Finishing Event Horizon V3.2 Part 2: Machining

Much progress was made today. I will need to make a trip to the local plastic supplier to get the stock for the wheels and new front blocks, place an Online Metals order for the armor plates, and place a McMaster order for new shoulder bolts and a few other things. In the meantime, however, I got to work machining the new drum internals and side plates. I also need to work on machining the blades, which I have been avoiding for several months, but I am going to continue putting that off.

Before I do a spin up test with the blades, I'll need to make a testing box. It could be extremely dangerous if one of the blades comes off with the drum at full speed. They are sharp enough to shave hairs off of my arm.

The first things on the table are all of the 3/8" UHMW parts. I have taken to doing my CNC work in large sheets. Here is a sheet containing all of the parts that need to be machined. I will need to make fixturing pieces to do the finish machining on the new front blocks, but that is a project for another day.

CNC Sheet of changed parts

If anyone is curious, I use the HSM plugin for Autodesk Inventor for writing G-Code. My CNC router is running Mach 3.

I tried a new endmill for these parts. It is an Amana Tool 1/8" plastic cutting bit, which I tacked onto a re-stocking order of 1/8" aluminum cutting bits made by the same company. The finish was slightly better than the old 1/8" straight flute mill that I have used in the past. I used twice my normal cutting depth and it worked well. In the future, I think I will use a slower feed because the finish is a bit rough.

After finishing the new UHMW pieces, I went back to the drum and machined a new idler axle. Originally, I was going to make a press fit for the axle, but I decided that there are several situations that may warrant removing the axle, so I enlarged the hole slightly so that it is just a tight slip fit.

Idler shaft and motor in drum

The bearing system on the idler side of the drum is just the aluminum shaft resting in a hole in the frame member. I used a reamer to bore out the hole, which left a good finish. I then added some spindle oil. This resulted in a surprisingly smooth bearing, though I am concerned about frame deformations causing it to lock up. I think I'll leave it for now, at least until I have the opportunity to do some testing.

Drum attached to the new frame

Finishing Event Horizon V3.2 Part 1: Design

I have finally un-killed myself from the FRC season.

My first priority on Event Horizon is to fix the misalignment issue I saw after spinning up the new drum for the first time. It seems that I will need to make a solid connection from the idler shaft to the motor shaft in order to make a continuous solid body.  My first idea was to make a 3/8" aluminum shaft that presses onto the motor shaft. I bought a reamer for this purpose and re-designed the drum internals slightly.

New idler shaft

Then, I looked over the last revision of the design, and found a bunch of things that I was not particularly happy with and re-designed them. I was going to need to re-make the side pieces to accommodate the new idler shaft design on the drum, so it seemed reasonable to make more changes. The first of these was the serpentine belt run. I mostly used the belt run to reduce space and weight while still maintaining high traction wheels. After thinking about my design more, I concluded that I did not actually care about traction. If I ever get into a pushing match, I am probably going to lose that match anyway. As such, I got rid of the BaneBots wheels and replaced them with pulleys, which do not use serpentine belt runs and make everything thinner.

New wheels and bottom view of armor modifications

I then decided that the way I had mounted the front braces might result in stress concentrations near the weapon bearing mounts. I switched the mounting to pins, which resulted in interference between the pins and mounting screws. Thus, I offset the side plates and rounded the front corners of the braces. This is actually beneficial for a few reasons: 1) It makes it less likely that an undercutter blade will catch the edge of the armor plate 2) It lets me switch from plastite screws, which tend to strip out, to bolts.

Pinned front joint

Inside of the finished front block design

Outside of the finished front block design

It looks like I pretty much redesigned everything... I guess I have some machining to do.

CAD Model