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.
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.
The machining of Event Horizon started with a large amount of work on the CNC router. I cut all of the UHMW pieces first, then cut the aluminum side plates and the bottom plate. UHMW cuts very easily on the router. All UHMW was cut with a single flute 1/8" endmill. Aluminum pieces were cut with an aluminum cutting router bit (one of these).
Preparing to cut the side pieces
Some of the pieces completed.
I had not actually cut 7075 aluminum on the router before, and it basically consists of dumping lots of flood cooling onto the piece continuously and hoping that nothing breaks.
The bottom plate after machining
I assembled all of the router pieces, which generally fit well. The grooves in the back piece were not quite wide enough and I had to file them out slightly. This is because the UHMW stock is actually slightly thicker than 3/8", which is a common problem with UHMW.
Initial assembly of the frame
Next was the machining of the drum pieces. I did most of this with the big lathe, which I attached a quick change tool post to. The first drum piece was the drum itself.
I started by cutting the stock roughly to length using the horizontal bandsaw, and then faced off the ends to the correct length.
Drum end being faced down
Drum stock cut to length and polished with fine grain sand paper
I initially planned to drill the holes on the mill with the small rotary table, however, after fixturing the piece initially, I realized that the small rotary table does not even come close to holding large parts straight. Additionally, the locking mechanism that allows the chuck to tilt is not strong enough to allow me to drill the holes farthest from the chuck jaws without slipping. I thought of three possible solutions to this: 1) put a block under the drum piece at the end 2) buy a lathe chuck for the big rotary table 3) drill the holes with the drum piece held in the vise. I decided to go with option 3 since blocking the piece up would not solve the issue of the chuck being off center, and buying a lathe chuck for the big rotary table would be expensive. I used a height gauge and the small rotary table to mark the end of the drum every 60 degrees and then clamped the drum piece in the vise, using a parallel block as a stop. The parallel block doubles as a point of alignment for the marks on the drum, allowing me to drill the holes at 60 degree intervals with good accuracy.
Drum piece clamped in the vise
After the completion of the drum, I made the two bearing rings and the motor mounting hub. This required several hours of machining on the lathe since all three pieces have the majority of material removed from the original piece of stock. I also machined the axle piece for the free-spinning side of the drum.
Completed drum piece and motor mounted to motor hub
I managed to break not one, but two 4-40 taps off in the bearing ring for the 3/4" bearing, which means that I have to leave two of the six screws out. This is fine for now, but I will probably re-make the piece at some later point.
Frame with drum attached
At this point, the majority of work was done on the bot and I just had to finish up a few minor parts. The first of these parts were the armor support blocks, which back the front half of each aluminum armor plate. I cut these pieces from some leftover EH 1 frame stock and beveled them on the mill.
My solution to putting beveled edges on things
Next, was finishing off the drive train. I finally got around to generating G-code for cutting the pulley blanks (the pulleys have a hex bore and I don't have a hex broach), and CNCed four, which I then added grooves to on the lathe. I also machined hubs for the front wheels from some pieces of aluminum hex shaft. The hubs were a little rough while spinning on the shoulder bolts, so I put a little spindle oil on the shoulder bolts, which solved the issue. I also made the disk for connecting the motor to the drum, which I cut from the same piece of UHMW sheet that the frame came from.
EH with completed drum, side armor supports, and front wheels attached
Aside from the top plate, the bot was mechanically done. I weighed it with electronics, and found that it was ~5-6 oz. over weight, which is a lot. I removed the side armor braces, drilled holes in the frame side plates and enlarged some of the holes on the drum (also useful as vent holes for the motor). The side armor pieces should be unnecessary against all robots but powerful horizontal spinners. Hopefully, the angle of the armor will be sufficient to deal with these types of robots. After looking over the electronics system, I realized that the drive motor controller that I weighed the robot with is actually an ounce heavier than the two Vex Motor Controller 29's that I was planning to use, which helped as well. These changes brought the weight down to a more manageable 3 lb. 2 oz, so I started working on the electronics.
I have not yet mentioned the control system for this bot, so here it is:
Drive controllers: modified Vex Motor Controller 29 (2x)
Weapon: HobbyKing 40A ESC
Radio: HobbyKing 6 channel radio
Battery: E-Flite 3S 1300 mAh LiPo
Power Switch: FingerTech Mini Power Switch
I started by removing the casing of the Motor Controller 29's and cutting off the connectors. I then removed the casing from the ESC and soldered the V_in wires of the 29's to the ESC board where the power wires are attached. This allows me to eliminate the ground wires running to the receiver from the drive motor controllers, saving some weight and reducing the number of wires cluttering the inside of the bot. I cut down the output wires of the motor controller 29's, and soldered on the bullet connectors, then taped everything together in a small block. Before competing, I will make a second block for a quick replacement should anything in the electronics system decide to spontaneously combust.
Electronics block soldered together and mostly completed
I finished the electronics system by adding the battery connector, PWM connectors, and power switch, then stuffing everything into the rather limited space between the motor and the inside frame member.
Electronics system mostly installed
With the electronics system now complete, I finished the top plate and assembled the full bot.
Completed bot
In all, the weight came out to 3 lb. 1.3 oz. I should be able to cut the remaining excess weight by changing the top and bottom plates to garolite and polycarbonate, and if necessary, lightening the middle armor support blocks substantially.
And, of course, here is some testing footage:
EH is more maneuverable than it looks in this video. I am just bad at filming and driving at the same time.
I noticed a few things while testing today that could be problematic:
The weapon can spin up fast enough to flip the bot over on startup, then send it shooting across the floor. This is why you see me spinning it up slowly in the video. I might be able to use this for self righting, which would be very useful.
The turning speed is very limited when the weapon is at full speed because the gyroscopic forces cause the bot to tip and ground out on the side armor.
One of the front wheel axle bolts came loose. I will need to loctite everything in place before competing.
