Team Death - New Heavyweight

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You'll note that it is an advisory at the moment (as of the 2017 ruleset) so with this ESC and battery chemistry, you'd be OK but the only option then is to fit a secondary meter/alarm into the balance plug (https://hobbyking.com/en_us/hobbykin...arm-2s-6s.html) for each battery pack.

That's a neat little thing. I've just picked one up, although it gets shipped from the Hong Kong depot so takes a while to arrive

I wonder if itd' be possible to modify the Cytron to cut power in the event of a battery approaching its absolute minimum., if its already low voltage aware, it might not be too difficult.

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You know what day it is, because I do!

So today, another interesting day.
We started by charging the old battery, which had been tested to ensure it wasn't damaged from last weeks test, and the new battery, to an equal amount that should give us plenty of test time later on.
Whilst these charged, we set off on rectifying a few issues we noted last week;
We started out by applying some additional castors further up the underneath of the shovel, in the hopes that it'd give a little extra weight to the rear to fix some of the driving issues, notable lack of grip and lots of wheel spin.
I spent a while going through the manual for the transmitter - trying to find a way to correct some control issues we had last week, and improve upon the new 'tank' style driving. However, to no avail. We had a bit of better luck fiddling with the cables, and plugging the wires into different ports on the receiver. However, in the end we settled for going back to using what we had before. This is due to us finding evidence of one of the bolts used to hold some polycarbonate armor in place had been scraping on the floor of the last test - it was scuffed up and worn. We later figured out this may have contributed to some control issues last test, as the bot did not entirely lay flat on the floor - one wheel was always slightly above an ideal level for drive and was easily spinnable alone due to an extremely poor grip on the floor. So the excess thread on the bolt was cut, and the bot laid back on the floor - and this time both wheels made sufficient contact with the floor that neither could be spun alone without the entire bot moving.
With that, we were once again on our way to the designated test area.

However, this test lasted not long at all - due to an unfortunate collision with a pile of... varying items of waste.
After the bot was pulled out, we couldn't get it working again - our initial thought was that the wheel was spinning on its entral pole - due to it not being worn down to a flat enough surface for the wheel to grip on after coming slightly lose. We didn't have the correct tools to fix this out in the field, so we put it back on the truck and got back to the shop. Here it became quite quickly obvious the failure was something a little more sinister. In fact the weld joint on the sprocket to the pole had entirely sheered off - not sure if it was a poor weld joint, or if there was much more force than intended occuring here. However the sprocket is off an ancient Austin A40 car, and spent nearly all its life covered in grease and oil, so this may have caused the welding to not take as well as could be hoped. Either way, Colin is going to aim to correct it in time for next Sunday. When hopefully we'll be able to test it without any issues cropping up!

An image, showing the weld joint and its fairly easy to see cracking around the joint
weld.jpg

[team death]

A Saturday morning build session this week...
Half way through the build I decided that the rear of the Robot looked empty
and decided that there was room to fit a fail and housing as described previousley.

After consideration the flail idea was dropped and so the housing was not required
so today I removed the over hanging housing.
The new idea is to have the wheel exposed at the back so we can literally climb up
walls with a 280 degrees of wheel able to touch the surface of the arena overall.

After cutting the housing off and some refabricating I also re cut the tread on the
tyres to hopefully give more grip-this is a very messy job and everything gets covered
in rubber dust.
DSCN2115.jpgDSCN2116.jpg

[Maxamuslead]

when do think it going to be combat ready ? as it damn near close

[team death]

I think we are nearly there but we don't want to rush things to make any
specific event.
Originally we built the Robot for Robot Wars tv show which was of course cancelled
so I think Adam would agree that we would rather have a tried and tested machine
and get as much driving experience as possible rather than take it to the first event we see
after fitting the last nuts and bolts.

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It's that day again! It's sunday, which means when I got home, there was a load of takeaway menus waiting for me in the post box.

Oh right, the bot, yes!
Today was a day of success, after a few recent tests being let downs. It wasn't without a few issues, which will be revealed later on. However, it was by far the most successful test we've had for a while.

Today, we started by charging both of the batteries up to 16.5v. Whilst that was happening, Colin did a little show & tell and demonstration of the strength of some metals, and how large but compact a Gazebo can be - this is actually not for anything to do with this new machine, but it was a bit of an idea fest for the Northern / Scotland events I'm trying to get up and running. This only took 15-20 minutes, and as we have figured out the safe limits our batteries can charge up to, it's all it took to get the batteries, both of them, up to the charge we were looking for.

Soon enough, the batteries were ready to go, and we put everything in the truck and to the usual test area. Quickly putting up a few boundaries to stop us from going in some very unpleasant pools of disgusting looking stuff.

