This Guide is currently in progress! - 13/12/2012
A guide for building Successful Antweights
This is not meant to be comprehensive guide on how to do everything this is just meant to be an overview of what you need to get started and some discussion on design.
Safety
Combat robots are dangerous that is one of the reasons why putting them in an arena and watching them destroy each other is fun. This means that they are also capable of destroying you. Despite this building robot can be done in a safe manner if you think about what you are doing and take a few precautions. All the weapons you can build basically rely on the transfer of large amounts of energy into the other robot whether by spinning, flipping, launching, ect. So simply don't test these sorts of weapons in situations where you are not adequately protected. Do it in an arena or equivalent area with safety measures in place to ensure you don't get hurt! Antweights are only small robots, but they are to be treated with the utmost respect as they can be highly dangerous (You don't play tennis with a grenade do you?).There is many other things which I haven't covered here but if you have any doubts before doing something don't do it.
I take no responsibility for any injury sustained by building anything shown in this guide. If you don't have the skills, tools or patience to do it properly and safely STOP NOW
Rules
Most events now use the standard RFL rules set. Jump to the Rules Section and have a read before you go much further.Just quickly before you ask. "Why can't I build an EMP or use radio jammer or use a gun on the robot?" Have a think about what would happen...
With an EMP you would put the two robots in the arena one would set off EMP... other robot would sit still. Not going to be the most interesting thing to watch. There is a reason why there is restrictions on the weapons. Whether it is for safety, to keep things interesting or just prevent undue damage to the arena. The rules have been refined over 10 years so they are pretty well thought out. So just ask yourself why before complaining about the restrictions.
The Design
When it comes to building your robot, you should always have some form of design planned before you start physically building. This helps save possible heart ache, costs and time when you get half way through and realize X part of the design just won't fit or won't work as expected. Below we will go through two common designs of antweight robots and explain what thought process and design ideas went into each robot. This will hopefully give you an insight into what you will need to look at when designing and building your own antweight robot.Design - Wedge
Robot - FLS aka Face Like a Shovel
Video - FLS vs Slash at Robowars Nationals 2012 Ipswich∞
The Plan
FLS is a 150g antweight that was thrown together for a 2011 event. Since then it's had parts swapped out, tweaked and fine tuned and has gone from a rookie to winning several events including the 2012 nationals. The idea for FLS was to create a super reliable and fast wedge which could fend off the big spinners and push people into the arena's pit.
Here's the pile of parts (POP) that went into FLS along with costs (no shipping).
1: Two cell (2S) 180mah Lithium Polymer Battery Pack∞ - $4
2: 3 Channel Hobbyking Receiver∞ - $5 / Comes with Radio
3: BotBitz GM12 50:1 LV Gearmotors x 2 (30:1's shown in photo)∞ - $20
4: Lite Flite Wheels 2" Dia x 2∞ $5
5: BotBitz 10AMP ESC x 2∞ - $24
6: 5mm thick strip of UHMW Plastic - Free!
7: Paint Scraper Blade - $1
8: Servo Mounting Screws∞ - $2
Not shown: GTX3 Radio Transmitter∞ - $35
Not shown: Botbitz ANTswitch∞ - $7
Total Cost (sans shipping): $98
Drive
FLS runs two 50:1 botbitz LV gearmotors. These have proven extremely powerful and provide the large 50mm diameter wheels with lots of pushing power and huge speed. It's important to note that all botbitz LV motors shouldn't be run on more than 2S lipo (7.4v) or they will burn up.
The drive motors in FLS are secured to the robot using a small piece of 0.5mm thick carbon fibre. The motors attach using their faceplate and two 1.6mm screws. This plate is screwed to the robots plastic sides using servo mounting screws.
The wheels on FLS use hubs from much cheaper, lower grip foam wheels from hobbyking with the lite flite wheels. These hubs have been carefully drilled with a 3mm drill bit and pressed onto the gearmotor shafts. With a tiny dab of superglue these have never come off in battle however removing them is quite a challenge!
Weapon
FLS uses drive power and its bent paint scraper blade to control other robots and deflect spinning weapons. Scraper blades make perfect armour; they are extremely tough and hard to bend. To drill them, a centerdrill is recommended using a drill press on low speed. Bending scraper blades is tricky, as they will crack if bent cold. FLS' blade was bent to shape using a vice and a blowtorch to help soften the bend area.
Electronics
Originally FLS had hacked servos for drive motors, which was terrible and it barely moved. Using the botbitz 10A escs it is very controllable and reliable. The pistol style radio is a personal preference, some may prefer a stick radio such as the popular T6A∞.
To reduce the weight of the robot, the receiver was removed from its casing and wrapped in kapton tape. It's very important you make sure nothing can short out on the electronics! Sharp edges can break through kapton tape so be very careful. This is a sure way to release magic smoke from your robot and for it to stop working.
