Questions-Thoughts/Input On First Drivetrain Design

[Matthew.Mc]

Recently our team has "revived" an old (but new) CNC Router

I've had a chance to get the CNC figured out and thought it'd be good to get started on working out the kinks on Designing and Building these things before build season.

Notes/Features:

*The Drive Plates are constructed out of 2 sheets of Aluminium, with 1"x1" C-Frame wedged in-between the sheets. This is because be don't have a very reliable Break at our school and therefore I can't do complex flanges.

*It features Andy Mark Shifters. I don't have any experience with them so I'm not sure what the configuration is on how to mount them to the Assembly.

*It features 0.050" Sheet Aluminum. I've done some reading on this but still am unsure about the "normal" of what teams are using. Input would be nice to have if you have experience with them

*Also, so far on sheet metal projects i've been using 3/16" Aluminium rivets








Any input (positive or negative) would be appreciated on the Design

[msimon785]

Overall, that is a solid chassis. I do have a few suggestions, however.
Right now, your AM Shifters are relying on the bellypan for all support. You can easily fix this by lowering the height of the frame such that it lines up with the top of the shifters and flanging it over, allowing the frame to rivet into the shifters from top and bottom.

Your pocketing isn't as efficient as it can be. Based on the style that you seem to be using, you may want to try a 118-esque Isogrid.
You could also go with the ever popular (254+1323+233+ many other teams) diamond style bellypan pocketing.

Other than that, it looks like a solid start to a drivetrain. Good luck!

[sanddrag]

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

[Matthew.Mc]

Originally Posted by msimon785

Overall, that is a solid chassis. I do have a few suggestions, however.
Right now, your AM Shifters are relying on the bellypan for all support. You can easily fix this by lowering the height of the frame such that it lines up with the top of the shifters and flanging it over, allowing the frame to rivet into the shifters from top and bottom.

Your pocketing isn't as efficient as it can be. Based on the style that you seem to be using, you may want to try a 118-esque Isogrid.
You could also go with the ever popular (254+1323+233+ many other teams) diamond style bellypan pocketing.

Other than that, it looks like a solid start to a drivetrain. Good luck!

Thanks msimon785, I'll definitely try out the diamond cut on the belly pan as well as the AM Shifter mounting.

sanddrag, I wasn't sure what the correct spacing was for rivets, so I figured i put in a lot and then remove later if necessary

[Matthew.Mc]

Thanks msimon785, I'll definitely try out the diamond belly pan and the AM shifter mounting. Thanks

sanddrag, i wasn't sure about spacing between rivets so I put a lot and remove later id needed. Thanks

[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

[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.

[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 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.