Combat Robotics Tutorial

Written by: gadgetguru

***DISCLAIMER: Some of this information could be better or is inaccurate.  Specifically how big of a battery you need.  I plan on making a new tutorial eventually, but for the most part this tutorial is accurate.***

Have you ever wanted to build a combat robot (battlebot), but gave up because you didn’t know where to start? Well, hopefully this tutorial/instructable will help. I condensed a lot of information down into a step by step process, taking out most of the stuff you really don’t need to know, but leaving the crucial information. This tutorial is focused on the insect weight robots (75grams to 6 pounds), because the majority of competitions held are for insect weight robots, and they are the least expensive.

Throughout this tutorial I will be putting a robot together for demonstration. I used wood for a material,and you shouldn't.  The reason why I used wood, was because I was just putting the robot together for this tutorial, and I am never going to compete with it.  In fact I already threw it away, because it was a mix-match of a bunch of different ways to do things.
 

Step 1: Weight Classes

Before you do anything else, you have to pick a weight class. The weight constraint helps determine which parts are needed.

Insect Weight class:
• 75g Fleaweight (not common)
• 150g Fairyweight (5.3oz)
• 1lb Antweight
• 1kg Kilobot (Canada Only)
• 3lb Beetleweight
• 6lb Mantisweight (not common)

I suggest building an antweight or a beetleweight as a first robot, because you don’t have to be as concerned about weight as with lighter robots. It is less expensive to build a antweight, but you will find it easier to stay under the 3 pound limit. Also, beetleweights are more common than antweights, but any competition that has beetleweights will have antweights, and vice-versa. So, it is really up to you, just pick a weight class and go with it, you can always build another robot for a different weight class.

Step 2: Weapons

 

 

The different types of weapons seem to be endless. There are two main categories: active weapons and passive weapons. Active weapons are any weapon that moves. Passive weapons basically turn the whole robot into a weapon, via a wedge, spear, or something of that sort. I have a bias towards active weapons, because the matches are more action packed, but robots with passive weapons are very successful due to their inherent strength.

Passive Weapons:

Wedge Robots:
  These robots use a wedge to flip the opponent over. They usually have very strong drive motors. To defend against wedges, make sure your robot can flip itself back over, or can drive upside down.

Spear Robots:
  These robots use a spear to pierce the opponent’s armor. They require very strong drive motors, and sometimes even that isn’t enough power to get through the armor. Spear robots are very uncommon in insect weight robots, because it is difficult to find motors powerful enough to make the robot able to pierce armor. To defend against spear robots, make sure you have strong armor.

Active Weapons:

Horizontal Spinners:
  These robots usually have a fast spinning and heavy bar that does a lot of damage. They also put a lot of strain on their own parts though. The best defense against these robots is to have strong armor and all of you electronics shock mounted (Velcro). This area of weapons includes but isn’t limited to:
• Horizontal Bar Spinners
• Full Body Spinners
• Undercutters

Vertical Spinners:
  The robots usually intend to flip the opponent over, and do damage with weapons that have “teeth” on them. The best defense against these is to either have armor that won’t get chipped apart, or will let little pieces come off at a time, not all at once. This area of weapons includes but isn’t limited to:
• Saws
• Drums
• Vertical Bar Spinners

Flippers/Hammers:
  Most of these robots use pneumatic cylinders to quickly move a flipper or hammer. Most of the time hammers aren’t very effective on insect weight robot, because it is hard to make one with enough force to pierce armor, and keep it under the weight limit. The best defense against a hammer is having durable armor. Flipping robots are effective against robots that can’t drive upside down. But with the exposed arms that are used for flipping, they aren’t very durable. The best defense against a flipping robot is being invertible. This area of weapons includes but isn’t limited to:
  • Hammers
  • Flippers
  • Motorized wedges

Rare Weapons

   • Fire breathing
      These robots usually aren’t very effective, unless their opponent has some parts made of wood. Also some events don’t allow fire breathing robots. The best defense against these robots is to make sure no electronics are exposed, but you will probably never face one of these robots in the insect weights.

    • Multibots
       These robots are more than one robot working as one. An example would be three 1 pound robots competing as a beetleweight robot. These robots are slightly more common than fire breathing robots.

