Robot Weight Gain Techniques

2023 is the year of light weight robots. Let’s list out ways to add weight to the robot, besides bolting the heaviest piece of scrap you have to it.

Backstory: We are 90% finished with robot wiring and mechanical assembly and we currently weigh in at 61 pounds. We are hoping to change some things on the robot to finish with an inspection weight of 100 pounds. Below are some things our team and other teams can do to both add weight, and lower their robots center of gravity. Some of these only apply to west coast drivetrains.

Steel Belly Pan
Steel Hex Shafts in the Drivetrain
Steel Gears in the Drivetrain Gearboxes
Solid Steel Frame Rails
Steel Plate Frame Gussets
#35 Chain Drivetrain
Steel Drivetrain Sprockets
Solid Steel Bumper Frame Supports (R410)
Steel Brackets on Bumpers (R408)
Steel Angle Bracing On Bumpers (R408)
Heavier wheels on the drivetrain
More wheels on the drivetrain
1/4" Hardware vs. #8 or #10


Figure out if there’s a way to add some functionality, and implement it.

Weigh with the battery installed. (If I’m inspecting and someone passes weight with the battery in I just make a note that it’s in. No sense making them take it out.)


We are just throwing 4 of these on the belly pan.

A carriage bolt holds them to the frame.

We are also making our bumpers out of cabinet grade Baltic birch. We have historically been able to get them very close to 15 lbs this way, and it’s “free” armor for your robot.

Another high density item some teams should consider is CIMS. They would probably make great ballast if you had space, and many teams have plenty. They also bolt on with 10-32s.

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Given brushless motor shortages, more teams should be considering using CIMs as motors, not just ballast…



Use a heavier compressor with a better duty cycle


We have a 16-lb steel weight on the bottom of our robot, but it’s functional, not ballast.

Does that come in osmium?
1966.72 dollars a gram.

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We had to add weight so we could do defense in the playoffs, we attached a vice and bolted it on, we won the competition so it worked


We were practicing with two 10lb dumbbells zip tied to the front our robot. We were fairly certain that this wouldn’t pass inspection, so milled two steel “swerve protectors” that each weigh in at about 8-9lbs. Worked great. Not tippy at all and driver said they even improved robot drive performance.

This is the swerve protectors referenced.

Don’t skip leg day? Also, more reps, less resistance.

Jk. We had a parent run out to a sporting goods store and pick up 2 8 pound weights to use as ballast in the bottom of our robot in order to help stop it from tipping over. Between first and second comp we have cut the robot down from 48 inches tall to ~ 20. We plan to take it to the vet to weigh it, and add ballast to get us closer to our goal weight.

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We attached 4 bar stock in our KOP frame. 2 front and 2 rear. It smoothed out the drive capability of the bot. It added about 20 pounds to the overall weight. We were also looking at steel plates for the belly pan…about 1/4" plate. That hasn’t happened yet. Still an option.

She wasn’t pushed pushed around like week one…she held her own.

We saw a lot of high COG bots running…and falling.

We added 20 pounds to our robot between our two competition. The way we accomplished it was going to our local used sporting goods store and buying barbell weight plates.

We had issues at our first event with our sheet metal drive rails bending so we made them out of steel for the second event. We had the weight so why not.

We threw rebar into our 2x1 frame rails.


We had some scrap 1/4 in steel sheets, so we cut them to size, sandblasted the rust off, painted them (to prevent rust going forward), and attached them to the bottom of our robot on the outer most ends (to help with inertial rotation). Got us another 20 lbs, which was closer to our goal. The lower down and further out the weight is, the better for anti-tipping.

Lead weights (like dive weights) are also allowed, but only if they’re coated.

Things we’ve done:

  • Scrap chain in 1x2 tube, held in place permanently with epoxy
  • 5-pound weights from Target held in with baling wire (and then hot glue over the twisted end for hand protection)
  • Steel 1/8" thick angle to clamp our fabric

Of those, the 5-pound weights were the most fruitful in putting on weight. For something lower-profile, I might entertain these composite sheets from McMaster-Carr.

We stopped by a local metal place and picked up some 5”x1.25” steel bar stock out of the offcuts bin. Had to cut it down a bit (took a long time on our little horizontal bandsaw) but now we have 30lbs of reasonably low profile ballast on the robot for about $30 (the actual segments were ~25lbs each). We also have a couple of small 10lb bars for whenever those might be appropriate.

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If space is at a premium but budget is not