Smallest SS Gearbox - COTS or Custom?

[jkelleyrtp]

I'm trying to fit some gearboxes into our frame and space is very precious at the moment. I was wondering what the most compact way to add a gearbox onto the robot would be. We have some CNC capabilities so making custom gearboxes wouldn't be too bad, but it would be our first time doing so. We're also worried about an 11-72 tooth reduction not holding from the impact loads in this game, so unless there's a great testimonial, I'd rather do dual stage. (Leaning towards single stage but want to make sure it's robust.)

[Joe Johnson]

Originally Posted by jkelleyrtp

I'm trying to fit some gearboxes into our frame and space is very precious at the moment. I was wondering what the most compact way to add a gearbox onto the robot would be. We have some CNC capabilities so making custom gearboxes wouldn't be too bad, but it would be our first time doing so. We're also worried about an 11-72 tooth reduction not holding from the impact loads in this game, so unless there's a great testimonial, I'd rather do dual stage. (Leaning towards single stage but want to make sure it's robust.)

11:72 in one stage is not your problem. Tooth strength is the problem and you can build 12:72 gearsets that will fail on your first crossing and others that will last the whole season with nary a complaint.

What is the face width of the gears involved? What Pitch? What is the size of the wheel you are going to be driving with that 72T gear.

By the way, chain done right can be many many times stronger than gears (largely do to the fact that multiple teeth share the load). Can you fit a stage of #25 chain? 11:72 is fine in one stage of chain (~1"OD to ~5.9"OD)

Dr. Joe J.

[jkelleyrtp]

Originally Posted by Joe Johnson

11:72 in one stage is not your problem. Tooth strength is the problem and you can build 12:72 gearsets that will fail on your first crossing and others that will last the whole season with nary a complaint.

What is the face width of the gears involved? What Pitch? What is the size of the wheel you are going to be driving with that 72T gear.

By the way, chain done right can be many many times stronger than gears (largely do to the fact that multiple teeth share the load). Can you fit a stage of #25 chain? 11:72 is fine in one stage of chain (~1"OD to ~5.9"OD)

Dr. Joe J.

I'm just poking around at the Vexpro SS. Unfortunately it seems as if a 1:7.52 isn't enough (we're looking for around 10fps with 6" tire)

So perhaps a 14:72 gear reduction then compensate with a 15t to 32t sprocket reduction. Vexpro gears are 1/2" wide with 20DP and a 14.5 pressure angle.
Are you confident this will hold up?
Although I would prefer to do most of the reduction in the gearbox if we were to direct drive any of the wheels.

[ThaddeusMaximus]

Keep in mind: Can you stand to have the output gear that low to the ground? If you're running a 12 tooth cim to a 72 gear direct to a 4" wheel, I would hate to run that because you'd destroy/damage the gear upon going over some of the defenses. For clearance reasons I'd go with a 2 stage. The packaging isn't that much larger if you do it right.

As far as tooth strength goes, the larger the output gear, with equivalent torque, the less force on the teeth. τ = r x F => F=τ/r

[jman4747]

Originally Posted by jkelleyrtp

Vexpro gears are 1/2" wide with 20DP and a 14.5 pressure angle.

The pinions are .5" but remember the gear it's meshing with is only 3/8".

[jkelleyrtp]

Originally Posted by ThaddeusMaximus

Keep in mind: Can you stand to have the output gear that low to the ground? If you're running a 12 tooth cim to a 72 gear direct to a 4" wheel, I would hate to run that because you'd destroy/damage the gear upon going over some of the defenses. For clearance reasons I'd go with a 2 stage. The packaging isn't that much larger if you do it right.

As far as tooth strength goes, the larger the output gear, with equivalent torque, the less force on the teeth. τ = r x F => F=τ/r

That's what I was thinking as well... I'm trying to feed it into a 2x1 tube setup and am afraid of actually destroying the gearboxes when going over the defenses. What if we went down the WCP SS style - with enough placement fixing, could we package it ontop of the bellypan or just call it a day and get the Vexpro SS DR at 1:9.52?

[Joe Johnson]

Originally Posted by ThaddeusMaximus

Keep in mind: Can you stand to have the output gear that low to the ground? <snip> I would hate to run that because you'd destroy/damage the gear upon going over some of the defenses. <snip>

Roller Chain for the Win! I'm just saying...

Dr. Joe J.

[ThaddeusMaximus]

Originally Posted by jkelleyrtp

That's what I was thinking as well... I'm trying to feed it into a 2x1 tube setup and am afraid of actually destroying the gearboxes when going over the defenses. What if we went down the WCP SS style - with enough placement fixing, could we package it ontop of the bellypan or just call it a day and get the Vexpro SS DR at 1:9.52?

Remember that you don't have to direct drive the wheels. I think Joe has the right idea. It might help packaging even more.



Running a dead axle WCD is also a possibility.