Build Diary - Plastic Fantastic - FW

[Maxamuslead]

looks like a beauty, your going to take to Manchester ?

[Ocracoke]

Looks niiiiccceee, can't wait to see it in action.

[Al_]

looks like a beauty, your going to take to Manchester ?

Yep, I'll be there with both of them.

[Al_]

Quick update following a fantastic weekend at Manchester. Other than one very annoying and recurring problem, I’m pretty happy with how Plastic performed at the event.


Melee 1 – I started with my colson wheels that give me about 5mm of ground clearance. These are fantastically grippy, but I got hung up a few times on the seams between the arena floor panels and had to sit there until someone hit me off them so I could get going again. Now a good portion of this was down to my poor driving and could defiantly be minimised but I decided I would swap wheels after the fight to be safe. When I wasn’t stuck on the seams I was able to get stuck in and mix it up a bit. Lots of speed and pushing power from the bot which I was pleased to see.....and then it just stopped. Power lights still on but no movement from it. Resetting the transmitted did nothing either.


Back in the pits with Plastic on it’s cradle, I put the link in and it worked fine, wheels turning but under no actual load. Nothing felt too hot in there and although its a good 10 minutes from the robot stopping to getting it to back to the pits and taking the top off, I would have thought if something were overheating it would be obvious. Damage suffered to the top from Shrekt, but nothing else other than the usual bumps and scratches.

IMG_20180421_145131208.jpg


Melee 2 – Bigger wheels fitted which give 10-12mm ground clearance. They were homemade HDPE wheels with bike tires screwed on the outsides. Not as grippy as the colsons, but no more issues crossing or stopping on the arena seams. Also the grip did seem to improve as the newness was scrubbed off the tires. I don’t remember much about this fight, but the same problem happened again with the robot just stopping after a couple of minutes.


Back to the pits again, same diagnosis again. At this point I was wondering about voltage sag from the Lipo not being at its best in some way, and maybe this was causing the ESCs to cut out due to low voltage. However having no way of reading the voltage during the fight I’m only guessing. The battery voltage still showed fine after the fight (under no load of course) and each fight was only taking about 1000mAh out of what should be a 4250mAh battery. The charger was happy to charge it each time too. Neither of these rule out voltage sag from a loaded battery though.


I decided at this point I would switch to Pressure Point’s battery for the next fight, its smaller (but still ample) capacity and the same voltage at 5s. I took a nice hit from Binky in the fight, a gouge out of the side and some bending of the top panel above it. The top panel was sorted with the heat gun and some brute force but I think it’s a bit of a design flaw. The vertical spinners will always want to rip the edges of the top panel up and bend it out of shape like in this case. I think in a future re-design I'll extend the sides to where the top panel currently is and the top panel will sit recessed inside them instead of on top of them to minimise the chances of this happening more. The fact that the sides of the robot have taken all the hits while the front wedge is essentially unscathed speaks volumes about my driving!

IMG_20180421_173052840_BURST000_COVER_TOP.jpg


Melee 3 – AKA the 5 spinners of doom. Some serious damage flying around in this one, somehow I manage to miss the worst of it. However the same issue happened again which was getting frustrating.


Since there was only one more fight left for the weekend, I decided I would remove the sponge that the ESCs have around them just in case they were getting too hot, though there were not much more than warm each time I had checked them.


Melee 4 – Not a lot to say other than the same thing happening after the same amount of time, capping off a promising but ultimately frustrating start for the bot.


Now I am considering the possibility I have knackered both my batteries. I didn’t storage charge either of them over the winter and they were left in my shed. Maybe it got too cold in there and the 2 things combined has somehow damaged the cells. I have ordered a new battery to test this out. I have also already swapped the Rx and checked all wiring as a precaution but this made no difference. If this doesn’t work, then unless both ESCs are somehow failing/stopping at the same point I don’t see what else it can be.


Anyway, that’s enough rabble, sort this problem out, a couple of other minor tweaks and off to Portsmouth in a few weeks time.

[Maxamuslead]

but didnt Pressure Points battery work fine in The feather fun time match ? ( has anyone got a video as that was really fun)

[Al_]

but didnt Pressure Points battery work fine in The feather fun time match ? ( has anyone got a video as that was really fun)

It did but the bot didn't run for very long before I stopped due to the wheel problem and also the current draw in Pressure Point is generally lower then on Plastic. Therefore if it was going to do the same thing it didn't really get the chance. I'll be looking to test this battery too if putting the new one in Plastic fixes the problem.

