dual driven raack and pinion

[bahorton]

so my design is: a V-track on top of 2x2 square tube and rack gear on the bottom. an upside down cross woth v rollers on the sides and the motor engageing the rack on the bottom. the long part is where the y axis will attach. i figure with the rack hanging down it would stay clean and free. and i would be able to tighten down the rack and pinion by sliding the motor up.
is dual rack drive a good idea? i want a motor on both sides of the x axis.

[bahorton]

heres the rough sketch.

[Splint]

Yes it is a good idea, do a search for a machine built by Greolt, he uses this set up with the motors hinged and spring loaded to acheive zero backlash in the rack and pinion. Works beautifully.

[bahorton]

his is machine is verry nice, but more complaex than mine will be. i dont think i could afford all that aluminum. and i dont want to have to build a gear reduction. so im wondering if i drive both sides of the x axis if it'll be cheaper. maby like two 450 oz stepper motors one on either side in step with each orher. Or could maby one of them loose a step somewhere and cause the gantry to bind? im not looking for a super fast machine 10-20 inches per min is fine as it will be for cutting .25 to 1.0 inch thick steel plate to build bobcat buckets and some brackets for attachments. im new to the electronics but can fabricate any thing. any guidence is much apreciated.

[Splint]

Certainly binding could be an issue if for what ever reason is lost a step or is loosing steps while it works, any system with dual moters per axis is faced with this dilemma. I think the only way you can avoid a gear reduction is to run a motor directly to a leadscrew. Having limited funds you may want to have a look and do a cost estimate on both types of drive mechanisms. If your machine is a simple flame cutter you may be able to run a leascrew down one side of the bed and run a cable system in a figure 8 to drive the other side of the gantry. There are a number if different ways of using a cable as a drive/balance mechanism, do a search, there may be something suitable for your application, failing that have a look for my router build log, I use the figure 8 as a single centerally mounted leadscrew turned out to be inappropriate for the width of my gantry.

[TOTALLYRC]

Originally Posted by bahorton his is machine is verry nice, but more complaex than mine will be. i dont think i could afford all that aluminum. and i dont want to have to build a gear reduction. so im wondering if i drive both sides of the x axis if it'll be cheaper. maby like two 450 oz stepper motors one on either side in step with each orher. Or could maby one of them loose a step somewhere and cause the gantry to bind? im not looking for a super fast machine 10-20 inches per min is fine as it will be for cutting .25 to 1.0 inch thick steel plate to build bobcat buckets and some brackets for attachments. im new to the electronics but can fabricate any thing. any guidence is much apreciated.

Running motors on both sides is a great idea and they can be electronically coupled in the software. Driving the pinion directly off of the motor shaft without any gear reduction may not work. Rack and pinion is basically overdrive and you need to underdrive it some. I guess that worst case, build it the way you are planning and if it doesn't work, add in some reduction later.

Mike