pic: Spectrum Fall 2013 Drive V2

CD-Media: Photos
#24

I have experience with reversible bumpers and I wasn’t a big fan. I was with the Discobots in 2011 when we did flip bumpers. They were great for week 1 but by the middle of our second event they started fraying, the velcro started breaking away from its stitching, and they just looked awful. Maybe the parent we had do the stitching didn’t do it right or something but I’ve been hesitant ever sense. I’m also not really a fan of the seam running down the middle of the bumpers. If our design ever required us to leave our bumpers on, it’s something I would consider. I also liked 33’s skirt system this year but that would require a pretty good seamstress as well.

For completeness to this thread anyone looking to do reversible bumpers. This is the whitepaper by 2809 that is most often linked as instructions.

#25

well main part is the ethernet port as an IT brain I think it is ingenious. Also yes what had inspired to you make a drive train like this. I saw v1 also and was curious.

#26

Directly it was all from Madison and the people that posted in these threads.
FRC488 – Fall Project
FRC488 - Fall Project, Rev. A

I’ve liked the idea of a gear drive, ever since looking at 25’s robots from the behind the design books from 06 and 07. The bellypan setup is inspired by 968, 1538, and the other west coast teams that have been doing it for years. 971 and 148/JVN/VEX both contributed to the sheet metal inspiration.

We also talked as a team about the things we liked and didn’t like in our chassis from last year.

#27

Nice! I really like it keep up the good work.

#28

We worked on the twist latch system today at our meeting. The basic prototype worked way better than I ever expected. You can see the pictures below.

Twist Latch Bumper Prototype

We made a very simple mock board to act as the bumper and didn’t modify the VEXpro chassis in any way (The 2013 KOP frame would need slots cut into it). I’m pretty sure this is a setup that most teams could use.

We will probably modify our 2013 robot to use this system for our last off season in November. That we can test it against other robots and make sure it can stand up to abuse.

These are the latches I purchased for $2.45 each.

#29

Not a bad start.

I keep seeing people here make the same mistake, and it bothers me enough that I’m going to say something.

Think of sheet metal like paper. Go ahead and grab a sheet and play with it. Bends add lots of strength. Wherever you break the bend, you make the part significantly weaker.

The first thing that I see when I see the side rail parts is that you broke the bend both around the transmission and on the outer edge all over the place. This significantly weakens the frame. I’m going to make a wild guess and say over 2x weaker when in compression. (Props for anyone who does FEA to get a better estimate.) Do yourself a favor and figure out how to not brake the bend. Space the wheels in away from the edge, or whatever it takes to make that happen. That will take your frame to the next level and make it bullet proof and incredibly stiff, which is exactly what you want.

If you don’t believe me, print your robot out on paper at partial scale, cut it out, and assemble it. Try twisting and bending it, and see what happens.

#30

Weird, people keep telling me to think of paper as sheet metal.

#31

Thank you for the feedback, Austin. I agree with you and this is the type of feedback I hope to get by posting these, I’m still learning. However, I don’t think it would be able to be assembled if the belly pan had a full flange along the outer edge of the wheel wells.

#32

Hi Allen,

If I’m understanding you correctly, I think it is still possible to assemble with a full flange along the belly pan. Take the clamshell, angle it at ~45 degrees, and then slide the inner edge into the frame rail. Then, rotate it to the correct angle and slide it in until it is in place.

I would recommend moving the flange from the bellypan to the clamshell. That is what we do and works marvelously. It makes it so that the brake doesn’t need to be the correct length for the front and back of the bot.

Also, consider adding some ribs inside your clamshell. That will add quite a bit of strength. Take a look at how we do our frame. There should be pictures available somewhere online. I expect to only make small modifications to it next year, assuming that the game cooperates.

What machines do you have available to cut out those parts? That will require a lot of laser time if the bellypan is being laser cut, and is a pain to punch if it is going to be punched due to the triangles. Some small changes should make it a lot easier on your sponsors.

Consider integrating your battery box into the frame. There should be some pictures of how 971 does it somewhere, or you can read my suggestion in Madison’s thread.

Austin

#33

Since it’s all dead axles does the clamshell really need ribs? Don’t the bolts and spacer act as ribs? Also how would you go about getting wheels in and out of the robot in your configuration? The current system has them drop out the bottom very easily. Also when I said it couldn’t be assembled I was talking more about getting the wheel and gear assemblies into place not just attaching the sheet metal.

