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.
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.
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.
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.
A few weeks ago, one of my father's co-workers, Dave, decided to sell his 12" Hendy Lathe. I had been wanting a larger lathe for a robotics project, and at only $400, this was a superb deal.
After doing a bit of research, I determined that the lathe was made between 1887 and 1917, making it over 100 years old. Mostly due to the price, we decided to go to look at it.
We made the 45 minute drive to Groton, Mass and were immediately struck by the size. I had been expecting a large machine, but this basically took up the entire back of a garage bay. Upon inspection, everything appeared to be in remarkably good condition. Most importantly, all of the ways and bearings looked to be un-damaged. It also came with two four jaw chucks, a three jaw chuck, and two plates, which appear to attach to the spindle in place of a chuck (my father theorizes that these have largely been replaced by rotary tables/ CNC machines). One plate and one chuck appeared to be from a larger lathe, perhaps an 18" machine. We attempted to try turning a piece, however, the ancient flat belt snapped almost immediately, so we headed home to make a final decision. From looking around the shop, I determined that we did, in fact have space, as long as we relegated my father's crap to the attic made some organizational changes. We decided to buy the lathe.
I spent the remainder of the weekend rearranging everything in the shop, which was something I had been intending to do for a while, but never got around to.
Transportation:
Transporting a 1500 lb. piece of steel is not exactly an easy task.
We left around 10:00 and rented a UHaul trailer, which was rated for a few thousand pounds. We towed the trailer with my mother's Honda CRV to Dave's father's house, which was we were picking up the lathe and arrived around 12:00.
Disassembly commenced immediately and everything that could be easily removed (motor, tailstock, etc.) without moving the machine was taken off and put outside for the time being. We then used a jack to lift one of the legs and a pry bar to rotate the machine so that it was facing out the garage door. Pete, a friend of Dave's showed up with a pickup truck, and he backed the trailer into the garage. Next, we jacked up the lathe under the bed and removed the leg closest to the door, backed the trailer partly under it and used two 6x6's as a set of rails on which to roll steel pipes. We tied straps from the bed to the rails of the trailer to prevent the machine from tipping and I used a come along to pull it into the trailer. Once it got close to the end, we removed the other leg and finished pulling it in. We tied from several points on the bed to the (somewhat under-sized) tie down points in the trailer with straps to prevent sliding during transit.
Pete towed the trailer with his truck (the CRV trailer hitch is only rated to tow the trailer empty...) and we drove to my house. We backed the trailer under the car lift that we have in our shop and using a large strap and a 2x4 wedged between the rails of the bed, we lifted from the center of mass and pulled the trailer out.
It was now around 10:00 pm and after 10 hours of moving, we lowered the lathe down on the 6x6's and called it a night.
Lathe in the position we used to lift it out of the trailer
In the morning, my father and I lifted the lathe up, set it down on a pair of blocks (actually, the stand for the drill press), and re-attached the legs.
Lathe with legs on, still attached to car lift and on blocks.
We lifted it up slightly again, pulled the blocks out and lowered the entire machine down onto a set of carpet sliders, which were a last minute purchase. The carpet sliders turned out to be a great idea and it was fairly simple to just push the lathe into position. We used a bottle jack to prop up the legs side at a time when it was in place in order to pull the carpet pieces and sliders out from underneath it.
Lathe while removing carpet sliders.
Cleaning/ Reassembly
The rest of the day was dedicated to cleaning/ reassembly.
Lathe at the end of the day.
We cleaned the ways and rods, and removed the thick layer of grime on all of the handles.
The lathe makes the Bridgeport mill look small... This was kind of a disturbing effect after having the mill dominate the corner since we got it a couple of years ago.
Later in the week, we got the pulley on. There was still quite a bit more cleaning to go, however, and we were waiting on a McMaster order to come in with alligator lacing for joining the flat belt so that we could actually run it.
After getting the alligator lacing, we finally got it running. I fixed the tailstock locking mechanism, too. It seems that the cam that locks the bottom piece was slightly out of alignment.
This will be an ongoing project as there are lots of small improvements that can be made, such as attaching the extra quick change tool post that we have lying around. For the moment, however, my focus is going to shift to a few other projects that I have been neglecting, such as my new beetle weight combat robot, Event Horizon (Actually, Event Horizon V2, but more on that later).