No weapon is the best, if it is built strong; it is just as effective as any other weapon. Some weapons such as a full body spinner may seem unbeatable, but when the robot has to spin something that heavy that fast, it puts a lot of strain on all the components, causing things to break. Also certain weapons work better against certain types of robots.

To conclude for the best defenses: make sure your robot is invertible, has strong armor, no electronics exposed, and all the electronics are shock mounted.

One thing I learned with my first robot, Titan, is that you should use a bigger shaft size than you think. For example, on Titan I used 1/8” diameter shaft for the drum, but it snapped in 4 out of the 6 matches I had. That being said, generally these sizes will work:

-Fairyweight – 1/8”
-Antweight – at least 1/4”
-Beetleweight – at least 1/4", but 3/8” would be better.
 

Step 3: Design

This is step is just tips, because everyone designs in a different way.

Tip 1:
When designing a robot one important thing to keep in mind is weight.  I usually start to pick out parts, and make a chart with the weight. 

Tip 2:
Draw it in a CAD program.  This is probably on of the most important tips I can give.  Not only does it help you end up with a better robot, but it can save you money too.  When you draw it in a CAD program you can try out designs and different parts without ever buying any parts.  I usually go through 10-25 different designs until I get to the prototyping stage.  Then I refine it once or twice, and the robot is just the way I want it.

Tip 3:
Leave extra space.  Although all if you draw it out it may look like all the electronics will fit in one tiny area.  But, when it actually comes to putting it together it doesn't fit right.  Most of the time it is because there isn't enough room for all the wiring.  I am currently running into this problem with my antweight.

Tip 4:
Tell someone about it.  If you have a friend that is interested in this kind of stuff, talk to them about your design.  They might point out some key things that you overlooked.  I have found that working on a robot with someone else yields a much better end result. 

Tip 5:
Don't jump right into building the robot after you have designed it, unless you have a very short amount of time.  If you just think about the design for a few days you will usually come up with some improvements.  I usually draw about 5 times on paper (not to scale), changing a little every time, and then I draw it it Rhino (CAD program).

Step 4: Basic Parts

 

 

The basic parts that you need are:

• Drive Motors
• Wheels and Hubs
• Drive Speed Controller
• RC Radio / Receiver
• Batteries
• Power Switch / Link
• Weapon Motor (If Design Requires)
• Weapon Speed Controller(If Design Requires)
• Wire
• Connectors

All of these parts can be found at:
www.robotmarketplace.com

Suggested Parts:

Drive Motors:
• Fairy – 100:1 SRV Drive Motor (or similar)
• Ant – 100:1 SRV Drive Motor (or similar) or FingerTech Spark Series
• Beetle – FingerTech Spark Series or B Series Motor

FingerTech Silver Spark motors are great  motors and have plenty of power for an antweight.  Some builders use them in beeteweights with success too.

Wheels / Hubs:
• Fairy – Lite Flite Series Wheels w FingerTech Hub
• Ant – Lite Flite Series Wheels w/ FingerTech Hub
• Beetle – Lite Flite Series Wheels w/ FingerTech Hub or BaneBots Wheels/Hubs

Drive Speed Controller:
• Fairy – FingerTech tinyESCs
• Ant – FingerTech tinyESCs
• Beetle – FingerTech tinyESCs or BaneBots 3-9

When choosing you speed controller, choose your drive motor first, and then match it up with a speed controller that can handle the amps of the motor.

RC Radio/Receiver:

For combat robots the radio/receiver HAVE to have failsafes on all channels.  That means that if signal is lost, or the radio is turned off, then channels will turn off, and the throttle channel returns to its set position.

I suggest the Spektrum DX5e radio paired with the Spektrum AR500 Receiver, or if you need a lighter receiver go with the Spektrum AR6110e. I suggest these, because they have failsafes built in, making them legal for use in combat robotics. Also the DX5e and AR500 combo package is only $100. That gets you a radio and receiver with the best technology on the market. They have great range and virtually no interference. Also since it is 2.4GHz all you have to do is bind it once (very easy to do), and then you don’t have to deal with frequency crystals. Most of the 72MHz (radios that use frequency crystals) radios and receivers are more expensive than this too, making it almost a no-brainer. But, there is a GWS brand system available for around $80. Sure, you can go for the GWS system and save $20, but it won’t have as good of range, you will have to carry different frequency crystals for competition, and it won’t last as long. As far as I’m concerned the only way to go is the DX5e paired with either the AR500 or the AR6110e.

