ridgid. I have a pair of belt
tentioners that have a fixed mount. they wrap the belt around the
drive pulley so it has much more contact than it would have otherwise.

In my case, I have a long belt, 2 screws and one motor. the motor
drives both screws.

Dave