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Thread: Obligatory First Featherweight Build Log (FeatherDozer)

  1. #1
    Last edited by Sam_Gad; 12th May 2021 at 10:16.

  2. #2
    Design Philosophy & CAD

    As was mentioned my in previous post, I wanted to build a reliable first build but apply the engineering knowledge gained at both university and in my day-to-day working environment. So, in its most basic form, FeatherDozer in a compact 2WD robot, armed with an electronic, rear hinged lifter.

    Before this final design, there were many concept that ended up being shelved due to an aspect that I wanted to keep to: manufacturability. Due to my limited shed and tool capacity as well as my desire to make as much of the robot in house, I wanted to be sure I can achieve the design before starting the build.

    Due to the compact design, it became clear that I did not have the space or the weight for conventional brushed motors. Therefore, the drive comes from 2 brushless outrunners connected to a live driveshaft via a single gear reduction. This was to limit the number of moving parts for each side of the drive as well as the inherent lack of space (maybe I should have just made it a bit bigger). The chosen wheels come from an industrial belt sander as they were an off the shelf part with have good grip qualities and a solid aluminium inner hub.

    Front Scoop and Weapon Mechanism
    The front “scoop” consists of 4 main sections:

    • 1 main upper Hardox section
    • 1 HDPE Front sacrificial panel
    • 2 Lower HDPE “forks”/ side scoops

    The “forks” are designed to not only get underneath opponents, but due to being made from HDPE, they can flex with both impacts and the floor to always be as low as possible. I decided to make the whole scoop lift as one as it seemed simpler to me at the time (not sure why now I think of it) as well as be able to act as a raised shield when required. This causes a number of issues which we will get to in later posts. When fully lifted, the front is protected by an inner HDPE impact panel. This is shown below.

    The lifting mechanism is powered by a linear actuator, however after initial testing of off the shelf systems, I found a number of limitations such as weight, size and quality of materials used (due to being a mass-produced part).

    Therefore, I chose build my own system using parts from a car scissor jack, a brushed motor with a planetary gearbox and a decent amount of hope. The leadscrew from the jack is retained in the centre of the design by the weapon motor and gearbox housing and the front plate that separates the fuse module from the rest of the machine. This was the first aspect of the design modelled which gives the robot its final structure characteristics. For now, this system will remain brushed as the electrical system can be basic (2 high power relays to create a H-bridge motor controller). The image below is in the early build phase (hence the mock up of the arm in wood) which shows the full final actuator mechanism in the robot.

    IMG_20190915_203435 - Reduced.jpgDF MK1.0 CAD 5 Lifted.PNG

    With the weapon mechanism determined, the main chassis can be split into a left and right module. Each module consists of a main longitudinal bulkhead, inner bulkhead to support the weapon mechanism and a transverse bulkhead that acts as the battery separation from the wheels, driveshaft outer bearing carrier and retains the rear armour/ wheel guards. The two modules are then connected together by the rear bulkhead as well as a number of internal spacers (as shown in red in the picture below).

    DF MK1.0 CAD 2 Inner Structure.PNG

    Electronics and battery positioning
    As the central part of the inner structure is taken up by the weapon system, the main electronics had to go either side of the module to keep the design balanced as well as be accessible between fights. Each side of the main inner structure houses a battery and drive speed controller. The electronics are protected by a HDPE curved cover that is shock mounted to dissipate the energy of blows from an overhead weapon (e.g. an axe).

    DF MK1.0 CAD 4 Top View.PNG

    Other aspects
    From the images it might be apparent that the self-righting mechanism was a bit of an afterthought. This is because it was! From initial testing it became clear that without an additional structure at the rear of the lifting arm, the robot did not have the articulation to self-right. This system shown was limited due to time constraints and was added just before my first event. As a result it is a poor design. This has been changed in the latest version (Mk1.5) but is untested and seems to be a major limitation to this design which will be fixed in the next robot.

    In the next entry I will go over some of the build process leading up to my first event in late July 2020.

    Last edited by Sam_Gad; 2nd January 2021 at 19:09.

