Version 2 was fine for driving around my makerspace, but the shoving power = 0, the timing belts are annoying to maintain, and I just wasn’t happy with it. SO! 3 weeks until Motorama YOLO let’s do this!
Go 4WD so I don’t have to worry about shoving matches
Keep using the brushless rage babies but up them to 4x
Non-polycarb top plate
I iterated so much on this design that I ended up with a half-done version 4 when I went to Motorama.
The picture above is as after an all-nighter with my pal Ryan (part of Valkyrie this year). He helped me with some NOT best practices wiring (that we both agreed on, and a new issue for V4). We left for competition the next day and had some last minute changes that needed to be made, like, OH HEY! The hammer only works in one direction, not the other. Doublechecking the design:
Consider the forces at play for the positions of a hammer. First, the forces and torque at play;
P = power; D = diameter; T = torque
So in the case of a hammer robot, it can be considered as T(sprocket) > T(inertial force of the hammer)
This is the starting position for the hammer. We have a big sprocket and a small sprocket; the small sprocket is attached to a Aerodrive 6374 - 149kV brushless motor (I figured if its strong enough to be retrofitted onto my old intern’s longboard, it was definitely more than needed for my 30lb robot… and i had a few lying around).
The first hammer I used was a plushie head that Amazon says weighs 57 grams, so, the arm is all that the motor has to drive (assuming negligible weight seeing its attached directly to the sprocket). I tried to go big with an ~8lb aluminum brick.
When I tested it, it worked in one direction and not the other. I adjusted my settings to 100% power on my transmitter and the hammer still couldn’t swing back. (I learned later from Xo that the settings for the 12-fet rage I was using doesn’t do the same forward as it does backwards, with the forwards being the stronger of the two.) Luckily, I had brought some spare 1/2” aluminum to quickly smash together a new hammer.
While I scrambled to get everything sorted for competition, I forgot to switch out my batteries, so! First match, I ran out of juice before the three minutes were up. Second fight I won, but not particularly fairly (the team started smoking when I shoved them). Third match I lost to one of the event organizers (and Blacksmith teammate) James. Going into a fight knowing you’re going to lose makes it way more fun. I learned why folks don’t use stainless as armor.
My top plate got pretty dented and then it also acted like a brake pad on the weapon outrunner so I lost my hammer a minute or two in. I also lost a resistor on one of the drive controllers as well as one of my Markforged corner blocks (I’ve been lazy and not wanting to drill/tap my wall ends.. but no longer). I know the stainless was a bit thin going into it but I didn’t have any other material lying around so I figured it’d be worth the try.
Next version will have a wedge, better armor, a different hammer head, more space for smarter wiring decisions and likely another color change.