2583 Off-Season Drivetrain Help

Hey guys

Our team wanted to prototype a drivetrain in the next few weeks and this is my first try CAD-ing a drivetrain. I would appreciate any help or comments you guys have

A few notes:
I havent added all of the electronics yet like the router and the power distrubution board

The two inner wheels will be connected to the toughbox and the two outer wheels will be connected to the closest inner wheel using Gates HTD 5mm pitch timing belts

It is 8 wheel drive with the two inner wheels dropped 3/16in

The wheels are 4 inch wheels, I am deciding between AndyMark 4 in Hi Grip wheels or Colsons but I dont know what to base my decision on

Are there any changes I should make? As of now our team has access to a sheet metal break and bender and a lathe

First big problem I see is that you only have one Pulley on the Transmission while you NEED 2 from there, one for each wheel it goes to. and you need 2 on the 4 middle wheels because you need a belt going from the middle wheel to the outside wheels.

You can probably make the distance between the inside and outside rails (the rails that have the pulley’s in between them) closer together, will save space and can make your electrical board bigger.

You’re gonna need more support on the transmissions. Trsut me, they will bend/flex, and it isn’t just a small amount, it will be a big enough movement that your belts can fly off the pulley’s. Leaving you lifeless o the field.

You may want to make an easy way to mount bumpers, pretty common is putting some bigger rail’s between the wheels.

I’m sure for this you just threw the things on the electrical board but you are missing come stuff, and may want to add it all in.

Adding a pattern to your electrical board will help you lose a ton of weight, probably 1lb.

Great start, keep up the work, you wil get better as you design more and more.

Ohyeah, now I remember why I left the second pulley off on the transmission
Right now, the axle from the toughbox is only long enough to fit 1 pulley, it has space for about half a pulley after that, how do I get around this?
Is there a way to get a longer axle out of the toughbox?

Also, how would I put more support on the transmission? This happened to us last year as well, luckily it doesnt cause any catastrophic problems

Any reason you’re going wide?

Not particularly, our team has only done long and offseason is the time to try new things, right?

Battery mounting:

That seems unnecessarily large and heavy. Use 2 pieces of Al L bracket on opposite faces of the battery, with this to support the other faces.

Gearbox supporting:

Span these between each gearbox to support them on each other, as shown in this picture.

Long Toughbox shaft:

This should do the trick.

Those are Toughbox Minis.

Now I see, the plastic housing is twice as thick. And a bit taller.

My bad.

It looks like you are going with a live axle system to transfer the power, however i do not see bearing in the aluminum extrusion. If you do not put bearings the abrasion of the shaft rubbing on the profile of the hole will damage both the metal and the shaft.
Also in a live axle system you will need hubs on/in the wheels rather then the bearings (i think) you have currently.
Also you may want to add another corner gusset on top.

Excellent first CAD, i look forward to seeing great things in the future!

I think you may want to increase the vertical dimension of the frame members (1x2 instead of 1x1) and then add bearings for the wheel axles, the way it is now with the live axle going straight through the frame member will not work (at least not work well). Also you should probably get the live axle hub into those wheels instead of the bearings for a dead axle.

Another thing you should probably do is add a gusset on top of the outer frame members in addition to the ones on the bottom. Doing this should really increase the strength of the chassis.

As always you should consider whether or not you need that much material for whatever application you are using it for, my guess is that you could drop the thickness in a few areas, though its hard to tell from the picture.

It’s a good start nevertheless.

As others have said, the pics look really good. I have some suggestions (don’t we all?), but they’re more in the vein of improvements or decisions rather than criticisms, however they may sound.

