Are there any single speed COTS gearboxes with a reduction of around 22:1-25:1? So far the largest reduction I’ve seen is the WCP SS Gearbox, which can be configured to about 19.28:1. I know that there are some 2 speed gearboxes with that large of a reduction, but I would prefer not to spend twice as much money for a shifter with an unusable top speed.
My team is planning on using 8 inch wheels so the large reduction is necessary to get to a goal speed of roughly 7 fps.
Also because of large wheels, we’re not using our gearbox for direct drive, but using chains with different sized sprockets for additional reduction.
The only gearbox we’ve found that will allow you to direct drive an 8" wheel at a reasonable speed is the West Coast Products Single Speed gearbox. I’m fearful for rookie teams that attempt to direct drive their KOP frame using 8" wheels using the Toughbox Mini’s, it’ll be hard to control at such a high speed on such a sectioned field.
Just wanted to add that I’m really impressed by the flexibility the WCP SS gearbox gives. 4 different pinion choices allowing you to basically go up or down ~1 ft/s at a time. We could go 7.5 ft/s or 10 ft/s by swapping pinion gears, love it!
If you can’t find a COTS gearbox, try adding another stage of reduction in the sprocketing.
Also, is there any reason why you chose 7 fps as your ideal speed? Why not a bit faster?
Your target single speed of 7 ft/sec is much lower than is normally used, and with large 8 tires, it pushes it out the required gear ratio to 22.2:1. There are no COTS double reduction gearboxes with that type of ratio.
There are the COTS IR3 Modulux gearbox that you could customize (expensive).
It you had the ability to manufacture a triple reduction gearbox
A (50/12) (60/24) (64/30) = 22.2
12 tooth CIM
Stacked 50 & 24 (CIM drives 50)
Stacked 60 & 30
64 on Output Shaft would do the trick
Spacing is 1.55" CIM Center to First Shaft
2.10" First to Second Shaft
2.35" Second Shaft to Output Shaft
7 fps is just an rough initial estimate. Through initial testing my team has discovered that with too fast a speed (we tested with 14 fps), a robot will either struggle over some of the obstacles (we specifically cheval de frise and ramparts) or will go flying. We are looking for a lower speed that will offer more control. However, we may decide that 7 is too slow and go up to 9 or so.
QFT most of the AndyMark Toughboxes are 12.75:1 stock.
2:1 can be obtained and that’s more than you ask for.
Our team is only using 6 inch wheels. Please help us all.
Now that I think about it, it is kind of interesting that Andymark is selling a kit where the slowest possible configuration is 14 fps and not warning people. I can see there being a lot of surprised rookies who cannot control their robot.
Oh, you don’t remember the 2011 kitbot that was geared out of the box for 18 fps? Man those were the days…
What sort of help do you need?
Are you trying to target a certain number of feet per second?
or
Are you trying to target a certain ratio?
Resources on ChiefDelphi that can help you:
JVN:
http://www.chiefdelphi.com/media/papers/2059
Thad house:
http://www.chiefdelphi.com/media/papers/2681
Chris L:
http://www.chiefdelphi.com/media/papers/2165
As pointed out before if you can’t get a ratio high enough from an existing gear box use that gear box to drive a belt or chain sprocket and then select those pulleys/sprockets to multiply the ratio.
For example: If a AndyMark ToughBox has a default ratio of 12.75:1 and drives a double 1/2" bore #35 sprocket with 12 teeth. Then drive the wheels with a 24 tooth sprocket (which happens to even fit a 4" AndyMark wheel) you have an additional 2:1 so that’s total a 25.5:1 gear ratio at the wheel hubs. If you used the 15 tooth double #35 sprocket that chain will be a ratio of 1.6:1 so total that’s 20.4 at the wheel hubs. If you play around with alternate gears within the ToughBox you can take that further. It’s easy to get an additional 3:1 in just sprockets and chain using a 12 tooth #35 to a 36 tooth #35 sprocket especially if your tires are larger than 4" to add clearance for the chains (so with 12.75:1 and 3:1 that would be a total ratio at the wheel hubs of 38.25:1 and that’s not even the maximum).
Make sure to consider the losses in the system that’s why I linked the various common calculators.
I see AndyMark clearanced out all the StackerBoxes. I bought a bunch. They can feed into each other to multiply over and over the gear ratio just by assembly. Too bad they had 3/8" shafts. Each StackerBox had a 14 tooth and 50 tooth gear stock. So you could easily stack 3 and get a ratio over 45:1.