BUILD REPORT FOR DM-1

DM-1 HOBBYWEIGHT COMBAT ROBOT

DESIGN CREDITS:

The inspiration for many of the design concepts emulated in DM-1 must be attributed to the highly successful UK robot Tornado. The greatest attribute of the robot Tornado is not it's active weapon but the very strong basic ram bot design. The attribute elements I emulated from the Tornado design are: the very strong structural frame, superior traction; high speed and quick maneuverability. Another successful UK robot Razer must be given credit for another emulated concept, the ability to wedge under the other bots. A clarification maybe in order at this time about the term 'emulated'. Emulation is not the direct copy of a design, it is only the use of the design function result. So please do not copy another persons design.

Building techniques were acquired from many unique sources. Nonspecific credit is given for the multitude of building techniques and tips I found on numerous robot web sites and in robot building books. A specific acknowledgement is given to Team COSMOS for their superbly built robots and their very informative web site. I gained much building insight from their build reports for IO and Solaris.

THE MAJOR COMPONENTS:

Why start with parts? Because off-the-shelf parts selection dictates the final design. I knew that I wanted to end up with a short compact ram bot that was very strong and able to push with great power. My first parts to evaluate were wheels. I ordered 4 different sets of wheels from Grainger Industrial Supply and ended up using the 1.5 inch wide ones because they gave a lot of contact area using just four wheels. I wanted a close coupled four wheel layout for quick turns. The 3.5 inch dia. wheel was selected because I wanted a fast bot. I had wheel hub adapters made at Scott's Machineshop, to press fit into the wheels.  Next came the motors. I selected four of the 6V Ryboi drill motors from the local Home Depot and used a 6 cell 7.2 volt battery pack to power them. For testing and training I made battery packs from the 1100 mAh cells that came with the Ryboi drill motors. For combat I ordered packs made with CP-2400 Sanyo NICAD cells from battlepack.com/. I use Traxxas XL-1 Electronic Speed Control w/Reverse from Tower Hobby because they had the current capacity to handle the motors and they did not have a delay between forward and reverse. The radio used was a Futaba R138DP PCM 1024 8-Channel Receiver with a Futaba T6XAPS 75Mhz PCM Transmitter and a Deans antenna from The Robot Market Place.

CONSTRUCTION STARTS:

All parts were received except for the ESC, it was on back order. I did accurate measurements on the parts and started drawing the plans with a CAD program. DM-1 Frame Next I bought 1/4 inch 6061 Al for the frame from Metal By The Foot in KC. I printed out the drawings 1:1 and transferred dimensions to the work pieces with dividers. Because our sponsor only provided funds for the parts I was left with using the existing tools in my shop or farming out machine shop work. I did not have a milling machine or a lathe. I did have a metal cutting band saw to cut out parts and a heavy duty 12 speed drill press with a cross slide vise. I ordered in a set of end mills from lathemaster.com (good price and quick service) and started machining the frame. This was the first manual milling I had done since 1967 when I was in college machine tool class. The machine work went well all the parts fit. The big problem was the very hot machine shop (over 100 degrees Fahrenheit in KC the summer of '03). Next came all the drilling and tapping. I used 8-32 button head cap screws to attach all the frame parts together. I ordered hardware from the McMaster-Carr Supply Company in box size lots of 100 pieces, much lower price than your local hardware store. They also have a large selection of parts not easily found at your local stores, like the aluminum piano hinge used for the front blade attachment. DM-1 Rear view showing battle damage Note: I did not think the aluminum hinge for the front blade was going to be very battle worthy but it held up well. It was damaged but still functioning after the last battle with Chigger at GPRS '03, see the battle video. The only part that was missing after the last Chigger battle was one of the spikes on the back side. When I got back home from GPRS '03 I wanted to see how the bot was operating. With the same battery pack that was in the bot during the last battle with Chigger the bot ran just fine for two minutes before the battery went dead. DM-1 Front wedge and hinge after battle with Chigger Now back to the build report. I made two center supports to help hold the drill motors from pieces of composite flooring scrap, they weighted less than polycarbonate. Note: The composite flooring supports did not hold up well during battle. After the battle with Chigger they had to be replaced, this time I used polycarbonate.  Next I found some scrap 3/16 inch polycarbonate at Fantastik Plastics in KC and machined the top and bottom covers. The ECSs were still on back order from Tower Hobby and I needed them to test the unit. I found some for a higher price at The Hobby People and had two of them shipped out. When the ECSs were received I wired up everything with Deans 'Wet Noodle' 12 Gauge Wire and used 45 Amp Anderson PowerPole Connectors for the master disconnect. With all parts installed and the top and bottom in place it was weigh in time. Over Weight! Oh yes that nagging always present problem, the weight limit. The bot was right at 11 lbs. and it had no front wedge or back spikes installed. On paper when I first added up all the parts, the calculated weight was around 10 lbs. That gave me about 2 lbs for any weapons that I wanted to add on to the basic BMW design. Things do get overlooked, like the hookup wire, connectors, mounting foam tape, thicker top and bottom covers, disconnect link, the heaver 2400 mAh battery pack, foam padding around radio receiver and all the 8-32 cap head screws. It was back to the milling operation for a little bot weight reduction. Ok the milling was over and the front blade (wedge) with hinge and the back spikes were installed. The weight was now under the 12 pound limit.

TESTING PHASE BEGINS:

With a fresh battery pack installed it was test time. Transmitter switch on and stick forward yes we have wheel movement. First problem was the right wheels were moving forward and left wheels moved backwards. Ok I reversed the motor leads on the left side motors, problem fixed. Full power test next. New problem, when I moved the stick forward fast the motors started to pulse on and off. A quick check with my oscilloscope showed a large voltage drop to the speed controllers when I went to max power very quickly. This voltage drop was also cutting the required 4.8 volts receiver power down. To save weight I had used the receiver battery elimination circuit in the XL-1 Electronic Speed Control to power the receiver. To solve this problem I just installed a small receiver battery pack. But this made the weight limit close, we were only 1.2 oz. under. Now off to the driveway for some real testing. The bot was working great. DM-1 was pushing a 40 pound steel tool box around with no problem. The front wedge went right under the tool box adding extra weight over the front drive wheels and giving great pushing power. Battery pack was now drained and off I went back to the machine shop, to take the battery pack out and charge it up. When the top cover was opened up I found the ECSs were very hot. The drill motors were hot but not bad. I needed to get some cooling air over the ECSs. I ordered a cooling fan from The Robot Market Place and installed it on inside of the bottom cover with plastic screws right below the ECSs. This made the weight of the bot close to the limit. Adding the cooling fan made a big difference with how hot the speed controllers and motors got when running the bot with the top cover on. Next was more testing and driving. Using only a single stick for steering and speed control was not working for me. I had never used a RC stick controller for any serious driving. In past years I had only helped my children with their RC toys. I own and operate a Bobcat skid loader with two lever tank style steering control. It was only natural for me to make the bot control with two sticks tank style. The best information I could find on the subject was at the Team Run Amok web site. I made mechanical modifications to the left throttle stick to make it spring loaded to the center, same as the right stick. This made driving tank skid style much easer for me. I set up an 8 X 8 foot arena for the start of much needed driving practice.

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