Coyote - The Robot Wars Chronicles

**RogueTwoRobots** · 16th August 2017, 19:34

Frantic Finale!

Apologies for the lack of updates, life got in the way a bit. But time for one final update as we reach the finish line ready for Robot Wars! I may have to split this over two posts if I reach the photo limit.

So last time, we'd relocated to Aberdeen, made some progress and shot our VT. At this point we had three-and-a-half weeks to get the robot finished and in a working condition.

Expansive to-do lists were a common feature at this point, and one of the main outstanding items remaining was to make outriggers. These would be needed to stop the robot tipping forward when trying to lift an opponent, helping to maintain traction between the wheels and the floor. Due to a whole heap of variables that hadn't been determined at the time of the CAD design of the front jaw assembly, the outriggers weren't incorporated into the plasma cutting process so had to be designed, fabricated and fitted by hand. The process started off with getting a rough shape from holding a piece of cardboard up to the side of the robot to work out angles and shapes. Once we were happy with the look, they were transferred to metal:

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We then clamped the pieces to the robot to check the fitting before continuing with the fabrication. The outriggers would have to double up as mounting points for the armour panels as, again, these weren't designed in CAD. By this point, any new work on the robot was being done ad hoc. We also realised that the two outrigger plates that would be the outermost panels on the left and right would have to have an extra crescent shape cut out of them to let us slide the wheels on and off without having to unbolt the jaw assembly every time. In addition to this, they needed some bracing plates across their width to try and stand up to horizontal spinner (cough, Carbide) attacks. Finally, to reduce the friction between the outriggers and the floor when lifting a robot thereby not impairing our ability to drive, we decided to fit Nylon blocks to the base of the riggers. When you put all of that into a picture, it looks like this:

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Who needs CNC? All cut and shaped by hand with a grinder, all holes marked by hand and drilled on a pillar drill. Without blowing my own trumpet, I surprised myself a few times during the build with what could be achieved by hand with some care, precision and effort.

The outriggers then had to be welded on to the front jaw assembly, and once they were, we could test they worked properly:

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What a relief that was! I was worried about the ability of the actuators to lift heavy weights and while I'm only 76kg, it didn't appear to struggle too much so I was confident in its fighting capabilities.
The eagle-eyed among you may also notice bike tyre screwed to the wheels. Having had problems with the same tyres on PP3D in Series 1/8, which were solved with bike tyre, we opted to go straight to that solution before even being near the arena. It also helped to give the robot a slightly more industrial look.

With robot builds, getting the big things out the way is important, but often the little things take up just as much time or are easy to forget. Another thing to tick off the list was power LEDs. We opted to go for 12V orange LED strips (not as easy to find compared to the standard colours!) which were mounted in the underside of the top jaw. We put a thin layer of polypropylene over the eye holes to diffuse the light and give a menacing glow. Looked great in a dark room but we found during filming that it was easily washed out by the studio arena lights, so wasn't that effective in practice:

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Another LED feature that didn't really get covered on the show was a couple of RGB strip LEDs running down the back panel of the robot. The original plan for these was both to try and convey the 'mood' of Coyote and to double up as a rev indicator for the chainsaw (dim being low revs, bright being high). Rachel created the circuitry for them using an Arduino and bluetooth module which allowed the LEDs to be controlled from a phone app, giving a full range of colours and intensity. Again in practice and the heat of battle, it proved difficult to match the LEDs to the situation, so they became primarily aesthetic:

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Before starting work on cutting the armour panels, which were to be a 5mm steel sub-structure with 10-20mm HDPE on top, we stuck everything we had on the scales to see where we were sitting:

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Talk about close! Thankfully the wooden board we put on the scales to increase the surface area weighed 6kg so that, along with weighing full sheets of material but knowing we wouldn't use it all, meant we should be comfortably in weight. Fingers crossed!

We cracked on with the armour. The steel plates took the longest to cut and shape as they were pretty large and a bit awkward, though the brackets to mount the armour to the chassis at the rear were equally as time consuming despite being a fraction of the size. Nevertheless we managed to get them done, as well as knock together a top panel of aluminium and angled HDPE. Nothing great, certainly not Thor or Terrorhurtz proof, but it would give us protection at least. Pretendo-bot time:

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Adding these panels gave a sense of scale to the robot previously missing. Coyote's on the small side, especially when it's sharing a garage with PP3D, but finally it looked like a heavyweight robot size wise! I couldn't help but grin when looking at the robot like this. Still a long way to go though.

