907 4 inch IFI Sheet Metal Drivetrain Feedback

[BJC]

Hey there, nice drivetrain. I'll put my comments in red.

Originally Posted by Matthew.Mc

Hey CD,

So recently our team has been delegating with potential sheet metal fabrication sponsors. We have come to an agreement that our team would like to pursue a sheet metal construction for next year. (Well at least Drivetrain)
This is a really good step, sheet metal is a very powerful construction method in FRC. Congrats to your team on finding a sponsor.

I posted on CD about a month and a half ago on my first sheet metal drivetrain that I made in Pro Engineer. Since then, I have taken the information that some members of the site gave me, and created roughly 6 drivetrains. All better each time. I haven't posted one since the first, so I believe that this is another that can be criticized. I believe that I have much room for improvement, and hopefully you guys can help me address the issues I have.

The Drivetrain will consist of the following:

-6 Wheel Design (Dropped Centre (0.125)
-4 inch IFI Wheels
-Super Shifter's (OR Custom Shifters)
-Lightweight Design
Do you know the aproximate frame weight?
-Rigid design
-Belly Pan With Electronics
-0.090" 5052 H32 Aluminium
.09 is a pretty good sheet thickness for 5052. My team used .06 last year but also used either 6061 or 7075 which is a bit stronger (can't recall off the top of my head.)

Please don't mind the massive amount of rivets. They are simply to demonstrate where all the "possible" holes are to rivet. Not going to rivet everywhere their are rivets in the assembly.

Things that we would like answered even after hours of searching for answers are:

-What is the best method of securing the two outside plates?
There are a lot of good ways to do this. It seems you've taken some inspiration from 1114. They make stellar drivetrains. Your connection methods seem solid, I would suggest placing some "Simbot" box plates inbetween your driveline plates. That would stiffen them up considerably.
-Direct Drive vs No direct Drive. One of our alumni said that a few years ago one of our pinion gears on the cim motor had shattered because of the sheer amount of force that was struck upon the gear when we would stop the drivetrain or hit something hard. Basically he was saying that when you have chain driving from a sprocket off the output shaft of the gearbox, that takes the load, and not the cim gear.
Both ways have been proven very effective. I personally would go with an indirect drive for this up-comming year while your still just getting into sheet metal.
-Belly pan thickness (0.125? 0.090?)
.09 will be plenty strong provided that you support everything correctly.
-"Reinforcements" on the axle points. I obtained the idea from 1114's robots from the past couple years (thanks guys). Im sure that other team's use the same idea but more or less it provides that extra strength to dissipate the load more equally when you get hit. I will post a link to their website to the picture with the idea.
If I'm thinking what your thinking then that is actually a method of holding a dead axle and providing structural support. Our team does this to great effect as well.

-I want to make circular lightening holes because they are easier to make meaning less time. But my team-mates, want to use the "118 iso-grid", because they say it obviously better but in reality it takes longer to CAD and I'm not sure that its a whole lot better in terms of a drivetrain. Maybe though?
Circles are theoretically the best because they don't have corners providing stress points that you get with with triangles. That said, either can and have been used to great effect. I would suggest, however, that you try to make your holes 3" or bigger so they can be used as access holes when trying to reach inside the robot. You'll thank yourself later

"118 iso-grid"

http://www.simbotics.org/files/image...isplay/038.jpg

Included is the render done on CAD. This is about the fifth revision.

Thanks, CD. I look forward to the feedback as I'm looking for lots!

Also, something that really stuck out with me was the cutting away the top flange to make room for the gearbox. In my experience you don't want to do that. That flange is a key structural piece and by comprimizing that one spot you basically comprimize the tortional stiffness of the piece. The second thing I noticed was that I saw nothing in the way of chain tensioning. Lastly, .125" drop on the middle wheel gives you .25" of rock in the chassis. If you want .125" of rock lift an outer wheel .125" or the middle .063".

Good Luck!
Bryan