From my previous post, there were a few things I wanted to keep in the design. I've been loving how well the layered, through bolted UHMW has been working for this bot. Still relatively cheap and easy to make, tanks big hits, and is light enough for the large body needed for a horizontal spinner. I also really liked the weight distribution in its previous event. It was much more drivable than its previous iterations.
There were still a lot of down sides though, mainly related to reliability. The drive system itself needed some work to prevent the brushless motors from braking themselves, either by impact, or by loosening from the pinion gear. The weapon system also needed some work. Before it's last competition, I had worked on increasing the reliability of the weapon stack itself, but that meant that there was more stress on the weapon motor, leading to the pulley shearing off the motor, leaving the weapon useless.
Drive Train Upgrades
With this new motor being an outrunner, I knew I needed to protect the spinning can from the wires on the inside of the bot. I took that need and combined it with my desire to better support the rear of the motor to prevent the relatively small face mounting screws from ripping themselves out during impacts. I created a 3D printed bearing block that supports the end of the motor while simultaneously shielding the spinning can of the motor from the rest of the electronics.
I decided to keep the 4" Banebots compliant wheels as they seem to work really well in this design and give me a little extra ground clearance that the bot definitely needs. With some left over weight from the re-design, I added another 3D printed bearing block to help support the end of the drive wheel shaft to make the system even more bulletproof.
Weapon Upgrades
The core problem is that when the weapon hits something, that change in velocity in the form of a big impulse gets transferred back through the weapon belt to slow down the motor. With a properly tensioned belt, there is only a small amount of slip when this happens, but some of the energy is transferred to the drive pulley, to the weapon motor through whatever is joining the two. This is roughly equivalent to using the weapon pulley as a hubmotor and hitting things with the pulley. The joint between the pulley and the motor has to be able to endure these shock loads.
Looking at the motor, there isn't a lot for a large diameter pulley to grab onto. Traditionally, these motors are designed for airplanes, so the propeller of the plane would be mounted to the motor shaft through a prop adapter that clamps onto the 5mm shaft. This won't work in this application as the motor itself is almost the entire height of the robot. The can is smooth and relatively hard. Only the top of the motor bell has any features that could be used to lock a pulley onto the motor. There are 3 tiny M2 screws around where the rotor attached to the main shaft. Again these are designed for ultralight propellors to attach to the motor, not the shock loads of combat robotics.
My decision was to design a custom part to be machined out of aluminum if it isn't crazy expensive to make. The part would slip over the end of the motor, locking into place with positive features that matched the recesses in the end of the rotor, and held in place with the M2 screws. This way the shock loads should transfer through the bosses on the underside of the pulley to the motor can, leaving the M2 scews to only handle tensile loads trying pop the pulley off of the motor. In theory at least. I plan to have this test printed at least once before I try and place an order for a real machined part.
With the new weapon motor upgrades, the weapon only has a theoretical top speed of around 4,500 RPM, which is relatively low compared to some spinners in the field. The hope is to have a much faster spin up time as most arenas for 12 lb bots are relatively small given the speeds at which these things move. This will hopefully let me land more consistent hits and stay spinning the whole match. Top speed is less important for this right now as the weapon is still over 3 lbs and almost 10" effective diameter, should still hit hard, even at lower speeds. I've never successfully made it to "top speed" with this bot anyway as the weapon system has been plagued with issues it's whole career.
Given this lower top speed I wanted to try and design a disk with more teeth for when I fight wedged opponents and am not going for the knockout hit, but rather lots of highly controlled hits that don't send me flying everywhere. I had this concept in my head to make a disc look like knives as the bot is named "The Butcher" after all. I'm actually really happy with how the design came out actually. Looks really sturdy, uses the same pulley interface as my disk blade, has both positive rake and tooth relief, and comes in almost the exact same weight as the other disk. Even if it isn't as effective as I'd want it to be in combat I think it looks really cool. Might have to get some stickers made up of this as a logo to throw on the top of the bot.