EDIT: spozman has brought this radio: HK-T6A and this receiver: HK-TR6Ato my attention.  They are sold by FingerTech and are legal for use in combat robotics.  They are also 2.4Ghz, but almost half the price as the DX5e and the AR500.  I can't vouch for how well they work, but they appear to be perfectly fine for a robot.  If you are on a budget, definitely go for this radio and receiver, but if you don't mind spending a bit more, then go for the DX5e and the AR500. 

Batteries:
For insect weight robots Lithium Polymer (LiPo) batteries are the most common. The reason is because they are so light. They may be a little pricey, but if you take good care of them they can last 5 – 20 years (depending on how and where they are stored). I won’t go in to all the details about charging and care for LiPo batteries, because there are many websites that can explain this better than me (just type “safely charging discharging and storing LiPo batteries” into a search engine). But I will say this: Don’t short them out, because they will swell, catch fire, or explode (none of which have ever happened to me). But don’t let that discourage you from using them, because if you just use some common sense the batteries will be fine.

When deciding how many Amp Hour you need for batteries add up the stall current of all of your motors, then divide the the Amp Hour value of the batteries by the total stall current.  If you multiply that number by 60 you will get how long the batteries will last in the worst case scenario (stalled motors) in minutes.  The batteries should be able to last at least 3 minutes.

*EDIT*: The above advice about battery size is bad advice. You will end up with a battery size that is much bigger than necessary. 


Power Switch:
• Fairy – Removable Link
• Ant – Removable Link
• Beetle – Wyachi MS05 or Removable Link (If you need to save weight)

Removable Link
• A very simple power switch that can be made by follow the steps in this video:

 

Wyachi MS05
• A bit expensive, but very effective switch. It takes 4 turns with and allen wrench to turn it on and off, making it unlikely to fail during combat. I suggest it over a removable link, because it is much more durable, and there is less of a chance of it shutting itself off during combat.


Weapon Motor:
I highly recommend brushless motors. I don’t have a specific motor to suggest, because almost all brushless motors are well built, and they come in so many different sizes that only you know what size you want for your robot. If I had to suggest a brand it would be E-Flite. The reason why brushless motors are better is because they don’t draw as many amps, they are much faster, and they don’t get nearly as hot. I had a brushed motor get so hot that it started to melt the plastic mount.


Weapon Speed Controller:
Once you pick a motor, most of the time there will be a recommended speed controller on the motor’s page. If there is not, you can look through the speed controllers on Robot Market Place if you know what specs you need, or you can leave a comment asking which speed controller to use, and I will be more than happy to answer it (usually within a day or less).


Wire:
When choosing wire go for Silicone wire of Deans Ultra Wire, because they are the most flexible, and can handle the most current for their gauge size. The wire is a little bit more expensive, but well worth it.
As a general rule for wire gauges:
- Beetleweight – 14 to 16 gauge
- Antweight – 16 to 20 gauge
- Fairy - >22 gauge


Connectors:
It’s good to use connectors for attaching electronics together, that way it is easier to swap parts if they break. I like Deans plugs, but any of these connectors will work (as long as they aren’t way to big): Connectors

Step 5: Materials

One major question is: What material should I use?  There are a lot of different materials that will work, you just have to decide what properties you must have (i.e. strength, weight), and what properties don't matter to you.

Properties:

Material Family - Plastic/Metal
Impact Strength - How much of an impact the material can handle.
Tensile Strength - How well the material can handle being pulled.
Flexibility - How flexible the material is. (Relative i.e. grabs material, twists it, yes it flexes)
Density - Density from Machinist -Materials 
Main use - Armor/Base-Plate/Etc.

