"Modular" Chassis

[Jon Stratis]

Originally Posted by AdamHeard

If you do this then all configurations combined must be under 120 lbs unfortunately.

Some inspectors (incorrectly in my mind) even consider modular swaps of identical components to be something that requires re-inspection.

dmaciel10123 - Please note that the combined 120lb weight limit only applies if the modules are different (different wheels, gear ratios, etc), per the 2014 rules:

R5
The ROBOT weight may not exceed 120 lbs. When determining weight, the basic ROBOT structure and all elements of all additional MECHANISMS that might be used in different configurations of the ROBOT shall be weighed together.

emphasis mine.

Adam - something like this would definitely warrant a re-inspection. This isn't something small and simple like replacing a COTS gearbox with an identical item... this is a large, complex portion of the robot that impacts several areas of the inspection sheet. Off the top of my head, a team could do this replacement and fail re-inspection for overlooking simple items in the following areas:
- Weight (How do I know that the modules weigh the same? I've seen teams with identical looking red/blue bumpers weigh in over half a pound different!)
- Size (are the modules all exactly the same size? Were the modules attached without any gaps? Do they still fit within the 112" frame perimeter? Do any other structures still retract within the starting configuration?)
- Bumper mounting (Are the mounts all the same? Are the bumpers attached securely? Are they within the bumper zone?)
- Bumper backing (are there any gaps that are introduced with the swapped module? Do the bumpers still fit snug against the frame perimeter?)
- Risk of damage to the field (is there anything different about this module that would cause it to damage the carpet? Different wheels? Different gear ratios? A dragging chain or idler sprocket that'll hit the ground?)
- Safety (Is it still safe to operate? Same/minimal risk of getting fingers caught in chain? Was it attached properly so it won't come off mid-match?)

Ideally, it wouldn't be an inspection issue - replacing one module with an identical module shouldn't be a big hassle for teams. In the real world, however, modules are rarely identical, and those small differences (even something as small as having a weight holes in one plate but not the other) can make a difference when it comes to compliance. Regardless, a re-inspection for it shouldn't take more than a few minutes.

[bkahl]

Also note that every inspector interprets the rules differently...so at one event, Adam could be "right", and Jon could be "right" at the next. The only real way I see to get around this is to ask Q&A, and print out the question and answer for inspection.

Anyways, I really like where you're going with this, David. I always love the idea of being modular of any sort. The idea of essentially changing drivetrains between matches is interesting. I'm looking forward to see exactly where this goes.

[dmaciel10123]

I'm currently working on reducing the weight of the spacer plate, but right now without the gearbox and wheels the entire assembly weighs in at about 36 pounds according to Inventor.

Edit: About 1/3 of the way through cutting out unnecessary material the weight dropped down 2 lbs in total on the final assembly.

Edit #2: Finished reducing the weight of the spacer plate, managed to bring the full assembly weight down to about 30 pounds.

I had to render it in Inventor Studio with the Illustration shading to make it easier to see, but this is what the spacer plate looks like now, rather than a solid plate like it was before:

[chrisfl]

I am the lead designer from team 1699. I've also been thinking about a modular drive train design that can be changed quickly. Our teams should work together on a design! I do have a few extra ideas that I would like to add too, like being able to use different drive styles(6wd, 8wd, Mecanum, Omni) and being able to use something different each match.

[dmaciel10123]

Originally Posted by chrisfl

I am the lead designer from team 1699. I've also been thinking about a modular drive train design that can be changed quickly. Our teams should work together on a design! I do have a few extra ideas that I would like to add too, like being able to use different drive styles(6wd, 8wd, Mecanum, Omni) and being able to use something different each match.

This design can easily be modified to work for mecanum wheels. The side plates can have holes drilled at the front and back to fit hex bearings rather than having a 6 wheel center-driven set up. Making an 8wd would merely be a matter of relocating the churros and wheels on the wheel modules.

All-in-all it's a very versatile chassis now that I realize it, but as was mentioned before, all of the configurations together would need to weigh under the set limit, and with each side module weighing approx. 10 pounds, there wouldn't be much room for separate configurations alongside a full robot.

[chrisfl]

True, true. I didn't see that

[bkahl]

Originally Posted by dmaciel10123

I'm currently working on reducing the weight of the spacer plate, but right now without the gearbox and wheels the entire assembly weighs in at about 36 pounds according to Inventor.

Edit: About 1/3 of the way through cutting out unnecessary material the weight dropped down 2 lbs in total on the final assembly.

Edit #2: Finished reducing the weight of the spacer plate, managed to bring the full assembly weight down to about 30 pounds.

I had to render it in Inventor Studio with the Illustration shading to make it easier to see, but this is what the spacer plate looks like now, rather than a solid plate like it was before:

Be careful here, David. I don't know exactly how load bearing that plate is, but I do know that there is a lot of metal cut away there, especially around the (what I assume to be) bearings. Be careful with that. Lightening is important, but the strength and integrity of the base is more important.

[dmaciel10123]

Originally Posted by bkahl

Be careful here, David. I don't know exactly how load bearing that plate is, but I do know that there is a lot of metal cut away there, especially around the (what I assume to be) bearings. Be careful with that. Lightening is important, but the strength and integrity of the base is more important.

That plate is just a spacer. It doesn't have any bearings. The holes on this plate a solely meant to be clearance holes (besides the triangle formation ones which end up on the same bolts as the churros). The reason I was able to cut away a lot of metal on this was because it isn't a structural support, it only gives room for the bolt heads on the two assemblies to rest without interfering.

It's slightly easier to see in this section view:


Item 3 is the Spacer Plate. It sits between the wheel module (2) and main body (1).

[BrendanB]

Originally Posted by dmaciel10123

That plate is just a spacer. It doesn't have any bearings. The holes on this plate a solely meant to be clearance holes (besides the triangle formation ones which end up on the same bolts as the churros). The reason I was able to cut away a lot of metal on this was because it isn't a structural support, it only gives room for the bolt heads on the two assemblies to rest without interfering.

It's slightly easier to see in this section view:


Item 3 is the Spacer Plate. It sits between the wheel module (2) and main body (1).

Consider making your spacer plate out of a plastic or lexan since its just there to take up space and save some weight.

[dmaciel10123]

Originally Posted by BrendanB

Consider making your spacer plate out of a plastic or lexan since its just there to take up space and save some weight.

Good idea. Thank you.

Edit: Changed the material in Inventor from Aluminum to clear polycarbonate. Shaved off another pound.

[dmaciel10123]

I played around with adding a few small mounting brackets to the ends on the final assembly. They're basically just small rectangular pieces of aluminum with holes in them that are meant to provide a little extra hold to the ends since the only real attachments are the bolts that attach to the churros. I don't know how much of a benefit it would really give though.

[dmaciel10123]

I printed out the assembly at a. 0625 scale. It gives a pretty good physical representation of the overall feel but because of the scale it doesn't really do justice for the function.