NOTE: This page will soon be retired in favour of a new PDF that is being written that will cover this in more detail.
So you want to build a fighting robot? Great! I highly encourage this! Of course, you do know how to build one?
Well, let me enlighten you. This guide will detail the procedure I used to build the robots for Team Kaizen and this guide will likely be revisited. The stuff here is merely a guide as per the Fighting Robot Association rules.
- Building your first robot
- Decide on a weight class
- Decide on a weapon
- Pencil + Paper = Design / CAD it
- The rules
- Prototype in cardboard
- Repeat the previous two steps until happy
- Buy components
- Sealed Lead Acid (SLA)
- Lithium Polymer (LiPo) and Lithium Phosphate (LiFePO4)
- Radio control
- Start building
Building your first robot
Decide on a weight class
This may sound weird but knowing what weight class you are going for is crucial as to what size of robot you are likely to have, what design and what materials are used. There are a number of weight classes available but the two most common ones are the Featherweights (1.5kg to 13.6kg) and Heavyweights - 55kg to 110kg.
If this is your first time building a robot, I would advise the Featherweight class. It is generally cheaper to build but no less complex, largely just coming down to scale.
Decide on a weapon
A weapon is something practically every robot has but it isn't actually a requirement. The very basic designs are rambots that use spikes to jab the opponents with and if you are a first timer, it will be worth sticking with static weaponry to learn with. Progressing on, you get into axes, flippers and lifter weaponry. These are generally powered by either pneumatics or by a mechanical mechanism, like a linear actuator. You can then also go into saws and the like.
Spinners deserve their own mention. Like saws, they are powered by a motor which spin either a disc, drum or an arm up to a high speed and crash into the opponent, causing frankly insane amount of damage. However, whilst they are very effective, they are also dangerous - ALL WEAPONS ARE DANGEROUS
but the potential energy in them make these very dangerous. So much so that live events more often than not, do not allow spinners in thr arena. Consult with the event organisers if you do want to bring a spinner but in our experience, spinners are not allowed at Robots Live! and only in a limited fashion at Extreme Robots.
If you really needed a reason as to why spinners are banned/extremely limited at live events, watch Robots Wars Series 10 Episode 3 Track-tion vs Apex and then wonder why.
Pencil + Paper = Design / CAD it
Take some time at this stage. Now you know what weight limit your robot is going to be, you can spend a bit of time designing your robot. Take a look at other robots in the weight class and note down any technical specifications they have. Watch any episodes of Robot Wars and Battlebots you can find and take some inspiration from them (note that Battlebots have a different rule set to the UK scene) and then begin sketching. I would highly advise staying with what you (or your team members) can build as building something you can't work with is going to be a pain later on.
If you are suitably savvy with using CAD software, you can also use this, it will help inform where fixings should go. If you are building your robot with HARDOX or similar, a cutting service (like K-Cut) will accept a CAD drawing as the basis to cut the pieces out of, though do speak to them first before committing.
UK robotics competitions are generally covered by the Fighting Robotics Association. They have a set of rules which should be followed at all times
, which can be found here
Prototype in cardboard
Next step is getting some thick cardboard and then making a to 1:1 scale prototype so that you know how big it will be and wherever you can actually build it. It doesn't have to be very pretty but just accurate enough to inform you as to the dimensions of the parts you need to build.
Repeat the previous two steps until happy
This may look weird but seriously, sleep on the design and then look at it in the morning. Consult the FRA rules to see if the mandatory items can easily be added. You don't want to compromise the design to accommodate the removable link or power lights for example. You also need to make sure that you can build what you've designed!
This is where it can get expensive, especially if you don't know what to get. In short, you would be looking for the following:
Depending on the theme of your robot, you can either go low tech and bolt on armour from pretty much anything (I've known a microwave or two to be entered into a live event!) or high(er) tech using new pieces. For Featherweights, the choice does seem to be either Nylon or HDPE as the basis of the robot.
This can be a minefield so tread carefully. In the original run of Robot Wars
, it was typical for robots to use SLA (Sealed Lead Acid) batteries. However, technology has moved on a pace and now we have the oh-so-fashionable Lithium Polymer (or LiPos) batteries. This guide won't touch on NiCD batteries.
Sealed Lead Acid (SLA)
As alluded to, robot combat rarely features SLA batteries, even more so in the Featherweight division because for the amount of power they provide versus the amount of weight they are, SLAs are a bad tradeoff. However, The Honey Badger 1.0
does use a set of SLAs because they are simple to charge up and are subject to less rules than LiPos are. The trade-off is they weigh more than a equivalent LiPo and give out less power. The Honey Badger 1.0
uses 2x 1.2ah SLA batteries and a 2.1ah SLA battery for the weapon.