Here is a list of commonly used materials:

UHMW (Ultra High Molecular Weight)

Material Family - Plastic
Impact Strength - High
Tensile Strength - Low-Medium
Flexibility - Medium-High (I wouldn't make a base-plate out of it)
Density - .034 lbs/in3
Main Use - Armor

This is a great material.  I use it for armor on all of my robots.  I wouldn't worry about the low tensile strength, because with its high impact strength and low weight it is the perfect armor for insect-weight robots.  Also, this material is very affordable.

Delrin

Material Family - Plastic
Impact Strength - Medium-High
Tensile Strength - High
Flexibility - Rigid
Density - .051 lbs/in3
Main Use - Baseplate/Armor

I am using this for a baseplate in my current robot, Slash.  It is very rigid, and is still fairly light.  Also it is affordable.

Polycarbonate

Material Family - Plastic
Impact Strength - High
Tensile Strength - High
Flexibility - Rigid
Density - .043 lbs/in3
Main Use - Baseplate/Armor

This is a good material for armor, but has a tendency to crack after big impacts.  Also it is quite a bit more expensive than Delrin and UHMW.
 

Aluminum

Material Family - Metal
Impact Strength - High
Tensile Strength - High
Flexibility - Rigid
Density - .101 lbs/in3
Main Use - Baseplate/Armor

I don't suggest using aluminum, because once it bends, it doesn't bend back.  The Base-Plate of Titan is proof of that.
 

Carbon Fiber

Material Family - Composite
Impact Strength - High
Tensile Strength - High
Flexibility - Rigid
Density - .0643 lbs/in3
Main Use - Baseplate/Armor

Don't use carbon fiber, or any composite for that matter.  Carbon fiber has great properties, until it breaks.  When a normal material breaks, usually just a little piece breaks off, but not for carbon fiber.  Since carbon fiber is made of woven strips of carbon fiber fabric, when it breaks it ones spot it starts to break all the way through.  In other words, with composites it's all or nothing.  They sound like the best thing ever, but with one little break all those awesome properties go away.

*EDIT: I have since changed my mind a little about carbon fiber.  It will work in lower weight classes (<1lb, 3lb is pushing it), but don't be surprised if it breaks after a big impact.  Personally I would sooner go for delrin, because it is just as rigid, and will stay together better in big impacts.  Also delrin is surprisingly lighter.  
 

Titanium

Material Family - Metal
Impact Strength - High
Tensile Strength - High
Flexibility - Rigid
Density - .16 lbs/in3
Main Use - Baseplate/Armor

Titanium is the perfect blend of strength and weight.  It does weigh more that twice what UHMW and Delrin weight, but it is worth it on some pieces.  Most of the time Titanium wouldn't be used for armor unless the robot is a wedge robot.  It is very useful for use in a weapon though.  It is what I am using on Slash.

 

I picked these materials because they are the most commonly used in insect-weight robots.  I left out some materials like steel, because they are rarely used, and when they are it is for the weapon.  If a material isn't listed here that doesn't mean that you shouldn't use it on a combat robot, it is probably just a material I forgot to mention or didn't know about.

Step 6: Motor Mounts

The easiest to make, and the best motor mounts in my opinion are clamp style. Basically it is a square block with a hole for the motor, and a notch to allow tightening.

This video gives the step by step process of making one:
 

 

Step 7: Base Plate

Most of the time insect weight robots don’t have a chassis, instead the armor is attached together, and the components are attached to the armor. You could consider the base plate to be the chassis, but it is also armor. Things to keep in mind when designing:

Placement of electronics-
  Make sure to have plenty of room, otherwise it will be difficult to repair between matches, and things are more likely to break if they are packed together.

Wheel Placement-
  Combat robots use “tank style” driving. This means that there are 2 to 4 wheels, and both sides operate independently allowing for a agile robot with a short turning radius. Also you have to protect your wheels, because they are the first target during a match. Exposed wheels are easy targets for a robot.

