Antweight Combat Spinner Bot - Shrapnel
by Fryddog, published
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Found two issues with Shrapnel. First, I would never be able to go to full speed with the weapon and would always vibrate wildly when at greater than half throttle. Second, due to the strength of the weapon motor and because the motor is only mounted to the top half of the chassis, the motor ripped clean out off the chassis on more than one occasion.
This version fixes these issues:
- Shortened the chassis by 5mm.
- Made the motor mounting area a little larger.
- Allowed for an M2 screw and nylock nut to be held in the front bottom section hole. This screw is trimmed to sit inside the center hole of the weapon bar. I also trimmed the shaft of the motor to make room for this screw.
With these changes, Shrapnel can now spin the weapon to full speed and the motor hasn't ripped out yet!
Also uploaded a shorter weapon lock and a stand for Shrapnel.
Gave Shrapnel a wedge on the back, increased the underneath clearance by 0.5mm and changed the side columns so that they are hollow. Each of these hollow columns hold two nylon spacers that get secured by two M3 nylon screws each.
These changes were added after a few fights using the V8.0 Shrapnel. The layers split at the columns and he got stuck around the arena sometimes. If you're interested in printing or messing around with V8.0, I've now added it to this thing.
This is my 3D printed design of a bot used in our 150 gram Antweight combat league. I've named him Shrapnel.
He is a horizontal spinning weapon bot and weighs in at 148 grams! (not counting the weapon lock)
This bot leaves a lot for you to customize as far as the internal components go but please use this list of components that I used to make Shrapnel as a guide to get you started:
- 2x 50:1 microgear motors. http://botbitz.com.au/index.php?route=product/product&path=64&product_id=55
- 2x Pololu 40x7mm wheels. https://www.robotgear.com.au/Product.aspx/Details/3699-Pololu-Wheel-40-7mm-Pair-Black
- 2x brushed ESC's. http://www.ebay.com.au/itm/131645159656?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
- Orange micro aircraft receiver. I use a Spectrum DX6 aircraft transmitter to control Shrapnel. I used this receiver because it was compatible with Spectrum and gained me a lot of spare weight and free space for this bot. http://www.hobbyking.com/hobbyking/store/__47012__OrangeRx_R415X_DSMX_DSM2_Compatible_4Ch_Micro_2_4Ghz_Receiver.html
- 260mAh battery (this higher capacity is required to maintain a high discharge current but 180mAh could be used too). http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=37342
- Turnigy brushless ESC. http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=30734
- 2300kV brushless motor. http://www.ebay.com.au/itm/Genuine-DYS-BE1806-2300KV-Brushless-Motor-2-3S-for-Mini-Multicopter-QAV250-/251939269040?hash=item3aa8c029b0&_uhb=1
- Power Switch and power on led (robot fighting safety requirements).
- Weapon bar to mount on top of the brushless motor. I went with a stainless steel piece that measured 10mm x 90mm x 3mm. This bar weighed in at approx 23 grams. I made this component last so I could make the largest bar I could with all the weight I had left.
- 5x M3 screws, socket or phillips head. These will hold the lid onto the bot. Usually the mounting holes don't print through perfectly, so I run a 3mm drill bit through the column section and the rear mounting holes and a 2.5mm drill bit through the bottom section rear mounting hole. Nylon screws like these would be suitable http://www.jaycar.com.au/25mm-x-3mm-nylon-screws-pk-10/p/HP0142
- 4x M3 nylon spacers. These slot into the columns to provide added strength to the columns and should prevent the layers from splitting. Spacers like these will be suitable.
- 6x M2x6mm screws, socket head. These will hold the brushless motor to the chassis and the weapon bar to the motor. The chassis holes will need to be drilled out with a 2mm drill bit to clean them up a bit. http://www.ebay.com.au/itm/371010680689?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
- 2x M2x10mm screws. Drill the holes out to 1.5mm this time because these screws will thread into the chassis to secure the microgear motor brackets. Alternatively you can use the small self threading screws that usually come with R/C servos which I almost never use and so have heaps spare!
- Print out The Version 10 top and bottom sections and two motor mounts. Drill out the holes described above.
- Mount the brushless motor up front and the two drive motors on the sides, using the motor clamps to secure the motors.
- Solder up your power circuit. Connect the battery positive to one side of the power switch. Connect other side of the power switch to all of the ESC positives and to the anode of the led. Connect the battery negative to all of the ESC negatives and to a 220ohm resistor. The resistor then connects to the cathode of the led.
- The ESC's may come with switches of their own. Cut these off and short together these wires on only ONE of the ESC's.
- Shorten your ESC leads that go to the receiver and either solder them directly to the receiver or splice in connectors that can plug right in. You can lose a save of weight doing this and it is far easier when fitting everything inside. The plugs you use will depend on the receiver you select. The micro receiver listed above uses Micro Molex 3 Pin connectors. (I prefer using the plugs, I like to make sure everything can be unplugged and swapped out easily).
- Plug the ESC leads into your receiver. I connected the brushless ESC to the throttle channel on the receiver. This is important because this bot will vibrate a LOT and likely damage itself if your weapon bar is not balanced well enough. By using the throttle control, I can increase the throttle gradually and find the sweet spot before the bot starts vibrating and still be effective in the fighting ring. You can avoid this issue all together by using a lighter aluminium bar or blade (approx 10 grams). It won't be as effective when fighting but the bot will barely vibrate at all.
- Secure the ESC, battery, power switch and any loose wires with some super glue or hot glue.
- Manufacture your weapon bar with the material of your choice. Follow the diagram on the brushless motor's eBay page for screw hole placement.
- Mount the weapon bar to the brushless motor with the M2 screws.
- Attach the top section to the bottom with the M3 screws; two on each side and one on the rear of the bot.
- Before you power your bot on, always power the transmitter on first and always have the weapon lock fitted. The weapon lock should be printed or spray painted afterwards in a highly visible color for safety.
Here's a video of a time lapse build of Shrapnel:
And here's a video of him in action:
Layer height: 0.2mm
Print speed: 40mm/s
Print material: ABS
Supports: Required for the rear of the top and bottom sections.
Designed using Sketchup.
I gave the whole chassis a coat of red spray paint, faded with some black. I used Tamiya hobby spray paint. What ever works for you really.
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Antweight Combat Spinner Bot - Shrapnel by Fryddog is licensed under the Creative Commons - Attribution license.
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