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Thread: Team Death - New Heavyweight

  1. #131
    Redirect Left's Avatar

    Wakefield, West Yorkshire
    It's sunday!

    Myself & Colin got together this Easter Sunday, and focused on electrics again.

    During the week, Colin had worked on the lid for the ESC box, it's now got quite a strong lid to it that should easily do nothing more than be a little dented from something like an axe attack.

    We started off by creating the cable that'll link the two LiPos together in serial, seeing as that needed two connectors on both sides, and last week we had a few issues getting the soldering going accurately. This week was greatly improved in that regard, using a soldering iron I brought up that's a little more powerful, only by 10W, but it made all the difference. Again, we used a gas torch to help melt the solder deep into the bullet connectors base instead of just around the edges to get a much better and hard wearing connection. We then moved on to all of the other places that'll later need wiring together, adding connectors so we don't have to do these as we come along to them.

    We also setup the status LED to wrap up with, it's currently being fed through a seperate set of 3 AA batteries, which will be reduced to two with a small modification to the battery holder next week, as 3 slightly overly stresses the LED. The LED circuit is looped through the main link, to ensure despite its seperate circuit, it'll always accurately reflect the status of the bot being armed or disarmed.
    The LED is shone through a hole in the lid of the ESC box, which gives a very vibrant and immediately obvious effect.

    Next week, we're hopeful we'll be able to wire it up and have a proper test run. We've still to determine which of us will later go on to drive it, so we may setup a quick assault course and see who can drive it more accurately. We also need to work out the best way of firing the weapon, using a simple extra remote that is standalone with its own receiver, or an extra panel wired into the main transmitter on a long cable.

    Todays not many images, next week, we'll make sure we get a proper shot of the lid of the ESC cover. It's shown here in the second image, with the new armed status light brightly shining through it.


  2. #132
    A day and half session on the Robot build this week....
    Yesterday I decided to change the springs on the castor suspension hinges-
    during testing they were too weak and were allowing the Robot to drop too
    low to the ground, thier main purpose is to reduce the shock to the bodywork
    when 110kg Robot is flipped 4 to 6 ft in the air.
    Earlier in the year I changed the clutch on a 4x4 pickup truck and after looking
    at the old clutch on Friday, I decided the springs inside were a perfect substitute
    for the castor hinge springs.

    Sunday-Unfortunatley Adam was unavailable this week due to a Tummy upset
    and generally feeling bad so I set too on my own.
    Fortunatley Adam had left some items with me last week so I could finish the wiring
    I started by re wiring the LED to the removable link, adding a suitable resistor to
    the circuit and a new LED, I also reduced the battery to 3 volts and cut down the
    battery cradle to 2 cells ( it fits much better into a reserved space ) .
    After this I lengthend the motor wires from the fuses and tidied up the layout
    with the aid of bolts and zip clips.
    I sent a message to Adam saying I might take the Robot for a test run if there
    was time but finishing the wiring took while 4 pm so I didn't.

    I will try to find time to test the drive through the link for the first time-
    next mid week (wheels off the ground) and if this is all good we can take it
    to our cicuit first thing next Sunday.
    Here's some pics due to internet busy more pics later
    DSCN2104 (2).jpgDSCN2102 (2).jpgDSCN2112.jpgDSCN2110.jpgDSCN2109 (2).jpg
    Last edited by team death; 8th April 2018 at 19:53.

  3. #133
    Redirect Left's Avatar

    Wakefield, West Yorkshire
    Another Sunday has past us by, which means another update!

    It's been a day of ups and downs, however we learnt from the experience - and that is what counts!

    Before I arrived, Colin had setup the wiring ready for a test. So before we went anywhere specific to test, we plugged everything up, at this point only the batteries were needed, and ran an off-ground test just to ensure nothing silly would happen. It wouldn't try running away when the link was plugged in, unfortunately this did lead to one problem being spotted immediately. The motors had been wired in correctly, leaving one going forward whilst the other reversed. This is due to a simple forgetful mistake, in that in the past the motors were mislabelled red/black, however that was accounted for at some point in the past and fixed - but had forgot we did that so the motor was purposefully wired wrong under the assumption that was to do still.
    Not to worry, the Cytron ESC is very quick to do a rewire and it was fixed within a few minutes.
    Another issue shot up when we got it on the floor, now we were happy it'd maneouvre as anticipated motor wise.
    The castors springs needed a little adjustment, as it ran one side of the bot tended to be on the ground a little firmer than the other, causing some one sided wheelspin. So a little tinkering was made there, to balance out the weight distribution a bit more.

