ORIGAMI-BASED TRANSFORMABLE WHEEL ROBOT: STAGE I
Designing soft robot for rough and soft terrain
We developed a robot car with two transformable wheels, which can detect and climb over stairs, run on the sand and go through tunnels. Based on the literature review of transformable wheels, we chose origami structure for its compactness and mobility on the soft ground.
PROBLEM
In the rough terrain, traditional solid wheels are likely to result in a failure, which holds back the application expansion of vehicles and robots. In this project, we turned to the idea of using transformable wheels to build a robot, which can adapt to different terrains by changing shape and size.
CURRENT SOLUTIONS
Many different types of transformable wheels had been developed in robot design and real-world applications.
1. Wheel-leg based passive transformable wheels
Pros: Passive transformation eliminates additional actuators; Large deformation ratio
Cons: No leg mode when roll in the counter direction. The legs may bog down in the soft ground, especially when the soft layer is thick.
2. Origami based transformable wheels
Pros: simple structure, lower weight; quick transformation; continuously variable wheel radius. Large supporting surface to reduce pressure
Cons: complicated wheel structure; difficulty in fabrication
Based on several literatures, we decided to use the water-bomb origami structure to make the transformable wheel.
Wheel-leg Based Passive Transformable Wheels
Origami Based Transformable Wheels
ROBOT DESIGN
Two designs have been developed in sequence. The improved design enabled better performance.
Design 1.0
Transformation mechanism:
2 servos pushing wheel hub, 1 motor with long shaft
Test results:
Failed
(Large deformation in the long shaft after a few runs)
Reason:
Servos made the transformation slow.
(Undesired for origami-based transformation— the shorter the time, the less harm to the wheels.)
Solution
We compared our design with the model in Lee and Kim’s paper and decided to use similar design principles.
Improvement Principles:
Lightweight / Centroid close to the wheels / Small and Compact size / Quick transformation
Design 2.0
Transformation mechanism:
1 motor pulling with strings + 2 driving motors with gearbox
Improvements:
Better transformation mechanism — use pulling instead fo pushing
Centroid close to the wheels — place driving motors in the front
Reduced weight — replace long shaft with string
More compact — change design of chassis
MANUFACTURING
Transformable Wheels
Major obstacles: Composite Material Fabrication
Though we found fabrication methods in the literature review, the hydraulic pressure oven used for the composite material is out of our access. Without detailed information about the mesh fabric and advanced manufacturing machines, we failed in fabricating a composite plastic wheel.
Alternative solution: Paper Card (1mm) + Adhesive Plastic Sheet
The paper card provides the strength and the plastic sheet promises flexibility.
Wheel Fabrication
To manufacture the wheel, we first use laser cutter to cut the patterns on the paper card (step 1); Then cover a plastic sheet with glue on one side (step 2); After that, cut the pattern of the frame and then fold it (step 3-4); Finally, attach the wheel grousers and rubber band to the wheel (step 5-6).
Assembly of components
1) Assemble the motor to the shaft; 2) Assemble the bushing, gear set and pulley; 3) Assemble the origami wheel ; 4) Assemble the wheels to the chassis; 5) Assemble the Arduino, L298N and battery; 6) Assemble the ultrasonic sensors; 7) Put nylon string through the wheel; 8) Attach one side of the nylon string to the outside of the wheel; 9) Attach the other side of the string to the pulley.
PROTOTYPE TEST
Land Test
Sand Test
FUTURE
Manufacturing Improvement
The strength of the paper wheel is out of the expectation, which proofs another advantage of this “water bomb” origami structure. One possible improvement for future manufacturing is to reduce the resistance of pulling by changing the plastic sheet and using a thinner paper card. We did a pilot test with poster paper and a 0.5 mm high-density paper card. Though not tested on the car, the new wheel provided much less resistance during the transformation.
Application
Our design has the potential for broad application. It can be used on special vehicles to complete some emergency tasks on soft ground, like rescue in the sand or in deep snow. Also, the origami structure enables mini robots for life detection to reach the area which normal equipment and human can’t
OUR TEAM
YUXIN CHEN
Model Design