I've reached the picture limit so will continue this in another post below.

**RogueTwoRobots** · 16th August 2017, 20:28

Frantic Finale! (continued)

With the armour finally out of the way, the focus turned to the one last big challenge, one that I had been putting off again and again; making the chainsaw gearbox. I had a plan in mind but the trickiest part would be working out how to connect the chainsaw driver tooth to the gearbox and incorporating the chain bar support, all while making sure everything lined up with regards to bearings, pulleys, belts and shafts. The motor powering it was the same one that was in Drumroll for the drum, so 1100kV and ~2kW. At 6S, the motor would be kicking out 24,420rpm and the target for the chainsaw was 3000rpm (this was taken from the Series 1 house robot intros where Matilda's chainsaw is quoted as 3000rpm. Finding actual realistic chainsaw rpms was difficult as most gave figures in m/s and a long oval bar isn't as easy as a circle for converting those figures). We opted for a 9:1 ratio, putting it just under 3000rpm, so two stages of 3:1 was looking like the most compact way to achieve this. First up was playing around with the pulleys to sort the layout:

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The whole mechanism would be sandwiched between three layers of 10mm aluminium plate. First thing was to get the pulley centres spot on. Devised a simple setup for this:

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I didn't take too many photos of the process since time was tight, so a few drilled holes and some pockets bored out on the mill later, and it was starting to look semi-decent:

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A few more holes, grub screws and fixings later, and voila:

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Another thing I was proud of making from scratch. It wasn't the smoothest mechanism around, but it worked and didn't fall apart, so I'm counting that as a success. With the mechanism complete, attention then turned to mounting it on the robot. This part was no-frills, just a couple of pieces of steel angle bolted to the back with a pivot hole drilled in. A small 50mm stroke actuator conveniently attached to the bottom threaded rod of the gearbox and allowed the chainsaw to move through a decent distance:

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This picture was taken about 10pm two days before we had to pack and travel down to RW. You can see the 'hackle' spikes on the top panel and the angled brackets on the rear corners for attaching the armour to (all of which had rubber in between to try and reduce shocks). The spikes were meant to be more like Dead Metal's but they were a last minute job so had to improvise and simplify. Things still to do at this stage included completely wiring up the insides, devising and fitting some sort of link mount for top and bottom, assembling the whole robot including Loctiting all connections, painting the thing and making locking bars. May not sound like a lot but all very time consuming. There were various other small things still on the to-do list that would have helped in general but that weren't too important and had to be sacrificed as we just couldn't do it all in the time we had. A 10-hour shift at the day job the following day was followed by working from about 8pm til midnight in the workshop, most of which was spent trying to wire it. I took this picture at the start of wiring then became too frantic to document the rest until we got to the warehouse:

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The Thursday involved an early start to go and collect the hire van (a horrible-to-drive Fiat Doblo), getting everything packed up at my flat then heading over to the workshop for some finishing touches. Despite planning to leave by 5pm-ish to head down the road, the finishing touches took from midday til 9pm non-stop (which I didn't realise until I did stop!) followed by a 4-hour drive back home to my own workshop. The only finishing touch I did manage to photograph was a bit of painting on the front jaws:

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We had to be at the warehouse for 8am on Friday, so after just a few hours sleep, and with several things still to do on the robot to pass tech check, I threw a few last things in the van from my workshop and headed to Glasgow. We then spent 15 hours in the warehouse, from half 8 in the morning til half 11 at night, getting Coyote finished. This included completing the wiring, cutting the rest of the HDPE to layer over the metal armour, working out and making locking bars for the front jaws, chainsaw blade and actuator and little cosmetic bits and pieces. Finally, after all that, we had a robot that had passed tech check and was ready to fight......Coyote.

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Thanks for reading if you made it this far. Apologies if the content seems rushed towards the end but it perfectly sums up what it was actually like at the time! I won't go into details of how we got on in the competition as I'll mostly just be repeating what was shown on TV, but upgrades are on the cards after Coyote got well and truly mangled. I'll share the changes in update posts sometime soon. Til then, happy roboteering