So if you saw my post last week, you’ll know I’ve been building a 150 gram battle robot that I’m going to try to compete with in September. This past week I made some progress on the build and wanted to show off the parts that finally came in. Here it is, in all its glory:
Of course there’s no wiring yet cause hot irons scare me, and I haven’t figured out mounting brackets for the motors or anything else so I’ll probably just use tape until I decide on a permanent place for everything, and half the robot is literally a brick of plastic, and those screws are actually just for show cause I messed up the tapping for the threads, and … yeah, its got some issues. Anyway, I’m not even sure if it drives yet, but it sure looks like it could!
So far, the front wedge is the part I put the most thought into. First of all, I made it modular so that I can pull it out and slot in another shape if I want just by removing the lid and sliding it up and out. Also if it gets damaged, I can hot swap the parts really fast. I’ve chosen a forked shape for now because I had this idea about the best way to push another robot around …
The basic function of a wedge is to slide underneath the opposing robot to lift their wheels off the ground and make it easy to push them when they lose traction. Often times, this doesn’t go as well as you’d hope though. If neither robot can get underneath the other, then the robots end up in a shoving match. Usually the winner is determined by a combination of torque and traction, but I had an idea to tip the odds in my favor if it comes to a pure shoving contest. I noticed while watching battles between similar wedge-shaped robots that most everybody uses a flat wedge, and that with a flat wedge, the robots end up pushing directly against one another. In other words, if a flat wedge hits another flat wedge, both robots tend to apply even pressure across the width of their faces. In this case, the match is reduced to a contest of drive power like I mentioned. But with the forked wedge, I’m hoping to deflect an opposing robot off of one of the wedges so that it turns one way or the other to push on the inner face of the wedge. This should put the opponent at about a 45 degree angle so that their pushing power is split between a force that pushes my robot directly backwards and a force that pushes it sideways. This means that a portion of the force they might have been able to resist my pushing power with is now pushing in the wrong direction. We can even calculate the factor by which they’ll be pushing in the wrong direction using trigonometry.
Assuming the opponent gets caught perfectly in the wedge and ends up pushing into one side at a 45 degree angle to my wheels, all we have to do is multiply the total force that they can generate in the forward direction by the cosine of 45 degrees. COS(45 deg) is equal to about .71, so my robot should only have to beat 71% of the total force that the opponent can exert in order to push it around! By simply having a nice shape, I’ve already created close to a 30% advantage in pushing power (in theory).
This all ignores what will happen to the rest of the force (it will serve to spin my robot around) so maybe it won’t be as effective as I hope, but hey, the theory is there at least. If it doesn’t work, I’ll adjust. Oh and if you’re wondering how this affects my own pushing ability, I think I should still be able to impart all the force my robot is capable of generating since both sides of the wedge shape should still come into contact with the opposing robot. I get to push with both sides of my wedge so that the angles cancel out into a line parallel to my wheels while the opponent only gets to push on one side of my wedge.
But yeah it can’t even turn on yet so I’m actually just talking out of my butt. I’ll put out another update once I get it driving around. And I haven’t come up with a name yet, so let me know in the comments if you’ve got any bright ideas!
Thank you for reading,
Benjamin Hawley
Dangerous Day Job 