FLS also uses a botbitz ANTswitch∞ which allows easy, fast and reliable switching of power when it's time to go into the arena.
ADVANCED: The pistol radio used with FLS has been modified using custom firmware to allow tank mixing and advanced settings, competent electronics knowledge is required. The hacking guide can be found here: OverkillRC GT3B Firmware Hacking Guide∞
Battery
Any small two cell lipo pack will do. FLS uses less than 100mah of charge per 3minute fight.
If you're just starting out, a great low cost charger is the TG-3∞ balance charger, which can plug directly into the wall socket. Make sure you buy a battery pack with a balance lead if you intend to use this charger.
Armour/Chassis
The main chassis of FLS is constructed from UHMW plastic. This plastic doesn't crack and is extremely tough but a little tricky to find. If you're located in Australia, your local CBC∞ store may have small offcuts at their counter and this is where I source my plastic for next to nothing (but be prepared to be ripped off if you intend to buy it from stock). HDPE plastic is also great for robots and sometimes easier to find. A substitute material is chopping board but make sure the plastic is PE and not PP, with the latter being very fragile and prone to cracking. 0.5mm thick aluminium sheet is used to cover the top and back, with servo mounting screws securing the whole machine together.
And the clear thing out the back? That's polycarbonate coreflute plastic often used for greenhouse and porch roofing. It's proven superior in its ability to keep spinning weapons away from the robot's frame and wheels and weighs almost nothing.
Design - Spinner
Robot - Scarlet
The Plan
Scarlet was build to be an all round performing robot with out sacrificing in any one area. The weapon system is powerful enough to inflict good levels of damage on the opponent, but is only 1/3rd the robots total weight. The drive is powerful enough to make Scarlet fast enough to chase and evade opponents, but isn't over the top. The chassis and armor are strong enough to survive even the biggest of spinners, but still light enough to not compromise the rest of the robot.
Having built a few other spinners in the past, the main goal was to make Scarlet drivable. It's no good having a big weapon if you cannot hit your opponent or spend most of the fight going in circles. With Scarlet, weight balance and placement of the wheels and weapon were tweaked to make the robot controllable.
Drive
Scarlet utilises a pair of BotBitz HV 50:1 gear motors, these were chosen since they can handle 3S lipol batteries without burning out and they are not too fast, allowing the robot to be driven easier. Fitted to the gear motors are a pair of Lite Flight 36mm foam wheels on BotBitz PolyHubs, these foam wheels have a lot of traction and are soft enough that they provide good levels of shock absorption on the drive train (preventing them from breaking, something that happened in previous robots.) A further modification was pinning the hubs to the gear motor shafts using a diode leg (1mm piece of wire). This prevented the issues of wheels coming off during fights due to the when the grub screw no longer gripped firming on the motor shaft.
Weapon
Scarlet runs a 110mm single tooth, counter balanced 28g titanium disc, powered by Turnigy 2205-14T brushless motor which is controlled by a Turnigy Plush10 BESC. This weapon system I had previously used on other antweight spinners, but I added some valuable modifications. Previous setups I had run a spinning bar instead of a disc (including a counter balanced 1 sided bar!), the problems with the bars was during impact, due to distribution of weight, load and axial forces, it would generally destroy the motor, the bearings or even the weapon bar itself. Moving to a disc design seems to negate most of these issues. The weapon motor also had the factory shaft replaced with a M3 12.9 grade bolt with a nyloc nut. This helps fix the issues of the weapon motor coming apart under impact and it also allowed a basic clutch system to work between the motor and the disc, which reduces some of the impact into the motor.
Electronics
Scarlet uses a Pololu B328 board with custom firmware loaded onto it to make it function as an ESC. The B328 was selected due to it's compact package and the ability for customisation. Connected to the B328 is a modified AR6110B reciever, which is a Spektrum DSM2 compatible reciever, one of the lightest units available (1.5g when modified). Scarlet also uses a BotBitz AntSwitch, which is a simple main power switch that allows the robot to be turned on and off quickly and safely.
Battery
The battery uses in Scarlet is a custom built 3S 11.1v battery, using 3x Turnigy NanoTech 180mAh 25C lithium polymer cells. These are stripped of their factory connectors, modified and assembled into a single pack with a JST connector. These cells were chosen for their light weight and compact format, but most importantly, their ability to provide the required current and capacity for an antweight spinner.
Armour/Chassis
The armor and chassis on Scarlet is fairly tough for a spinner design (where most people drop armor in favor of bigger weapons), it uses a 3 piece design, using 1mm carbon fiber for a base, a HDPE chassis which was CNC'd from a solid block down to the required design with 3mm wall thicknesses and a final top cover which is 0.7mm polycarbonate. The 3mm wall thickness of the HDPE chassis makes it extremely resistant to spinners yet the design of the chassis only makes it weight 20g.
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