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.
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