pic: 8wd 6 cim WCD with PTO

[traxxasracr1]

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[Nathan Streeter]

This looks like a tank! Seems like a good design, that could pack a lot of capability in a reasonable weight. I've not designed a WCD, so I can't comment much on that...

As others have said about your gearbox in its own thread, it seems on the "overkill" side of things and seems to be geared aggressively high... I understand though that this is an "R&D drivetrain" and the goal is to evaluate how fast is "too fast" and such... so I won't comment further on that.

One little thing I thought I would comment on though, it seems to me that you may want to swap your belts from inside/outside... move the belt across the center two wheels into the middle and move the two belts that go to the outer 2/4 wheels closer to the frame. The 15mm belts require a lot of shaft on the inside of the frame, so the cantilevered axle length seems pretty long. By swapping like this, the moment arm that the belt tension on the two end axles is pulling on will be shorter and the middle axles may be better able to tolerate that dynamic loading because they have belt tension pulling in opposite directions... Seems like with all the available torque from that gearbox your dynamic loading could be pretty intense! This could mitigate any shaft deflection and resulting belt hop...

[traxxasracr1]

Originally Posted by Nathan Streeter

This looks like a tank! Seems like a good design, that could pack a lot of capability in a reasonable weight. I've not designed a WCD, so I can't comment much on that...

As others have said about your gearbox in its own thread, it seems on the "overkill" side of things and seems to be geared aggressively high... I understand though that this is an "R&D drivetrain" and the goal is to evaluate how fast is "too fast" and such... so I won't comment further on that.

One little thing I thought I would comment on though, it seems to me that you may want to swap your belts from inside/outside... move the belt across the center two wheels into the middle and move the two belts that go to the outer 2/4 wheels closer to the frame. The 15mm belts require a lot of shaft on the inside of the frame, so the cantilevered axle length seems pretty long. By swapping like this, the moment arm that the belt tension on the two end axles is pulling on will be shorter and the middle axles may be better able to tolerate that dynamic loading because they have belt tension pulling in opposite directions... Seems like with all the available torque from that gearbox your dynamic loading could be pretty intense! This could mitigate any shaft deflection and resulting belt hop...

The problem with switching the belts is that the belt in the middle has to be close to the frame to clear the PTO cylinder. If we end up ditching the PTO, i will definetly switch the belts, although the majority of the load will be on the center 4 wheels, considering the outside wheels only touch the ground when the weight shifts to the front or back. So I feel that the belts in this configuration wont be a problem.

[Chris is me]

If you make custom pulleys from stock instead of using Vex pulleys, you can run two belts on one pulley. That saves you a little bit of shaft length and reduces your part count.

Do you need the huge clearance pocket under the frame for the belts?

[sportzkrazzy]

Looks sweet. I have a few questions though.

Can you pull the gearbox from the drive-train without removing the belly pan? I say this because a few gears and the frame of the gearbox appear to hang below the belly pan. These gears would prevent you from sliding the gearbox in and out in one piece. If you allowed the whole thing to be removed without taking it apart you could build up a spare that you could swap in with little effort to allow you to trouble shoot your main if you did not have time to in between matches.

Can you extend the belly pan to connect at a few points in the middle in between the edges of the gearbox and the outside 1x2? It looks like right now you can not due to the belts hanging below your belly pan but if you did extend it out to the edges more it would act as as sheer plate and greatly improve the frames strength.

Can you offset the bearing holes on your drive axles towards the top of the 1*2 to allow for the belly pan to extend out if that's the case? I dont know how large the od of your pulley's are so its hard for me to tell from your picture. This would sacrifice ground clearance in order to do so although not by much. If the field is relatively flat that might not even be an issue and it will make you less susceptible to tipping from rapid acceleration.

Good work keep it up!

[lewislongbottom]

On your gusset plates holding the frame together, I think your hole pattern maybe wrong? It seems like the holes are too close to the walls of the tubes, most gusset plates have holes centered on the center-line so they don't interfere with the constraints of the tube. The amount of holes is over kill.

As for your belly-pan cutout pattern, you may want to simplify it. Its probably killing the performance of the CAD model (the time it takes to render every time you move the model). Its prob not optimized for all your electronic components either. But I assume you designed it like that to be FANCY!!!