From what I am seeing, the best way to keep costs down and obtain reasonable precision, is to focus your spending on as few of components as possible.
An example - the rack and pinion option. There are a number of assocated parts that go into a drive like this
- Rack (s)
- Pinion (s)
- reduction gearing
- stepper motor
- stepper motor driver
- one motor on each side, or a mechanical linkage
- Mounting the pinion on the stepper motor
Each part adds either to the precision, or frankly, non precision of the total system, so just like a chain, the most out of precision part, or installation of a part, can really harm the end result.
For my own project, I have NO fancy tools to build up the system, and I have poor craftsmanship, so it has to be constructed as simply as possible or it simply will not work.
First items on the list - get rid of gear reduction - nothing good can come from building this up myself - so I am going down the path of hefty stepper motors with lots of low end torque, direct driving a modest size pinion gear. This is done routinely by the mechmate projects.
Rack is actually quite cheap - esp if you stay with the one I pointed out.
Second item on my list - driver circuit - I don't have $ 100 / each for 6 stepper drivers (2 per axis) - so I am using linistepper drivers. They aren't perfect, but for $ 35 / each, it is ok. Even with only 1.5 amps, you can get some amazing torque from a nema 34 motor. That brings up another point - sometimes, a nema 34 motor is CHEAPER that a nema 23 motor for the same torque due to the cost of high end small magnets.
Third item - drive from center, or both sides - I have decided to drive from each side - this is my splurge area, but it gives me more confidence that the motion will be under control. I thought about a mechanical link between sides, but once again - lots of room for mistakes / imperfect components.
Linear rails - I am still deciding on this area, but it won't be a fancy linear truck concept - budget drive decision.  |