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Unread 05-14-2012, 10:34 PM
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Re: pic: 6WD Sheetmetal Chassis

Quote:
Originally Posted by akoscielski3 View Post
Okay I am looking at it wrong then. What are the circle on the outside wheels, that to me look like bearings?
They are bearings inside a bearing block for support.
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Unread 05-14-2012, 10:42 PM
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Re: pic: 6WD Sheetmetal Chassis

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Originally Posted by O'Sancheski View Post
They are bearings inside a bearing block for support.
yea I would lose them. All you need for a Dead Axle is a threaded rod with two bolts to hold it in place. 1/4-20 bolts will work fine. That is what we use, and dont have a problem with them

Heres and example of what I have designed. As you can see you don't need bearings for those wheels
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Last edited by akoscielski3 : 05-14-2012 at 10:44 PM.
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Unread 05-14-2012, 11:08 PM
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Re: pic: 6WD Sheetmetal Chassis

Looking very good, especially if this is your first!
(Love the general configuration -- very 'wrangler. )

A few comments:
1. Is there any reason the front/back wheels need to be live axle? You're not tensioning them. My suggestion is to make them dead-axles, and make them structural. I love something called a "tube axle" here -- 1/2" OD, 1/4" ID tube, with a 1/4-20" bolt running through it. It'll stiffen things right up around the wheels (where it really matters!).

2. I don't like using sheet-metal as standoffs for gearbox plates. I recommend you use standoffs there, though other (equally as experienced) mentors would disagree with me, and have, loudly. YMMV.

3. You've got loooooots of rivets in places where it doesn't matter. That vertical row of rivets in the front bumper? Yeah... you need less than half of that. Hit the top and bottom hole, then space a few out in between. Then again, it doesn't matter -- rivets are almost "free."

4. Your lightening pattern can be a LOT more aggressive if you want. Even if you decide to stick with rounds, you can add additional smaller holes around your big holes. Remember the bumpers will add a lot of strength if done correctly.

5. Since you've adopted a "no belly pan" design -- make sure whatever upper structure you add provides torsional rigidity (helps prevent cross-corner flex). You can test this by holding three corners down, and lifting the fourth.

If you have the opportunity, build it, test it, and tweak it.
This is a low risk design which you should feel comfortable going into a season "cold" with, but another revision of lessons learned is worth its weight in gold.

Kudos again for a great first design!

-John

PS - Just noticed you're Potsdam bound -- enjoy Clarkson!

Last edited by JVN : 05-14-2012 at 11:47 PM.
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Unread 05-14-2012, 11:12 PM
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Re: pic: 6WD Sheetmetal Chassis

He is ALIVE!!!!

Quote:
Originally Posted by JVN View Post
Looking very good, especially if this is your first!
(Love the general configuration -- very 'wrangler. )

A few comments:
1. Is there any reason the front/back wheels need to be live axle? You're not tensioning them. My suggestion is to make them dead-axles, and make them structural. I love something called a "tube axle" here -- 1/2" OD, 1/4" ID tube, with a 1/4-20" bolt running through it. It'll stiffen things right up around the wheels (where it really matters!).

2. I don't like using sheet-metal as standoffs for gearbox plates. I recommend you use standoffs there, though other (equally as experienced) mentors would disagree with me, and have, loudly. YMMV.

3. You've got loooooots of rivets in places where it doesn't matter. That vertical row of rivets in the front bumper? Yeah... you need less than half of that. Hit the top and bottom hole, then space a few out in between. Then again, it doesn't matter -- rivets are almost "free."

4. Your lightening pattern can be a LOT more aggressive if you want. Even if you decide to stick with rounds, you can add additional smaller holes around your big holes. Remember the bumpers will add a lot of strength if done correctly.

5. Since you've adopted a "no belly pan" design -- make sure whatever upper structure you add provides torsional rigidity (helps prevent cross-corner flex). You can test this by holding three corners down, and lifting the fourth.

If you have the opportunity, build it, test it, and tweak it.
This is a low risk design which you should feel comfortable going into a season "cold" with, but another revision of lessons learned is worth its weight in gold.

Kudos again for a great first design!

-John
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Unread 05-15-2012, 02:45 PM
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Re: pic: 6WD Sheetmetal Chassis

Quote:
Originally Posted by apalrd View Post
And finally, any plan to remove the transmission in vehicle if you ever have to? It looks like it would be very, very difficult to work on anything inside the transmissions as it is now. Even though it would possibly weigh slightly more, you could pocket out the space of the transmission side plate that is integrated into the frame, and put another plate over it. The transmission would then be a single assembly bolted into a hole on the frame.
This. I went back and forth over integrating the gearboxes in Scorpion this year, and eventually decided to make the gearbox have two independent plates, and a big pocket in the frame, like mentioned above. It was invaluable when we had to service one of the gearboxes at the Dallas regional. Because we built the gearboxes independently, we could bring a whole spare gearbox, and when a screw sheared on the dog shifter, we just pulled the broken one out and swapped in the spare. A 10 minute fix instead of possibly 30 minutes or more. And even if we hadn't had a spare, it's still much easier to work on a gearbox that's on a table than one buried inside a robot.

