Introduction: Phoenix - 30 Lb Combat Robot

Picture of Phoenix - 30 Lb Combat Robot

I've been involved in robot combat (BattleBots) for the past three years now. My first robot Shish-Kabot was extremely successful with one 2nd place and two 3rd place finishes but it had one weakness. Every time it fought a flipper robot called Upheaval, it would get tossed around and lose via knockout. (see 2nd image) After spending way too much time thinking about how to beat Upheaval with Shish-Kabot I decided to build a better flipper bot...

Step 1: Background

I guess I should probably explain a few things about what I'm talking about.

Robot Combat is an sport often referred to as BattleBots, but that term is trademarked so I'm probably not supposed to say it. But the basic idea is two robots fight to the death in an enclosed bullet proof glass box for 3 minutes or until one can't move anymore, when a knockout is declared. There are basically three groups all robots can be categorized into. Spinners are probably the most prevalent. They have some spinning mass (think exposed lawnmower blade) and try to slice or blunt force the other robot into submission. Pushy bots are the simplest to build. They often have a wedge to get under the opponent. They win by dominating the flow of the fight. The third group is flippers or lifters. They are designed to get under the other robot and flip them over or chuck them across the arena and hope something breaks on impact. This is often done using pneumatic rams. Flippers are not very common anymore because the introduction of cheap imported Chinese brushless motors and the difficulties associated with pneumatics.

The design goals/constraints for Phoenix were

1. Powerful flipper weapon

2. Entertaining

3. Cost must be under $700 (I'm a high school student without a high paying job)

4. Must be under 30lb weight limit

Step 2: The Flipper

Picture of The Flipper

I design robots a little differently than most people. Many people start by making a CAD drawing or a cardboard mockup. I simply lay out the parts on the floor and begin arranging them until I find a layout that works, and design from there.

The arm is .25" thick 7075 grade aluminum with an adjustable .125" titanium spatula on the front to get under opposing robots.

The pneumatic system in Phoenix is a very simple. It's single direction flow with a bleed hole to retract the ram after its shot. It uses a modified 16oz paintball tank, and the solenoid valve is a Burkett 5404. The valve is actuated by a RC relay switch. The ram is 2.5" bore 4" stroke.

Step 3: Frame/Drivetrain

Picture of Frame/Drivetrain
Now that I had the flipper weapon designed I could work on the frame for the robot.

I first made part of the frame that would hold everything. My material of choice is the 1/2"X1/2" box steel they sell at Home Depot. After welding the basic shape I once again test fit the components and worked on re-arranging them to make everything fit.

The drivetrain for Phoenix, as described earlier was two Harbor Freight 18 volt drill motors with 4" wheels,'s hubs/motor mounts and one drill battery to power it. I decided on this drivetrain because it offered both adequate speed and power for the robot and was cheap. The speed controller I used was a Sabertooth 2X25 that I had won at a previous competition.

I then did a test assembly of the robot and then test drive...

Which reviled a major design oversight on my part. There was no weight on the drive wheels which made the robot almost impossible to drive. I needed to change that... with more steel....

I ended up welding 4lbs of steel to the front of the frame to help counteract the weight distribution  issues. The added bonus was now it had 1/8" thick steel armor on the front.

Step 4: Armor/Assembly/More Testing

Picture of Armor/Assembly/More Testing
Between the weight of the frame, pneumatics, drivetrain and front armor/ballast. I didn't have much weight for the armor. I needed something light and strong... like... titanium. Titanium is really expensive and would have blown my budget, but I got really lucky because another robot builder was cleaning out his shop and had some old titanium armor from his 120lb bot that was too damaged for him to use but was still usable for a smaller robot like Phoenix.

In order to mount the armor I needed to make the frame grow...

I increased the width of the frame so that it could support the armor protect the wheels. There are three parts to Phoenix's armor. The steel plate welded on the front and the two 1/16" titanium body panels which are removable to allow access to the internals to recharge the batteries, refill the Co2 tank and so I can repair any damage from combat.

Phoenix only has 29 screws in it which makes it very easy to assemble and disassemble it, which is critical to success in robot combat competitions. But because of that ease of assembly I don't have any pictures of it partially assembled... so use your imagination.

After assembling it, I needed to do some testing, mostly of the pneumatics because I needed to find the optimum hole size for the bleed hole but also because there's something fun about launching heavy objects with a robot. I tried three different sizes; loose fitting, 1/16" and 1/32". The 1/16" worked the best because it brought the ram back down in a reasonable amount of time.

Here's a video of the 1/32" bleed hole test.

Through testing I discovered that I got about 12 flips before Phoenix runs out of gas.

Step 5: Phoenix in Combat

Picture of Phoenix in Combat
Weight: 28lbs
Speed: 10mph
Weapon: Flipper (generates 2700lbs of force and gets about 12 flips before it runs out)
Armor: 1/8" steel and 1/16" titanium
Rank: 2nd
Cost: Around $800 spent, parts probably valued at around $1500

Phoenix is currently (as of 5/17/2012) the 2nd ranked 30lb bot in the US and Canada. Its got a fight record of 7/3 with all but one of its fights ending in a knockout.  Its also finished in 2nd and 3rd in the two events its fought in.