  1. It looks like you’re using 1x1x1/8 wall tubing. You may want to look at using 1x1x1/16 wall instead. Half the weight, and the bumpers should be taking most of the impact load anyway.
  2. You may want to bring the wheels inboard of the outer frame elements. This would protect the wheels, reduce torquing/twisting through the frame, and make mounting the bumpers easier/more solid.
  3. The comments others have made about the dual pulley systems are spot on. If you need to attach a second pulley and don’t have enough shaft, you could bolt the second pulley to the first with two bolts.
  4. You may want to consider a means of tensioning the timing belts you are using. There’s nothing more frustrating than mounting everything up and then finding out that the pulleys are too far apart for the belt to fit over the flanges.
  5. Since you have the time right now, see if you can design up or find a common design that will allow you to demount and remount the timing belts without doing anything other than detensioning the belts. Although FRC is not as brutal on timing belts as industrial machinery, I’ve seen too many oddball thing happen to discount the possibility.
  6. You may want to change how the shafts are set up. Rather than putting shaft holes through your frame structure, try mounting a block off the frame that accepts the shaft end.
  7. I personally am a big fan of bronze bushings over ball bearings in FRC. I’ve never had a chance to use them in a drivetrain and am not sure I would want to, but if you used them, your shafts can sit in the bushings and the bushings can be Loctited (641) into place.

After looking more closely I see the problem in my CAD
I have never dealt with hubs separate from the pulley because our team has always chained our drivetrains with the sprocket directly attached to the wheel

The pulley is attached to the axle with a set screw so they will spin together
How would I go about connecting this wheel to the axle so they spin together?

I looked at Andymark’s website and found these hubs
http://www.andymark.com/Hubs-s/215.htm

Most of them used keyed axles and we do not have the resources to machine a keyed axle, can you buy those?

Yes, you can get keyed axle from many sources. Mcmaster is a fine source to get keyed axle if you don’t need much bulk. Because you said that you have a lathe, I highly recommend hex axle though because it makes assembly easier. Andymark sells both hex bearings and hex hubs. West Coast Products sells colson hex hubs and 1/2 undersized 7075 hex.

I made the pulleys have a hex bore and attached a hex bore hub to the wheel so they will spin with the axle

Now how do I deal with the axle going through the frame right now with no bearing?

I thought about using a bearing hub and mounting it to the side of the aluminum channel but the axle is now a hex axle and I cannot find bearings that fit hex axles

Any thoughts on how I fix this?

Honestly there have been quite a few links to andymark already. They sell hex bearings. Go and look.

I have included a link for the .step file of the chassis now

I included a lot of the changes you guys suggested

I still have to include the rest of the electronics and figure out a tensioning design but that will come later

The red things on the wheels are the colson live axle hubs
http://wcproducts.net/wcp-00053/

The blue things on the aluminum channel (seen from the bottom of the robot) are AndyMark hex bearings with flanges
http://www.andymark.com/product-p/am-0279.htm

The hole in the aluminum channel is slightly smaller than the OD of the bearing so they will be pressed in and there is a small flange on the bearing which will keep it from going too far.

Also the axle is now hex and the pulley has a hex bore so they are connected

Do you guys have any more comments or suggestions?
Your help has been very useful so far, im learning a lot

Download Link:
http://www.2shared.com/file/kdrucknG/chassis1.html



I think this is much better.

However a few things I notice:

  • Is there a reason you have the large plate on top of the frame rather than below it? If there isn’t a reason, you could probably move it below and protect the electronics a little easier.

  • I would recommend that you try to support the gear box output shaft on the end.

  • I would also only make the shafts 1/2" hex at the wheel. By turning it down to regular 1/2" you save yourself the need to purchase a broach. Additionally you can save money by purchasing regular 1/2" bearings ($7 vs $9.50) rather than hex bearings.

Again, this design is much better now, good job.

Would it make it the structure stronger if I put the board below or is just for the sake of protection? I could definitely put it below if its better

I thought about doing this for the axles but we only have a lathe and I dont think we have any tools to turn a round axle to a hex axle
Mcmaster sells hex axles which are long enough but the hole axle is hex

Is there a way for us to make the part of the axle hex without buying anything?

You can buy 1/2" hex shaft and turn it down to just regular round 1/2" shaft with a lathe its a pretty standard operation. You would then just use either set screws or cotter pins for the sprockets.

Putting the plate on the bottom of the frame is what is normally done. In my opinion it looks cleaner, helps lower the Center of Gravity, and allows you to attach a superstructure easier.

A. WCP is selling hex bearings for $7.5.
B. You can turn hex into round shaft with a standard lathe that has a 3 jaw check and just HSS tool. Also the hex pushing up against the bearing would help retain the shaft in place