pic: Drivetrain Side View

[AustinSchuh]

[cdm-description=photo]26093[/cdm-description]

[Rafi Ahmed]

Looks like it is inspired from the 254/60/22 drive train.

Why couldn't the wheel be only two pieces by incorperating the hub into the wheel itself?

[Travis Covington]

I love the button head screw to tension the chain. Nice touch.

[amos229]

Just a few thoughts as 229 had a drive similar to this for triple play. Are you using a solid chain linking all the wheels together. We decided that we should use 2 chains one mid wheel to front wheel and one mid wheel to back wheel. in case one breaks you still have 2 wheels driving. Also if you use this in a game try to keep the robot balanced front to back otherwise you ed up with massive tread wear. But other than that great design, good luck in '07'

[AustinSchuh]

I modeled the drive train off of ideas behind of 254's drive train, and 968's tensioner.
Why couldn't the wheel be only two pieces by incorporating the hub into the wheel itself?
I designed the wheel so that it could be swapped out easily. All we have to do is to remove the six bolts, and the wheel is free to be swapped out. Also, one of our sponsors is a sheet metal manufacturer. They can easily cut out the 5 pieces of sheet metal that make up the wheel. The wheel has an 1/8 th inch thick rim, a 1/4 inch thick spoked section, two 1/4 inch body sections, and another 1/8 th thick rim. They would then spot weld these together in that order to make the wheel. By incorporating the hub into the wheel, we would have to start with a larger block of aluminum and wouldn't be able to make the wheel out of sheet metal.

We decided that we should use 2 chains one mid wheel to front wheel and one mid wheel to back wheel. in case one breaks you still have 2 wheels driving.
I am doing the same thing. You can see the two sprockets on the main drive shaft in the other picture that I posted. Thanks for the advice on tread wear

Here is a render of our tensioning device. Once again, it is made out of sheet metal.
http://www.boardsailor.com/austin/WheelTensioner.jpg

[Nuttyman54]

Are the wheels being held on the shaft only by the clips, or is there something I'm missing?

[AdamHeard]

Are the wheels being held on the shaft only by the clips, or is there something I'm missing?

It looks like snaprings. Those do a great job, I know 968 (and 254 as well?) used them this year. We also had all six of our wheels held on with snaprings and never popped one.

[Rafi Ahmed]

Are the wheels being held on the shaft only by the clips, or is there something I'm missing?

It seems like it. The clips would be enough to keep on the wheels. 254, 60, 22, 968, 980, and 4 (thats all i can remember) used only clips and they work just fine

[Nuttyman54]

It seems like it. The clips would be enough to keep on the wheels. 254, 60, 22, 968, 980, and 4 (thats all i can remember) used only clips and they work just fine

well then, I'm convinced. I've never used them, so I wasn't sure how strong they were.

[AustinSchuh]

It looks like snaprings.
Yes, those are snap rings. Good call.

[Madison]

I modeled the drive train off of ideas behind of 254's drive train, and 968's tensioner.

Here is a render of our tensioning device. Once again, it is made out of sheet metal.
http://www.boardsailor.com/austin/WheelTensioner.jpg

Can you show a more detailed look at how the tensioner interfaces with the frame? I'm not clear on how it's supported.

I've been working on a similar design that requires as little complex machining as possible, as I'm the person who does all the CNC work on the team and there're few things I dislike more than sitting in front of the machine. The tensioning mechanism is one of the few details remaining, so it's interesting to see how others have decided to implement that detail.

[AustinSchuh]

Here is a picture of how the part that I posted earlier fits into the frame. I moved one of the side plates out of the way so that you can see how the part fits in the frame.

http://img50.imageshack.us/img50/1556/wheeltensionerandframeur8.jpg

[Madison]

Here is a picture of how the part that I posted earlier fits into the frame. I moved one of the side plates out of the way so that you can see how the part fits in the frame.

Thanks for clearing that up. Are you relying on the tension of the chain to prevent the buttonhead screw and tensioning mechanism from moving outward (left in the picture)?

Also, I like the display style a lot.

[AustinSchuh]

Correct, I am relying on the tension of the chain to prevent the buttonhead screw from moving outward.

[Bill_Hancoc]

that my friend is beautiful...i wish i had the patience to design something like that. Very nicely done.

