Dozer Mk2 Build Report

"Running? Running's not a plan, its what you do when a plan fails!"
-Earl, Tremors

After the mixed results with Scarab Mk2 at Steel Conflict 2, I knew I was on to something with the general design of my pneumatic flipper, but I also knew it was going to be tough to really pull it off in a 12lb robot. The power system alone weighed 3+ lbs, which becomes really unmanageable in that weight class. I'd contacted several manufacturers about getting smaller/lighter tanks, but no dice so far. (In fact I just received an email back from Catalina cylinder indicating that they won't be able to help me... ever... bummer.)

When Bob Pitzer came calling with BotBash by the Sea, but indicated that there'd only be 30lb and 60lb robots, I knew just what direction I'd head in. So I took the general layout of Scarab, and scaled it up. Bigger motors, more piston, an actual air buffer chamber, and luxury of luxuries: 4 wheel drive and wheel armor!

Keeping the Power to Weight ratio of Scarab would mean more than doubling the force from the lifters. I looked into bigger cylinders and different lifter geometries to get more favorable leverage, but it just wasn't going to fit the way I wanted it to. Then I realized that with 30lbs to play with, I could afford a lot more weight for the pistons, considering that the paintball tank no longer accounted for 25% of the total mass of the machine! So I starting moving towards a dual-piston design. I liked the symmetry and it let me use smaller bore pistons and still get the power I needed.


