Wheel Platform Robot

History

While Parallax was designing the Motor Mount and Wheel Kit (MMWK), they needed a platform to test and demonstrate on. Here are the two prototypes I designed to demonstrate the MMWK. One was made from wood and ABS, and the other was made from metal and ABS. Both were originally set up to run from a standard hobby radio control system, using the Board of Education to do the servo signal mixing, which allowed me to drive them around manually.

The First Prototype

Wood is easy to mill and assemble. With that in mind, the first platform I created was made from standard pine boards you can buy at any lumber store (Figure 1). I did have Parallax’s laser guy, Matt Gilliland cut me a piece of ABS for the top platform. I could just as easily have used plywood.

In Figure 2, you can see that I used a 12V @ 7Ah SLA (Sealed-Lead Acid) battery to drive the motors. The BoE was powered by a 9V battery, while the R/C receiver was powered by its own NiCd battery (the red block in the photo). In Figure 3, you can see the underside of this platform. I used a standard caster wheel for the tail and mounted two metal strips to the bottom of the MMWK brackets for stability. The two HB-25 motor controllers were mounted to “L” brackets. Figure 4 gives you a closer look at the wiring.

The Second Prototype

While wood is easy to mill, the end goal was to make a metal chassis (Figure 5) for the MMWK. I chose square steel tubing because, like wood, it was easy to cut and could be found at most hardware stores, fairly inexpensively. Unlike wood, which could just be screwed together, the metal chassis require a lot more hardware.

In the first photo above, you can see flat “L” brackets hold the corners of the chassis together. These are on both the top and bottom of the frame. The center frame is held together with the two caster wheels. Lock nuts were used on all the bolts. Shims had to be installed above the MMWK blocks to adjust the height to work with the height of the caster wheels.

In the second photo above you can see that the HB-25 motor controllers were installed and wired to each motor. Standoffs were also installed for the ABS top plate. In the third photo above you can see the power wires to each HB-25 motor controller. These wires run up through the ABS to the battery.

In the first photo above, you can see that the ABS top plate is being installed and the positions for the battery and BoE are being adjusted. Because the battery is so heavy, it is being mounted in the center to avoid throwing off the center of gravity. In the second photo above, you can see that terminal blocks have been installed for the main power bus.

On this platform, the power for the motors and the BoE both come from the SLA battery. You can also see the main power switch as well as me having run the servo cables up from each HB-25 to the BoE. A USB cable is connected for testing the motors. In the third photo above, you can see the underside of the platform after all the wiring has been completed and everything is mounted.

In Figure 12, you can see the final version of this test platform chassis, complete with Infrared sensors on the front, as well as front and rear PING))) sensors that can rotate 180 degrees each. Figure 13 provides an alternate angle of the completed platform. Finally, Figure 14 shows the chassis (prior to being completed) next to a BoE-Bot for size comparison. As you can see, this platform dwarfs the BoE-Bot, which is a desktop robot. One wheel on this chassis is larger than the BoE-Bot!

Unfortunately, the videos of this robot in action were lost when I moved from CA. For more information, please see the History & Changes page. Hopefully, this project will inspire you to build your own larger platform robot. Because this platform moves fairly fast and is fairly heavy, please exercise caution when running this around people or vehicles.

Resources

Budget Robotics (Base on a Budget) – Project

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