Gantry design help needed

[hierlevelz]

We have a Gantry application that weight approx 18,000 lbs driven by two racks; one on either side of the gantry. That means that one rack & pinion needs to be able to drive 9,000 lbs. We are driving the gantry with two 4 HP AC servo motors; one on either side. The motors have a max RPM of 1350. We do not want to drive the pinion faster than 52 RPM (300 IPM rapid rate). We will therefore be gearing the speed down from the servo to the pinion. How do i design my rack and pinion accordingly to accomodate the criteria and also have a safety factor of about 1.5. Or is 1.5 necessary? Please point me in the right direction.

 

[CESSNA1]

HEIRLEVELZ: First off crane and rigging applications typically have a safety factor of around 5. Assuming the gantry is on wheels or rails, you only have to overcome friction and account for the slight acceleration load, you do not need the full 9,000# load you have assumed. How far does the gantry tavel? That will define the length of the rack. If it is a significant distance then you will need to assemble the rack from individual sections. Is there a reason you want to use a rack and pinion? Cranes I have seen ride on tires or rails and are driven through them. If possible I would consider doing that.

Regards
Dave

 

[tygerdawg]

It appears that you need to do a full torque analysis to verify that your gearmotor has the juice to move your load at the speeds you want, with the safety factor you desire, and at the frequency you want to move it. Once you prove that, then it should be able to select rack & pinion sets based on torque carrying or stress capacity. Failure to prove it will require resizing your gearmotor first.

Resources to dig for on the internet: "Smart Motion Cheat Sheet" (PDF file) and/or gearmotor manufacturer engineering catalogs (SEW Eurodrive has a great engineering reference in PDF for free at their German electronic documenation site).

TygerDawg