60kg Beater/drum bot

Hey guys,

So it turns out that combat robot competitions have slowly been growing in popularity here in India at the collegiate level. And one of the biggest events they have is robowars at IIT Mumbai in January.
www.techfest.org/robowars

The weight class for event is 60 kgs(132lbs) and the budget alloted by our college is low.

This is our design so far:


The frame is to be welded out of 3/4'' square tubing(1/8'' wall)

The beater is about 20kg (44pounds) made from 4'' thick mild steel, with a 14'' effective OD

For weapon motors we have 2Turnigy L3040A-480G Brushless Motors running at 24v using cheap birdie ESC's

THe motor:weapon V-belt ratio is 1:3

We understand this maybe underpowered for the weapon, but it should be able to get the job done seeing how the level of competition here is lacking compared to what is there back in the USA(mostly because the sport is just getting started here.) Videos from the Past few years competitions(Youtube)


The drive motors and batteries, were taken from 4 cheap branded drills:

The battery packs are 12v, 1.5ah NiCad packs. Plan to use 2 for drive, 2 for weapon.

The motors Were RS-550 motors with 36:1 gearboxes. These will be driving 4'' diameter wheels
-The RS-550 motors as seen online have a nominal voltage of 12V-14.4V, but we hope to run at 24V, so if
anyone has any experience with that, please let me know.

Any comments, suggestions, and criticism's would be appreciated.

Love the beater provided it spins up thats going to hit really hard.

That's really awesome CAD work.

What are you going to use for armor?

first off... sweet rendering


you need more drivetrain. cheap drill motors are not enough for a 132 lb robot. they aren't even enough for a 60lb robot

the plastic casings will crack and the carrier pins will shear. i've sheared them in my 30lb bot plenty of times.

550 drill motors don't like 24v. the brushes tend to melt at that voltage. 18v is the maximum you can safely run them at. you *will* smoke them when you try to push against another robot. from my experience 550 drill motors tend to smoke when you draw more than 20 a for an extended period of time.

you might be able to get away with a pair of dewalts in low gear.

I lack experience in battlebots larger than 15lb (Do deal with 120lb FRC robots), but P60s with RS775s, and hacked Tz85 amp ECs may be a good solution you can manage for under 250

(for hacking of EScs http://www.robowars.org/forum/viewtopic.php?p=77588&sid=1ac016ff0b273cdb14a27cbdce860e65#77588)

This design will be representing B.M.S. Institute of technology, Bangalore, India

The school uses an older version of Solidedge so the parts were all drawn up in that, but then I had solidworks on my laptop , so assembly and rendering were done there(because photoview 360 is awesome)

armor will be some 1/8'' steel sheet on the sides, and 1/4'' steel tread plate on the back.

We actually have no esc's at the moment, seems like we are going to have to just go for
full-forward/reverse using servos as relays(ghettoish?) mostly becaue shipping/import taxes to india seem to be ridiculous but I havent looked into botbitz yet.

We were sortof hoping for wheel-slip before the the gearboxes gave out. we'll just have to see.

We really have to be stingy here, total budget for the build is 20,000 indian Rupees(about $400)

I like the use of tube framing and the de-integration of armor as a chassis component; when the time comes, that makes it much easier to make some slight changes to bring it into the 120 lb class for stateside competitions.

I strongly suggest looking into building a brushless motor from the ground up for this robot, especially with the number of ways to get your hands on good stators and magnets for micro electric vehicle construction. The calculations involved are fairly painless, and the machining isn't anything all that special; it can all be done with manual tools. Plus the weapon motor is then set to your exact specs, which improves the robot's reliability.

EDIT: the one downside with building a motor is you can very easily overdo it and make something outside of your budget. Take a look on ebay and hobby sites for damaged large-size brushless motors. While they may be inadequate for flying RC planes, most are still good enough to be used for ground vehicles and robots with a relatively small amount of effort put into repairing them.

Frames Welded:


Next We'll lathe down the shafts, machine motor mounts and bearing supports

Then Tackle making the beater, which is proving to be difficult to find material for...

That frame looks nice

Looks amazing. It must of taken some time to make that frame

That was fast!!!

For a robot that size, i'm not surprised you're having a hard time finding material for its weapon

Ya, we got to move fast. The competition is in january. But to compete we have to send in our full documentation and a video of the of the completed working robot in action to the event organizers by november 20th. If they like what they see, we get to compete. but there is no registration costs.

It took me and a group of 5 other students, about a total 9-hours over the course 3 days to complete.

tubing was cut on a miter saw with an abrasive blade, then welded on one of the sketchiest arc welders I have ever seen.(you can the transformer outputs sticking out in the bottom left of the picture)

The frame weighs about 15kg. so at 65 rupees/kg and additional charges for using the tools/ electricity of a local steel shop. The frames came out to cost 1200 rupees or about 22 US Dollars

We knew from the begginning that we would never be able to find a slab big enough to cut the beater as a single piece.
So the Idea was to get 4 sections o 4'' wide, 1'' thick solid steel flat bar and key/ weld them together into the rectangle shape. but thats been hard to find as well.


I can find plenty of steel tubing, because it is used commonly for architectural purposes here(window/door frames, reinforcing concrete.)

So if I dont find anything soon here are the back up plans:

1. Weld together 4 sections of 2''x4"-1/4'' wall rectangular hollow steel tubing and then fill it with cement. (I dont have much faith in this idea...)

2. Or buy a 3/8'' sheet of steel and bend it into a drum instead.

Im a huge fan of the cement beater

Why is it so difficult to find steel plate ?

Why not take a tube frame and Bend it into a cylindrical shape, like wrapping up a garden hose?

I don't know if mcmaster carr ships to you but they may be a start.... just a thought tho best of luck

Found a local machine shop that said they could get the steel we required, so the beater has been machined out of a single slab.

we've also finished all the motor mounts and bearing mounts.

We did a test spin by hand and it just keeps going!

We need pics!!!!

also what flavor steel did you go with for the beater ?

Its just a slab of a mystery mild steel. but it works for us... may have it hardened later










The plan is to assemble the thing on friday and have it wired/testworthy by saturday afternoon.

That looks totally wicked!!!!

I feel sorry for the bot thats going to face that beater

Can't wait to see that weapon in action, how much does it weight about?

The beefiest beater i have ever seen i bet even with the teeth rounded off that would kick a wedge in

it looked a little bit off balance or maybe an illusion

that is really impressive what are you going to use to drive the weapon: belts/ pulleys or chain and sprocket, and what kind of weapon motor

We will be using V-belts weapon:motor ratio of 3:1

we will be using 2 of the motors:http://www.hobbyking.com/hobbyking/store/__14740__Turnigy_L3040A_480G_Brushless_Motor.html Which will be run at 24V

Yes it is slightly off balanced because it was gas cut on the inside, and so the is a bit of extra material on the inside on one side, but it will be ground out to correct it.

The thing weighs roughly 25kg(45-50 lbs)

ShamWOW! jeeves that is looking nice, my only other comment is welding in sandals is ballsy.