Objectives

The New Design

The initial design, built from older robotic kit pieces, is not an ideal model. With the parts available, the construction required mounting plates to be overlapped, motor mounting plates to be hung around the wheels, putting the wheel axle encoders in a place where they can slip, and the DSP, PWM, and DC to DC boards are all difficult to get at without removing parts from the assembly. Also, the initial design used an old, and very heavy set of batteries. When it was decided that we were going to switch to a longer lasting, and lighter Lithium polymer batteries, one of the old batteries was left on the robot to keep the center of mass higher. To fix these problems, and make the model more durable, a redesign was required
For the redesign, many requirements were set. As work went on with the control of the initial design, some were changed, and some were thrown out:

1. Allow for ideal sensor placement
2. Design a model that can be easily switched from direct drive to gear drive
3. Allow for almost every part to be taken off without losing overall shape or structural rigidity
4. Mount the DSP boards in a manner that provides protection, yet easy to get at all required access points, such as the reset button, or the dip switches.
5. Mount the PWM boards in a manner that they can be turned on while still holding onto the handles.
6. Allow for “training wheels” and support structures that will protect the components from fall damage.
7. Allow space for additional boards, both additional daughter cards, and new boards stacked on top of the DSP.

During the redesign, it was decided that we would like a 2:1 ratio for the gear driven version. Stainless steel gears were chosen from Stock Drive Products. With the gear driven version, there is a greater chance for slip. This normally wouldn’t be too much of an issue but the encoders mounted to the drive shaft require a minimum amount of slip. To minimize wheel shaft slippage, e-clips are put onto the shaft, on the outer sides of extended race bearings. This prevents the e-clips from rubbing against any rotating surfaces, while still allowing the e-clips to do their job. For the main case, aluminum square beams connect the aluminum motor mount plates to the upper case top. This allows for greater durability and strength. The faces are all made of clear Lexan plastic for visibility, and large ports are provided on the sides and front of the case to all access points. The PWM boards are mounted inside the case, yet with access to the on/off switches under the side handles. The handle brackets double as sensor mounting points as well. The top of the case is available for camera and LCD mounts, and aluminum square bars wrap around the front and rear for additional sensor shelves. Areas for improvement, are creating a bit more space, and shortening the case. Greater utilization of standardized parts will also help reduce the cost of construction as well.