[AustinSchuh]

If anyone is interested, here are the Solidworks files for the drive train and transmission. If you end up using any part of them durring the season, I would love to know about it. Please let me know if there is a problem with the files, or something doesn't make sense.

http://www.boardsailor.com/austin/CDExport12-28.zip

[Travis Covington]

Correct, I am relying on the tension of the chain to prevent the buttonhead screw from moving outward.

It also clamps onto the 1x2 frame rail I assume.

[AustinSchuh]

Correct.

[Madison]

If anyone is interested, here are the Solidworks files for the drive train and transmission. If you end up using any part of them durring the season, I would love to know about it. Please let me know if there is a problem with the files, or something doesn't make sense.

http://www.boardsailor.com/austin/CDExport12-28.zip

Thanks for making the model available. It's always fun to get in and dig around somebody else's models.

I've been curious about how you're planning to attach tread material to your wheels. Because they're made from several layers, it seems like it'd be difficult to rivet the material down. Can you give any insight into how you're going to do this?

[Gabe]

I have always wondered if it is possible to avoid using any sort of tensioning whatsoever for roller chain. If you properly calculated the measurements for the location of the sprockets you would never need to tension the chain. I reference this website: http://www.battlekits.com/
This drivetrain uses no tensioners, though granted, they do use #35 rather than #25. Smaller chain stretches more than larger chain. I really like the Battlekits design and function, and simplicity. What do others think about not using tensioners?

[AustinSchuh]

I haven't looked too far into this, but I was assuming that since the wheels will be tig welded together pretty solidly, we would be able to ignore the fact that the wheels are just layers of sheet metal, and just drill holes for the rivets. We would of course try to drill the holes through the centers of the layers and miss the gaps between the sheets, but I don't see anything wrong with drilling in the gaps between the sheets. If the wheel breaks because we drilled a couple holes in the wrong spot in the rim, we have MUCH BIGGER problems.
Thanks for your feedback.
Did I use the PEM nuts correctly? Our machinist recomended PEM nuts instead of threading metal, but since I have never used them before, I don't know if I used them correctly.
Also, I sent the design to our machinist for inspection, and he thought that I needed to strengthen the transmission case by making it more of a box. Is his concern valid?
(PEM nuts are cool parts that are pressed into a special sized hole in a piece of metal and presto, the hole now has threads. http://www.pemnut.com/)

[AustinSchuh]

I have always wondered if it is possible to avoid using any sort of tensioning whatsoever for roller chain.
After watching our 2004 robot go from having tight 35 chain, to 35 chain with around a link and a half of slop in the chain without driving it very much, I would be hesitant to get rid of chain tensioners.
Theoretically it is possible, especially with short chains, but I don't feel comfortable without a chain tensioner.

[AdamHeard]

Also, I sent the design to our machinist for inspection, and he thought that I needed to strengthen the transmission case by making it more of a box. Is his concern valid?
(PEM nuts are cool parts that are pressed into a special sized hole in a piece of metal and presto, the hole now has threads. http://www.pemnut.com/)

Look at how 22 (maybe), 60, 254 an 968 have been doing it. You have no problem with the curved plates.

[Madison]

Did I use the PEM nuts correctly? Our machinist recomended PEM nuts instead of threading metal, but since I have never used them before, I don't know if I used them correctly.
Also, I sent the design to our machinist for inspection, and he thought that I needed to strengthen the transmission case by making it more of a box. Is his concern valid?
(PEM nuts are cool parts that are pressed into a special sized hole in a piece of metal and presto, the hole now has threads. http://www.pemnut.com/)

The captive nuts looked fine to me; just make sure the ones you use are sized properly for the sheet metal thickness.

I think your transmission will be fine as long as it has the spacers across the top, though I was curious why you decided to use sheet metal spacers instead of simple tube. It may be heavier to have a bolt run through tubing, but it'd also be a lot easier and might alleviate some of the sheet metal production time.

Did your machinist express any concern about the bearing holes lining up from one side the the next? The limited experience I've had with sheet metal parts makes me concerned that you may not get bends that are accurate enough to keep the shafts orthogonal to the plating -- especially if you're bending something as thick as 1/4" plate.