A New Drum Motor for Event Horizon

Rather than re-build the drum in the same configuration that failed initially, I decided to modify the motor mounting to make it more robust. This was achieved by replacing the giant stock mounting plate with a mounting piece that is actually the right size.

Now that I have a large lathe, my design of simple round pieces has changed from Computer Aided Design to Lathe Aided Design.

The final motor mounting piece.

This piece is tapped and has the mounting pattern of the motor. I drilled the mounting holes using the old mounting plate as a guide, which seems to have been effective. 

This slips inside a sleeve, which has a slot for the wires and is the right diameter for the bearing and frame holes. A single screw tightens it onto the frame, which should be sufficient to take the relatively minimal torque that this will see. Best of all, however, the sleeve is large enough diameter to cover the heads of the screws attached to the motor, which should prevent them from falling out.

The motor mounted to the frame side.

Everything fit together nicely, and I was able to spin the drum up successfully. The 3/4" bearing seems to have picked up some dirt (because it is open), which has added friction. I will probably replace it with a shielded bearing eventually.

Event Horizon, mostly reassembled.

As you can probably see, I have not yet re-machined the drum to take care of the screw that was ripped out. This picture also shows the new fastening system for the drum motor (the screw sticking out of the frame). If this design does not self-destruct, I probably will not bother making the hub motor that I was considering previously.

Some testing on Event Horizon and why I need to use Loctite

One of the single greatest factors in making a combat robot successful is durability.

With this in mind, I decided to do some testing on Event Horizon. I spent some time looking for large and relatively solid objects to hit, and finally settled on the EH 1.0 carcass with a large chunk of scrap aluminum in it to make it heavier.

I found that running into EH 1.0 slowly with the weapon at full speed produced only small impacts, which would not be sufficient in an actual match, so I rammed it at full speed. The EH 1.0 frame flew three to four feet, which is much more in line with the power that I want from the EH 2 weapon (Sorry, no video, I can't drive and take video at the same time).

Upon initial inspection, EH 2 appeared not to have sustained damage in the impact, but after looking closer, I noticed that one of the teeth (1/4-20 flat head cap screws) had been completely ripped out of the 1/4" thick aluminum drum. Also, the drum did not spin freely anymore, and the wires for the motor had been partly sucked inside of the drum.


I took apart the drum.

... and was confronted with a scene of absolute destruction. The motor mounting plate was completely deformed, and the wires for the motor (all three of them) had been completely sheared off. Interestingly, all of the screws that hold the motor mounting plate to the hub were missing, and the threads on the hub were completely intact, showing no signs of an impact. Thus, we reach the title of this post: As far as I can tell, the screws fell out at some earlier point, meaning that the drum motor had been solely held in place by its wires. When the drum hit the EH 1.0 frame, it seems that the motor flexed somewhat and the mounting plate caught on the inside of the drum somehow, bending the plate and shearing the wires. Using loctite and/ or jam nuts might have prevented this failure. Thankfully, this is an easy fix since I have another motor.

Yes, that hole was round once.

As a backup, I am also going to start development of a hub motor using the parts from the broken motor. More on this later.