  3. #3
    Ocracoke's Avatar
    Team Kaizen

    The chassis design looks to be quite neat, better than the implementation of my left and right sections in my Middleweight at any rate, well done How thick are the front and rear bulkhead in that design?
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

  4. #4

  5. #5
    Great machine, and a nice write up. I saw the videos of Featherdozer at Robodojo on youtube, really nice looking machine.

    How did you get on with the sander wheels, were they grippy enough? Could you post a link if they're good, nice to file away these options that have been tried and tested!

  6. #6
    Ocracoke's Avatar
    Team Kaizen

    Construction sounds fine to me The 6mm HDPE, as you say, won't be too much of an issue as it is anchored down quite well by the diagrams, Azriel has a 6mm front plate for deflection which I figured would be enough because of that and being well bolted down. Looking forwards to the construction posts.
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

  7. #7
    Hi Sam,

    Thanks for your comments. The wheels great for the surfaces usually used in robot combat (steel, wood etc.). I will be using these wheels again in my next featherweight which I am designing now.

    These wheels specifically are 86mm outer diameter x 50mm width. There are many other options (both diameter and width) on either Banggood/ Aliexpress or ebay directly from China (Link to the ones I use listed below):

    Similar wheels have been used before in featherweights to great affect on both shrapnel and the latest version of Get Shrekt.

    There is an option for either the serrated or slick tyre options. I have both, but so far haven't used the slicks yet as in the next event (whenever it will be), I will be using new drive speed controllers and don't want to make too many changes at once in case of an issue.

    I did have to do a lot to them to suit my needs as they are quite heavy due to the amount of rubber. On FeatherDozer, the width is reduced to 45mm (still very wide) and bored out to fit the axle-to-wheel interface. Before an event I usually cover the wheels in gaffer tape to help clean the tyre surface before it is needed.

  8. #8
    Nice one, cheers! That's not a bad price and much easier than making them from scratch from bike tyre and HDPE.

  9. #9
    Mr Manuva27
    Hey Sam,

    Was great to meet you and see Featherdozer in action at it's first event back in July. You've built a fantastic machine and I'll be following this thread with interest!

  10. #10
    Before we start I would like to thank all who have taken the time to read the log so far and the complements made .

    Time to Build Part 1

    As there are a vast number of aspects to cover during the build process, I will split this into a few posts.

    The decision to start making combat robots came at a transition period for me as I gave up one hobby (restoring classic cars) to start this one. Therefore, I sold my track car to fund tools, the build etc. I chose to buy workshop tools tactically for this build and buy additional tools on demand. As a result some of the more complicated/ hard to make parts were water jet cut by our friends at K-Cut. These were:

    • Front Hardox wedge/scoop section
    • Outer drive bearing carriers (also made from Hardox)
    • Rear aluminium bulkhead
    • Centre transverse aluminium bulkheads (replaced later in the build by HDPE due to weight constrictions)
    • Hardox arm scoop backplate

    This meant that some main aspects of the chassis were built very quickly.
    IMG_20190623_170550.jpg IMG_20190614_075958.jpg

    Mock-up of a side module with the drive motor, gears and live axle.

    Chassis mock-up with wheels and weapon mechanism front plate.

    Weapon Arm Mock-up
    Before investing the time in building the final arm mechanism out of a number of different materials, I wanted to check that the mechanism works as intended. Therefore the components were initially made out of MDF. These images also show how the front end of the robot is stiffened up by weapon mechanism front plate.

    IMG_20191006_141246.jpg IMG_20191124_221135.jpg

    Final Arm installed with the leadscrew mechanism to the side.

    The front impact plate & electronics covers both made from HDPE in 6mm and 8mm thickness respectively. Note that the electronics covers are shock mounted in 2 directions to be able to flex down during an impact but not too far to damage the electronics inside.
    IMG_20191223_181951.jpg IMG_20200103_173845.jpg

    So this is where I will leave this entry with most of the chassis, drive system and weapon arm made and semi assembled.


    The next entry will (hopefully) complete the Mk1.0 build leading up to the first event.
    Last edited by Sam_Gad; 24th March 2021 at 14:42.

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