Ultralight Beam: The Climbing Robot

In my mechanical systems design class, we were tasked with designing a robot that climbs 1 meter up a steel I-beam at a 41.7˚ angle while holding a 2.5lb payload as fast as possible. Our robot consists of two wheels, two cylindrical roller wheels, a beam, a payload “basket”, and a chassis that ties our components into one system. We conducted FBD’s and FEA to ensure the robot would stay in static equilibrium with the payload, and then conducted a transmission analysis to maximize the power (and therefore speed) of the system.

Calculations

FBD’s

First, we conducted free body diagrams for the system in static equilibrium to evaluate all of the forces acting on the robot. In order to maintain the payload weight in equilibrium, we found that we needed a total of four wheels (one top wheel, one bottom, and two side) to counteract the reaction moments. We then calculated the ideal distance between them to remain in static equilibrium.

Speed Optimization

In order to optimize the speed of the robot, we found that the time to travel up the beam depended on the radius of the driving wheeel (rw) and gear ratio (Rg). In order to determine the ideal values, we first found the minimum value of force (Fd) required from the driver wheel to overcome the friction forces from the system. After obtaining this value, we created an optimization program on Matlab that calculated the ideal radius of the driving wheel for each of our 8 gear ratio options from the provided motor kit, given Fd, then created a separate script that loops through all combination of radius, gear ratio, and time. We found that using a wheel radius of 1.089 in and a gear ratio of 100:1, we would ideally be able to achieve a travel time of 2.89 seconds up the beam.

CAD Design

The chassis spans the 6 inch distance of the I-beam and serves as the connection between all of the components in our system: the motor, the beam, the cylindrical rollers, and the wheels.

FEA Analysis

The most important finding from the FEA is the chassis’s deflection. We found that the chassis will deflect the most at the right side wheel with a displacement of .01054 inches and found the maximum stress is located at the beginning of the extrusion that connects the chassis to the side wheel and has a value of 3.444 MPa.

Chassis Assembly

The chassis’s main function is holding the wheels and beam in place to maintain equilibrium on the I-beam. Because the robot climbs at an incline, we designed its foundation that holds the beam with an incline of 41.7 degrees to increase the clearance and to make most of the bending happen in the y-axis. There are through holes dimensioned to secure the motor and bottom wheel support. The wheel is fastened in place by a bearing and the side wheels are also attached to the chassis by press fit bearings that allow the cylinders to rotate along the edges of the I-beam.

Beam FEA Analysis

The most important finding from the FEA is the beam’s deflection. We constrained the left side of the beam to be fixed at the point where it connects to the chassis to mimic the press-fit connection. We applied a downward force of 10.67N at the right end of the chassis to represent the payload. As a result of this FEA, we learned that this design gives us enough clearance for our beam to not make contact with the I-beam and meet criteria of keeping payload deflection to less than 0.5 inches.

Beam Design

The beam is a two-part member that is press-fit into the chassis on the left end and holds the payload bucket on the right end. We created two separate beams that are fastened together in order for them to fit on the print bed of the Ender3. With a factor of safety of 2, our goal is to minimize deflection while being mass efficient, which is why the beam is relatively thin and long. At the end of the beam, there is a 2 prong extrusion which serves as a connection to the basket that holds the payload.

Bottom Wheel Support

Through FEA analysis and an iterative process, we designed successful support for the bottom wheel. The piece is fastened to the chassis under the motor using 4 screws and its geometry is mass optimized to support the normal reaction force on the wheel. We also press fit two bearings to the sides of the wheel to allow the shaft to spin freely and be supported from both sides.

Final Design

  • Final CAD

    Based on over 10 different prototypes and multiple FEA studies, this was our final CAD model (not including the basket that holds the payload).

  • Top View of Static Equilibrium

    This shows the top view of how the robot attaches to the I Beam and stays in static equilibrium. As you can see, our FBD’s checked out and our design was able to stay steady in static equilibrium. The next step was to get it to move up the beam…

Success! Our robot had the second fastest climb in the class.