Lithium Polymer (LiPo) and Lithium Phosphate (LiFePO4)
Nearly all robots these days use a Lithium battery in some form or another. Lithium batteries are more powerful than SLAs for the same size but do come with their own caveats. As of September 2017, the rules around LiPo batteries include the following:
Lithium Polymer batteries have specific limitations and extra precautions which must be adhered to.
LiPo batteries MUST be balance charged to prevent damage occurring to the cells. Chargers that do not
incorporate an integrated balancing circuitry are not permitted.
7.8.2 Voltage Cut-out (Advisory)
The robot may be fitted with an under voltage cut-out or alarm set at or higher than the battery
manufacturer’s recommendation to prevent the batteries from becoming damaged by over-discharge.
A fuse rated below the maximum burst discharge of the battery MUST be fitted. The maximum burst
discharge current is calculated by multiplying the C rating by the capacity. E.g. 25C 2200mAh = 55 Amp
7.8.4 Extra Equipment
Roboteers using LiPo batteries must provide a LiPo sack.
LiPo batteries must be removed from the robot, inspected and placed into a LiPo sack prior to and during
the charging process.
Lithium batteries must not be left unattended at any time during the charging process. Leaving batteries
unattended while charging will be considered a serious breach of pit safety and may result in you and
your robot being removed from the event. Event organisers may provide a dedicated area for charging.
LiPo batteries showing any evidence of damage or swelling must immediately be placed a LiPo sack and
removed to a safe, well-ventilated area such as outdoors. Note that LiPo fires occur rapidly and there is
a serious risk of personal injury. Use extreme care when handling any battery that shows signs of
As for LiFePO4 batteries, these don't appear to be subject to the same rules as LiPO batteries as the chemistry is inherently safer but we do recommend following the rules for LiPo batteries as a matter of safety. The Honey Badger 2.0 uses a pair of LiFEPO4 batteries ran in series to up the voltage.
Robot combat can be expensive but it doesn't have to be. If you are starting from the very beginning, you could conceivably spend a few hundred pounds on a Featherweight. The Honey Badger 2.0
would cost roughly £350 just to get it into a running state without any weaponry. You could conceivably make it cheaper, it comes down to how much you want out of your robot. Spending mega amounts of money does not present an advantage in combat.
This guide will only cover electric motors, petrol drive robots do exists but electric motors are simpler to get running and less... flammable.
For Featherweight robots, drill motors are a good choice though do keep the gearbox on. A early attempt of The Honey Badger 1.0 used 12v drill motors that didn't use a gearbox per motor which was fine when it didn't have much on but as soon as weight was added in terms of weaponry and the shell, it drained the batteries too quick and didn't have any pushing power at all. The gearbox that drill motors have is called a planetary (or epicyclic) gearbox and often, they come attached with the motor (such as the Gimson 13.7:1 12v motor). These would be my recommendation for a beginner as these are compact units that work extremely well.
Alternatively, you can opt to make a reduction drive using sprockets and chains but this can be a bit fiddly.
Most controllers are now 2.4GHz and we recommend sticking with that. If your robot is a basic rambot type affair, then getting a simple 2-channel controller is going to be enough but we recommend getting at least a 5 as that allows for expansion to have a active weapon later on. What is important is that the controller can preform mixing (where two channels are activated at the same time) - some controller do support "elevon" mixing. This would enable both sides of the robot to be driven from the one control.
The Honey Badger managed to side step this with a controller that has sprung, tank controls on both sides of the controller however this does make control a little fiddly. You can also get a secondary mixer which does this for you as well (this plugs into the two channels on the RC receiver and into the two speed controllers).
OK, so you know what you are building, go build it! This is easily the most time consuming step as you might imagine, so I find it easier to build to a bullet point list and then cross them off once achieved. Spend a little bit of time doing this list because getting it wrong can mean wasted time and money. Such a list may look like this (taken from the The Honey Badger
rebuild in August, correct at the time of writing):
- Buy HDPE plastic sheeting
- Get second drive motor
- Get new speed controllers
- Get replacement wheels
- Affix battery/speed controllers/motors on the chassis board
- Assemble top and rear parts of the shell
- Measure and cut side panels
- Assemble side panels onto the top and rear panels
- Drill motor shaft holes into the side panels
- Smooth out wrinkles in the shell (smooth front of the wedge)
- Drill holes in bar for the weapon motor hub
- Drill holes in front wedge for weapon motor
What tools you need depend on what materials you are working with. HDPE requires only basic woodworking tools though a Dremel can be used as well, noting that if you do use a high speed tool like this, it can make the HDPE melt and become snow, which can be hot, so appropriate clothing is needed.
Written by Ocracoke - 4