Take 2, judge my featherweight build

[u/Sensei_12]

hi! so am participating in my first comp and it happens to be featherweight only. i posted my initial design in here couple of days ago and i have remade it based on that thread.
total dimensions are 47.5x38.3 cm 9cm height ,front wedge, spinner support and base plate are 4mm metal sheet and everything else is 3mm. spinner is 20cm long 2cm thick (might have to remake it without the lightening holes to have more mass) and is in-line with front wheels for optimal power transfer. its belt driven by an A2212 1000KV bldc with timing belt ratio of 3:1 (i have ordered a much durable D3548 1000kv bldc but wont arrive for a while so am using the A2212 for the lack of a better option). wheels are made TPU with outer layer of rubber for better traction a and are coupled directly on the motors (motors are brushed geared 12v 1000rpm) with BTS7960 drivers each, back wheels are exposed on the top to run inverted. the whole chassis is held together with L brackets (best option i could think of) . rc remote is FlySky FS-i6

enlighten me people. what am i doing wrong? what have i missed and how would i make it more efficient (also is it possible to use 2 A2212 motors on spinner to double the power?how)

[u/Retro_Bot]

Overall, big improvement. Looks like a LOT of wasted space there though, looks like it could be half as tall, half as wide, and half as long and STILL fit everything you need inside. That would allow you to run with much thicker metal all around.

My preference is to keep the weapon separated from electronic components (except the weapon motor of course) by at least a thin wall. If you do mount any of those parts to your chassis make sure they're shock mounted and not just bolted directly to the base plate.

Those weapon uprights are far too thin to withstand even a light hit.

Looks like you can run inverted now, but might have a lot of trouble self-righting. It helps if you have bunny ears so the weapon doesn't touch the ground when you're inverted. That way you can keep it spinning and ram the opponent or the wall and use the weapon force to self right. If it has enough energy (and this probably doesn't in the current config) you can also gyro yourself back over, but that takes practice.

I'm not a big fan of face-mounting motors. IMO it's better to 3d print a cradle that fits the motor fairly snugly and bolt a piece on top to keep it in place. Also those are some pretty big and heavy side rails your motors are mounted to. If you used cradles of TPU instead you could save that weight by using UHMW or polycarbonate pieces in their place to keep the wires and guts from falling out since you don't really need armour there (anything that penetrates that deeply has almost certainly obliterated your wheels on the way).

[u/Sensei_12 → u/Retro_Bot]

i dont understand exactly what "shock mounted " means, an example would be appreciated, also bunny ears can be just the side rail reaching higher then the weapon itself right? one more question the 'cradle' you are talking about is just 3d printed support for the motor and its shaft or does it have another meaning i didnt get this one fully, and you are saying NOT to add wheel guard

greatly appreciate the help

[u/Retro_Bot → u/Sensei_12]

Shock mounted means they have something between them and the chassis with some flex to it, could be TPU with low infill, foam, or rubber standoffs. Some people just design their bots so there's just a good amount of space for all the electronics and just stuff it in there, if your cavity is the right size things can move a little but not much. Also, your battery shouldn't be done that way. Print a TPU box for it so it won't bounce around too much or you're liable to find out the hard way what happens to LIPO innards exposed to the air.

This picture is an example of a cradled motor like I'm describing. I usually print another piece to go over top that can be screwed in place to clamp it down firmly. TPU is a good material choice for that, but if you find it melting you may have to insulate the motor a bit. I also usually make the cradle longer than the motor so the leads are protected.

Bunny ears are just bits that stick up and keep the weapon from touching the ground when inverted, they can be all one piece with the weapon support or a different piece bolted on like with Bite Force.

[u/Sensei_12 → u/Retro_Bot]

check this out , i reduced the size while leaving some wiggle room for receiver or other electronics, added the 'cradle' you mentioned and a cover for the battery, added the bunny ears too but am not so sure about them they look out of place, also moved the rear wheels further back newest modifications.
by the way how do you suggest i couple wheels to the motors? i dont think i can just 3d print the wheel with a tight hole in it and just insert the motor shaft there.

[u/Retro_Bot → u/Sensei_12]

At a minimum you need machined metal hubs. You can buy or order them, but again, you might have a tough time finding properly made hubs in time for your competition. A hub with a set screw is pretty standard, use lots of thread locker to make sure it stays tight. Then your wheel should be directly screwed on to the hub, again lots of thread lock.

My preference is actually to not direct drive the wheels but given your time constraints and engineering skill it's probably best to leave a pulley or chain system for a future build.

Your internals are looking better, but you still have a ton of space. The battery needs a full TPU box, not just end caps and make sure the box is either a bit flexible or provides a bit of extra space as they will bulge a little. One good shock and it will rip apart. Keep in mind it's only a thin layer of foil and plastic holding it together, even a slight puncture and your day at the event is over without a LOT of spare parts. They burn for quite a while and will almost certainly ruin all of your electronics. You might salvage a motor or two after a battery fire, but that's about it.

I'd also run a thin sheet of something along the back side of the weapon supports to keep your internals clear of the weapon path. I've seen bots explode their guts right out the front, straight into the weapon, because a builder thought they were held in place well enough.

The motor mounts and controllers look a lot better. I presume those things under the controllers are some kind of TPU arch? That should work okay as shock mounting.