Battery wise, there were still some concerns however. To begin with, the batteries depleted at even rates. However towards the end, one battery started tailing off a lot quicker than the other. Going from 16.5v each, to one being 13.2v, and the other 14.5v - up until the 15v mark, they were near enough depleting at an equal rate - with us frequently pausing to test the voltage and heat. When we got home, it was discovered that one of the cells in the 13.2v had become quite unbalanced with the rest, whereas the 14.5v battery was still all within 0.02vs of all other cells internally.
However, and - as pictured below, the lower 13.2v cell was quite a mixture. With the cells being 3.18, 3.30, 3.25 & 3.35. However, once charging had started, it only took a few minutes for the charger to balance everything back out before it charges them all up again, still in sync with each other.
This gives me and Colin some concern, as we are unsure as to why the cell are discharging at differing rates, and why the one discharging faster, is also becoming out of sync voltage wise with the independent cells. I therefore hypothesize this is the cause of the previous battery fault, where one discharged beyond its minimum without us noticing, and the other not doing so, resulting in a dead battery, and a bit of an unhappy hot one. It's worth noting here, that the new one is the one that ended up being the most discharged with uneven cell voltages, so it isn't the old one that is damaged here. So if you have any idea why this may be happening, i'd very greatly appreciate any feedback or suggestions. As the batteries were all charged to the same total voltage, and all cells were balance charged - so this all happened during discharge?

Colin notes that the drive is still a little off. Driving in a straight line is still quite hard to achieve. As hes been doing all the driving during the testing phase, I'll leave him to note down the specifics in a post soon after this, and hopefully someone can aid us in that area too.

Here is the video from todays test. Here we are able to demonstrate the speed it can attain when going straight(ish) - and how it manages to always get itself free from any debris its stuck over, including working its way out from awkward wedged positions. Furthermore, Team Death finally manages to beat a wall. Outdoing the infamous Piece de Resistance, now two decades ago.
Overall, the bot is certainly starting to behave in a manner we are aiming for, with a few little niggles - but we are definitely getting there, and the to do list after each test is getting fewer and fewer.
Note: you may wish to turn audio down - the wind was being unhelpful, and my phone has quite a high gain mic on it, so the wind is rather irritatingly loud.

and images
Note: on the cell voltage - the two last cells are non existant, as its a 4S battery, so we haven't lost two cells here! - here demonstrates that faster discharging batteries odd balance after the test (the other was higher overall voltage, and still balanced)
IMG_20180429_144102.jpg
Not content with knocking the wall down, we also managed to push the bricks some distance too. At some point, we may line up some bricks and see how much push we have on them - we also may try to pull or push something like a pallet.
IMG_20180429_141012.jpg
There is however, one downside to Colins modified wheels. The new treads seem to be ripping off slowly over time, this may or may not cause an issue later down the line.
IMG_20180429_150012.jpg

[Maxamuslead]

err what batteries are you using ?

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They're Zippy LiPo, 14.8V (nominal) 4500mAh, 4S @ 45C
(or specifically; https://hobbyking.com/en_us/zippy-fl...___store=en_us)

[Maxamuslead]

did you say you are running 2 in series or parallel ?

Side note: I would check them again as the cells can recover some voltage, and depending how far out they are, run a balance charge on them as that should bring it back in line

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They are in series, as in parrelel they wouldn't amount to the higher voltage, just double the mAh
So in the configuration they are at, they are 14.8 + 14.8v (29.6v nominal), and 4500mAh (mAh doesn't get doubled in a series setup)

[Maxamuslead]

i am aware, 4.5ah does seam a tad low as i know coyote ran a 8ah 6s battery

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I wouldn't have thought that would cause the batteries to discharge at differing rates, with one of them getting very poor balancing between cells over the other?

[Maxamuslead]

It could be as when i have completely drained my batties that when they have been the most out of sync.
It could also be the wonderful chinese hit and miss quality

[Ocracoke]

I would have said 4.2aH was too low. Tango used a set of 2.1aH 6S Zippy (2x 3S in series) LiFe batteries from The Honey Badger and they were thoroughly dead by the end (all puffed up and such with the cells well out of sync). I would have mooted at least 6aH in that case and I'll possibly be looking for 8.4aH for Kaizen.

There is however, one downside to Colins modified wheels. The new treads seem to be ripping off slowly over time, this may or may not cause an issue later down the line.

That is possibly down to where it is being tested. I would have thought laying down some plywood sheet on the ground may help.

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Colin has suggested using larger capacity batteries already, so we may have to go down that route, which is a little unfortunate as we are already a little over the expected cost of this build.

That is possibly down to where it is being tested. I would have thought laying down some plywood sheet on the ground may help.

Yeah, a proper arena will be a lot more smooth and not that rough on the wheels, one would hope. We do our testing a short drive from the workshop, as its possibly the furthest away from things of concern getting damaged. So i'm not sure how viable it is to take something up there to be softer on the wheels.