pic: 4wd Geared WCD

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Hey everyone,

After experimenting with inventor for a few months now I felt as if I needed to see if my work was up to par.

This design is a 4wd, geared WCD with 8" wheels and a rectangle tubing frame. I in no way designed this drawing, I merely modified a pretty well accepted WCD design, baseplate and all.

Other specs:
2x1 tubing
8in wheels
14 gears
Wheels and gears were designed to be held in with C-clips
Center 4 wheels dropped 1/8"
Inventor says the system weighs 56 lbs. So probably not a realistic DT.

And comments or critiques are welcomed! That was the purpose of creating this.

http://www.chiefdelphi.com/media/photos/26312 A couple years ago 703 did a 14 wheel system. I don’t think they ever said a weight for it though. I know the upper structure of that machine was sparse and had to use a decent amount of fancy materials.

You are probably familiar with another no-chain-gang, 25. They use a similar approach to you and use larger wheels.

As for cutting weight, what thickness is the wall on that tubing? Going from 1/8" to 1/16" wall cuts the weight in half. You could also probably be more aggressive on your lightening of the gears. Steel is quite dense after all. (This applies to inside your shifters too) And don’t forget, sometimes having a lot of weight down low is a good thing.

This setup makes it somewhat difficult to attach bumpers outside of the wheels, particularly with 8" wheels and bumpers that have a very specific ‘zone’ of placement. The Poofs get away with this by mounting their chain on the inside of the wheel rails, allowing them to mount metal brackets to reach the outside for bumpers – is it possible to do the same with the gears?

I’m also not sure that the setup would weigh 56 lbs; if it’s an issue you may want to double check it, or investigate using other materials for gears (or thinner gears).

One of the big ways to save weight, and what 25 does, is to take advantage of the massive idler gears to provide a massive speed reduction. If you put a tiny pinion on your CIM output and use the same giant gears for your wheels, that’s a large reduction you no longer need to do inside your gearbox.

Thank you very much guys!

You are probably familiar with another no-chain-gang, 25. They use a similar approach to you and use larger wheels.

As for cutting weight, what thickness is the wall on that tubing? Going from 1/8" to 1/16" wall cuts the weight in half. You could also probably be more aggressive on your lightening of the gears. Steel is quite dense after all. (This applies to inside your shifters too) And don’t forget, sometimes having a lot of weight down low is a good thing.

I would consider 25 our sister team, and yes, they are the ones that inspired our team to create a gear-driven DT in 2007. And 12 lbs of the weight is from the 1/4 in gears. I did not go crazy with lightening holes because it was just an exercise I was working on. I am sure I could get the weight of the gears down to about 8lbs or so, but like I said, it is more of a exercise.

This setup makes it somewhat difficult to attach bumpers outside of the wheels, particularly with 8" wheels and bumpers that have a very specific ‘zone’ of placement. The Poofs get away with this by mounting their chain on the inside of the wheel rails, allowing them to mount metal brackets to reach the outside for bumpers – is it possible to do the same with the gears?

I understand that this design would make it hard to mount bumpers outside of the wheels if the bumpers were down low again like 2007-2009. And yes, I very well could mount the gears inside of the frame. Thats a great idea actually!

I’m also not sure that the setup would weigh 56 lbs; if it’s an issue you may want to double check it, or investigate using other materials for gears (or thinner gears).

Another note, it weighs that much with the Supershifters and the motors also. I could cut a lot more weight on the gears if I spent the time on it.

One of the big ways to save weight, and what 25 does, is to take advantage of the massive idler gears to provide a massive speed reduction. If you put a tiny pinion on your CIM output and use the same giant gears for your wheels, that’s a large reduction you no longer need to do inside your gearbox.

Very good point. The only reason that I set it up this way is because our team is very happy with the speed of our robot with a direct output shaft to the wheel. Our robot goes 16 fps in high and about 10 fps in low I believe, and this is with 8in wheels, and a direct output to one of the wheels.

We like speed. :smiley:

It’s also possible that Inventor is giving you a weight for solid Alu CIMs. Try unenabling any COTS or premade parts, and letting it give you a weight for only the drive base. Then add in everything else. I’ve found that with that method, Inventor is never more than 1/8th of a lb off, even for our robot this year. Good Luck!

Looks good. Need to put some titanium on there, though :cool:

Just to nitpick, most people would call this an 8WD :slight_smile:

How are you planning on keeping the gears/wheels on there? You would probably want to extend shaft all the way through the 2x1 tubing in order to provide two points of support.

Looks like an interesting concept. A Few Suggestions to look into, many said by other people already:

  • move the gears to the inside of the frame
  • utilize the reduction provided by using those large gears, this may involve looking into using the standard Andymark shifting gearset with a custom final gear ratio.
  • have the electronics/base plate one piece, with cutouts for the trans
  • Add Bumper Mounts, check front clearence for bumpers, it looks like the wheels are infront of the chassis’ leading edge.
  • consider alternate wheel sizes and types, there are many options out there (I’m currently in the colsons are great line of thought)

Keep up the good work!

That is a good point. I never thought of that. Is there any way to put in a weight for a certain part without calculating a density that will give you the same weight?

You are right. It needs more titanium.

And yes, that is my daily, no, hourly mess up. It should be called 8wd.

Snap rings do the trick for us.

If I were to actually create this, I would definitely extend the shafts all the way through the tubing.

With the gears on the inside of the frame, how would I be able to mount the transmission? The gears would prevent any mounting unless I was to create a custom mounting setup which would add more weight and pain. Plus, the gears would be mounted to the wheels in the way it is right now. If I were to bring the gears inside of the frame I would need a collar for the gears to keep them in line and connected to the shaft. I just thought thought of this too: With the gears on the inside, the base-plate could only be mounted on the front and back of the bot. There are other problems with that idea also.

This is a point I wanted to do, but I am very unsure as to how to go about that. As you can tell, I am not great at Inventor, so creating a custom gearbox that will perfectly line up with the gears on the wheels is a few steps above my head. Maybe in the coming years.

Believe it or not, they are one piece (they continue together on the frame). Once again, if I were to make this, I would just make the base-plate a cutout where the transmissions stick out.

The wheels are in fact past the frame. I did this with respect to 2010’s game, so I was going for ease of getting over the bump, even though they could be flush and still contact the bump before the frame. Once again, my beginner showing (this was from a while ago actually, January 4th to be exact).

Check out some of my new stuff. I would love your input!:

WCD Cheesy Poof Inspired with a twist