    After this, it was time to do a proper test for the first time, we packed up the bot and some tools, and headed for a secluded section of tarmaced area near the workshop. After noting the batteries at this point where about 60-70% charged, and we managed to get a good few minutes of usage out of it. Certainly more than the typical battle would last. We found out quite quickly that control was a little sketchy - unless you had perfectly positioned the controllers stick, there was a noticeable difference in output in the two motors, and driving was a little harder than we'd like. There was also a few further issues with the weight distribution, we'll try to see if we can correct this with more tweaking to the springs as we were still wheel spinning a bit on one side more than the other, although this may be related to the control issue. After a while, unfortunately but obviously, the batteries became a little drained to keep things moving along at a pace of value. We went to check up the bot - the batteries were both very warm, overly so. thinking nothing of it, we tried to have one last run straight line run to gather some speed up, however it just sat and didn't move. So we packed up and headed back to the shop.
    Upon arrival, we decided to try to get around some control issues, by setting up a 'tank' style driving. Lifting the bots wheels off the floor, the batteries still had enough power to run the wheels, so we could test this new control method, and it seems to work. However, that is indeed all she wrote. With the batteries at this point being unable to spin the wheels, even off the ground.

    We got out the charger, and set to work charging the now drained batteries for a later date. However, it's at this point we unfortunately found out that one of the batteries had been killed, my best guess is by the heat. It was so broken that the charger wasn't even able to detect it was a four cell battery, and only gave a total voltage (of 5 volts, on a 14.8v nominal LiPo!) and was unable to display individual cell data. We double checked and connected up to the other battery, and sure enough this one was seemingly in working order, with the charger correctly giving data for all four of the individual cells, and happily charging upwards. Whereas on the other, the charger just flat out refused to charge it due to a voltage discrepency.

    I am thinking that the current battery holders are simply not getting any airflow, allowing the heat generated during discharge of the batteries to build up to damaging levels. I've included a picture of our battery holders below, so if anyone has an idea about this, and can confirm my suspicions, i'd be grateful. As if it wasn't damaged due to the heat, it may be a more severe problem than originally thought with the wiring or some other electrical part of the bot. We have a few ideas for alternative battery holders with much more airflow potential up our sleeves, if the heat and no airflow is the problem.

    So all in all, today was certainly interesting. But we learnt from the experience, made some fixes already, the rest we will tackle on further sundays, here we don't hide the stumbling blocks. We share the entire experience for sure!

    Some images, and some video taken during the test run. We managed to get up some good speed in parts, and we also know it spins well, so that's something.

    I've cut down the video so the first minute is the most relevant to capabilities, and after that its mostly farcical stuff and spinning. Whether out of control, or intended - i don't know! It does however look like it spins with enough force to be somewhat damaging just from that!

    All wired up and ready to go
    All packed up for its first time leaving the workshop - note that we decided to put the lid on top of the ESC box for this drive out, incase things got a little bumpy as the ESC is loose in the box currently although the sides and bottom of the case inside have been isolated with non conductive tape, just incase. We took a brush and a shovel so we could clear debris from the area, to help traction and make sure we didn't run into anything too nasty.
    These are the battery compartments. I suspect these are the cause of the overheating and battery failures, as there's very little airflow, especially to cool down the cells in the centre of the pack. Especially as the battery is 45C at 4500mAh so should be capable of over 200A sustained flow, and we shouldn't be touching even 100 of that.
    The first battle damage! - It was also running on the bar on top, based upon the scratch marks. So we're not sure if it was just bouncing upon it occasionally, or actually dragging it across the floor all the time.
    Last edited by Redirect Left; 16th April 2018 at 01:42.

  4. #134
    A few problems here to iron out
    What looks like bad driving was due to the transmitter not been calibrated
    on the trim for one-when I pressed forward it was wanting to go left or right.
    secondly-there is still a lack of traction for the wheels, resulting in wheel spin
    and wasted energy-the castors may need to be just under the shovel or jaws
    when fitted.
    The batteries were not fully charged and so combined with the other problems
    was not showing the true potential of the Robot.
    We need to buy a new lipo battery due to it overheating-any heavyweight
    Roboteers with advice on this is welcome ie what run time you should get
    and what is the lowest you would let your cell voltage/overhal voltage go to
    and what methods you might use to prevent the voltage from going to
    dangerously low levels when robot is in use.

  5. #135
    Ocracoke's Avatar
    Team Kaizen

    Osu, Ikari - AW / Shu! - BW / The Honey Badger - FW / Kaizen (Building) - HW
    Somewhere on the Wirral
    Roboteers with advice on this is welcome ie what run time you should get and what is the lowest you would let your cell voltage/overhal voltage go toand what methods you might use to prevent the voltage from going to dangerously low levels when robot is in use.
    Most ESCs these days have a LiPo function that automatically cut power when the voltage level is too low. The Cytron definitely has the facility to detect undervoltage (< 3.0v per cell) ( - Section 7b) but it doesn't cut it out, only on overvoltage apparently.

    This had me panicked a little as section 7.8.2 of the rules (specifically pertaining to LiPo batteries) state the following:

    Voltage Cut-out (Advisory)
    The robot maybe fitted with an under voltage cut-out or alarm set at or higher than the battery
    manufacturer’s recommendation to prevent the batteries from becoming damaged by over-discharge
    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 ( for each battery pack.
    Team Kaizen

    AW - Osu, Ikari
    BW - Shu! (Build Thread)
    FW - The Honey Badger (Build Thread)
    HW - Kaizen (Build Thread)

  6. #136
    Redirect Left's Avatar

    Wakefield, West Yorkshire
    Quote Originally Posted by Ocracoke View Post
    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 ( 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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