This idea demonstrates a way to securely attach a servo motor to a omni wheel.  It is a low cost way to non destructively mount the wheel to a servo motor mounting horn.  You will need the following parts:

• 1/4"-20x5/16" T-Nuts, quantity 6
• 1/4"-20 Nylon Machine Head Screw, quantity 3
• 5/16" Internal Splined Tooth Washer, quantity 6
• 5/16" Copper Finishing Washer, quantity 3
• 42-Pack of 2-56 Machine Screws
• 40-Pack of 2-56 Hex Nuts

Most of these parts can be found at home building supply stores such as Lowes, Home Depot, etc.  The 2-56 machine screws and hex nuts can be found at Radio Shack.  Total estimated cost for all the parts is around $16.00. 

Use the T-Nut as a template to drill the holes in the servo horn.  Drill holes with a #48 size drill.  Then use the 2-56 screws to fasten the T-Nut to the servo horn as shown below.  Also place the 5/16" copper finishing washer over the T-Nut so that the wheel hub will have a flat surface to rest against.  Then place the 5/16" internal splined tooth washer over the T-Nut, so the wheel will not come loose. 

Cut the 1/4"-20 nylon screw to a length of 1-3/8".  Place the hub of the wheel over the T-Nut in step(1) as shown below:

Insert the second T-Nut into the front of the wheel hub. 

Finally, place the 5/16" internal splined tooth washer on the shaft of the nylon screw.  Then, thread the nylon screw into the second T-nut and into the first T-Nut as shown below and you are finished with the modification. 

Thanks to Abraham L.  Howell for contributing this example and images!

Related Links:

Deluxe Brainstem PPRK Overview