Our moon rocks will go straight up via conveyer and be shot using spinning wheels. Our method for aiming will be using a turntable to spin a mounted plate to deflect the moonrocks to the trailer. We have considered direct drive, gears, and belts. What method of power is a good way to spin the turret?
Get a big sprocket like one of these:
You might have to cut out the center depending on your design but they might be what you’re looking for.
Sprocket on a turntable is what I’ve designed before and also probably the easiest. Try the 96 tooth sprocket from ifi.
We attached a 25 chain on the outer rim of an aluminum plate mounted to the lazy susan.
Then, we attached a FP motor (with the accompanying plastic gearbox) with a custom hub/sprocket attachment to directly drive and spin the fixed chain.
The speed and “smoothness” of running it is to our liking. 
No jitters of course.
Will take some pics and post once we get our encoder on for camera control purposes.
One way we came up with, was to rivet some gates belting (ribbed side out) to the outside of the turntable (This basically turns it into a a giant gear).
Then loop a second belt around it and a gear that goes to the drive motor.
I thought about that and realized that the bend in the belt would alter the spacing between the teeth on the belt, thus making the two belts not fit together. This was true with the KOP belts and pulleys, but i don’t know how this effect would play out on a larger wheel.
We purchased a larger turntable than the KoP one from McMaster Carr. We attached bolts in a circle around the border of it. We then put a timing belt around the bolts which we’re turning with a window motor.
Is your turret going more than 360 degrees in rotation?
We figured on my team for simplicity sake and since we will never have to shoot behind us into our own trailer, we only will be rotating our turret 270 degrees. Because of this, we’re using belting, and we’re just permanently attatching the belt to a part of the turret, and spinning it with a motor. Since the fastened part of the belting will never come away from the round turret, we’ll be good. Just a suggestion if you dont want 360 degrees.
Make sure that if you’re using a straight motor that you have limit switches around the back, I doubt you’re going to wanna be shooting in to your basket, or spinning loops in circuitry for that matter.
We thought this might be a problem as well, but with the testing we did, It wasn’t an issue for some reason… Maybe we just had good luck that day… :rolleyes:
We’re using a V belt. Other ideas we consider include a toothed belt, attatched at the ends to the turret, and a chain, same thing. The plan is for less than 270 degrees rotation, so there really is no need to put a big sprocket on the turret.
We took one of the AndyMark globe motor hubs, attached it to a little nylon pulley we had left over from last year that was about the same diameter (1.5" maybe?) and screwed some scrap wedgetop tread to it. Then we just touch the tread to the outside of a 13" lazy Susan we got and turn it on. Works like a charm, and it’s very simple. Not to mention, if something gets jammed and the turntable won’t move (like that would ever happen, right?) it provides a failsafe so that the tread will just start slipping instead of snapping/cutting/otherwise breaking whatever was in the way.
It would be good to mount an encoder on the mechanism to tell if it was slipping and give you closed-loop feedback as to the position of the turret.
As to the OP’s question, I’ve used a couple different mechanisms, including a 60 tooth #35 pitch aluminum split sprocket (used in go-karts) and the Gates Powergrip GT-2 timing belts and pulleys (like those supplied in the kit).
It’s probably going to be less than 360 but we could use 360 to shoot into our own trailer if the strategy is necessary…
We took a lesson from old record player turntables (ask an older mentor :yikes: ). The platter was often driven by just a rubber roller in contact with the platter inside edge. We are using a non KOP turntable that has an edge about 0.5 inches high. Turn a Keyang motor gear’s upper portion (not the lower portion) to .625 OD. McMaster Carr sells drive rollers with a compatible ID for about $20. Slip the drive roller onto the Keyang, mount near turntable so frictional contact made to inside or outside. Works great. Our rotation rate about 10 seconds for 360 degrees. Denso’s would probably yield about 7 seconds per 360 degrees on our design. Design will slip if rotation is limited for some reason and not break. There are ways to tell where you are rotationally without limit switches and encoders… Design is safe even if exposed.
Stop by our pit at Hartford and the team would be happy to show it off. Good luck!
Sounds like a neat way to make it! We thought about using a different motor/transmission, but decided we wanted the turret to move 180 degrees in about a second, so we used a Banebots RS-545 motor with a 64:1 planetary transmission, and we have a belt pulley ratio of about 8:1
We’re just using a KoP window motor connected to a piece of plywood with the shaft bolted to a piece of 80/20 mounted on the lazy susan mount mountedto the plywood, the cannon (made of flue pipe) will attach to the top of the 80/20.
Horray for low budgetness!
3 years ago our team did the exact same thing you are doing now to shoot the 8" Nerf balls. We manufactured our own polycarbonate turntable and it worked fairly well.
A window motor is perfect for this application as it has excess torque but also enough speed to get the job done. The Fisher price motor is also a good choice.
Cut a big circle out of plywood and pin chain along the circumference, then drive with a sprocket pinion like a gear.