Dinnerware Demolition Robot

 

Awards Won

2006 Kansas City Robotics Society Robofest 1st Place Line Following

Prize

Video




I decided to build a robot for this competition around March 2006. I came up with a preliminary design and ordered all of my parts. Unfortunately, due to obligations with work and school, I couldn't actually start building until a couple weeks before the competition. I ended up completing the robot in about 3 days. I wasn't able to implement some of my ideas because of the lack of time, but overall I produced a quality robot. It didn't look very good, but it worked.

Processor

I went with the PIC 16F876 as my processor. I choose it because I already had familiarity with it from past applications. My original plan was to use an AVR processor, but I didn't think I could learn to program it in the limited amount of time I had. It ended up working just fine.


You can see on the board that I went with the SN754410 quad h-bridge. It is made by Texas Instruments and is incredibly easy to use. Each chip can handle up to 1 amp, but I stacked two on top of each other (not shown). This made it possible to handle up to 2 amps. In spikes, more amps can be handled. One of the good things about this chip is that when the amps get too high, it will shut down. Because of this, I never once blew a chip (except for when I plugged it in backwards right before the competition...oops).

Sensors

The sensors I used for line following were from www.lynxmotion.com. They sell a really easy to use array of line sensors. All I had to do was replace the header on the board with a straight header. The picture below is from the Lynxmotion web site so you can't see the headers I used on my board.


For the tabletop competition I had to detect the edge of a table. I did this with simple switches. I found some very useful switches from Jameco (www.Jameco.com) that actually had a little wheel on the end of the lever. This made it easy to roll on the tabletop and to slide off the edge and back onto the table easily.


To wire the switches to the microcontroller, I just used a simple 47k pull-up resistor. This meant that when switch was in the normal position (in this case, on the table), the microcontroller saw 5v on the pin. I know it would have saved power if I used a pull-down resistor, but I didn't for some reason.

Batteries

For power, I used two batteries. A regular 9 volt battery supplied power to the electronics. This battery lasted a really long time. I only used one for development and testing, and replaced it right before the competition even though I probably didn't have to. For motor power, I choose a 12 volt NiMH battery pack. I liked these batteries because they are easy to charge, lightweight, long lasting and relatively cheap.

Motors

Like the line sensors, I got my motors from Lynxmotion.com (item #GHM-13 ). The specs are:

• Weight = 7.15 oz
• Reduction = 50:1
• Stall Torque = 231.5 oz-in
• Length (motor and gear) = 2.33" (5.92 cm)
• Length (shaft only) = 0.89" (2.26 cm)
• Diameter (motor and gear) = 1.45" (3.68 cm)
• Diameter (shaft) = 6mm
• Outside Diameter = 37mm
• Current (at 12v no load) = 145mA
• Current (at 12v locked shaft) = 3.8A

As far as power goes, these motors were perfect. They are very strong and weren't stressed at all. But, I wish they were a little faster. I could have just changed wheels to a larger diameter wheel, but I wanted to keep the overall height of the robot small. For next year's competition, I'm going to look into using non-gearhead motors. Probably from the Maxon company.

Wheels

The wheels I used were foam wheels from Lynxmotion.com (item #TSR-03). The specs are:

• Diameter = 2.50"
• Width = 1.5"
• Weight = .90 oz.