Sehome Seamonsters (FRC Team 2605) Swerve Drive
This swerve drive design makes use of twisted belts, 3D printed parts, and a custom fabricated bearing to create a very compact yet relatively simple-to-build omnidirectional drive.
The design is pretty tightly constrained and there is not a lot of leeway for modification.
However, the base place can easily be redesigned different mounting configurations and for different steering motors, and the wheel can be modified for different tread patterns or for adding on a separate tread material or tire.
Initial testing indicates that twisting the belts does not appear to damage them, but we have not done full life testing. We highly recommend keeping a spare set of belts on hand for competitions.
Similarly, the 3D printed (PLA) wheel, idler block and steering pulley seem sufficiently durable for competition. These parts should be printed nearly solid. Again, we recommend having spare sets of printed parts on hand for competition.
Complete Solidworks design files are available at:
http://www.thingiverse.com/thing:1135618

Swerve Drive Bill of Materials
[Base Plate Assembly]
1 CIM motor (AndyMark - am-0255)
1 Base Plate (Machined)
2 10-32 x 1/2" FH screw (McMaster - 92210A302)
1 AMT103 encoder (Digikey - 102-1308-ND)
2 M2 x 6mm screws (McMaster - 92005A023)
1 Long 18t pulley (from GT2 3mm pitch pulley stock SDP/SI - A 6A52M018GT13 )
1 Hub Collar (Machined)
1 6-32 x 1/2" sockethead cap screw (McMaster - 92196A148)
[Caster Plate Assembly]
1 Caster Plate (Machined)
1 Wheel Flange (Machined)
2 1/4-20 x 3/4" FH screw (McMaster - 91253A540)
2 4-40 x 1/4" sockethead cap screw (McMaster - 92196A106)
[Bearing Assembly]
1 Fabricated bearing:
1 inner race (Machined)
1 top outer race (Machined)
1 bottom outer race (Machined)
35 7/32 steel balls (McMaster - 9528K14)
6 6-32 x 3/16" set screw (McMaster - 92311A143)
1 Steering Pulley (3D printed)
6 8-32 x 0.625 screws (McMaster - 90272A196 )
[Caster Plate Assembly]
[Steering Assembly]
4 8-32 x 3/8" pan head screw (McMaster - 90272A192)
[Bearing Assembly]
[Base Plate Assembly]
[Idler Assembly]
1 Idler Block (3D printed)
4 1/4" dia x 3/4" long dowel pin (McMaster - 5227T232)
[Wheel Assembly]
1 Wheel (3D printed)
2 1/2" bore x 1 1/8" OD flanged bearing (AndyMark - am-0030)
[Complete Assembly]
1 10-32 x 1 1/8" button head screw (McMaster - 92949A826)
1 #10 washer (McMaster - 92141A011)
[Steering Assembly]
[Idler Assembly]
2 Idler125 rollers (Machined)
2 Idler138 rollers (Machined)
2 125t GT2 3MM pitch x 6mm wide belts (SDP/SI - A 6R53M125060)
2 138t GT2 3MM pitch x 6mm wide belts (SDP/SI - A 6R53M138060)
[Wheel Assembly]
1 1/2" dia x 1 1/2"L shoulder screw (McMaster - 91259A716)
1 NeveRest Motor (AndyMark - am-3102)
2 M3 x 10mm pan head screw (McMaster - 92005A120)
1 Short 18t pulley (from GT2 3mm pitch pulley stock SDP/SI - A 6A52M018GT13 )
1 8-32 x 1/8" set screw (McMaster - 92311A188)
2 8mm bore x 22mm OD bearing (McMaster - 5972K222)
1 8mm dia x 16mm L shoulder screw (McMaster – 92981A202)
1 8mm or 5/16” washer

Swerve Drive Assembly
1. Base Plate Assembly
Assemble the Base Plate to the CIM motor with 2 10-32 x 1/2” flathead screws

2. Add Encoder and Long Pulley
Screw the AMT103 encoder base to the aluminum base plater using 2 M2 screws.
Solder five 26 gage wires directly to the pins of the encoder and insulate with heat shrink tubing before proceeding with the encoder assembly as there is no room for a proper connector.
Assemble the encoder as per the encoder instructions. Snake the wires thru ths slot in the base plate.
Assemble the hub collar on the long pulley and slide onto the CIM motor shaft.
The collar should ride just above the encoder body. Secure the collar with a 6-32 socket cap screw. Make sure the pulley hub does not interfere with the encoder housing. (You may need to trim the head of the 6-32 screw a little bit.)

