Team Darklight - Broadax 2 (Featherweight Axe/Hammer)

[qbnut]

So now back from KOB UK, here's a writeup on the event from us!

The good
- The drive
- The polyurethane cast wheels
- The axe mechanism itself

The bad
- The drive
- Hobbyking VESCs
- Losing a battery
- The link
- The current wiring for serial batteries

The ugly
- The lids

Preparing for KOB UK
Once I knew Broadax 2 was in the event, I started to make extra preparations to give it a better chance.

First of all, we cast new wheels out of 60 shore Polyurethane onto HDPE hubs. This made wheels that we extremely grippy, with a cost that they wear out very quickly. I used liquid casting rubber from MB Fibreglass (http://www.mbfg.co.uk/polyurethane-r...60-rubber.html)

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I replaced the axe motor with a Racerstar 5060 BRD5060 280KV from Banggood (https://www.banggood.com/Racerstar-5...r_warehouse=CN). This was a gamble, but I think that this is a better motor than the Propdrive 5060 it was originally designed around. It also doesn't have a tapered 6mm shaft but a full 8mm shaft. I made a custom mounting plate for this out of 6082 aluminium.

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We painted up the axe(s) to make it pretty. Note we did the one from Broadax 1 at the same time in preparation for when that's put back together at some point.

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After we heard that there would be a total of 5 Axe bots going to KOB UK, we added extra plate to the lid, laminated with a 5mm HDPE insert, to mitigate overhead blows.

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We also added a front wedgelet ground into a fine blade, which rides on the floor with the aim to make the front much closer to the ground and thus makes it much harder for things to get under us. I was a little concerned about a side effect of this, that the side clearance got raised when it was added, but we ran with it anyway.

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The event itself

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Tech check
Broadax 2 was only passed to run at 4s, rather than the 6s/8s it was originally designed and demoed for. This was due to an circuit oversight on my part which was the lack of a second link on the Axe which meant the VESC for the Axe remained live with the link out - still safe as the receiver would not be connected or powered up so the VESC 'does nothing', but was not satisfactory to the stewards. There are diodes in the circuit to stop this, but this should also have a diode in the ESC receiver servo line, but this causes VESCs to behave erratically.

So unfortunately I had to loop out one of the batteries which boosts the voltage up from 4s to 6s/8s before feeding the Axe, and ran at 4s the whole event. As a result, the axe was still hitting far harder than Battleaxe (a previous scooter motor based axe Featherweight of ours) from last years event, but nowhere near what it is actually capable of.

System check
We managed a system check prior to kickoff, and it worked brilliantly, albeit at 4s only. The drive is FAST but controllable, and the amount of grip we had was incredible. However, the axe twitched if you went too hard on the drive throttle. I did some transmitter changes to mitigate it, but there wasn't enough time to resolve it correctly before the first fight.

Fight 1 - versus Rocket and Saber-X
Going in we weren't confident about this fight, as we thought we would just get ejected from the arena. As it turns out, Rocket stopped working, and although Saber-X tossed us about and over around a dozen or so times, it kept running.

The axe was still twitchy, but we compensated as best we could with it. A larger problem was however exposed - the lids both came off. This was to be a problem all weekend.

2 Points!

Fight 2 - versus Binky and Microswitch
Blink and you miss it - we took one hit off Microswitch and the link came out. That was it, we were immobile in the corner for the fight after that.

However, this also did more - as we found out when we got it back to the pits, both drive ESCs had been damaged, both with the #1 issue with VESC 4.12s - the DRV chip had failed on both. I attribute this down to a less than great build quality on the Hobbyking VESC 4.12

Luckily, Kevin from the Microswitch team delivered me the spare Maytech VESCs that I had bulk ordered with him, so they would have to go in Sunday morning. Comparing to the Hobbyking VESCs, which are identical in design given the open-source nature of these controllers, the Maytech ones are put together MUCH better, with better component selection and soldering work overall.

1 Point

Fight 3 - versus BFT Remix and Forge Master
Sunday morning came, and I had to resolder and rewire the drive ESCs, reprogram them, reinstall all the rest of the internals, reattach the lids, and make sure it was running again. Unfortunately, this took longer than the 3 hours I had to fix it, so had to forfeit this fight.

0 Points

Here's a pic after we had the Maytech VESCs installed, just a little too late to enter the fight
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At this stage, we were out of the competition, with only 3 points scored.

Whiteboard
We had it working again for a Whiteboard with the drive fixed, the axe twitch was resolved, and so this time, it performed magnificently, winning a 5 out of 5 Judges score!

One side of the lid came off again though!

Tag Team with Apex FW
Finally, we went in for a tag team with Apex FW as our tag team partner. This is what Broadax 2 looked like pre fight. I nylon thread tape and gaffer taped the lid on - no way it was coming off this time!

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I was more worried about hitting a working Apex FW by accident than I was the opponents, with only Take Cover being the only other cause for concern. However, I found I could push it around with ease, it giving me very little damage beyond scratches.

This was another win for Broadax 2 and Apex FW!

The drive fail

At the end of the whiteboard, I noted it wasn't turning correctly, but post match cease, I did a little spin for the crowd anyway. The drive was clearly not working, so once I got it out of the arena, I turned it over to see what was wrong, and noticed that the motor bolts had sheared off entirely. The drive certainly works, but perhaps a bit too well!

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The motor also clobbered the back of the LiPo battery, so that had to be thrown out as it had worn all the wrap on the base of the battery away and was perilously close to being pierced through, so would be unsafe to ever charge again.

Conclusion
Overall I'm pleased with how Broadax 2 performed. We will have to resolve the issue with the lid, and remount the drive motors with larger bolts, but otherwise there's nothing fundamentally wrong. A few tweaks here and there and it's ready to run again.

The axe mechanism itself has held on for the whole event without an issue - no jamming or pinion slip problems which were initially a concern. It does need the electronics sorting for the 8s it is designed for to show it off at full capability.

It's still up for debate if Broadax 2 is entered into next years competition, or we build something new that is not-an-axe for it; given there were 5 Axe entries this year, it will have to be on top form to be accepted next time. It will still go to live shows though once repaired!