pic: 4587-Sheet Metal Chassis V.2

[Cash4587]

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[Joe G.]

Do you have plans to make use of the rather large dead space within the space created by the beveled sides? If this area was a little more open, it would seem to be an ideal location to tuck some electrical and pneumatic components.

I really like the one piece sheet metal battery mount design.

[AllenGregoryIV]

Cooper this is looking really good, do you have pictures of the underside? Looks like the motors aren't directly driving the omni wheels shaft anymore.

One thing we did this year was make it so the front and back rails of the chassis were easily replaced. It worked out very well for maintenance.

[Cash4587]

Originally Posted by AllenGregoryIV

Cooper this is looking really good, do you have pictures of the underside? Looks like the motors aren't directly driving the omni wheels shaft anymore.

One thing we did this year was make it so the front and back rails of the chassis were easily replaced. It worked out very well for maintenance.

The motors still drive the Omni shafts directly. I just have removed the "Gearbox" that would have previously been inside the frame and moved the gears to inside the wheel rail. I had to add another gear to make room for the long cim motor shafts to still keep the wheel rails small-er. I kept them about a 1/2" smaller or so by adding another gear.

As for removing the back rails of the chassis, It would be convenient but I wanted to make the belly pan one piece. I plan to not put a whole lot down there to make it hard to work on. Maybe like a flip up electronics pan that hangs the electronics in the frame. Idk. Majority of the parts for the actual drive train have to be accessed by the bottom anyway, the modules will drop out from the bottom, and the motors have to be bolted on through the bottom too as well as all the gears and other parts.

Here is a picture of the underneath with the belly pan transparent:
http://prntscr.com/406565

Nice! Looks like a solid design, and like you got all the tricky bits right.

I'd put some material back in the front and back of the frame. Those parts take a beating... You can drop some of the material on the top of the frame, and on the rails holding the wheels. The frame itself will be strong enough, and the holes make it easy to inspect your robot for wear. Point impact loads from other robots and field elements should be your biggest loads. You can take the inner frame rails down to 060 as well. Reinforce the bearing holes when you do that.

Consider lightening the belly pan, and adding PEM nuts in for your electronics. Those small touches take a design to the next level.

I didn't know exactly how much to take out from the back and front but it's good to know that more is needed back in. I do however plan to take material out from the rails. A lot of that is doubled up so it will be .180" instead of just .090" It will see some heavy patterns in the near future. I probably will end up making the belly pan either an X pattern Like 254 or lots of big round holes. Last season my team ran a belly pan made of .090" with the 254 style pattern with holes for every electronic hole there and ready to go for bolts. I put in the correct tap drill size in the CAD and sent the dxf off to the laser and they had enough tolerance to where I could just tap the hole directly from the sponsor with out having to do any drilling. After we tapped the holes we then bolted down all the electronics with plastic bolts and used a pair of dikes to cut off the extra bolt that would stick out bellow the belly pan. I really liked this method and I plan to do it again, it was simple and made doing electronics TONS easier as far as mounting them. Wiring is always a different story..

[Cash4587]

I forgot to mention again. This entire frame will be made out of 6061 T6 .090". My sheet sponsor doesn't have a problem bending or cutting this alloy.

[Cash4587]

Idk if I am doing this right but, It now looks like a block of Swiss cheese..

http://prntscr.com/406s5y

[AllenGregoryIV]

Just a thought, can you make the wheel wells thinner by moving the pulleys that connect the two modules to the same shaft as the new gear for the MiniCIMs?

Also make sure to look at access holes for the motor mounting screws and which tool you would use to replace them. Same with shaft collars, and retaining rings.

Overall its looking really nice, I'll probably be borrowing some elements of this if we are given another flatfish field.

[Cash4587]

Originally Posted by AllenGregoryIV

Just a thought, can you make the wheel wells thinner by moving the pulleys that connect the two modules to the same shaft as the new gear for the MiniCIMs?

Also make sure to look at access holes for the motor mounting screws and which tool you would use to replace them. Same with shaft collars, and retaining rings.

Overall its looking really nice, I'll probably be borrowing some elements of this if we are given another flatfish field.

