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Thread: Obligatory First Featherweight Build Log (FeatherDozer)

  1. #11
    Time to Build Part 2

    Scoop Build

    As the scoop design is a combination of materials and manufacturing techniques, this aspect was a little more complicated than first expected. The most difficult aspect was that the lower scoop sections had to be at the same angle and height. After a couple of adjustments I was happy with the result once it was mocked up on the robot.


    Really starting to come towards the end of the mechanical assembly.

    Only main aspect left to do was the install of electronics ready for final assembly (with rear armour) and paint.

    This I knew was going to be the real challenge. Not because of a limited knowledge of electronics, but due to a lack of any space inside (as usual). Despite this, I wanted to have some form of order to the main loom so I can access most of the vital components (batteries, link etc.) without taking the whole machine apart.
    To help simplify the electronics as much as I could, the robot has separate low and high power circuits. The low power loom feeds the battery eliminator circuit to the RX, power lights and weapon limit switches/ low power side of the relays. The high power circuit, feeds the drive ESC's and weapon high power relay circuit directly from the battery.
    The drive speed controllers are Hobbyking F80 brushless speed controllers programed for bidirectional control via SimonK. I found SimonK to be limited way of flashing ESC's, but for my first play with brushless drive it was more of a set-and-forget job that was an already tried and tested method throughout the community.
    The sides of the main arm assembly are dedicated to the two 4s (1500mAh) lipo batteries and drive speed controllers. The front section houses the main fuse, main power distribution and weapon motor wires. As is seen by the image below, this meant both internal and external wire routing around the main bulkhead as the "high power" wires of the weapon drive relays and link would not fit (note that the main fuse is not in the image below). The external wires are then protected (somewhat) by the front impact panel. Changes to Mk1.5 have been applied to help better protect these wires.

    IMG_20200419_212129.jpg IMG_20200322_001035.jpg

    Lifting Arm limit switches
    As the arm electronics are "simple" it meant that the endpoints could be controlled in the same way that a conventional linear actuator works - limit switches at either end of the desired travel. As I had made my own system, I could position these limits wherever I wanted. This however had to be completed last to test the limits in real-time and adjust accordingly.
    The front limit switch is positioned under the arm scoop spacer block and moves with the weapon mechanism. When the arm is lowered, the switch contacts the front inner impact panel to stop operation in that direction. The rear limit switch is positioned above the weapon gearbox and is switched by the arm link to the leadscrew. Both systems are shown below.

    PXL_20201229_163653531.jpg PXL_20201229_163713088.jpg

    Final Assembly
    After a couple of setbacks which included robot weight reduction and self-righter last minute testing, FeatherDozer was ready for it's first event - Robodojo on 26/07/2020. I will go into minor details and analysis of the event in the coming entry. For now here is the completed build of FeatherDozer Mk1.0

    IMG_20200724_172232.jpg IMG_20200725_142730.jpg IMG_20200724_174739.jpg

  2. #12
    Ocracoke's Avatar
    Team Kaizen

    Dang, I love the neatness of this, you should be pleased with the outcome. What drive motors is FeatherDozer running? I see they are brushless, presumably outrunners?
    Team Kaizen - Build Diary for all the robots

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

  3. #13

  4. #14
    Happy New Year! Lets hope that more events are given the go ahead in 2021.

    Event 1 - Robodojo 26/07/20

    I decided to start in the Sportsman class as I wanted to learn how the robot performs before it gets annihilated in the spinner heavy full combat.

    Rather than going through the fights which can be found on Joe Brown's youtube channel, I will go over the event listing the good and bad parts of the robot. This will lead into the subsequent changes made for the second event on 26/09/20. Obviously the events last year were put on under difficult circumstances, but it was only due to the Robodojo team as well as competitor's obedience to the additional regulations that made them possible so thank you all.
    Before the event, there was little to no time to practice driving the robot other than a quick functionality test. This was a definite issue as I wanted to be as prepared as possible before the event but did not prepare for one of the most important aspects - driving practice. Despite this, I packed the car and headed to Leeds not sure what to expect.

    IMG_20200725_145652.jpg IMG_20200726_095556.jpg

    My aims for the first event were pretty high based on the competitors that were there:
    • Pass tech check
    • Function in the arena
    • Not break down from my own doing
    • Win 1 fight

    The robot passed the main tech check apart from initial weight check where the robot was 2 grams overweight! A quick removal of a bolt from the rear armour fixed this . As I was busy concentrating on maintenance throughout the event, I didn't get much of a chance to take many images post fights.

    Below is a quick list of good and bad points of FeatherDozer Mk1.0 on its first outing:
    • It works!
    • Won a few fights - Better than expected
    • Driving practice required!
    • Rear ground clearance is a little bit too low as it did get stuck on the raised floor sections due to poor driving
    • The robot is way too fast for the arena size but reasonably controllable when trimming the rates on the transmitter
    • Last minute self-righter doesn't work - New one to be designed.
    • When lifting, the robot tends to lift the rear (depending on the opponents weight distribution) meaning that it cannot move when lifted. This was a major flaw in the design that could only be found in real world testing.

    So, to conclude, Featherdozer ended the day with 2 wins and 4 losses as well as still being fully functional. This is far better than I expected based on the level of the competition. Therefore I would give the robot's first performance as way above my expectations and with a few modifications, it could be much more competitive.

    The images below are post event which showed very little damage caused. Note that the red paint used tended to peel off very easily, so if anyone from the event wondered where random red paint chunks came from......

    IMG_20200727_120843.jpg IMG_20200727_120857.jpg IMG_20200727_120906.jpg

    In the next entry I will go over the changes made for Mk1.5 to fix some of the issues listed above.