[mrsam]

Tough little robot you’ve got there, did the most amount of damage to Shrekt it’s taken so far. After watching the first fight back it seems that the slice in your lid wasn’t caused by Shrekt bouncing off the wall, it hit another robot and managed to backflip several times, over the top of PF.
C507DC74-A8C9-4376-B179-5B7B2075365D.jpg

[Al_]

Tough little robot you’ve got there, did the most amount of damage to Shrekt it’s taken so far. After watching the first fight back it seems that the slice in your lid wasn’t caused by Shrekt bouncing off the wall, it hit another robot and managed to backflip several times, over the top of PF.

Oh yeah, nice catch. I haven't had chance to watch the vids yet that have been posted, going to view them this evening. 10/10 on style from the judges for the backflip!

[Al_]

Update time following a weekend of rumbles at Portsmouth and my attempt to fix the ongoing issues I was suffering at Manchester.

As detailed earlier in the thread, I was having problems with the robot stopping after about 2 minutes of battle. Power was still on to the robot and worked fine once it was back on the bench. I had already done a few things to try fixing it at Manchester including swapping batteries and Rx. I still felt the batteries were probably the culprit as they had been left in a cold, outside shed over the winter in a full state of charge. Maybe this had hurt them somehow?

I went into the first fight with the new Rx, a brand new battery from Overlander and a new main wiring loom. I checked the loom over between events and while there were no issues, the main feed from the battery to the link to the ESC's was clearly getting warmer than I would like, so this was increased to 10AWG size cable fromt 12 AWG. The robot performed fine at the start and then after about 2 minutes, the same problem occurred again, very frustrating.

Back in the pits there was only one thing left to try and that was to swap the ESCs. I removed the TZ85s and swapped them for a pair of single channel feather 2s. The wiring was a bit of a bodge as I only had the few bits I had with me but it was enough to get them in and working.

IMG_20180519_160738647.jpg

Into rumble 2 and it was apparent that these ESCs were driving the motors harder than the TZ85a's. Maybe its better components or different programming but there was a noticeable difference. However them main thing was the the robot finally did the whole 3 minutes flawlessly! Zipping round the arena, slamming into things and shoving the other bots into the walls and what not. I can only assume that I was pushing the TZ85a's too hard and that they were getting too hot and shutting themselves down even though they were cool when I got back to the pits.

Speaking of the pits, after doing the full fight I was able to check things over and I found a couple of things out:

1. A charge of the batteries shows I took a shade under 3Ah out of them. That means over 3 minutes my average current draw was about 58A. Certainly higher than I was expecting and that explains point 2.
2. The robot gets hot. Really hot. Like starting to melt itself hot. The areas around the motors showed that tell tale sign of the dull, rough, cloudy texture of HDPE where it has been melty. A couple of bits were still clear and the HDPE soft.

In hindsight its probably a combination of a couple of things. The first been that running the Argos drill motors on 5s is really pushing them. 4s is fine and if such a thing as 4.5s existed it would probably be a better limit. Also with the robot being made from plastic and the motor enclosures sealed in, there is no where for either the heat to vent away to or sink in to. In isolation I would probably get away with these but together its probably a bit much. I could help things by making some vent holes in the base and lid but I'm still on the fence about if I actually want to.

Anyway, this wasn't effecting the performance of the robot to any significant degree so I left as it and ran it for the rest of the weekend. For rumbles 3 and 4 I wasn't driving so I can't say much about those. The only issue happened in Rumble 4 where the driver felt like one side of the drive wasn't right, so stopped as a precaution. Having stripped it down today I found one of the motors was a bit off. Unfortunately I damaged the motor when removing it so I can't be sure what exactly was wrong. I have put a spare motor in, then I have the wiring to the ESCs to neaten up and it will be off to the next event.

[Maxamuslead]

good to see that you fixed that issue, although i want a pushing match now 2 775 at 6s vs 4 550 at 4/5s. XD

[Al_]

I think you would win that fairly easily as it seems I have spent most of the fights so far turning my tires into bits of rubber left all over the arena. Only 8 fights the bike tires are almost worn smooth. Got some fresh ones to put on for the next event.