I like that idea, however looking at it, it would make the module only about 1/4" smaller due to the fact that the versa wheel is so wide becasue of the versa keys. If I wanted to make the module smaller than the versa key on one side of the wheel would need to be milled off. Even though that is not hard to do, I would rather not make the versa wheel a "custom part" in order for it to fit in the butterfly module.

As for access holes, we will be using retaining rings and right-angle allen keys down there to be able to get in there. Not too big of a deal considering that I don't expect to ever need to do maintenance to a module while still on the robot. The whole module will come out if you remove 2 retaining rings. The only "hard to reach" item is the motors which really isn't too bad

[AllenGregoryIV]

Originally Posted by Cash4587

I like that idea, however looking at it, it would make the module only about 1/4" smaller due to the fact that the versa wheel is so wide becasue of the versa keys. If I wanted to make the module smaller than the versa key on one side of the wheel would need to be milled off. Even though that is not hard to do, I would rather not make the versa wheel a "custom part" in order for it to fit in the butterfly module.

As for access holes, we will be using retaining rings and right-angle allen keys down there to be able to get in there. Not too big of a deal considering that I don't expect to ever need to do maintenance to a module while still on the robot. The whole module will come out if you remove 2 retaining rings. The only "hard to reach" item is the motors which really isn't too bad

Removing the module requires removing the hex shafts and from dealing with it this year I would try to avoid it at all costs. You don't have time during a competition to do that. During events we had motors come a little loose even with lock tight on the bolts. Someone mentioned thread locking bolts in another thread that I'm probably going to look at for mounting CIMs next year. The other idea that I might look into is doing something like 148 did with Raptor and other robots where they have plates that mount to the CIMs that have easy access fasteners that make swapping motors easy.

Also have you thought about a way to retain the bearing? Our press fits (which I'll admit weren't good to start with) came loose during the season and made maintenance even harder.

[R.C.]

Originally Posted by AllenGregoryIV

Also have you thought about a way to retain the bearing? Our press fits (which I'll admit weren't good to start with) came loose during the season and made maintenance even harder.

In situations where the bearing isn't geometrically retained we like to use bolts or rivets to retain the bearing.

[Cash4587]

Originally Posted by AllenGregoryIV

Removing the module requires removing the hex shafts and from dealing with it this year I would try to avoid it at all costs. You don't have time during a competition to do that. During events we had motors come a little loose even with lock tight on the bolts. Someone mentioned thread locking bolts in another thread that I'm probably going to look at for mounting CIMs next year. The other idea that I might look into is doing something like 148 did with Raptor and other robots where they have plates that mount to the CIMs that have easy access fasteners that make swapping motors easy.

Also have you thought about a way to retain the bearing? Our press fits (which I'll admit weren't good to start with) came loose during the season and made maintenance even harder.

Knowing that, I will make a plate that allows you to mount both motors as a pair and then bolt them via the other side like 148's Raptor. I will also use our heavy duty lock tight on the bolts, which has never come loose on our drivetrain wheels this year.

Hadn't thought about it but R.C. has a great idea with the rivets. I like that method and probably will use that method it it ever becomes a problem. To prepare for the press fit issue, I did however subtract .003" from the bearing bore hole so the bearing would have a tighter fit. Should I subtract more from the hole size for a press fit or will that be tight enough?

[tim-tim]

Three thou is way too much interference for a press fit.
Around half a thou (.0005") is pretty standard in FRC. I suggest getting a 1.1245 (or 1.124) and .8745 (or .874) reamers to do the final finish.

Here is an old thread to reference: http://www.chiefdelphi.com/forums/ar...p/t-98825.html

[Adrian Clark]

I really like this drivetrain, like a lot. Great job! It's been a lot of fun watching it get better and better. That being said, I think there's a few things left that could be optimized.

The first thing is space. I think electronic placement space is a very important aspect of a drivetrain. Without enough space you have to spend time coming up with ways to get everything to fit, and some of the solutions can make maintenance difficult. YMMV and I know a lot of teams are willing to make space sacrifices that make electronics placement difficult, and sometimes that trade off pays off. There's nothing wrong with finding sneaky ways to fit all your electronics on the bot, but I consider an ideal drivetrain one that keeps electronics placement simple. For that reason I suggest space as something to try to optimize.