This video shows the step by step process of making a base plate:

 

Step 8: Armor Attachment

These are good way to attach armor pieces to each other and the base plate:
• “Angle-Iron” (available in plastic)
   -Works when the armor needs to be attached at a 90 degree angle. Screws or glue can be used to hold it in place.
• Glue
   -Just gluing everything together can work in insect weight classes. I don’t recommend using glue, because it isn’t very strong, and good robots will tear the armor off in seconds if it is held on only be glue.
• Hinges
   -Hinges are popular in attaching wedges to a robot, because it allows them to sit as close to the ground as possible.
• Milling entire robot out of one block of material
   -This way there are no joints; the problem with this is when part of it breaks the whole thing has to be replaced instead of one piece of armor. But this solves the problem of entire pieces of armor being torn off. This is usually very expensive, because it requires a lot of milling.

Video:

 

 

 

 

 

Step 9: Mounting and Powering a Weapon

The best way to mount a spinning weapon is to use bearings that are inside bearing blocks to support the shaft. I have found it difficult to find places to buy bearing blocks from. So, you will need to find bearings that will work for you shaft, and then make your own bearing blocks. It is difficult to make bearing blocks by hand, so it is best if you have them machined. The blocks should attach to the base plate by screws of bolts, providing a sturdy support for the weapon shaft.

A pulley should be attached to the shaft to power the weapon, because if the weapon is attached directly to the weapon motor, the shaft of the motor is likely to break. Replacing a weapon shaft is much cheaper than replacing a motor.

This video provides a step by step process of mounting a weapon:

 

 

 

 

 

Step 10: Mounting Electronics

For insect weight robots Velcro works the best for mounting electronics. This is suggested in the RioBotz tutorial, because it absorbs shock, and it makes it easy to remove the electronics. Some Velcro is very “flat”, and doesn’t move around much, this Velco won't work as well.

Duct tape will also work in little loops. But it needs to be switched every few matches, otherwise it will come loose.

 

 

 

Step 11: Wiring Your Robot

Haven’t given up on your robot yet? Congratulations, because it will soon be up and running and you will have that satisfaction of driving it and knowing that you finished. It’s hard to explain in writing how to wire the whole robot, so for some of the parts that apply in general I will explain it in words, but the video will include everything.

Here are the videos:

Part 1:

 

Part 2:

 

Part 3:

 

The receiver uses a 3 prong connector, one for positive (5v), on for ground, and one for data. The Sabertooth 5RC has cables that come off of it that will plug into the receiver. Make sure that the red wire matches up with the pins on the receiver that are label with a “+”. Most of the time the cable labeled “drive” should be plugged into the “ELEV” slot on the receiver. Also the cable labeled “turn” should be plugged into the slot labeled “AILE”. If you have a weapon, then that speed controller should be plugged into the “THRO” slot, so that you can control it with the throttle stick that stays in place on the radio.
If you have a weapon and a Sabertooth or RoboClaw speed controller, then the red wire MUST be removed from the plug on the weapon speed controller. The video contains instructions on how to do this. If you don’t remove the red wire, both the weapon speed controller and the drive speed controller will try to supply the receiver with 5 volts. This function on the speed controllers is called a BEC, or Battery Elimination Circuit, because there is no need for having another battery to power the receiver. The result if you don’t pull out the red wire is that one, or both, of the speed controllers with be fried (it has happened to me).
On most speed controllers there is a screw terminal label B+ and B-. The power wire should be put in the slot labeled B+, and the negative power wire should be put in the B- slot. For the motors, the wires don’t have to match with the labeling, as long as both wires on motor 1 go to motor 1+ and 1– on the speed controller, and vice versa for motor 2. The reason why “+ and –“ don’t matter, is because if it is backwards, the motor will just go in reverse instead of forwards when you try to drive forward. So, you have to try different arrangements until the motors behave correctly. For help on troubleshooting this, look at the video. The video also contains how to configure the DIP switch (the thing with a bunch of switches on it).

 

 

 

Step 12: Adding Weight

An easy way to add weight to get your robot closer to the weight limit is washers. They can be bolted on to the armor, making them easily removable. If you have a spinning weapon that is causing the robot to shake a lot, placing the weight by the weapon will help the robot not shake as much.

 

 

 

 

Step 13: Losing Weight

One way to lose weight is replacing the armor with armor that weighs less. This will work if you need to lose a lot of weight. But if you need to lose just a little weight, you can drill holes in the base plate. Another alternative is to get lighter parts.

