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By: Bryce Paputa
New: 03-01-2014 19:55
Updated: 03-01-2014 19:55
Views: 2344 times
Here is the robot we designed in the past month or two as practice, and also probably as a base design for this season. It's CAD files (both Inventor 2012 and STEP) are available on google drive: https://drive.google.com/folderview?id=0B0soKk9hjXfLejVfd1VTM2hQMEk
It's main design goals were low weight/CG and repeatability, as we were disgusted with our very high CG and weight last year, and because we plan on building two robots this year which will have to be almost identical. Almost all of the chassis is waterjetted 1/16th inch 5052 aluminum, the bumpers are welded 3/16th 6061 aluminum, and the drivetrain has 1/4th inch aluminum plates. The drivetrain is a simple 2 speed supershifter, 4 CIM, 8 wheel drivetrain with #25 chain, the wheel axles are on moving plates instead of having tensioners for simplicity. The bumpers were designed for rigidity above all else and will be reversible so that we can put many bolts into the chassis as we want and only have to undo them once or twice per competition. The robot, with everything except battery, bumpers, and wires, weighs 48 pounds with a CG about 3 inches above the ground, the bumpers weigh around 15 pounds without fabric or pool noodle.
In the inventor formatted version, "FF14-C-18-AA Parameter File.ipt" contains many exported parameters that can change just about anything on the robot, for example, there are width and length parameters that change the robot's width and length. This allows many changes to be made with almost no effort, however the controls board may get messed up by some of them. Also, in inventor, since everything was made using the sheetmetal template, you can click "Go To Flat Pattern" under the sheet metal tab to get the flat pattern which can be exported to dxf for a waterjet machine to use.
Each non-COTS part has a part number in the pdf log file, a render is included, and zipped STEP and inventor formats of the CAD are included. All of the files are also
Feel free to ask questions and/or give suggestions.
Discussion
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03-01-2014 21:27
MetalJacket
Re: pic: 2014 Offseason CAD
Looks pretty good! Only have two questions/concerns. First - it looks like the belly pan only extends to the inner side panels; did you consider having it go to the outer rail and if so what made you chose not to? Second - you probably won't need that many wing nuts to hold the bumpers on 
. Overall though, I like the design. Good luck in 2014!
03-01-2014 21:34
OWilliamson
Re: pic: 2014 Offseason CAD
First off, I'm really digging this chassis 
One thing that I will mention though, is that you might want to consider having a cutout in your belly pan beneath the gearboxes. If you do this you can disconnect the gearbox and then slide it out the bottom. Last year in competition we had a problem with one of our gearboxes, and it was a nightmare to pull it out to perform the repairs that we needed to. It took way too long, and almost cost us a match. It shouldn't compromise the strength of the belly pan too much, and it could possibly be the difference between missing a match or not in competition.
03-01-2014 21:50
Johnny_5
Re: pic: 2014 Offseason CAD
Careful with waterjetting that thin of material, depending on what kind of machine you are using, you can end up with some pretty bad cuts.
When the machine begins the cut, it uses a much high pressure to first pierce the material and then it lowers it to actually run the cut. Sometimes the back of the sheet metal can blow out with that initial jump.
However, this can be pretty easily solved with the Omax jets (I'm sure Flow does this stuff too) they have a drill attachment that goes on the head to first drill through the sheet. Or you could opt to drill it yourself and then use the camera locating tool to tell it where to begin the cut.
This is an issue we are going to be facing this year. Luckily enough we have 5 pretty large laser fabrication shops that even have CNC press brakes that we are going to ask for sponsorship from.