The reason I think this drivetrains electronics space could be optimized is because of the large voids in between the modules and the voids created by the hexagonal frame perimeter. I think hex and octo frames are great, but I also think there's trade offs that should be considered. The first is space, is having such a wide hexagonal robot worth it if it limits space? And how will the frame shape effect superstructure and manipulation design? You may have accepted these trade offs, but what is brought into question is how hexagonal should you make your robot given those trade offs? Looking at your frame I notice that your sides are steeper than most octo and hex framed bots I've seen. Given that there's trade offs to having a non-rectangular frame, the key in designing this type of drivetrain is to balance those trade offs with the benefits of an octo or hex to get a shape that is effective in terms of space and interactions with other robots. Hex and octo bots are pretty new in frc, so not much is know as to how design one with the right shape. To determine how steep to make your corners I suggest building bumpers of different angles and testing it's effects on robot interaction to determine the best shape. Once you've done that you'll know how important frame shape is and then you can determine if having such a wide hexagon is worth the sacrifices when compared to a slightly smaller hexagon. There's teams that have done testing on this very subject, i'm hoping someone chimes in.

The first thing I thought of when I saw this design was that you could save quite a bit of space by putting the motors in the void between the modules. I read the previous thread and I noticed you had the same idea but didn't pursue it because it would be too complex. I don't know where you or your team draws the line for complexity, but I encourage you to not give up on that idea just yet. I think there's ways of getting a gearbox and motors in that space that are a little more complex than your current design but could be a great improvement and really take it to the next level. The most obvious reason to move the motors is so they don't take up valuable electronic space, but I think by moving the motors you can actually reduce the width of each side of your drivetrain pretty significantly. When I look at your power train I see two things that make each side wider than it needs to be: the gears for driving the wheels and the pulleys that connect the omni wheels together. My suggestion for narrowing your sides is to take the whole power train and put it in the gap between the outside of the hex frame and the inner yellow frame rail. In order to pull this off you would need to come up with a clever way to either replace each motor or remove the entire gearbox, which I think can be done. The advantage of this is that by putting a gearbox in between each module you eliminate the need for a belt to connect them, making the modules narrower. The main idea behind this is to take everything that's making the sides thick and put it in the void where there is space. There's a lot of ways you could do this without making it too complex, I've got some ideas but I'd like to see what you come up with

There's some other things, I ran out of time to post everything, I might post more later.

Oh, and just fyi: as for using loctite for holding cim screws in using the strongest loctite you have is not the way to go. Look up what strength thread locker you need for the fastener you're using and use that. If you put the wrong strength loctite on you might end up with an irremovable screw.

Originally Posted by Greg Woelki

Am I approaching this incorrectly? Each side is the same length, is under the same load, and is the same weight. I started the triangles with 0.1" round radius and I worked up to 0.25" (in picture), adjusting their dimensions to keep the volumes the same as I went. There is still higher stress in the piece lightened with triangles and if I increase the radius of the round much more then they might as well be circles.

https://drive.google.com/file/d/0B4u...it?usp=sharing

If you're seeing unusual stress risers in your results the first thing you should do is check your mesh. (assuming that's applicable to whatever program you're using). Also, for accurate results make sure you have at least three layers of mesh in the cross section.

-Adrian

[tim-tim]

Originally Posted by Cash4587

Idk if I am doing this right but, It now looks like a block of Swiss cheese..

http://prntscr.com/406s5y

Unrelated to the reason for the picture, but I would change the front (or rear) frame member mounting method. While it makes sense to do this from a structural standpoint, I'm not sure it makes sense from a maintenance standpoint. If you ever have to replace the front (or rear) member, you will have to remove a side to actually remove it. Hopefully, this never becomes an issue, but in the unfortunate event that it does...

Overall, I like the concept and design.

EDIT:
I missed the fact the bellypan is the same piece of material as the front and rear "members". You can disregard my comment in this application; however, it is still good to keep that in mind when designing.

[AustinSchuh]

Originally Posted by Cash4587

Idk if I am doing this right but, It now looks like a block of Swiss cheese..

http://prntscr.com/406s5y

Big squares save even more weight for less machining cost.

Consider switching your ribs and some of your other parts to 060. You get a 33% weight savings all while taking less machine time with 060. It is quite challenging to take out the same weight out of something that is 090 thick.