Here's a compilation/highlight video of its best moments.


Step 6: More Information

For info about competing check out

The Builders Database This is the place where you can find out about and register for competitions

North East Robotics Club The premier robot combat event host in the North East

Combots/Robogames The largest events on the West Coast. They run weight classes from 1lb all the way up to 220lbs.

For a more complete and detailed build report of another 30lb combat robot (that beat Phoenix) check out Nyx

For parts check out

The Robot Market Place  They sell everything and anything related to robots for competitive 3-12lb kits and parts for robots up to 30lbs

FingerTech Robotics for 1-3lb robot parts and an awesome 1lb bot kit.

Holmes Hobbies for excellent 30lb robot speed controllers and other motors

HobbyKing for cheap stuff from China


soderhjelm (author)2014-01-13

Hello, im building a project with a drill motor thou 230 v. Is it easy to configure to get it forward and backwards? Is it the sabertooth that u have connected it with to get the respons to get it to move like u wont?

Sorry for the bad english
Best regards

derekiswise (author)soderhjelm2015-11-12

I know you asked a while ago, but the Saber tooth Will make it easy to drive in both directions. If you go read the information page, it specifies this information. It also states that it has a 50a peak current, with a 25A constant current. It can control 2 brushed motors at once.

bcdowney (author)2013-11-19

How did you prevent the liquid CO2 from leaving the tank and entering your system? Also that valve does not seem to be rated to 800 psi, but you say you are using an unregulated tank?

AlexHrn (author)bcdowney2013-11-19

The valve is rated for somewhere around 600psi. People in the UK had been running 1000+ psi through the 5404 for years before I built Phoenix.

To keep liquid CO2 in the tank, i removed the dip tube and angled the tank.

bcdowney (author)AlexHrn2013-11-19

Interesting. Thanks for answering! I am always wary of going over spec on any component, but if it works it works!

Have you had any trouble with liquid CO2 entering the system when it gets flipped over? Also, I am a little confused about how you bleed the system. Do you use an actuated valve or is it actually just a hole?

Sorry for all the questions. I am currently working on a 15lb flipper and I am having trouble getting a pneumatic design that can fit in it. I have worked with pneumatics before but never with a weight constraint like this. I am kind of hoping it can be done with just a single solenoid 2-way valve. (besides the necessary manual valves ).

AlexHrn (author)bcdowney2013-11-19

I bleed after a flip with a lose fitting.

I haven't had any blowout issues when the bot is upside down.

Personally I would not do a pneumatic flipper in the 15lb class because the weight of just the valves would be around 4lbs and the weight penalty of carrying CO2 on the robot. Phoenix's pneumatics weigh around 10-12 lbs.

bcdowney (author)AlexHrn2013-11-19

I have seen it been done pretty well in small weight classes. There is even a 3lb CO2 flipper called Flange that you can look up on youtube. I thought if you could do it in the beetle class you should be able to pull it off in the BotIQ class lol. We shall see how that works out for me.

Thanks for answering my questions! Also amazing bot you have there. Have any plans to bring it to more competitions?

AlexHrn (author)bcdowney2013-11-19

I've never seen a good flipper unregulated flipper smaller than 30lbs. Good luck.

Phoenix fought at FI 2013 (and took 3rd) and is registered for Motorama 2014 in February. At FI I broke the frame. I'm not sure if I'm going to rebuild with a better frame design or re weld it back together and save money.

TedRobotBuilder (author)2013-11-19

"But because of that ease of assembly I don't have any pictures of it partially assembled... so use your imagination."


Did you draw up any plans or just improvise as you built? O.o

AlexHrn (author)TedRobotBuilder2013-11-19

At the time I did not really use any CAD software, I laid out the parts, and made cardboard mockups.

mildlyimpolite (author)2013-04-30

Do you have a link for the ram that you used?

AlexHrn (author)mildlyimpolite2013-04-30

no because i bought it used and have no idea where it was originally purchased from. it is a nfpa large footprint hydraulic ram like

the one i use on phoenix is 2 1/2" bore 4" stroke

kelvinwolf (author)2013-03-08

Pretty cool did you win?

AlexHrn (author)kelvinwolf2013-03-08

Phoenix hasn't fought since February 2012 but it took 3rd at Motorama that year.

oldmechanic (author)2012-07-09

I've got an idea for an upgrade for you! You said it weighs 28 lbs, and the limit is 30lbs. Why not put in another gaz canister to increase the number of flips?

And I have one last question. Is the robot you mentioned(Nyx) called near chaos? And is it traversable?

AlexHrn (author)oldmechanic2012-07-10

"Why not put in another gaz canister to increase the number of flips?"

