Hey guys I was wondering what the best gearing is for a six motor drive? Our team is trying one outand right now we have green gear boxes in the motors and we’re gearing it up. Should we have blue gear boxes in the motors and then gear it down?
I always prefer to gear down as it reduces slop just a hare. i would go for 5:3 on 3.25in(62in per sec) wheels, 36:48 on 2.75in(64in per sec) wheels or 3:7 on 4in wheels(54in per sec).
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can’t resist…it’s a bit more subtle than “axel” instead of “axle”
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600rpm carts have less slop and less friction than 200rpm and 100rpm carts, so avoiding 200rpm and 100rpm carts on the drive is a good idea, although it’s not a big deal if you have to use the slower carts. You also want to decide how fast your drive should be (inches / second). Most people build drives somewhere between 50in/s and 80in/s. Two examples at opposite ends would be 200rpm on 4" wheels (42in/s) and 600rpm on 2.75" wheels (86in/s). Drive speeds can be calculated by multiplying your wheel size (inches), rpm, and pi together, and dividing by 60 (seconds per minute) to calculate drive speed.
Here are the calculations for the examples I gave above.
It may be difficult to know exactly what speed you want to choose, because it depends on things like driver skill, total robot weight, resisting defense, etc. If you’re unsure, then its always a safe bet to land somewhere on the lower to middle side of that range.
This design is using 600rpm motors geared down 3:5 on 3.25in wheels (I’ll let you calculate the speed as a challenge). Because the motors power 36t gears, it is easy to add more motors by raising them.
This is only one example and there are plenty of other great drive speeds to choose from so I would recommend doing research on what other teams have done so you can plan accordingly.
Have fun and good luck!
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There is no “best” speed for 6m drive. Different ratios have different pros and cons. Each drive has different spacing which depend on how long your drive is. You will also want more torque if you bot is heavier.
I really like this resource for ratios. For 6m drive you want between 55 in/s and 87 in/s with those being the far ends of the spectrum. Generally, you will want something somewhere around 60-70 in/s.
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I will be here to offer support for coding the drive if needed
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in my opinion, 400 rpm on 3.25" wheels is the ideal gearing. The geometry just works out really nicely as you can see in this model:
I used a 1:1 compound with 36t gears on the stacked motors, you don’t have to do this but it lowers those motors by a hole and makes it more compact.
It’s got plenty of torque with 6 motors, but it’s also very fast so it takes some practice and skill to drive.
my only issue with it is the lack of low strength 48 and 72t gears means that in order to fit the gearing into a 3 hole gap, you need to do funny stuff with shaving down those gears. I did this on my worlds bot last season, and I don’t regret it, but it was really annoying and I don’t recommend doing this unless you plan to use those thinned gears long-term.
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How would you recommend cutting the gears in half?
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you can’t just cut them in half, the metal core would fall out and it would be ruined. You have to shave off 1/8" of thickness on either side, so that the core stays in the middle of the gear.
if you have access to something like a mill, that would probably be best, where you could precisely face each side of the gear and get a clean, flat surface. I had access to one, but I was lazy and thought using a belt sander would be quicker. But belt sanding was really painful, you have to go slowly to prevent the core from heating up too much and melting the gear, and you have to be really careful that you hold the gear level so that it’s sanded even and straight. I did it by hand, pressing the gears into the belt sander by pushing on them with a c channel, I don’t recommend this method. It worked in the end, but took probably 4-5 hours to get through all the gears I needed, I failed on a few of them, and they were a little wonky and uneven, though that didn’t cause any issues on the robot.
Other ways you could probably maybe do it might be cnc-ing both sides, or shaving it down on a lathe. But if you’re not looking to put in this sort of work just for gear thickness, than just use a 4 hole gap and HS gears.
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For 6m drive on 4" wheels, we have found that 257rpm works really well. You have a speed advantage over teams that run 200 rpm 4", while still maintaining pushing power. Also works good with heavier bots.
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Would using a spacer like this, with a wheel on the other side work to hold the insert in?
Both sides would be constrained so they couldn’t slide around or anything.
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I very much doubt this would work, the metal core would be able to wobble and it wouldn’t have very much depth in the gear. I think if you’re going through the trouble to shave down the gears, may as well do it right on both sides.
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I’m trying to design a 450 rpm drive on 2.75" wheels, with 6 motors and 6 wheels. I’ve only got 8 48t gears for it though, 4 of which are currently on another robot and need to be kept intact, so can’t be shaved. So I’d like to cut them down in a way that I can get 2 thin gears out of each gear.
Do you think that sandwiching the gears with lockbars would be effective enough at keeping the hubs in?
here’s the drive I’m trying to design.
you don’t need thin gears for 4 wide gaps
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also pinion on drive is bad
more friction
you should probably do a raised 36t idler
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Screwhead tolerances.
I use screws/standoffs to attach the gears to the wheels, which I have found run into screws used on bearings/motors, making a 4 hole drive with 48t gears and the thicker omni wheels harder.
I’ve tested it, it’s really not that bad.
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Hang on, I figured it out:
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if you need more room, it’s pretty easy to drill little counter-sinks in the gear flanges so that screw heads don’t stick out.
I actually think it’s really annoying vex designed these gears with the flanges flush to the edge, would have been nice for screw heads to fit without needing to drill.
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how many watts
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