Questions-Thoughts/Input On First Drivetrain Design

[rcmolloy]

Originally Posted by sanddrag

I think it would be just fine with 1/3 the amount of rivets.

Yeah I would assume a 3/16" rivet every half inch should do you just fine. The current pattern seems to be way overkill.

Also, add some fillets to your pocketing patterns as well. It definitely helps the end mill for the router to eliminate the precise corners that you have going on there. Even more so, if you ran this, it will still have the mill's OD in each corner of your triangles. I would advise you make the fillets to your the mills exact OD or higher; never under.

Also, the normal/nominal thickness I have seen over the past years for sheet is a variance between .090" and 1/8". 1/8" for the beefier parts that require much of the static loads to be held and .090" for manipulation systems. (Correct me if I'm wrong guys haha)

Aside, it looks like a pretty decent sheet chassis.

[AlecMataloni]

We used .125 on our drivetrain this year IIRC, but I've heard of teams using .090. .063 is the thinnest sheet we use on our robot, and I doubt it would ever be on the drivetrain. Make it thicker just to play it safe.

Concerning gearbox placement, you'll definitely want to direct drive one wheel on each side to avoid losing an entire side of your drivetrain to chain failure.

Also, lay off the rivets.

[IndySam]

I'm not quite sure how you are using the AM Shifters. These do not have an output shaft but have two internal sprockets on the output shaft for chain runs.

If you want an output shaft you should be using an AM Super Shifter.

[Matthew.Mc]

Originally Posted by IndySam

I'm not quite sure how you are using the AM Shifters. These do not have an output shaft but have two internal sprockets on the output shaft for chain runs.

If you want an output shaft you should be using an AM Super Shifter.

I actually wasn't sure how these mount and where their output was since im new to them so thanks for clearing that up. In my next design I can integrate them the right way.

Also thanks to everyone for giving input, it's going to help me immensely

[apalrd]

Originally Posted by AlecMataloni

We used .125 on our drivetrain this year IIRC, but I've heard of teams using .090. .063 is the thinnest sheet we use on our robot, and I doubt it would ever be on the drivetrain. Make it thicker just to play it safe.

We built our entire chassis out of (flanged) 0.063" 6061-T6, and decided post-season we should have used 0.050".

If you design the flanges and structure correctly, and pick the right alloy, you really don't need very much thickness.

All of the waterjet pieces of this robot are 0.063" except the gearbox plates (they are 0.090").

[Garrett.d.w]

Originally Posted by rcmolloy

Yeah I would assume a 3/16" rivet every half inch should do you just fine. The current pattern seems to be way overkill.

I would space them further than every half inch. I generally go for one every two inches in the main body sections, and one every inch in the corners. You can also add silicone glue under the panels to dampen vibrations.

Riveting tip: if you are riveting into tubing, make sure that there is a hole for the mandril tips to exit. This will help you avoid the "rainstick effect"

All in all, sweet drivetrain. Do you have plans for tensioning the chains?

[Matthew.Mc]

Originally Posted by Garrett.d.w

I would space them further than every half inch. I generally go for one every two inches in the main body sections, and one every inch in the corners. You can also add silicone glue under the panels to dampen vibrations.

Riveting tip: if you are riveting into tubing, make sure that there is a hole for the mandril tips to exit. This will help you avoid the "rainstick effect"

All in all, sweet drivetrain. Do you have plans for tensioning the chains?

Thanks, and no not as of now. I don't see having the gearbox being modular to move up and down(which is what we did this year). I know we have used an in-shop made tensioner which worked pretty well and held up, but ill have to wait until school starts to get info on that.

[Garrett.d.w]

Originally Posted by Matthew.Mc

Thanks, and no not as of now. I don't see having the gearbox being modular to move up and down(which is what we did this year). I know we have used an in-shop made tensioner which worked pretty well and held up, but ill have to wait until school starts to get info on that.

I think that it has already been suggested, but if you can drive your center wheel (middle wheel with the most weight on it) off of the output shaft of the shifter you will be removing a chain run and making your drivetrain a lot more bulletproof.

For the other six chains you can calculate the runs down the the link, and place your wheels accordingly. Then tension the chain as it stretches using something like these from AM

http://www.andymark.com/product-p/am-0286.htm

If you prefer to manufacture in house, I am currently working on a more student machinist friendly version of the product shown above and I can share the files with you.

[Matthew.Mc]

Originally Posted by Garrett.d.w

I think that it has already been suggested, but if you can drive your center wheel (middle wheel with the most weight on it) off of the output shaft of the shifter you will be removing a chain run and making your drivetrain a lot more bulletproof.

For the other six chains you can calculate the runs down the the link, and place your wheels accordingly. Then tension the chain as it stretches using something like these from AM

http://www.andymark.com/product-p/am-0286.htm

If you prefer to manufacture in house, I am currently working on a more student machinist friendly version of the product shown above and I can share the files with you.

No, for something that cheap im sure it wouldn't be a problem to buy. I agree with driving one wheel directly, and wanted to do it, but im not sure on how to go about doing it. Especially with the AM Shifter's without experience.