We do it all on a laser cutter, but it’s run after work hours so they aren’t that worried about laser time. They don’t have a turret punch so it doesn’t really help to make them circles, the laser is doing all the work either way.

The battery in this robot will end up lying flat, I’m also not a big fan of the battery on either bumper rail. If our design ever needs that much weight shifted to one side of the robot we would probably do it but it has never fit our design.

#34

The dead axles will help maintain the width of the siderail, but I would not consider them a replacement for the stiffness ribs add. Ribs provide a shear wall which helps resist lateral load (parallelograming) and torsional loads, something that an axle alone does not provide much support to. A larger diameter tube coupled with a compression bolt will start to adequately resist lateral loads, but I would not consider a wheel with a 0.5 axle to be a sufficient replacement for a rib.

971 is able to drop our wheels straight out of the bottom because our tensioner blocks space the wheels out past the flange that bends inward. This could be achieved in your design by adding a spacer to the shaft. While a straight up round spacer could get annoying to keep track of and get aligned when putting the wheels in, I could imagine making a simple spacer block that gets affixed to the frame sheet. This could be done quickly on a mill, or even by hand with proper match drilling techniques.

I still think it is important to be cognisant of laser time. It is still costing your sponsor proportional to how long it takes to cut your parts. If they are cutting lights out, then your parts are being cut instead of a customer’s parts. If the machines are being attend to while cutting, then someone has to stay extra. Being respectful of their time and money helps maintain a good relationship. If you are interested in saving laser time, I would work on minimizing the number of unique holes. We have learned from our sponsors that the time it takes to pierce the material is significant compared to the time it takes to traverse a profile. Another factor is that it takes longer for thicker material. This has pushed us to going with thinner metal and fewer lightening holes when appropriate, a combination that works well together.

#35

To put ribs into a bend, the only way I’ve seen it done is with special brake tools used when you brake press the sheet metal into 90 (or 88) degree bends

http://www.3dvision.com/wordpress/wp-content/uploads/2012/04/sheetmetal-rib-011.png

These add massively increased rigidity to the structure.

#36

Why not just make some ribs separately, and then rivet them on?

#37

You certainly could, and achieve the same effect. At least with our metal sponsor, the difference between bending a part with ribs and bending one without ribs is just bolting tool “17b” to the brake press instead of “17a”. Adding ribs this way is marginally lighter than separate pieces and takes up less space. For a 1/16" radius bend the ribs extend probably 3/16" up the surfaces of the metal whereas separate ribs would have to have mounting holes somewhere. Also these holes have to be cut and it will take some time to manufacture and install more pieces. Again, these differences are very subtle, so do what you’d like.

#38

Thanks for sharing these parts – some really nice finds, all collected in one place. You might look at Clippard GTV-2-P12 or similar for the miniature air vent… Disclaimer: I have not used one of these, nor carefully checked legality/safety, even under prior years’ rules.

#39

Allen, been following along the past few weeks with your design…any updates?

#40

Not much, we have been doing a lot of different things (VEX competition season is starting), and working on this has been left behind a bit. We’re working on retrofitting our 2013 robot with the new bumper attachment system for our last off season event and that is going very well. We should have photos and videos soon of the new system. I’m slowly adding the slots to the drive train rails and we should be almost ready to send them off to be produced.

#41

Instead of 1 90 deg bend how about 2 45 deg bends.

You can also design in a radius bump bend in which a series of small tangent bends together form a large radius bend.

You guys ever wonder how Team 67 can get away with using the light gage round aluminum tube and why it is so strong?

#42

Our team is looking at making a gear drive as well and I had a few questions having never built one.

Dustin stated in an earlier post that you can use the 1/2 inch tubing that Vex Pro sells and run 1/2 inch hex broached gears on it with no issues. Can anyone else verify this? It’d be nice if we didn’t have to shave a few thousandths off the tubing to have the gears spinning with little to no resistance due to friction.

Using this setup would mean running 1/4 inch bolts through the tubing. Does anyone have recommendations on the type of fastener to use & what hardness grade? I’ve never ran anything smaller than a 1/2 inch bolt on a drive shaft so I’m curious what others have used.

Thanks for posting these designs, I know I’ve learned a lot from reading through these threads.

#43