as an EE, i’m looking for some help from an ME to explain what is available in the way of what i believe are called timing pulleys and belts.
i wondering if they might be suitable to drive a turntable using stepper motor. I’m wondering if sufficient gear reduction is possible to have finer resolution than the typic 1.8 deg of a stepper motor. I’ve seen Walthers turntables where a motor drives a worm that turns a gear that in turn drives a 2nd worm that drives a 200 tooth gear.
interested in hearing about sizes, gear pitch (?), shaft diameters, plastic vs metal, shaft suppots, … Is there stuff that’s relatively inexpensive for robotics? Or is this approach really not feasible?
Have not done it myself, but the guy at the Toy Train Barn in Wisc uses microwave turntable parts for that sort of thing with good results. You get the parts u need wife gets a new microwave. A win-win situation.
Interesting Greg, I’m no where near a EE and I’m just as far away from being an ME, but I do understand, somewhat, about gearing.
I had a couple of old battery screw drivers, the batterys are now obsolete, and no where to be found, so I took them apart, used some AA batteries to see if the little motor still works, and it runs great. It spins like crazy, and the little gear on the end, meshes with 3 other bigger gears to get the driver to spin at a slow rate. It seemed interesting.
I have to hand it to you, you are out to perfect turntable operation, going by your other threads.
Pulleys work the same as gears, there are just a few more factors, like the pulley length needed, which is computed from the pulley diameters and the distance between centers. The only difference a timing belt type pulley makes is that it doesn’t allow for the slippage you can get with a regular smooth belt.
If the large pulley is 2x the diameter of the small pulley on the motor, it will turn at half the RPM of the motor. Convert to degrees - if the motor turns 1.8 degrees, the larger pulley will turn .9 degrees.
You’ve probably seen turntables driven like this - only they weren’t for trains. A belt drive music turntable often has the big ‘pulley’ as the turntable platter itself, and a little tiny pulley on the motor, to get the platter to rotate at 33 1/3 RPM.
McMaster Carr has a very good selection of these components. The hard part is where to look. If you search for Timing-belt pulleys you will get a pretty good list of parts. Next would to narrow your search down by shaft diameter of your stepper motor and your turntable. You will also need a tensioning pulley to keep the belt tight (other option is to create slot where the stepper motor is mounted and adjust it.
Other place is amazon. They have a good selection of GT2 series components which will fit most stardard stepper motors.
As for size. you stated a typical stepper is 1.8 deg. per step. With this resolution you will get approximately .28 inches per step for a 130’ turntable (17.93 inches)
thanks for pointing me to McMaster-Carr. I liked how their web pages narrowed down the selection. I found a page listing timing belt pulleys for a specified belt widths that also specified the shaft dia. that are presumably compatible with one another.
that page showed the largest pully having 60 teeth and the smallest having 10 - 6:1.
i calculate an angle resolution of 0.05 deg for an 18" (130’) turntable assuming 1/8 (1/16" / 8) track width resolution.
i happen to find some very small 15% stepper motors with 63:1 gearheads (0.3 deg)
so even low 6:1 gearing makes using timing belt pulleys feasible.
If you are looking for small gears, timming belts or drives this place will have what you need. Not cheap, but if they don’t have what you need, you really don’t need it?
