Impulse Response

I saw the Robojackets 20th Anniversary Competition listed on one of the various competition listing sites and impulsively signed up for it. So began my latest beetleweight combat robot, Impulse Response. My initial plan for this competition was to resurrect Event Horizon with a new design that more heavily leveraged 3D printing, since I acquired a used Prusa i3 MK3 3D printer over winter break. After messing around with that design for a while and even buying some parts for it, I decided that I wanted something simpler and easier to maintain. This led to the conclusion that I should make a 3D printed undercutter.

Design

The vast majority of the design process for Impulse Response took place over the course of two days in late January. The design goals were simple:

• Minimize the number of machined parts
• Maximize reliability/ maintainability

Machined Parts:

The robot has only three machined parts; the weapon blade, one of the inserts for locating the weapon shaft, and a spacer that goes inside of the weapon pulley.

Reliability/ Maintainability

The weapon shaft is supported by two large bushings. This distributes the load from the weapon across a larger area of the frame. The bottom bushing is aluminum because it sees most of the load. The top is 3D printed. The weapon shaft includes a spacer that contacts the inner races of both weapon bearings and allows me to tighten down the shaft without side-loading the bearings.

The weapon motor drives the weapon with a belt, isolating it from shock loads.

The drive base uses brushed motors because they are easy to work with and are unlikely to have motor controller issues.

Foam wheels isolate the drive motor gearboxes from any hits the wheels might take.

The extensive use of 3D printing made the manufacturing of spare parts comparatively simple.

The frame is significantly over-built, allowing it to take direct damage without significant structural implications.

Impulse Response after two design days

I tweaked some minor details after this, but on the whole, things remained the same.

Manufacturing

 Manufacturing Impulse Response was exceptionally easy because almost everything was 3D printed.

I first printed a PLA mockup of the body to make sure everything fit.

PLA test print of main body

 Next I printed the body and some other parts in NylonG and waterjet cut the blade at the Invention Studio. Printing NylonG is interesting. I needed to add glue stick to the PEI printbed to get it to stick and I put the filament inside of a dehydrator beforehand to drive out all of the moisture. I observed some shrinkage in the Z direction with the NylonG, but it was not enough to cause an issue.

NylonG print of main body with quick fit of components

The electrical system was slightly unusual. I prefer driving with a pistol-grip transmitter, but the cheap Hobbyking transmitter does not mix channels for tank drive. To achieve this, I added an Arduino, which did the mixing and also controlled the weapon based on the channel three button on the transmitter. It took killing an Arduino for me to realize that the voltage regulators were not what I thought they were.

Code may be found here: https://github.com/echin98/robotEngineArduino

Rough electrical system fit

 After everything was together, I weighed the bot. It was substantially under weight. In hindsight, I should have waited to machine the weapon until after everything else was done and then adjusted the size to fill up remaining weight.

The robot is very under weight

 Testing

I took advantage of being home for Spring break to test the robot. The weapon immediately proved its power. Its first victim was the old frame from Event Horizon v1.

The corner of my test piece (the frame of EH v1) is machined off by the blade

In the course of testing, my weapon motor became hot enough to melt its PLA mounting block. I am still not entirely sure why it got so hot, though I suspect I just need to add some vent holes somewhere.

Whoops...

The weapon motor became excessively hot and melted its mounting block.

I replaced the PLA block with an aluminum plate. I also replaced the bottom retaining block for the weapon shaft with aluminum after cracking the original plastic piece.

Deeming it difficult to do more extensive testing, I decided Impulse Response was ready to go.

Impulse Response in its completed form

 Competition

Match 1: Loss vs Hypnotic

Hypnotic is a well-built drum spinner by a group of high-schoolers from Alabama. This was the first match ever for both robots, and I was eager to see how Impulse Response would fair. The match got off to a good start and I managed to bend Hypnotic's front floor skids. Shortly thereafter, my weapon embedded itself into the wood bumper in the arena. I was unable to get it unstuck and lost by KO.

Match 2: Win vs Large Hard

Large Hard is a drum spinner from the Rose Hulman robotics team. I was not entirely sure what to expect in this match as Big Hard had been partially disassembled by Hypnotic in its previous match. Unfortunately, my weapon failed to start up at the start of the match and it pretty much devolved into a pushing match. Big Hard lost its drive base partway through the fight and I managed to herd it into a corner where it couldn't use its weapon to get out.
By sheer luck, I won by knockout.

Watch RoboJackets 20th Anniversary - 3lb Combat Bots from RoboJackets on www.twitch.tv

I diagnosed the weapon problem to be a bad motor, though I was not entirely certain. I replaced the motor and added a ramp up to the firmware, which seemed to fix the issue. I also decided that I had limited the acceleration of the drive too severely and I increased that accordingly.

Match 3: Win vs Entropi

This was a quarter finals match.
Entropi is a beater bar style drum spinner from Robojackets. I was quite concerned about this fight because Entropi's beater bar was large and therefore high energy. I also was not 100% confident in my new weapon motor.

The fight started with us trading hits back and forth. I eventually landed a lucky hit on the inside of his weapon frame, causing his beater bar to eject.

Watch RoboJackets 20th Anniversary - 3lb Combat Bots from RoboJackets on www.twitch.tv

I took minimal damage.

Match 4: Loss vs Dynastinai

This was a semi-finals match.

Dynastinai is an undercutter with an extremely large direct drive motor. It was built by another Georgia Tech student and was formerly associated with Robojackets. I planned to try to take out his wheels and possibly damage his weapon motor since I had a reach advantage.

On the second hit Dynastinai flipped Impulse Response over. This proved catastrophic. The motor I used to replace the original weapon motor had a long shaft, which stuck out the top of the robot. This shaft contacted the ground before the intended contact point when the robot was flipped over and because the shaft was behind the center of mass, this left me unable to drive. Dynastinai cut into my top panel and stripped the battery wires, shorting them together. I lost by knockout and the battery went immediately into the sand bucket.

Watch RoboJackets 20th Anniversary - 3lb Combat Bots from RoboJackets on www.twitch.tv

Dynastinai's weapon is made from AR500 steel and this was what it did to my blade, which is made from AR400.

Match 5: Win vs Hypnotic 

This was the third place match.

Hypnotic and Impulse Response both sustained fairly heavy damage in our semifinals matches and we initially agreed to just run without weapons since those weren't working. We both managed to get our weapons working in time, though, so we used them.

I started picking away at Hypnotic's tires and eventually took off enough that it could no longer drive. Watch RoboJackets 20th Anniversary - 3lb Combat Bots from RoboJackets on www.twitch.tv

Impulse Response took third place behind Dynastinai and Mad. 

Post-Mortem

Overall, I am very pleased with the results of this competition.

Positives

• The frame proved to be quite effective even after it had taken damage
• All maintenance tasks were quick and easy to do
• The robot could deal out big hits
• The weapon system could take big hits without taking significant damage
• The drive base was reliable

Negatives

• Weapon electrical/motor system failed during the second match without obvious cause.
• Weapon motor durability is not up to par; I had to replace the weapon motor twice
• Weapon spin up time was too slow
• PETG is not an appropriate combat robot material. I broke all of it.

The positives here are significant and the negatives are (I think) easier fixes. I will likely upgrade the weapon motor and ESC and also change the PETG parts to some other material before the next competition, whenever that might be. I may also upgrade the AR400 blade to AR500.  I feel no need to do a major redesign at this point.