 

 

 

Step 14: Rules

Most events use the RFL Tech Regs. These rules have parts that can be changed, meaning most events will be close to the same rules, but not the exact same rules. Such as the part that allows or doesn’t allow fire. Make sure to check the rules of the competition you are going to before registering.

Some things to make sure you have:

-Safety Pin
It must be capable of stopping your weapon. Usually it sticks through the weapon or is in a position that the weapon will hit and stop.  It is also supposed to be painted a bright color

-Blocks
You are supposed to put something under your robot at competition to prevent it from driving off by accident.

-Power Light
At competition you will need a light that comes on when your robot is powered on. How to make a power light is covered in the wiring section.
 

 

 

 

Step 15: Tips

1. Don’t Give Up!!!
  At times building a combat robot can be extremely frustrating, but if you just stick with it, you will be able to finish. Also when you are finished you can brag to all your friends about how awesome robot..

2. Draw it out
  I highly suggest getting drafting software for your computer. If you are a student, you can get Rhino for <$200. Trust me, it is worth every penny. It isn’t just useful for this project, but for just about any project. If you have it drawn out, it will be much easier to build.

3. Mock it up
  Make sure to mock up your robot with cardboard or wood before spending money on more expensive materials, just to realize that your design wasn’t quite what you wanted. One thing that I learned from building my beetleweight, Titan, is that you should draw every part out and mock every part up. The reason I say this is because the problems I ran into were with the parts that I didn’t draw out and mock up, I just had their design in my head, big mistake. I would have saved me a bunch of time to just draw it out and mock it up to work out all of the kinks first, instead of trying to make it work on the final design.

4. Don’t be afraid to ask questions
Leave your question as a comment on this instructable, or PM me if you don’t want others to know your plans. I will be more than happy to answer your question, and I will usually answer within a day.

5. Have Spares!
  You might think that your robot won’t break, but trust me, something will break. Often it is something you never thought of until it is broke and your robot can’t function without it. So before you pack up your stuff and travel halfway across the country make/buy some spares.
For my first competition I travelled 8 hours, and if I hadn’t decided to make some spare shafts with the leftover rod I had, I would have ran out of shafts. In fact, I had 4 shafts, and in my last match the fourth shaft broke. It may seem like a waste to buy a bunch of spare electronic, but you can always use them on another robot. It is also a good idea if you have more than one robot to try to make them share parts, so you have to carry as many spares.

6. Buy a Scale
  Accurate postal scales (<5lbs) are available for <$30. It will be very helpful in staying under the weight limit.

7. Practice Driving
  In Dave Calkins’ (founder of RoboGames) Guide to Winning, he stresses how important it is to practice driving. I couldn’t agree more. After I finished my robot, I laid out a track with a lot of sharp twists and turns and started driving. At first I couldn’t stay within the lines at all, but after about 2 hours I was able to zip through the course. I wish that I would have practiced more on a moving target, because I still had a little trouble driving at the competition. You have to remember, your competitor is trying to get in the perfect position to strike also, so you have to be able to quickly maneuver to attack, and prevent form being attacked.

8. Registration
  To register for an event go to Builders Database.

9. Take pictures and videos at the competition
  Be sure to get video of all your matches. It will be very helpful when redesigning, because you can go back and see exactly what happened. When I went to Mecha-Mayhem 2010, the one thing I wish I would have done more of is take pictures. Now that I look at all the matches on video, I wish that I had pictures of the damage to my robot (I repaired it between matches so the damage isn’t still there, except from the last match).
 

 

 

 

Step 16: Final Thoughts

I have learned a lot of what I know about combat robotics from the RioBotz Tutorial.  So, a big thanks to the people of RioBotz.  I highly recommend checking it out, because whenever I have a question about combat robots I grab the copy of the RioBotz Tutorial I printed out and look it up. 

Many people think that combat robots is a dying sport.  I don't think that it is true, because there is a lot of competitions in the US, and even a few in other countries.  It may not be focused on the heavyweight robots like it used to be, but insect weight robots are very popular.  In fact there are 10 plus events in the US for insect weight robots.
 

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