Simon's Omnidirectional 4-wheeled Robot (modified Robodyssey Mouse)

thingiverse

My student, Simon Shao, made this to fit on the chassis of the Mouse robot by Robodyssey Systems (http://www.robodyssey.com/teensy-mouse-kit/). Normally the Mouse is a two-wheeled robot, but with these wheels, hubs, and servo mounts, the Mouse robot becomes an omnidirectional vehicle, which can move in any direction. See it here on YouTube: http://youtu.be/jVVpeu6Htxc. UPDATE: Users now have the option to print servo mounts and wheel hubs either with or without brass inserts. With brass inserts, the 4-40 and 8-32 mounting screws bite into the metal inserts, allowing them to be inserted and removed many times without damaging the plastic. However, some may not want to buy the extra hardware, so another version is now available that does not require the brass inserts. Instead, the screws can be inserted directly into the plastic, which is fine if the screws will not be removed often. (The latter option requires that the holes be tapped or self-tapping screws used.) Instructions Simon and I printed these with a MakerBot Replicator 2 at low resolution (0.3mm/layer). The conical wheel sections have 2 shells and something like 15% infill. The wheel hub and servo motor mounts were printed with 3 shells and 25% infill. Only the bottom portion of the servo mount is required. Again, it is designed to fit to the body of the Robodyssey Mouse robot (http://www.robodyssey.com/teensy-mouse-kit/). The top portion adds some stability and gives two mounting holes on each side for a Sharp Infrared sensor (http://www.robodyssey.com/sharp-2yoa21-infrared-ranging-sensor/) The wheels require a 4mm aluminum rod to serve as the axle rod. We ordered this from McMaster-Carr (http://www.mcmaster.com part number 1681T22) and cut each axle down to 35mm. For traction, each wheel needs one large o-ring (3mm, 29mm ID), although dipping the wheel in liquid rubber may also work. The o-ring was also purchased from McMaster-Carr (http://www.mcmaster.com part number 9262K742). It is recommended that a small washer be inserted between the wheel and the wheel hub to prevent the plastic parts from rubbing. The size of the washer depends on which file you download. If you print the hub whose file name includes the words "tap holes" then use a 4.3mm ID washer, for example 93475A230 from http://www.mcmaster.com. If you print the hub whose file name includes the words "brass inserts" you will need a 5.3mm ID washer so that it fits over the nylon spacer, for example http://www.mcmaster.com part number 91166A270. (In a pinch, the latter washer will work for either hub.) The servos are attached to the printed servo mounts with 8-32 screws. The wheel hubs are attached to a servo horn with 4-40 screws. (If you want to attach a Sharp IR sensor to the servo mount, 4-40 screws are also used for that.) UPDATE: You now have two options to choose from regarding the servo mount and wheel hub. The files that include the words "tap holes" can be printed and used as is -- no additional hardware (other that that listed above) is required. However, you will need to tap the holes for 4-40 and 8-32 screws or use self-tapping screws. The files that include the words "brass inserts" require the purchase of additional hardware. The brass inserts allow the screws to bite into metal rather than plastic. (This option also makes use of nylon inserts on the wheel hub so the metal axle spins more smoothly.) The additional hardware are as follows: Threaded brass inserts. Instead of tapping holes directly into the plastic, we find it is better to use threaded brass inserts, especially if the servos and the hubs are to be removed often. As you might guess, these are from McMaster-Carr (http://www.mcmaster.com part numbers 92395A114 (for 8-32 screws) and 92395A112 (for 4-40 screws)). Nylon spacer. This spacer fits in the large holes on the end of each arm of the wheel hub. The thinking was the smooth inner wall would reduce friction of the axle rod and support a metal washer between the wheel and hub arm. (http://www.mcmaster.com part number 93657A857). [* If you have some cash to spend, then forget this nylon spacer and purchase a double shielded ballbearing casing (http://www.mcmaster.com part number 7804K1) which spins like butter. The last wheel inserted will be a tight fit, though!]