pic: Single Stage Ballshifter

[Chris is me]

I've tried this concept a few times (putting the shifter shaft in the first reduction), and the problem I consistently run into is that the gear ratios end up way too close together if the CIMs drive the ball shifter gears. I've tried fixing this by having the CIMs drive the ball shifter output and using the shifting gears as pinions for a second stage, but then the gearbox gets HUGE. How have you gotten around these problems?

[jkelleyrtp]

Originally Posted by Chris is me

I've tried this concept a few times (putting the shifter shaft in the first reduction), and the problem I consistently run into is that the gear ratios end up way too close together if the CIMs drive the ball shifter gears. I've tried fixing this by having the CIMs drive the ball shifter output and using the shifting gears as pinions for a second stage, but then the gearbox gets HUGE. How have you gotten around these problems?

I'd assume either the shifting spread is going to be 14/11 or they're cutting their own gears to meet the teeth count. I was experimenting with gears around 14 teeth and either your driven needs to be huge (100+ teeth) or you need to have a secondary. Might be able to get away with 6inch wheels to reduce the driven gear, but he's still going to have to make custom cim gears to get anything near 2.5 shifting spread.

Edit: Did not realize a description had been posted. Your teeth count does not line up 71 vs 72, is that okay to use?

[s_forbes]

Originally Posted by jkelleyrtp

Edit: Did not realize a description had been posted. Your teeth count does not line up 71 vs 72, is that okay to use?

Vexpro sells a pinion gear that has 11 teeth, but the profile is set up so that it is used as a 12 tooth gear (as far as spacing between shafts is concerned).

One thing that I would double check with this kind of design is that the motors are spaced around the shifting shaft in a way that prevents the pinions from over constraining the shifting gears and binding. With the shifting gears being 54 and 60 teeth (both divisible by 3) I don't think there would be an issue with the motors being spaced evenly around the gearbox, but it doesn't look from the render like they are spaced that way.

[Rob Stehlik]

Originally Posted by s_forbes

One thing that I would double check with this kind of design is that the motors are spaced around the shifting shaft in a way that prevents the pinions from over constraining the shifting gears and binding. With the shifting gears being 54 and 60 teeth (both divisible by 3) I don't think there would be an issue with the motors being spaced evenly around the gearbox, but it doesn't look from the render like they are spaced that way.

You make a good point about over constraining things. It's not so much the location of the motors in the gearbox, but the angular alignment of the 11T and 18T gears on all of the motors have to be the same. This is probably not easy to do...

[s_forbes]

Originally Posted by Rob Stehlik

You make a good point about over constraining things. It's not so much the location of the motors in the gearbox, but the angular alignment of the 11T and 18T gears on all of the motors have to be the same. This is probably not easy to do...

After some more thought, I guess there's 3 main requirements:

• Spacing of the motors (easy peasy)
• Correct alignment of both pinions on each shaft (hmm, tricky)
• Assembly such that the pinions of each motor are in synch with every other motor (this part would be fun!)

For what it's worth, the Penguineers used a shifting design with two pinions per motor successfully in 2012. Their solution to these issues was apparently to make 4 gearboxes, one for each wheel.

[Chris is me]

Originally Posted by jkelleyrtp

I'd assume either the shifting spread is going to be 14/11 or they're cutting their own gears to meet the teeth count. I was experimenting with gears around 14 teeth and either your driven needs to be huge (100+ teeth) or you need to have a secondary. Might be able to get away with 6inch wheels to reduce the driven gear, but he's still going to have to make custom cim gears to get anything near 2.5 shifting spread.

Edit: Did not realize a description had been posted. Your teeth count does not line up 71 vs 72, is that okay to use?

I'm not so much saying that the two ratios literally wouldn't work / spin, though if that's an issue then there's another problem. I'm basically saying the two speeds / gear ratios on the ballshifter won't be very different, which really minimizes the benefit of shifting in the first place.

[apalrd]

Originally Posted by Chris is me

I'm not so much saying that the two ratios literally wouldn't work / spin, though if that's an issue then there's another problem. I'm basically saying the two speeds / gear ratios on the ballshifter won't be very different, which really minimizes the benefit of shifting in the first place.

That depends on what you want to use each gear for. I personally think 1.82 is perfect.

What is the thickness of the plates? They look like 1/4". You could probably get away with 1/8" or less depending on how they are mounted to the chassis.