[Garrett.d.w]

Originally Posted by Matthew.Mc

No, for something that cheap im sure it wouldn't be a problem to buy. I agree with driving one wheel directly, and wanted to do it, but im not sure on how to go about doing it. Especially with the AM Shifter's without experience.

You can put a hex output shaft in a supershifter. You then connect the shaft directly to a hex bore wheel. You should support both sides of the shaft with bearings.

Situate the wheels where you want them, then rotate the supershifters around their output shafts until you find a suitable mounting position. With the design of your frame, you will probably be mounting to the face of the supershifter.

This year, ours wound up rotated about 45 degrees and mounted to the frame using L brackets.

If you want an example, I can provide a CAD model and pictures.

[Matthew.Mc]

Originally Posted by Garrett.d.w

You can put a hex output shaft in a supershifter. You then connect the shaft directly to a hex bore wheel. You should support both sides of the shaft with bearings.

Situate the wheels where you want them, then rotate the supershifters around their output shafts until you find a suitable mounting position. With the design of your frame, you will probably be mounting to the face of the supershifter.

This year, ours wound up rotated about 45 degrees and mounted to the frame using L brackets.

If you want an example, I can provide a CAD model and pictures.

If you could post a picture of a CAD model of how you mounted the Shifter it would be nice. Thanks

[IanW]

Couple of things:

• The sheet thickness is almost certainly fine. See example below. However,
• Using a router to cut material will probably be challenging. As I understand it, the bit will tend to grab the material and yank it around with thin sheet. Granted, I don't personally have experience with this, but I've heard this said previously in other threads
• The sides are probably beefier than they need to be. Again, see example below

This past year my team and Team 1983 used a similar sheet metal design:
FRC 2374
FRC 1983
Both of these designs were from before kickoff and thus modified to address the challenges of the game.
Both teams only used one piece of sheet metal on the side panels, not a full box like you have. We then pop riveted the sheets to pieces of angle aluminum. Our rivets were on a 2" spacing. The chassis seemed to hold up quite well.

Good work though, good luck on your future iterations.

[Matthew.Mc]

Originally Posted by IanW

Couple of things:

• The sheet thickness is almost certainly fine. See example below. However,
• Using a router to cut material will probably be challenging. As I understand it, the bit will tend to grab the material and yank it around with thin sheet. Granted, I don't personally have experience with this, but I've heard this said previously in other threads
• The sides are probably beefier than they need to be. Again, see example below

This past year my team and Team 1983 used a similar sheet metal design:
FRC 2374
FRC 1983
Both of these designs were from before kickoff and thus modified to address the challenges of the game.
Both teams only used one piece of sheet metal on the side panels, not a full box like you have. We then pop riveted the sheets to pieces of angle aluminum. Our rivets were on a 2" spacing. The chassis seemed to hold up quite well.

Good work though, good luck on your future iterations.

Thanks for showing me the designs. There quite simplistic but look quite sturdy. Also I have done projects on the CNC with 0.050" sheet Aluminium and it just took some tuning with the spindle speed and feed rate.

Originally Posted by rcmolloy

Yeah I would assume a 3/16" rivet every half inch should do you just fine. The current pattern seems to be way overkill.

Also, add some fillets to your pocketing patterns as well. It definitely helps the end mill for the router to eliminate the precise corners that you have going on there. Even more so, if you ran this, it will still have the mill's OD in each corner of your triangles. I would advise you make the fillets to your the mills exact OD or higher; never under.

Also, the normal/nominal thickness I have seen over the past years for sheet is a variance between .090" and 1/8". 1/8" for the beefier parts that require much of the static loads to be held and .090" for manipulation systems. (Correct me if I'm wrong guys haha)

Aside, it looks like a pretty decent sheet chassis.

I have actually printed 2 Pieces from an old design of some front plates. They were merely a test but showed me i didn't need fillets on the sharp edges.

[Garrett.d.w]

Originally Posted by Matthew.Mc

If you could post a picture of a CAD model of how you mounted the Shifter it would be nice. Thanks

Here we go, hopefully this helps sort out my previous post (which after reading it again makes no sense).

The first pic is for context. The drivetrain is a 6wd West coast drive from this years competition robot. Even though the drive systems are different, the concept still holds true.Chains and extraneous hardware have been removed for clarity.


Here is a view of the rail.

And finally a fancy exploded view.

[Matthew.Mc]

Originally Posted by Garrett.d.w

Here we go, hopefully this helps sort out my previous post (which after reading it again makes no sense).

The first pic is for context. The drivetrain is a 6wd West coast drive from this years competition robot. Even though the drive systems are different, the concept still holds true.Chains and extraneous hardware have been removed for clarity.


Here is a view of the rail.

And finally a fancy exploded view.

Thanks. Ill look at super shifters, although there a bit more bulky which I don't really mind but it would be nice to learn more about the normal shifters. I'll probably just wait until I can buy them when its back to school so I can really understand them and perhaps make a variation of them.

Thanks again