  5. #15
    Time to Modify - Mk1.5

    Despite a lot of successes from the first event, a number of changes were required. Apart from the obvious driving practice, I needed to focus on two of the issues:

    1. Unable to lift opponents without become unstable (lifting the rear wheels)
    2. Unable to self-right

    Unfortunately the main reason for these limitations was the fact that a lot of the mass of the robot is in the lifting mechanism. So when the weapon operates, the centre of gravity changes significantly. However, as the robot baseline is a good, solid platform, only minor changes were required.

    Lifting Issue Fix
    The simplest way that I found to amend the limitation to Mk1, was to extend that front of the chassis with fixed forks. These forks are an extension of the front inner impact panel/ bulkhead brackets. When the robot is sitting on the floor, the fixed forks are lifted to reduce front contact patches (only the scoop is in contact). When the arm is lifted, the fixed forks stabilise the front to help prevent the rear from lifting. As the forks have to be very long to be effective and clear the scoop, lower bracing was added to the fork assembly. This is shown in the CAD images below.
    Mk1.5 CAD 1.PNG Mk1.5 CAD 2 (No Scoop).PNG
    Fixed forks mocked up in the robot.
    IMG_20200816_145913.jpg IMG_20200816_145918.jpg
    Cut-outs were made to the inner impact panel to accommodate the forks. The image below and to the right shows the final assembly (without the front scoop).
    IMG_20200818_214944.jpg /IMG_20200822_143253.jpg

    Self-Righting Issue Fix
    A complete redesign was required from Mk1.0 as it was clear that the design was very flimsy and didn't work well. This task however proved to be a very difficult and lengthy process. I think I went through 5 different design concepts ranging from a completely separate arm linkage running from the weapon actuator, to a fixed anti tipping beam. But in the end the only design that came close to the aims of functionality and not look as if I had lost my mind , was to revisit the MK1.0 concept with better geometry. After 10 prototypes of various geometries, the design is shown below. The design is much sturdier as the main polycarbonate sections are now part of the main weapon arm assembly. The self-righter inner bracing is now much more optimised to stop flex when upside-down.
    When testing, results were promising but once the robot self-rights in the arena I will deem this design as successful.
    Mk1.5 CAD 3.PNG PXL_20200924_191944424.jpg

    As additional items were added, some additional weight reduction was required elsewhere. Most notable areas of weight reduction were:
    • Front scoop mount (made from hardox) was replaced with an aluminium alternative of the same thickness.
    • Main arm inner aluminium mounts reduced in length to use less fasteners.
    • Cutouts in the self righting arm without compromising functionality.

    Final assembly went smoothly ready for my second event on 26/09/20 (Robodojo again) which I will go through in the next post. For now, here are some images of the final assembly (FeatherDozer Mk1.5).

    PXL_20200924_151323389.jpg PXL_20200924_151336540.jpg PXL_20200924_192009391.jpg

  6. #16

  7. #17

  8. #18
    Event 2 - Robodojo 26/09/20

    Confident in at least one of my modifications, I headed back up to Leeds for another dose of addictive, intense fun!
    PXL_20200925_140812601.jpg PXL_20200926_094221872.jpg

    As before I will go over some of the highlights from the event which can be found on Joe Brown's YouTube channel (link to full event below)

    As the day panned out, it was clear that the additional front forks worked as intended to be able to lift effectively resulting in 3 wins, 2 losses and an unofficial 4th place for the day. It is always good to see incremental improvements that are a direct result of a relatively simple modification.

    The Hells Angel 2 Fight

    This fight was by far the highlight of my day. Dave's formidable axebot can cause significant damage and is driven extremely well. Midway through the fight I was having drive problems due to the only non-loctited grubscrew in the entire robot (my bad) coming lose on the left side drive gear. What is clear when watching the fight back, is that I was relatively lucky winning this fight, as up to the very end when Hells Angel ended up out of the arena, I was taking damage and not driving well. The out of the arena came in the final few seconds of the fight and was my only real contribution, but a wins a win.
    However I did not get away without a number of axe marks in the robot and it was nice to see that some of the hits were lessened by the use of the scoop as a shield.....

    PXL_20200926_132402845.jpg PXL_20200926_132405326.jpg
    Dave came VERY close to the link....
    PXL_20200926_132408179.jpg PXL_20200926_132411329.jpg PXL_20200926_132417079.jpg

    Luckily all of the damage was superficial, so I swapped the lower scoop sections for the repaired ones from event 1 and kept going.
    Despite the positives from this event, it was clear that still I need more practice with this robot as the main contributing factor to both my losses was my driving which resulted in getting stuck under the HDPE floor panels. This hopefully has been rectified in my improvements listed below.

    Next Steps & further improvements

    As a result of facing many powerful axes, it is clear that I needed to better protect the lifter relay wires as well as the area around the link before it gets sniped as was done to a certain toaster .
    Therefore, I will be adding a guard to either side that needs to be substantial enough to take hits but not get in that way of either the lifter mechanism or accessibility to the link.
    Also as I get more experience driving FeatherDozer, I have come to the conclusion that in addition to practice, I need more low speed control. The F80 speed controllers are a good starting point for brushless ESC's but are lacking in low speed control and with an unfriending way of making adjustments on the fly. So I have decided to have them on standby as spares and use an alternative speed controller setup.

    I will go through these modifications in the next entry.

  9. #19

  10. #20
    Ocracoke's Avatar
    Team Kaizen

    I love the look of this, soooooo much better than what I am coming out with at the moment, gonna have to up my building game with Azriel 2.0.

    You mentioned F80 speed controllers with SimonK firmware. I am in the middle of writing a SimonK based program to flash speed controllers with and be intrigued as to validate what my program is coming out with against what you are using here. Would you be able to show what configuration you have in your .asm file at all?
    Team Kaizen - Build Diary for all the robots

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

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