16.2 - Design Process
Iteration 1: MotionGen Animation
Before building anything physical, we wanted to understand the link lengths that we would need to produce the desired wheel radius range. This was verified through a MotionGen Animation.
Iteration 2: Mechanism Validation with 3D Prints
Next we printed a singular wheel with 6 of our proposed mechanisms running in parallel. Links were connected with screws and we manually pushed the slider to see that under no load, our back-driven slider crank mechanism to increase and decrease the wheel radius was working.
Iteration 3: Rack Implementation
After validating the feasibility of our mechanism, we introduced a rack which we manually actuated to adjust the wheel radius. This will eventually be driven by a pinion that is actuated by a servo motor.
Iteration 4: Housing Integration
Here we attached our mechanism to the central housing unit which will sit at the center of the car. This shows us that we can successfully modify the wheel radius while it remains securely attached to the body of the car.
Iteration 5: Servo and DC motor Integration
Next we attached a servo motor to adjust the wheel radii and two DC motors to turn each wheel. We wanted to ensure that our 9V power supply could support all of the motors. We also see that both wheels are synced, so the servo expands the radius of each wheel equally, and the DC motors spin each wheel at the same speed.
Iteration 6: Driving on the Ground
Finally, we added a caster wheel to the back of the car and wanted to see how well it drives in both the large and small wheel configurations. With the larger radius, the wheel slipped as it moved forward due to the gaps between the spokes which reduced contact time with the ground. However, the car still moved forward at a reasonable speed despite this. Future iterations would focus on reducing these gaps by having a webbing run between the spokes or attaching rubber to the end of the wheels to reduce slipping.
Part | Usage | Quantity | Per Unit Cost | Total |
DS5160 Servo Motor | Rack and Pinion actuation | 1 | $34.99 | $34.99 |
DC 12V 110 RPM Motor | Accidental Purchase | 2 | $26.99 | $53.98 |
DC 12V 110 RPM Motor | Wheel Motors | 2 | $14.99 | $29.98 |
3 mm Linear Motion Shaft | Coupler and Crank Connection for final product | 2 | $11.17 | $22.34 |
1 mm Thick Washer for 40 mm Shaft Diameter Needle-Roller Thrust Bearing | Reducing friction between rack and slider | 4 | $3.76 | $15.04 |
M3*20 Screws | Coupler and Crank Connection for Prototype | 18 | $0.01 | $0.18 |
67.871 mm Wheel Slats (PLA) | Creates wheel | 6 | $0.19 | $1.15 |
67.871 mm Wheel Slats (ABS) | Creates wheel | 12 | $0.18 | $2.18 |
30 x 5 mm Crank (PLA) | Connects slider and wheel slat | 6 | $0.02 | $0.09 |
30 x 5 mm Crank (ABS) | Connects slider and wheel slat | 12 | $0.01 | $0.17 |
26 mm thick, 40 mm OD, 60 mm ID Slider w/6 connection points (PLA) | Slides | 1 | $0.99 | $0.99 |
26 mm thick, 40 mm OD, 60 mm ID Slider w/6 connection points (ABS) | Slides | 2 | $0.93 | $1.87 |
82.30 mm long, 40 mm OD Shaft (PLA) | Rotates wheel, acts as shaft for slider | 1 | $0.57 | $0.57 |
82.30 mm long, 40 mm OD Shaft (ABS) | Rotates wheel, acts as shaft for slider | 2 | $0.54 | $1.08 |
9.63 mm radius, 9.85 mm thick stopper ring (PLA) | Keeps slider from moving too close to gear box | 1 | $0.06 | $0.06 |
9.63 mm radius, 9.85 mm thick stopper ring (ABS) | Keeps slider from moving too close to gear box | 2 | $0.06 | $0.11 |
3.1 mm ID, 10 mm OD, 3 mm thick rack support ring (PLA) | Maintains rack vertical position in gear box | 3 | $0.00 | $0.01 |
3.1 mm ID, 10 mm OD, 3 mm thick rack support ring (ABS) | Maintains rack vertical position in gear box | 6 | $0.00 | $0.02 |
9.8 mm radius motor mount (ABS) | Attaches wheel motors to gear box | 2 | $0.01 | $0.02 |
30 tooth spur gear (PLA) | Turns rack | 1 | $0.24 | $0.24 |
30 tooth spur gear (ABS) | Turns rack | 2 | $0.22 | $0.45 |
65 tooth, 176.976 mm long rack gear (PLA) | Pushes slider along shaft | 1 | $0.52 | $0.52 |
65 tooth, 176.976 mm long rack gear (ABS) | Pushes slider along shaft | 2 | $0.49 | $0.98 |
170x76mm gear box (PLA) | Holds motors, rack, and spur gears | 1 | $4.83 | $4.83 |
170x76mm gear box (ABS) | Holds motors, rack, and spur gears | 1 | $4.58 | $4.58 |