Phoenix doesn't have enough room inside it to put in a tank of a usable size. I also ended up using the weight to make some modifications to increase the durability of the frame and keep it from getting stuck on its side. I'll probably add a bit of info to this instructable about the modifications.

"Is the robot you mentioned(Nyx) called near chaos? And is it traversable?"

The other robot mentioned at the end of this instructable is called "Nyx" it was created by the team Near Chaos Robotics.

oldmechanic (author)AlexHrn2012-07-13


oldmechanic (author)2012-06-25

This is epic. why not create a youtube channel for it. By the way, can you maybye put in pictures of your last battlebots on?

AlexHrn (author)oldmechanic2012-06-25

I have a youtube channel.

You can find all of Phoenix's fights on youtube by searching for "Phoenix" "Motorama" "Nerc"

Also you can read about my other bots on my blog which is linked somewhere near the top of the page.

oldmechanic (author)AlexHrn2012-07-03

Thanks! I really mean, thanks! even though i live in the uk, i can still have access to all the materials you used!

tomtortoise (author)2012-06-17

Hey, im working on a tank drive robot (non combat) and have the whole thing built but my only problem is that the wheels are horribly attached to the motors which happen to be the same exact motors your using, I was just wondering if you could go into a little more detain on how you attached your wheels, thanks.

Also quick tip, Amazon carries almost every type of structural metal, all the aluminum I got for my robot was less then half the price at Home Depot, you also get free shipping on almost all of it.

AlexHrn (author)tomtortoise2012-06-18

Thanks for the info about Amazon.

I use's drillmotor hubs and colson wheels.The wheels press fit onto the hubs which screw right onto the output shaft of the drill gearbox.

RoboTable (author)2012-05-27

How much PSI are you using?

AlexHrn (author)RoboTable2012-05-28

I run unregulated CO2 in Phoenix. Since CO2's pressure is dependent on temperature it runs anywhere from 600-900 psi but it is typically around 850.

RoboTable (author)AlexHrn2012-05-28

Do you know of a good rule of thumb to figure out how much PSI you need for any given weight class?

AlexHrn (author)RoboTable2012-05-29

No, not at all. The big thing about flippers that is often ignored or not given enough thought to is arm geometry (Phoenix's arm isn't very efficient at transferring the 2700lbs of force to a flip) and flips about the same height as Upheaval which uses much less force but uses it more efficiently. Upheaval runs at around 180psi with the same sized ram and gets a higher flip.

RoboTable (author)AlexHrn2012-05-29

I already understood that different configurations used different amounts of PSI. But now that I know that even a 30 pound robot can use only 200 PSI to have good flipping power I then think 300 PSI could be plenty for a beetle weight robot (3 pounds for those who don't know).

AlexHrn (author)RoboTable2012-05-30

I'm not following...
Force= Pressure * ((1/2 Bore)^2 x Pi)

a 1" bore ram generates ~78.5 lbs of force at 100 psi
a 2" bore ram generates ~ 78.5 lbs of force at 25 psi.

You can run whatever pressure you want if your ram is large enough to achieve the force necessary to launch the other robot.

There aren't any pneumatic bots below 12lbs. The available necessary components are too heavy to make it work.


"I then think 300 PSI could be plenty for a beetle weight robot"

Were did that totally arbitrary number come from? Most pneumatic components are rated for 200(ish) psi maximum.

RoboTable (author)AlexHrn2012-05-30

I understand that there are not many robots with pneumatic robots under twelve pounds. I said 300 PSI because I'm making a 'homebrew' pneumatic with PVC piping rated for 400 PSI. Thanks for claryifing about the bore ram.

AlexHrn (author)RoboTable2012-05-30

OK... but assuming you are using an pneumatic cylinder like these, not a hydraulic ram for the your actuator, it can still only see 200-250psi and you'll need a regulator to drop your 400psi down to a usable pressure. _______________________________________________________________ Do not mess with pneumatics unless you know what you are doing and or have prior experience working with them or have help/input from someone who does know what they are doing. (and just because you've read this does not make you an expert)

Do not exceed manufacturer recommended pressure ratings on pneumatic components. 

Always be careful when testing pneumatics and take proper safety precautions such as testing with the robot behind a lexan shield and everything in the robot secured.

RoboTable (author)AlexHrn2012-05-30


megaduty (author)2012-05-20

That's a great flipper!

crandolp (author)2012-05-18

I've been working on a flipper myself and the only part I havent been able to track down is the paintball tank cap to NPT fitting. Got any suggestions?

AlexHrn (author)crandolp2012-05-18

Take the flow restrictor off the bottle the bottle. It should have a 9/16" NPT thread.

Now if you do that keep in mind you won't have anything to hold back the Co2 so you will have to add a ball valve or something to regulate the flow.

About This Instructable




Bio: robots, machining, vintage mopeds, and other silly things....
More by AlexHrn:Robo-Rooter- 3lb Combat RobotHacking Drills- Cheap/Powerful Gearmotors for Robotic ApplicationsPhoenix - 30 lb Combat Robot
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