Thread: Rotating Ballnut - design ideas
looks really good
What's the gear ratio between motor and pulley/ballnut??
Is 10mm screw pitch?
It is 1:1 and 10mm pitch, but clearly one could use it with any pitch and to change the ratio just change the pulley on the motor. The mount for the motor is long enough to accommodate different pulleys without changing the belts. It will go faster with a bigger pulley on the motor, but with a 10mm pitch screw there's not much point ... you're just loosing resolution.
So I know I may be over simplifying and havnt researched this much but...
Would it be possible, and much simpler to use a hollow shaft stepper/servo and use feed the screw through the motor and mount the motor directly to the ballnut with a flanged hub
There are few stepper or servos available with hollow shafts. The common ones have too little torque or the bore is insufficient. Anything above 16mm would be useful. It may be possible to dismantle an existing motor, machine a new shaft with the hole through the middle and use bigger, angular contact, bearings. For the size of my machine (1.7*0.74*0.4m) it's just not worth it as the 3nm steppers can already run it more than fast enough.
The advantage with using a standard motor, other than simplicity, is the timing belt allows you to change the drive ratio and reduces resonance. Currently mine is on 1:1 ratio, however it does go faster with a larger pulley on the motor. I elected to leave it at 1:1 however as 10m/min is plenty and I prefer to keep the resolution than get 15m/min+, but at least I have the option which wouldn't be the case with a hollow motor. In short I'm saying you have to be very careful with the selection of the motor, which makes it even more difficult to find a suitable one.
Last edited by Jonathan; 01-03-2012 at 12:53 PM.
This is something we are developing, but it will not be for hobby use.
It will start with a servo system and the 2525 and 3232 ballnut,
We will then be moving to the 4040 and 5050 ballnut.
The only steppers that could have been used for this design were the IOS motor from IMS, but these are not made anymore.
Visit Us: www.zappautomation.com
really nice design on these- they still working a treat?
i came across these badgers http://www.drives.co.uk/fullstory.asp?id=3388- but as i say on my little build log thing- bet they're bleedy expensive-!
i'm tossing up rack and pinion vs this type affair for my long axis- (2.5m) so lurking about tying to decide to my way forward!
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that would indeed be interesting Jonathan- do you want to work it out and PM me- or post it's up to you-!
i'll work out the mounting of them- i was thinking of tucking them out the way under the x rails- so to minimise dust/ crap getting onto them-
Hi Jonathan, any chance you could knock 2 of these units up for me?
Im running the 2020 ballscrew and need someway of using a screw of 3000mm length without whipping and this looks ideal
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