Offseason WCD with 3 CIM inverted transmission design

This is something I've been working on since last night - it's nowhere near done, but I figured it was presentable.

WCD (High res image here):
-Dimensions: 28"L x 27"W
-Transmission is a repackaged WCP shifter with calculated speeds of 6 and 17 ft/s with inversed CIMs (more on that below).
-Weight is 39 lbs with everything featured. A little heavier than I'd like, but I haven't even begun lightening, so it has a lot of potential to be lighter.
-2x1 is Versatubing, and the 1x1 is all 1/16" thickness.
-6 4" diameter x 1.5" wide colsons with 1/8" center drop driven by 9mm HTD belts
-Yes I forgot to put the cams in the model, though the holes for them are there.

Inverted 3 CIM shifter (aka: The House):
-WCP DS guts with a 2.92 spread.
-Driven 42T gear is now outside the gearbox and cantilevered.
-Power is transmitted from motors to 42T through cantilevered 50T idler gears (not shown in model: switching from live axle gears to bearing bore gears on a dead axle).
-Entire module weighs 10 lbs
-With current drop and positioning the bottom CIMs are 3/8" from the top of the 2x1 tubing, and do no extend past the halfway point on the tubing, so any size wheel can be used without interference.
-Design opens up enough room in the bellypan for continuous electronics.

As always, constructive criticism is always appreciated, and I'll be happy to answer any questions anyone has.

[Tyler2517]

Have you thought about using belts for the first stage of gearing? Might save some weight.

Originally Posted by Tyler2517

Have you thought about using belts for the first stage of gearing? Might save some weight.

I considered it at first, but tensioning a gearbox wasn't really what I was looking to do, and that would require 3 separate belts with 3 separate pulleys. Plus I wasn't comfortable cantilevering pulleys 1.5" out on a CIM shaft. Overall gears were thinner, simpler, and the weight difference isn't a problem anyways.

[DampRobot]

Originally Posted by Andrew Lawrence

I considered it at first, but tensioning a gearbox wasn't really what I was looking to do, and that would require 3 separate belts with 3 separate pulleys. Plus I wasn't comfortable cantilevering pulleys 1.5" out on a CIM shaft. Overall gears were thinner, simpler, and the weight difference isn't a problem anyways.

Ahem. Seems to have worked out well for them.

Cool concept, I think I see some overdefinition issues with some gears though. Depending on the angle between the idler gears, they might or might not interfere.

[T^2]

Weight?

[Chowmaster4695]

Originally Posted by T^2

Weight?

39lbs

[Joey Milia]

Originally Posted by Chowmaster4695

39lbs

I think he means weight of the gearbox alone not the whole base. I would like to know how much the gearbox weights without motors too.

[cxcad]

Originally Posted by Chowmaster4695

39lbs

should weigh around 4.6 lb without cims. Each cimis 2.82 lb

Originally Posted by T^2

Weight?

The transmission (without motors) is ~2.31 lbs by itself, assuming 2.8 lb motors.

[Oblarg]

Interesting compromise with the inverted CIM design to allow different wheel sizes.

I only see two spacers at the bottom running between the gearbox plates. Are you sure that's stiff enough?

Originally Posted by Oblarg

Interesting compromise with the inverted CIM design to allow different wheel sizes.

I only see two spacers at the bottom running between the gearbox plates. Are you sure that's stiff enough?

There are two others you can't see in the model (hidden by the motors).

[asid61]

I would highly recommend you do not cantaliever any gears. My second gearbox I designed, which we neglected to test this year under load and plopped right onto the WCD, had gear mating issues on the second stage gear because it was cantalievered.
Keep in mind this was with two bearings on it, one on the wheel block and one right next to the gear in the gearbox. The gear still had massive mating issues.
Instead, try putting the cims offset by 1/2" or so to allow for the gears to be inside the gearbox and have bearings on them on both sides.

On a side note, that's a pretty sweet gearbox. I like the way you are holding the cims with the gearbox. Seems to save a lot of space.
Keep in mind those holes will need to be a bit larger than 2.536", the OD of the cim.

[Jared]

Originally Posted by asid61

I would highly recommend you do not cantaliever any gears. My second gearbox I designed, which we neglected to test this year under load and plopped right onto the WCD, had gear mating issues on the second stage gear because it was cantalievered.
Keep in mind this was with two bearings on it, one on the wheel block and one right next to the gear in the gearbox. The gear still had massive mating issues.
Instead, try putting the cims offset by 1/2" or so to allow for the gears to be inside the gearbox and have bearings on them on both sides.

I wouldn't worry about the cantilevered gears too much. We had problems when we cantilevered gears on our output shaft, but we had no issues cantilevering our 2nd stage of reduction (30t to 56t gears). The gears cantilevered on this gearbox are rotating quickly so they have less torque, and less force on the shafts than a cantilevered gear on the output shaft.

The only thing I'd worry about is the four gears (pinion, two idlers, and one more) that are engaged in a square. That center pinion might not fit in there. If it engages with one gear, the other gear may never line up. Unless you've designed for it, both gears that engage with the center pinion could always be slightly misaligned. A simple solution might be to replace one of the idler gears with the versa hub pattern with a smaller gear, so that the center pinion only engages with one gear.

Originally Posted by Jared

I wouldn't worry about the cantilevered gears too much. We had problems when we cantilevered gears on our output shaft, but we had no issues cantilevering our 2nd stage of reduction (30t to 56t gears). The gears cantilevered on this gearbox are rotating quickly so they have less torque, and less force on the shafts than a cantilevered gear on the output shaft.

The only thing I'd worry about is the four gears (pinion, two idlers, and one more) that are engaged in a square. That center pinion might not fit in there. If it engages with one gear, the other gear may never line up. Unless you've designed for it, both gears that engage with the center pinion could always be slightly misaligned.

It is designed in there.


Also in the second iteration the idler gears will be bearing bore gears on dead axle shafts that extend through both plates in the gearbox.

[highlander]

Originally Posted by asid61

I would highly recommend you do not cantaliever any gears. My second gearbox I designed, which we neglected to test this year under load and plopped right onto the WCD, had gear mating issues on the second stage gear because it was cantalievered.

Hold on a second; was your shaft 6061, 7075, or steel? I've seen 6061 shafts bend with a longer lever arm, but with 7075 and a short lever arm like in his picture the gears will be fine (as long as he has the two bearings he mentioned above: one bearing is generally a bad idea)


Also, I like the support you are giving the CIMS, but do you need the support from the sides? You could probably save some aluminum by just providing support from the bottom, if that makes sense.