So, while integration looks nice and is a little lighter... design for maintenance is important! A little thought ahead of time can save valuable time in the heat of competition.
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Unread 05-15-2012, 02:55 PM
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Re: pic: 6WD Sheetmetal Chassis

Where do the encoders go? Here is where keeping a live axle wheel might be useful as it would be a simple way to toss an encoder onto a shaft. Other options (if you wanted to go dead axle) would be to use follower wheels, I believe 148 has a great picture of one from 2009 on CDM here.
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Unread 05-15-2012, 03:28 PM
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Re: pic: 6WD Sheetmetal Chassis

Quote:
Originally Posted by apalrd View Post
A few questions:
-Why the 0.090" 5052? We looked at 5052 this year, but decided to go with 0.063" 6061 (and later decided we should have gone with 0.050" 6061). A thinner material would be lighter, and 6061 0.063" is strong enough for a FIRST robot with bumpers.
Sorry I'm a bit late to the party on this, but one huge advantage to 5052 Al over 6061 Al is formability. 5052 is much more conducive to sheet forming than 6061 is (bending, rolling, etc). It is also easier to weld if you plan on implementing welds in your design. I'd stick with 5052 for a sheet metal design like this, but thats just me. I'm sure 6061 can be made to work as well with special considerations like large radii etc.

-Brando
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Last edited by Brandon Holley : 05-15-2012 at 03:47 PM.
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Unread 05-15-2012, 03:31 PM
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Re: pic: 6WD Sheetmetal Chassis

Quote:
Originally Posted by Brandon Holley View Post
Sorry I'm a bit late to the party on this, but one huge advantage to 5052 Al over 6061 Al is formability. 5052 is much more conducive to sheet forming than 6061 is (bending, rolling, etc). It is also easier to weld if you plan on implementing welds in your design. I'd stick with 5052 for a sheet metal design like this, but thats just me. I'm sure 6061 can be made to work as well.

-Brando
We do our bent parts all out of 5052, and our flat sheet parts (gears, sprockets) out of 6061, for this exact reason.
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Unread 05-15-2012, 07:42 PM
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Re: pic: 6WD Sheetmetal Chassis

For gearboxes, we actually used AM shifters with a final drive chain to a live axle. The gearboxes used 0.090" aluminum plates, and there were four slots in the frame where the gearboxes would bolt, and we could slide the entire gearbox up/down up to 3/4" or so to tension the final drive chain. The encoder was integrated into the AM shifter output. We really liked this design, and would do something similar again. The ability to change the final drive ratio was very nice, we changed it three times during the season.


On sheet metal alloy, we've had no trouble bending 6061 0.050" and 0.063" in our shop on a manual finger brake, but 5052 is easier to bend, especially thicker sheets. Using 6061 allows us to use thinner sheets.
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Unread 05-15-2012, 08:54 PM
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Re: pic: 6WD Sheetmetal Chassis

Quote:
Originally Posted by apalrd View Post
For gearboxes, we actually used AM shifters with a final drive chain to a live axle. The gearboxes used 0.090" aluminum plates, and there were four slots in the frame where the gearboxes would bolt, and we could slide the entire gearbox up/down up to 3/4" or so to tension the final drive chain. The encoder was integrated into the AM shifter output. We really liked this design, and would do something similar again. The ability to change the final drive ratio was very nice, we changed it three times during the season.


On sheet metal alloy, we've had no trouble bending 6061 0.050" and 0.063" in our shop on a manual finger brake, but 5052 is easier to bend, especially thicker sheets. Using 6061 allows us to use thinner sheets.
Sounds like a very nice setup! Do you have any pictures to share?
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Unread 05-15-2012, 10:20 PM
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Re: pic: 6WD Sheetmetal Chassis

I don't have any pictures of the gearboxes. I'll see if I can take some soon.
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Last edited by apalrd : 05-16-2012 at 03:56 PM.
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Unread 05-16-2012, 03:59 PM
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Re: pic: 6WD Sheetmetal Chassis

I took some pictures. Here are two.



The case bolts go all the way through both gearbox plates, the spacers, and the frame. There is a nut on the outer gearbox plate, then some washers, the frame panel, more washers and another nut. The frame panels have slots to move the gearbox up/down to adjust the chain tension of the final drive chain. The final drive ratio is 12:22, the final drive sprocket is an AM 22T with AM 500 hex hub. The CAD model will be released in the next week or so.
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