Barróg - Featherweight Lifter Build Diary

[Shooty]

Pre-Dojo Champs

So with roughly a month and a half between XR Bolton and the FW champs hosted by Robodojo, and losing half a month between this time for holidays, we had a very short amount of time to upgrade both bots. Fortunately, there were a number of small fixes that could apply to both that were learnt from the previous event, and thanks to CAD some key orders could be made as quickly as possible to arrive in time.

Both bots had two major changes that could be used together. The first was an upgrade from the 12mm HDPE chopping boards of old (which I highly doubt were HDPE at all) to some green 10mm RG1000, a form of recycled UMHWPE. It’s a material that Sam Price of Get Shrekt has used a lot with great success, and he kindly suggested the material to me and where he gets it after exposing all of the flaws of the previous material in a rather practical manner. I’ll admit I was disappointed to lose the bright green colour of my bots, but even outside of combat some of the benefits were apparent; it behaved just like HDPE when cutting, and the end product was several hundred grams lighter than the original tops, which offered a great amount of flexibility for some of the other upgrades.


The old plastic compared with the new plastic.

The other universal change was to begin transferring to new fastening washers for the wheels. Previously the plastic tapped wheel was held in by screwing it tight onto the drill shaft, and using the provided reverse threaded screw with a regular washer to clamp it on the other end. They became more and more reliable, but due to using a countersunk screw with a flat washer, the washer would warp, and ended up slowly splitting the wheel over time. This setup was also used in the new lifter setup for Barróg Doom, and I really didn’t want that to fail. As such, I ordered some steel countersunk washers from a machinist in Dublin, and when it looked like they wouldn’t arrive in time, Rory Charlesworth was able to make a set of aluminium washers in exchange for travel to and from the event in August, and also just because he was a sound lad. I didn’t want to mess with any existing wheels, so I settled on only using the new ones with replacement wheels, and since Barróg Doom had lost two wheels in the event prior, it could get an early head start in the replacements.


A shot of the new braces with the larger 80A ESC attached. Also visible is one of the new washers being used, though the actual washers used are far wider.

For Barróg Doom, the old Botbitz 30A ESC that I had operating the weapon was replaced with an 85A equivalent, and while it would occasionally twitch while operating the drive in other areas, switching the receiver's BEC source from the drive ESC’s to the weapon ESC seemed to do the trick. Tougher bungees would be used so that the top could actually work as intended, and extra braces were placed at the back to offer more support for the top plate. I also needed more reliable ways of getting other opponents, and inspired by the forks Craig Jones used in his FW Bookworm, I designed them to use two 3mm Hardox plates sandwiching 20mm HDPE with a similar shape. Due to the holes at the front of the base of both bots, the forks had to have their mounting point quite far into the bot itself, and had to have a 20 degree angle to compliment the 30 degrees the main wedge is at, so they were quite a design challenge. I’m quite happy with how they turned out however. The HDPE parts were light but durable, and easily swappable if necessary. The Hardox forks could be fastened either way up, and because I used slightly larger holes in the HDPE, they could be adjusted to get the best final result on a whim. Finally, while the mounting brackets weren’t very strong, they could be bent back into shape after a fight, and because they were mounted only at the base, I could use 3D printed spacers to ensure that the forks were level with the ground. The end result was the perfect combination of ground-scraping forks with a shallow angle that didn’t get caught in the seams found in a lot of arenas, and that could be damaged and replaced without much damage to the bot itself.


The new Hardox forks. Very happy with how they turned out!


The new forks mounted.

Barróg was mostly left to my dad to work on this time around, but a surprising amount of positive changes could be and were made to the older of the two machines. Both lifter spines were entirely remade from scratch with some new HDPE, without many of the human error mistakes that could be found in the old spines. The other major change made to the old bot was in how the linear actuator connected to the front piece. A new lifter bracket was ordered for that was designed to spread much more of the load onto the spines instead of the front piece itself, being mounted to the spines and resting on them through two long 6mm bolts. This would reduce the strain on the front plastic itself, hopefully allowing the front to last for longer. The actuator was also no longer mounted directly to the lifter bracket; instead it would just sit in it while the top was fully down, itself held in with bungee cords. This meant that any hits the front would take shouldn’t transfer into the actuator itself, while also still allowing the machine to do what it’s always done.


The new lifter bracket, along with a pretty rubbish pic of some of the new washers


The new actuator mounting system, with Ziptie in place to stop it from leaning forward too much.