Pictures

Even with the dual-piston arrangement affording smaller pistons, I realized I couldn't completely bury them inside the chassis this time, the geometry just wouldn't work out. (There was actually some binding in the Scarab geometry as it was...) This meant the pistons would be semi-exposed even at rest. After some of the initial CAD renders, I realized it was time to ressurect a name from the past. This robot couldn't look like anything BUT a Bulldozer, thus, "Dozer", my first (and long-ago aborted) first robot project would live on in a new machine.
After seeing how much success others have had with CAD/CAM on their machines, I invested in a cheap CAD package and spent the time laying out every major part. Eventually when I got the price quotes, I realized the CNC time was going to cost as much as a small benchtop mill if I paid someone else to do it, so in the end I only had these piston mounts machined for me, since they were fairly complex.
Jim Wilson of Wilson Tool & Machine is a new sponsor this year and he did a fantastic job with the piston mounts. You get what you pay for, because the parts I had him machine were the only ones that lined up right the first time. I must also thank my friend Randy Rabb, he let me use the larger mill in his shop to do the rest of the major milling operations, it went much faster there than it would have on my employer's tiny mill, and it saved me a TON of money compared to what I would have paid for CNC machining...
Despite my cruder machining efforts, the chassis went together fairly quickly. Extruded 6063 wasn't going to cut it in the 30lb class, so the framework here is 6 pieces of 1/2" 6061, hogged out for weight and joined with 10-32 fasteners. Here I've got the DeWalt 12V motors/trannies in place and I'm doing some weight checks and checking the layout. The caution tape was a lucky find since it was the same width as the outer rails and make a quick way to put some nice durable color onto the aluminum. I'm getting really tired of black-and-silver boxes with grey wheels... yawn.
Still playing with the layout. The piston and arm pivots are 5/16" shoulder bolts riding on bronze bushings pressed into the mounts. Smooth... The CO2 tank and buffer chamber mounts are 3/4" UHMW Polyethelene, milled square, drilled with a 2" hole saw, and cut in half. Hose clamps will complete these later. This shot also shows the chains to slave to the rear wheels.
I tried to use the same free-running wheel/sprocket assemblies that I'd built for Tangled Marionette. This turned out to be a mistake for a 30lb robot, as with the extra torque at the wheels I had a lot of problems keeping the sprockets mated to the wheels, even with the roll pins you can see here. These two shots are actually from the competition, where I kept separating wheels and sprockets. Here the inner race has separated from the bearing.
I had a few spare wheels, so every time I had to face Tony Hall's Little Rat undercutter, I had to rebuild the rear wheel assemblies from my spares and try to keep everything pieced together. As soon as the BashWare stopped pairing us up, I stopped blowing up the rear wheels. Here' I'm milling slots in the hubs to accept the roll pins.
My CP-2400 Battlepacks nestled into the pockets in the front and rear rails, and I fastened them down with Carbon Fiber straps made from the offcuts of the armor. After an unfortunate demonstration of the conductivity of CF sheets (during testing continuity with the master switch) I lined the tie-downs and pockets with spongy weather-strip foam, just in case. It did manage to keep everything from chafing or shorting out, and I didn't have any problems here. The wavy appearance of the baseplate is the protective plastic I hadn't removed yet...
The only major injury sustained this time around. Long-time friend and sponsor Tom Deadrick of All-Wheel-Engineering and Kartboy Kustoms graciously helped me out with the welding of the steel tubes for the lifter arms. Unfortunately I was sitting on the ground when he set the second arm down after finishing the weld. Not paying attention I leaned over to get a ground-eye view of the first arm, and put my hand right onto the weld joint... A little cursing and a lot of cold packs later, I'm nursing a minor 2nd degree burn with a 5/8" tube-shaped blister. We're pretty sure it won't even scar... which is too bad considering how bad it hurt!
As I said before, I'm getting really bored with grey/silver and black boxes, so I applied some primer and 3 coats of Krylon the evening the welding was done. My wife thought my cardboard box-spray booth was hilarious. The painted forks looked great right up until the first fight when Tony Hall's undercutter got ahold of them. That's what I get for using mild steel. Next time it'll be chromolly boxed in with sheet steel or titanium to keep it all square. But at least the paint mostly stayed on...
Final layout of the pneumatics and plumbing. The HUGE buffer chamber actually had enough volume to fire both pistons TWICE, which was sort of overkill. I filled the space I had, next time I'll use a smaller one and save some weight. You can see I've used a Palmer Pursuit female "Stabilizer" regulator, into the manifold on the left that feeds the buffer chamber, pop-off valve, purge valve, LP gauge, and into the Norgren solenoid-pilot valve. Its all 1/8"NPT connections EXCEPT from the buffer chamber to the valve and from the valve to the pistons, which are 1/4"NPT to get the extra flow to make the pistons really "POP"!
CF top armor drilled and mounted, pretty much ready to fight 24 hours before things get rolling. That might be a new record for me. The white block between the wheel rails is the nylon mount for the antenna mast. I didn't have weight left to fit the chain guides/tensioners between the rails that I'd planned, but next time I'll make them fit.
In the heat before battle, clear labeling is critical. CO2 on/off and purge open/close were handled with a converted 3/8" nut driver that extended into the chassis. The LED is tapped off the Team Delta RCE-200 PCB, gives me a good indication of the valve status before I open the CO2 valve. The pistons could probably take my hand off if they misfired. You can also just barely see the seam in the carbon fiber sheet on the top armor. The force from the pistons firing actually caused the CF to split along this seam. Next time I'll know better.
A little laser cut vinyl to thank the sponsors, and we're ready to fight. As with my last few bots, I went with an R/C style antenna mast outside the aluminum and carbon fiber. This always nets me great signal and response, but VD3 did perform an antenna-ectomy in our last fight, forcing me to use the spare pulled from Scarab...
With Scarab Mk2 I was keeping track of every fastener in Excel and still came in overweight. With Dozer I just went on instinct and didn't weigh in until things were mostly together. Depending on the scale, I had just enough weight for a couple of pieces of Titanium to tie the arms together. I hadn't fitted these when I fought Tony Hall, and I wish I had. I fought Saturday afternoon with the top part fitted, but the scale in use at BotBash said I was overweight with both so I didn't use the lower piece until Sunday when my Team Delta switch went wonkey and I had to discontinue use of the pneumatics.


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