ExMod
From bildr
ExMod
The experimental module development platform
ExMod is a platform that was designed to be experimental but easy to use and build on. The design allowed for a large space to add sensors and boards. As well as a 3 omniwheel design to give it good maneuverability but also allow for both simple and complex movement to be tested. The name can from EXperimental MODule.
Frame Construction
This platform needed a lot of flexibility and room to add components such as sensors and breadboards. It needed to be stable and easy to use. I also wanted the ability to test complex motion controls. The omniwheel design allows for either simple forward motion with the third wheel used to steer or true omnidirectional motion.
The frame is constructed from PVC. I had some laying around but any material that is light and durable would work. Acrylic or wood are good options. There are 2 main pieces to the frame. They are identical pieces to allow them to be layered on top of each other. This creates a top surface to mount electronics to as well as an inside gap to mount the motors.
I chose a triangular design to allow for the three wheel design. Using a jig saw I cut the frame out and then spend several days trying to figure out a way to mount the wheels. I did find an interesting thing to note. A piece of U channel from Lowe's just fits over the end of a standard servo. So after drilling holes in the channel and sandwiching it between my frame pieces I was able to wedge my servos into the channel. After tightening the bolts down the servos are held secure enough to not come out but loose enough to allow for minor adjustment if needed.
A later addition to the frame that came in handy was a battery holder cutout. It secured my batteries and didn't look so bad. I simply cut the top layer of the frame and slid the holder into the slot. To add electronics to the frame you simple drill holes where needed and add spacers if you want. The frame is non-conductive so spacers are not necessary.
Wheel Mounting
The frame is designed to be experimental. Nothing is permanent and can be moved where needed. The wheels are about the only important part that cannot be moved. As I mentioned earlier I mounted the servos in Aluminum U channel. However servos don't get you very far without wheels. I found a tutorial on mounting the omniwheels to the servos [here]
However I didn't like the design so I modified it slightly. I didn't use the finishing washer. I just used a standard locking washer. Also I tried the nylon bolts but found them lacking in stability and strength so I upgraded them to steel bolts. These work great and have not failed me yet.
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