03-01-2014 22:02
Bryce Paputa
Re: pic: 2014 Offseason CAD
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Originally Posted by MetalJacket
Looks pretty good! Only have two questions/concerns. First - it looks like the belly pan only extends to the inner side panels; did you consider having it go to the outer rail and if so what made you chose not to? Second - you probably won't need that many wing nuts to hold the bumpers on
. Overall though, I like the design. Good luck in 2014! |
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Originally Posted by OWilliamson
First off, I'm really digging this chassis
One thing that I will mention though, is that you might want to consider having a cutout in your belly pan beneath the gearboxes. If you do this you can disconnect the gearbox and then slide it out the bottom. Last year in competition we had a problem with one of our gearboxes, and it was a nightmare to pull it out to perform the repairs that we needed to. It took way too long, and almost cost us a match. It shouldn't compromise the strength of the belly pan too much, and it could possibly be the difference between missing a match or not in competition. |
We originally had the bellypan cut out under the gearbox (If you suppress Extrusion2 in "Electrical/board/FF14-EP-2-AA Base Electrical Board.ipt" it will go back to this), however since we have never had an issue with the supershifters, we decided that we would take the repairabiity hit and go with taking them out of the top (having a easily removable gamespec element will be a design requirement) in order to get more rigidity. The electrical board is actually 3 pieces of 1/16th aluminum folded and riveted together, making 2 mini-crossbeams for torsional stiffness, having the control board go down to a thin section in-between the motors would greatly reduce the effect of these. A secondary design priority was to have as much rigidity as possible to help with handling, last year we did not have a structural bellypan, nor did we have rigid bumpers; we ended up with great front-back and side-side rigidity, but it was not up to snuff torsionally, which makes it scrub more, and scrub more inconsistently. We're trying to fix the rigidity this year with the belly pan, very heavy bumpers, and a more structural gamespec element. I'll talk to our other guys about it though.
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Originally Posted by Johnny_5
Careful with waterjetting that thin of material, depending on what kind of machine you are using, you can end up with some pretty bad cuts.
When the machine begins the cut, it uses a much high pressure to first pierce the material and then it lowers it to actually run the cut. Sometimes the back of the sheet metal can blow out with that initial jump. However, this can be pretty easily solved with the Omax jets (I'm sure Flow does this stuff too) they have a drill attachment that goes on the head to first drill through the sheet. Or you could opt to drill it yourself and then use the camera locating tool to tell it where to begin the cut. This is an issue we are going to be facing this year. Luckily enough we have 5 pretty large laser fabrication shops that even have CNC press brakes that we are going to ask for sponsorship from. |
03-01-2014 22:13
MetalJacket
Re: pic: 2014 Offseason CAD
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Originally Posted by Bryce Paputa
We can't go all the way to the outside because we have to put the axles, wheels, etc. up through the bottom.
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Not sure how much space you have between wheels but doing something like that will let you extend the belly pan farther out but still allow you to put the wheels in through the bottom
03-01-2014 22:23
Bryce Paputa
Re: pic: 2014 Offseason CAD
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Originally Posted by MetalJacket
If you wanted to get a little extra strength out of the belly pan, you could try something like in this picture
Not sure how much space you have between wheels but doing something like that will let you extend the belly pan farther out but still allow you to put the wheels in through the bottom |
04-01-2014 00:45
OWilliamson
Re: pic: 2014 Offseason CAD
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Originally Posted by Bryce Paputa
First off, what gearbox were you using and what was the issue (just for my curiosity)?
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The issue that we had was actually a drive motor coming loose. I'm still not certain how this happened, and was probably an error on our part. We ended up having to pull the gearbox out in order to reassemble everything, and it was just a general pain in the butt to do.
I still recommend that teams at least consider it because I heard of the theory (pretty sure I first heard it from the Killer Bees) that you should be able to work on your drivetrain from beneath your robot. Once you start adding game piece manipulators and the superstructure on top, you can't guarantee that you will have room to work on the drivetrain anymore. If something does end up happening, it will be much harder to fix things from the top.
But, I do realize that torsional rigidity is a big issue with a lot of teams. That's awesome that you guys had already brought it up in your design, and if you think you will be better off without them them go for it
04-01-2014 06:09
Navid Shafa
Re: pic: 2014 Offseason CAD
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Originally Posted by Johnny_5
Careful with waterjetting that thin of material, depending on what kind of machine you are using, you can end up with some pretty bad cuts.
When the machine begins the cut, it uses a much high pressure to first pierce the material and then it lowers it to actually run the cut. Sometimes the back of the sheet metal can blow out with that initial jump. However, this can be pretty easily solved with the Omax jets (I'm sure Flow does this stuff too) they have a drill attachment that goes on the head to first drill through the sheet. Or you could opt to drill it yourself and then use the camera locating tool to tell it where to begin the cut. |
It all depends on your fixturing methods. It's imperative to properly clamp and weight your material in place. Even plastics and low-density materials are not a problem.
As an OMAX employee and FIRST participant, I've never had to use a drill attachment before. If piercing is an issue, you can easily adjust the pressure ramping in software to achieve smoother piercing. Optical locating is also overkill...
If material blow-out or frosting is an issue, don't be afraid to throw a piece of wood or other sacrificial material underneath. It's a quick way to ensure a nice surface finish.
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