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Thread: Ullr's Hand - A Beetleweight Build Diary

  1. #1
    Hey everyone!

    After toiling in the featherweight mines for around a year trying, failing and trying again to make our first new bot of that weight class since Buttkicker arrived in 2019, we’re finally reaching a stage where we can bring the first of two to an event. In the meantime however, the beetleweight scene seems to have really taken off. Those of you who have been keeping track of the trials and tribulations of Team Hardrada (don’t do this, it’s not worth it) will know that we created a beetleweight for the Robodojo summer team event last year. This was a control bot called Ullr.


    Now, Ullr was our very first foray into beetles and as such we decided to follow the K.I.S.S. principle that's very much eluded us on previous builds. The design was a simple box wedge with a large grabbing arm to grab and push opponents. I must admit, I have always been very happy with the overall look of the design. Unfortunately, this made it all the more bitter when we found out how deeply flawed it was. The problems with original Ullr were as follows:

    • Weight distribution - This was the principle issue of the bot and the one that forced it into early retirement. The wheels were far too far forward and the heavy weapon motor was at the back. This meant that to move, the weapon itself had to be at the front of the bot, rendering the wedge and the weapon useless. I’m 90% sure it was Sam Price who mentioned this to us.
    • A poor weapon motor - To power the weapon, we got a brushed gearmotor from the beautiful land of eBay. Although seeming to be perfect for the job, immediately it was far too heavy for what we wanted. Furthermore, it couldn’t self-right poor Ullr. Further furthermore, it required a hub and grub screw to attach the arm which, when put against the vicious beetle verts, promptly detached and left Ullr’s arm uselessly floppy.
    • Receiver problems - After giving up on the beetle version, we had the idea to throw it in the featherweight fights as a small companion to Buttkicker. Christened Puttkicker and with a tiny HDPE putter on the top, we brought it along to a Robodojo. We even added a huge, thick steel bar underneath it to balance out the weight issue, as well as losing the weapon and motor. However, our original transmitter is an old one without a screen and any mixing options. As well as this, it was paired with only one receiver and that was being actively used in Harald (the second one). The reciever that we put in the bot therefore refused to pair with the transmitter. This all lead to Puttkicker not getting even a single fight in that format.

    All the components that weren’t the weapon motor have remained working and useable, even after multiple spinner fights (kudos goes to Bristol Bot Builders and their superb beetleweight drive kit) and so the opportunity to jump back into beetles has been open to us for a while. This leads me onto the future for Ullr. Introducing Ullr's Hand.

    The idea for an actually working beetle control bot is as follows. The weapon motor is going to be replaced by a 30-35kg servo. This seems like the natural fit for this kind of weapon, and the only thing that stopped us using one last time was sheer ignorance of their use and existence (we’re so far from engineers). The arm itself won’t be the plastic rake from before but two long wood screws sticking out of a 20mm x 20mm HDPE bar. In fact, it will look more like a rake than it did before.

    The front will no longer be a standard wedge but a Season 3 Sawblaze tri-prong thing. This will be made out of cheap, nasty aluminium kickplate, the same stuff we used for the structure of original Harald that caused all signal sent from the transmitter to be blocked. This will hopefully be easy to work with, cheap to replace and nice and sharp on the ground. It should also help the weight distribution as they will reach further forwards than the wedge previously did. Speaking of weight distribution, the overall shape of the bot will be wider and thinner. The wheels will be placed at the back with all other components placed at the front. This should balance out the length of the weapon and mean the front prongs stay firmly on the ground at all times.

    This is the general plan, and as a form of amusement for the denizens of the forum I thought I would share the build process with all of you. As I've always said, we have no idea what we’re doing half the time so please bear with us as we feel around in the dark for a working beetleweight.

    The next post should be about the components and potentially a simple design made of a paper based material. Look forward to my crafting skills.

  2. #2

  3. #3
    We found the previous beetle a little fiddly, but there's so much good information out there that you should be absolutely fine.
    The nutstrips are these from BBB, they're perfect for the job.

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