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 FIRST is not a "buy it and build it kit robot" competition. - sanddrag [more] |
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Here's something I've been working with Team 228 on-and-off-again over the past few months on, as an off-season prototype chassis based upon our 2007 sheet metal chassis with various improvements across the board. The frame is Safety Orange powdercoated .125" 5052 Aluminum, manufactured on CNC turret punch machines at our sponsor's machine shop (which is owned by the father of a team alumni). The sheet metal design is nice because it eliminates so many "intermediate" parts, such as gearbox standoffs, gusset plates, etc. and all their related hardware into a single component such as the gearbox body (single piece of aluminum).
Configuration: 6WD Live Axle, Direct Drive Center, 35p Chain, AndyMark aluminum sprockets (yeah, I know 25p is lighter and works, but the students want to use 35p).
Speed: About 9.5 ft/sec under normal load.
Gearbox: Single speed, uses AM gears. 50:12 first stage, 45:19 second stage. Second stage identical center-to-center distance as Toughbox second stage, and is thus able to choose from the three ratios offered by AM. 1"x1"x1/16" aluminum angle can also be attached between the two gearboxes to the PEM nuts pressed into them (visible on the sides and top flanges).
Wheels: 6x 5"x2" Performa Colson with knurled aluminum inserts with 1/8" keyway broach pressed into wheels. (Hex broach preferable, but still a season or two worth of capital improvements away).
Final SolidWorks weight with all hardware: 37.07 lbs
Discussion
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31-12-2008 13:34
gorrilla
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
why did you design it with all double wheels?
31-12-2008 13:36
Elgin Clock
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
That may be just the parting line from the mold of the wheel shown.
Yeah, some people like to get fancy with their CAD representation of things, & knowing Art, if he helped in this project, it may be just that.
But then again...
Edit: Yeah, looks like just the mold of the Colson wheels going by the description now.
31-12-2008 13:40
artdutra04
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
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Originally Posted by gorrilla
why did you design it with all double wheels?
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31-12-2008 14:07
daltore
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
They actually offer the Colson wheels in SolidWorks premade at 3D Content Central, it's just how accurate they already come. Nice desing, looks like it'll hold up very nicely to anything, and I really like how the gearboxes and the frame are essentially one part, less to go wrong.
31-12-2008 14:20
Tanwad11
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
Nice choice going with the colsons. We've had great success with them. Let us know how it turns out if u decide to use it.
31-12-2008 14:25
gorrilla
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
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Originally Posted by artdutra04
Those aren't double wheels, it's just the raised center of the Colson Performa wheels.
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31-12-2008 14:27
Madison
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
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Originally Posted by gorrilla
do you know why they have a raised center?
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31-12-2008 14:28
gorrilla
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
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Originally Posted by Madison
They're probably made in a split mold and require draft away from the seam line to get the mold off.
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oh yeah, never thought about that
31-12-2008 16:53
EricVicenti
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
Very nice, its almost like a perfect kit bot. We also used that ratio in our practice drivebase this year, and its fantastic. 12 fps and some real pushing power.
01-01-2009 01:12
artdutra04
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
Always listen to your gut instinct. ;-)
Something inside of me was screaming that 41.5 pounds was way too high, that something was wrong.
And after looking through all the models again, the error was found; I never manually entered in the weight of the downloaded Colson wheel model, so it used whatever the default density was. This estimated weight ended up being about 1.58 pounds per wheel! 
Properly entering in the weight droped the total weight down to 39.30 pounds.
And since I was already on this train of thought, I went back to the specs on the Colson wheels and found that by dropping from 2" width wheels* to the 1.5" width Performa wheels, an additional 1.932 pounds could be lost, bringing the total weight to 37.37 pounds. On top of this, a slight modification to the aluminum inserts pressed into the Colson wheels loses another 0.3 pounds, which brings the weight down to 37.07 lbs. (Which is right in the 36-38 pound range I was expecting).
* The original reason for using the 2" Colson wheels was because we already had a set on our 2008 competition and practice robots; of these the practice robot set would make the migration onto our 2009 practice robot.
01-01-2009 14:39
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
I'm not seeing any tensioning system. Am I missing something?
01-01-2009 15:51
artdutra04
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
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Originally Posted by CraigHickman
I'm not seeing any tensioning system. Am I missing something?
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The final one will probably be either a set of Delrin floating chain tensioners, or an eccentric Delrin disc. But I didn't feel like modeling actual roller chain, so I used a simple loop with the weight set to what equivalent roller chain would weigh.
Either way it's a simple lightweight part with simple operation, and that's all I'm concerned about.
02-01-2009 01:25
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
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Originally Posted by artdutra04
Either way it's a simple lightweight part with simple operation, and that's all I'm concerned about.
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Do you think the gearbox will be stiff enough?
02-01-2009 02:11
artdutra04
Re: pic: GUS Team 228's 6WD Sheet Metal Prototype Chassis
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Originally Posted by CraigHickman
Do you think the gearbox will be stiff enough?
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Every time another flange or bend is added to the part, the cold rolling operation strain hardens the material. Both of sides (which would replace standoffs) have a flange on the top, and the face where the CIM motors are mounted has a flange along the bottom. I'd love to do some advanced FEA on the part, but I'm still learning Cosmos.
So until then, I mostly rely on past experience. Like this bracket I modeled for our 2007 robot, which would have been near impossible to make out of anything except sheet metal.
And mounted on the robot:
... which took all kinds of abuse the entire season and never had any structural problems.
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