3.Bearing Assembly
Insert six 6-32 set screws into the top of the top outer race. (The top view is shown.) These set-screws are used to set the proper gap for the balls. Just get the set-screws started.
Place the inner race inside the outer race and carefully fill the gap with a full compliment of balls. Putting a little grease on the races will help keep the balls in place. Place the top outer race on top of the balls to hold them in place.
Temporarily insert six 8-32 screw into the bottom side of the bottom outer race and screw them all down lightly until the balls are no longer free to move. Now tighten all of the set screws just enough so that the inner race is just free to move. You will have to play around a bit to get it so that the bearing rotates freely, but with very little play.
Place an alignment mark with a Sharpie across the two outer race halves to make sure you keep the same alignment of these parts.

4.Caster Plate Assembly
Screw the caster plate to the wheel flange using two 1/4-20 flathead screws.

5. Bearing/Flange Assembly
Very carefully remove the 8-32 screws from the bearing and then slide the bearing assembly into the steering pulley. Use a small allen wrench to align the
8-32 holes in the bearing with the holes in the pulley.
Place the steering pulley on top of the caster plate and insert the 8-32 screws through the bottom of the plate and screw into the threads in the bearing's top outer race.
Tighten everything down, making adjustments so that the bearing operates smoothly but with very little play.
Make sure that none of the 8-32 screw ends or the 6-32 set screws are sticking out above the top surface. If necessary, grind them down flush.

6. Steering Assembly
Rotate the bearing inner race so that the screw holes are aligned with the access cutouts in the caster plate. Screw the inner race to the base plate with two 8-32 screws.
Rotate the caster until the other two inner race mounting holes are visible and install the last two 8-32 screws.

7.Idler Block Assembly
Press the 4 dowel pins into the idler block. Make sure the outer two pins don't interfere with the mounting screw slot. (You may want to grind an angle onto the ends of the outer two pins so that you can insert them further.)

8. Steering Motor Assembly
Insert two 4-40 socket head cap screws in the small holes on either side of where the idler block will go. The screw heads will keep the block from rotating.
Apply a little grease to the dowel pins. Slide the two “125” idler rollers over the inner pins and the two “138” idler rollers over the two outer pins.
Loosely screw the idler block to the caster plate with a 10-32 button head screw and a #10 washer.
Loosely screw the steering motor in place and attach the short pulley with the 8-
32 set screw.

9. Wheel Assembly
Press the two 1/2” bore bearings into the wheel.

10. Complete Assembly
Place one of the 125 tooth belts over the steering pulley and steering motor pulley. Assemble the two 8mm bore bearings over the 8mm shoulder screw and screw to the base plate as shown. Use an 8mm (or 5/16”) washer between the bearing and the base plate. Pull the steering motor back to tension the belt and tighten the motor mounting screws.
Place the 138 tooth belt over the CIM motor pulley and under the “138” idler rollers. This belt goes closest to the motor. Place the other 125 tooth belt just above the 138 tooth belt and under the “125” rollers. The belts should be twisted so that the flat side of the belts ride against the rollers.
Position the wheel above the idler block and slip the belts in place as shown.
Insert the 1/2” dia. shoulder screw through the wheel bearings and tighten into the hole in the wheel flange.
Rotate the wheel so that the allen wrench access hole aligns with the 10-32 button head screw holding the idler block. Slide the idler block to the outside to tension the belts and then use an extra long 1/8” allen wrench to tighten the idler block in place.
Check the tension on all the belts and make sure the steering and drive axes operate smoothly.