pic: 2-Speed Flipped CIM Gearbox

[AriMB]

So I saw a number of flipped CIM shifters posted recently, and I thought I would try my hand at it. My main goal was to make this as “thin” as possible (i.e. minimize distance from inside of the tube to the inside-most face of the gearbox). A lot of this design was inspired by this gearbox recently posted. The biggest difference here is that this gearbox is positioned on top of the tube, instead of the inside of the chassis. Shown with 1 CIM, 2 MiniCIMs for visual, would likely be run with 3 MiniCIMs.

Here are some more renders, and CAD is available here.

Some specs:
[list][]Suitable for 3 CIMs (or 3 MiniCIMs, 1 CIMs + 2 MiniCIM, yada yada yada)
[]3.5lbs without motors (including pneumatics & sprockets)
[]5/15 ft/s adj. speed as configured, but easily changed via 3rd stage ratios
[]~1.5" from inside of frame to inside of gearbox
[]8.9" max height from the ground, 6.9" max width
[]Designed for chain-in-tube WCD[/list]

Feel free to post comments, questions, suggestions, or reaction GIFs.

[cad321]

I really like the design of this; it’s unfortunate you couldn’t keep it down to 2 stages, but in return for the packaging , it all works out. A few questions.

One, what size wheel is this designed to be run with?

Two, is that gear ratio adjusted or free speed.

And finally, why a dog shifter over ball shifter (note i’d be asking the other way around if you had chosen ball shifter, just curious)?

[cbale2000]

Without seeing this on a chassis with bumpers it’s really hard to tell, but my initial concern is how far that cylinder protrudes past the wheel.

I feel like a better option would be to connect the cylinder using some sort of armature and mounting the cylinder inside the gearbox, pushing out. Alternatively, it also looks like you could also reverse some of the gear orientations and mount the cylinder on the inside of the frame.

True you would protrude into the frame area more with the later of those two options, but it looks like in the current configuration your bumpers would have to extend out to protect the cylinder anyways, so you’d either have a large wasted space past the wheels or a small wasted space inside the frame.

I suppose I might just be stuck in the “old school” line of thinking from back before bumpers were a thing and no one dared to extend anything fragile (and in this case, important) past the frame perimeter, so take the above critique with a grain of salt.

[AriMB]

I really like the design of this; it’s unfortunate you couldn’t keep it down to 2 stages, but in return for the packaging , it all works out. A few questions.

One, what size wheel is this designed to be run with?

Two, is that gear ratio adjusted or free speed.

And finally, why a dog shifter over ball shifter (note i’d be asking the other way around if you had chosen ball shifter, just curious)?

It’s designed to use a 4" wheel. That is the adjusted gear ratio, though I’m not so set on that final ratio. It’s super easy to change the final ratio by changing the 3rd gear set. Dog shifter because it packaged better in this application (all 3 gears between the bearings instead of just the shifter gears between and the third cantilevered).

Without seeing this on a chassis with bumpers it’s really hard to tell, but my initial concern is how far that cylinder protrudes past the wheel.

I feel like a better option would be to connect the cylinder using some sort of armature and mounting the cylinder inside the gearbox, pushing out. Alternatively, it also looks like you could also reverse some of the gear orientations and mount the cylinder on the inside of the frame.

True you would protrude into the frame area more with the later of those two options, but it looks like in the current configuration your bumpers would have to extend out to protect the cylinder anyways, so you’d either have a large wasted space past the wheels or a small wasted space inside the frame.

According to the CAD model, the back of the pancake cylinder is ~0.03" inside of the end of the colson retaining screw, so the bumpers shouldn’t need to move out substantially. To achieve that, I had to substitute the spacers that come with the hardware kit with custom spacers, and use a custom shifting shaft. I know it’s still close, but the bumper should help protect it, and I really wanted to keep the cylinder on the outside for space reasons (that was kind of the main requirement for designing this).

[Cothron_Theiss]

Did you fillet the corners of the plates? Those renders look REALLY good.

[AriMB]

Did you fillet the corners of the plates? Those renders look REALLY good.

Thanks! Right before I started rendering I put a 0.5mm chamfer on basically every edge of the custom aluminum parts. I found that helps reflect the light to define the edges in the renders so you can see where one part ends and the other begins even when they’re mated coincident with the same appearance. Each of the renders (except for the gif) took less than 20 mins on my laptop.

[Cothron_Theiss]

Thanks! Right before I started rendering I put a 0.5mm chamfer on basically every edge of the custom aluminum parts. I found that helps reflect the light to define the edges in the renders so you can see where one part ends and the other begins even when they’re mated coincident with the same appearance. Each of the renders (except for the gif) took less than 20 mins on my laptop.

I’ll have to remember that, thanks.