Specs:
-.09" 5052 Aluminum
This is my first sheetmetal chassis so any tips would help.
It looks really good.
I’d say the lightening pattern is rather conservative, so if you’re pressed for weight, you could probably take some more out.
Looks like you might have more rivets than you really need on the gearboxes, but better to have too many than too few I suppose.
This may be something you intentionally didn’t add, but you may want to consider a bellypan for reasons ranging from enhanced rigidity to convenient location for electronics.
My only other thought was that you might want to add more overlapping/connecting material at the corners. I have modeled a couple drivetrains like this, but have never built one of them, so I will defer to someone with more experience on this aspect.
That desgin, but i think chaining only the lower 4 wheels so the bot can turn better
I am planning on adding cross supports over and under the gearboxes for added rigidity.
Ummm. I’m not quite sure what you are saying here. I stated that I dropped the center wheel 1/8"
Tip: If you dropped the center wheel 1/8" you will have 1/4" of rock in your chassis because it will not sit as it does in your CAD. If this is the case and you actually want 1/8" of rock I suggest either raising an outer wheel 1/8" or dropping the center only 1/16" :]
Regards, Bryan
A few questions:
-What size rivets are they, and at what spacing?
-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.
-Any details on the shifter, specifically the ratio and shaft design?
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.
Seconded. We had a sticking transmission at Worlds, so we took the whole thing out and put in our spare in a few minutes. Definitely an important consideration.
Answers are in bold.
A few questions:
-What size rivets are they, and at what spacing?
3/16" at 1/2" spacing
-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.
I decided on .09" 5052 because that’s what I’ve seen many teams use and since it was my first sheetmetal chassis I thought that would be a good starting point.
-Any details on the shifter, specifically the ratio and shaft design?
The shaft is made custom on a lathe/mill. I will try to upload a pic of the actual shaft but it is not letting me put an attachment in this 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.
I am going to pocket out the flanges above the transmissions. I am also probably going to remove the rivets attaching the transmission to the chassis and replace them with bolts for easier removal.
Over All GREAT Looking Chassis!
But I still have things that I would recommend you change to improve it 
Great job for your First Sheet-metal Chassis!
ohh im sorry, i was saying that i really like the design but i would only chain four wheels, and in the front put like omni-wheels so the turn ability is increased. Like the way the u have it now, it will turn but not as fast as it could:yikes:
As has already been stated, the center wheels are dropped to ensure smooth turning. Generally, to improve turning performance, you can either drop the center wheels or add omnis at one or both ends. Doing both is not necessary.
Would you recommend the multiple powered omnis or the drop center?
That is not true. A drop center will act as if there is not an extra 2 wheels. In other words, it will act as if it is a 4wd with a smaller wheelbase.
The only live axles are the center shafts which are direct driven off the transmission. The outer 4 wheels are dead axles with a 22T #35 chain sprocket.
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.
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
Looking very good, especially if this is your first!
(Love the general configuration – very 'wrangler. ;))
A few comments:
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!).
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.
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.”
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.
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!
He is ALIVE!!!
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.
