SHOWALL HIGH VOLTAGE ROBOTICS
Figure 4 - The motors, drive wheels and front caster pulleys removed
Figure 4 - The motors, drive wheels and front caster pulleys removed

I am not planning to use any of the frame parts or tubing of the original wheelchair as it seemed flimsy and flexible, probably due to the fact that it is foldable for portability and that this older chair was designed to also have some usefulness without the motors and battery parts installed. Newer power chairs may offer a suitable frame for use in robotics projects, but the older ones I have salvaged seemed to be very flimsy, often made of thin wall half inch tubing. I wanted a rock solid and simple base to carry a hundred pounds of batteries and offer a stable platform to mount the rest of the body and hardware, so I decided to just make a new frame out of strong square tubing and then retro fit all of the usable hardware onto the new frame. I also made the decision that the larger wheels should become the front wheels as these are the ones that must drive the robot over any obstacles. It actually seemed silly to me that power chairs had the tiny caster wheels in the front as these would constantly be the weak link when trying to run over obstacles such as potholes or even up a curb. I guess the idea was to make the chair turn at the front to help the user control it, but this did sacrifice the entire point of having large wheels. Odd indeed!



Figure 5 - Coming up with a good layout for wheels and the battery pack
Figure 5 - Coming up with a good layout for wheels and the battery pack

The key to making a stable robot of this size is to carefully consider the placement of the drive wheels along with the heaver components such as motors and battery pack. I wanted to have an entire day of operation on a battery charge, so I purchased the largest deep cycle batteries I could find, which ended up creating an 80 pound bank that was about 16 inches square. To keep the robot from rolling over on very uneven terrain, the battery pack must be placed as low as possible and in the center of the robot between all of the wheels.

Another consideration as mentioned before is where to place the drive wheels - front or rear? Since the caster wheels are only 6 inches in diameter and the drive wheels are 16 inches in diameter it would seem pointless to place the small casters in the front of the robot as they would certainly get stuck in every hole and make your robot incapable of driving over branches or up a city curb. By placing the drive wheels in the front, your robot can now climb over obstacles at least half the height of the drive wheels and steering will seem more stable while navigating via video link since the camera will point you right to the direction you plan to go when making a sharp turn.

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