pic: Inverted CIM 2-Speed Gearbox

[KohKohPuffs]

Originally Posted by Chris is me

Once your wheels slip under load, gearing any slower doesn't do anything to increase your pushing force, it just decreases your power consumption. You're traction-limited rather than torque-limited.

For a 150 lb robot with roughtop tread, that "magic number" is around 6 feet per second, depending on your efficiency, exact weight, wheel design, etc.

I've been punching some numbers into JVN design calculator, and I managed 16.85fps high, and 6.76fps low.

This will be a new design (but I'm keeping the inverted CIMs), since to do this I had to have the dog gears be the driven gears rather than the driving gears in the second stage (shifting on upper shaft). Also, in order to have the gear space in the gearbox, I'm most likely going to keep the idlers:

1. The idler gears are easily replacable in case they wear out
2. Using my logic, the idler gears are made of steel, so I doubt wearing down is going to be significant

As for a belted gearbox, I think our team wants to move away from belts. It's a bit complicated, but even if it is better than idlers, I'd rather work on the current style I have going.

Thoughts?

[asid61]

Originally Posted by KohKohPuffs

I've been punching some numbers into JVN design calculator, and I managed 16.85fps high, and 6.76fps low.

This will be a new design (but I'm keeping the inverted CIMs), since to do this I had to have the dog gears be the driven gears rather than the driving gears in the second stage (shifting on upper shaft). Also, in order to have the gear space in the gearbox, I'm most likely going to keep the idlers:

1. The idler gears are easily replacable in case they wear out
2. Using my logic, the idler gears are made of steel, so I doubt wearing down is going to be significant

As for a belted gearbox, I think our team wants to move away from belts. It's a bit complicated, but even if it is better than idlers, I'd rather work on the current style I have going.

Thoughts?

Those speeds are much better, you should be able to withstand a pushing match for a least a little while (I'm getting about 50A current draw with 4.2" wheels, 150lbs, and 1.3 CoF).
Removing the idlers can only do you good, regardless of wearing out. Reduces complexity and weight. If you have to keep them, that makes sense, but I would remove them if at all possible.
What are you guys moving away from belts for? The epitome of flipped-cim gearboxes (192 in 2014) used belts for their first stage and it reportedly went swimmingly. Saves a lot of weight and space in these things IME.

[KohKohPuffs]

Originally Posted by asid61

Those speeds are much better, you should be able to withstand a pushing match for a least a little while (I'm getting about 50A current draw with 4.2" wheels, 150lbs, and 1.3 CoF).
Removing the idlers can only do you good, regardless of wearing out. Reduces complexity and weight. If you have to keep them, that makes sense, but I would remove them if at all possible.
What are you guys moving away from belts for? The epitome of flipped-cim gearboxes (192 in 2014) used belts for their first stage and it reportedly went swimmingly. Saves a lot of weight and space in these things IME.

I might be completely wrong about my team and belts, but we've been using belts for a while on our DT, and this offseason we're experimenting with chain DTs.

I mean... this only applies to the chassis, so perhaps I would attempt a belt system for the first stage. However, I'm using a large ratio for that stage, so I'm not even sure if there are the right pulleys for my configuration.

-Is there an online store that specializes in pulleys? It's been a while since I last been there, and my memory is fading away... -_-
-Also, is it possible to make your own pulleys? If so, is there a link to how to do that?

[asid61]

Originally Posted by KohKohPuffs

I might be completely wrong about my team and belts, but we've been using belts for a while on our DT, and this offseason we're experimenting with chain DTs.

I mean... this only applies to the chassis, so perhaps I would attempt a belt system for the first stage. However, I'm using a large ratio for that stage, so I'm not even sure if there are the right pulleys for my configuration.

-Is there an online store that specializes in pulleys? It's been a while since I last been there, and my memory is fading away... -_-
-Also, is it possible to make your own pulleys? If so, is there a link to how to do that?

SDP-SI has them, but seeing that in this case you have a very large reduction you wouldn't be able to pull it off and still maintain adequate belt wrap without idlers.

[Naveed Riaziat]

Originally Posted by KohKohPuffs

I might be completely wrong about my team and belts, but we've been using belts for a while on our DT, and this offseason we're experimenting with chain DTs.

I mean... this only applies to the chassis, so perhaps I would attempt a belt system for the first stage. However, I'm using a large ratio for that stage, so I'm not even sure if there are the right pulleys for my configuration.

-Is there an online store that specializes in pulleys? It's been a while since I last been there, and my memory is fading away... -_-
-Also, is it possible to make your own pulleys? If so, is there a link to how to do that?

We are moving away from belt in drivetrains because the tenioning was too much work for the benefit. However, tensioning similar to 192's 2014 gearbox is feasible, and in fact, 649 has cadded a similar idea already. It might be tough to get such a large first reduction however with belt. SDP-SI is basically the go-to for pulleys, and 649 already does make their own pulleys, either through our laser cutter or through our wire-edm sponsor.