Team Goal: To build a rowing-propelled vehicle that encourages exercise and is enjoyable for Putnam County students experiencing physical and mental challenges that prevent the use of traditional pedal-powered bikes.
We were introduced to students that struggle with riding pedal bikes but desperately need an exciting and rewarding form of exercise. We encountered a challenge that included designing a bike that is stimulating, fun and that accommodates to specific needs of PCSS students, while also applying design details that are considerate of the academic care takers helping students use the vehicle.
Our initial research sparked from discussions with last semester’s team and their bike project from previous semesters. The original bike had a ratcheting chain drive and unique clutch piece for reverse mobility. We believed the original bike had features that would meet some of the obvious and important needs for the student. Research expanded after meeting with Mrs. Draper, the student’s academic caretaker. Mrs. Draper elaborated on more detailed features the bike should have to optimize the student experience and bike mobility. This meeting helped us understand what we could add to the bike from the caretaker’s perspective. From here, the details of our objective became clear for overall experience of the students. We elected to start from scratch, rather than build off of the previous bike. New, necessary research was done with our awesome TTU shop engineers. We were guided on materials, framework, assembly and other critical points that would help us develop a timeline for a project that could be completed. More detailed topic points helped consider weight and structure purposes. Sawyer’s sleek wooden pedal bike and the unique Sandwich bike represent a lot of the ideas we talked about with the shop engineers. These examples provided the primary ideas for constructing with plywood, leading us in a strong direction to solve issues that previous bikes may have encountered in the past. Our two new concepts blossomed from here and more advanced geometry and functioning began taking shape.
• Spring/Fall 2022 Design:
• Sawyer’s Wooden Pedal Bike
• The Sandwich Bike:
• The Youtube Short Trike:
• Course study utilized:
Our first concept and initial design option was a 4-wheel steel frame bike from last semester’s rowing bike team.
Initial Frame Drawing:
This bike was our starting point because of the quality work put in by the bike’s previous teams. Before we met with the student therapist, we had the impression that we could continue this project by optimizing the bike’s systems and finishing the remaining work needed. The system in need of the most work was the steering. Our team was going to apply a mechanical steering system in the drawing shown below:
Using universal joints and slip yokes, the design- in theory- would allow for the ratcheting motion of the row bar for propulsion, and for steering through a center bar connecting to the tie-rod steering system that was originally planned by the previous team.
One reason for moving on from this concept came from observing sections in the steel frame that could require a re-weld. Weak points from sharp geometries were identified, causing concern.
Other features included:
With this concept, this old frame and design ultimately ended up as a starting point, and far from our actual design.
Concept #2 demonstrates the infant stages of the new plywood frame bike inspired by the TTU shop engineers. Notice in the third image below the basic concept of the “sandwich” design. A similar cable steering system carried over from Concept #1, remaining nearly unchanged. With the new plywood frame, new initial ideas surrounding the drive lead towards using a direct linkage drive with a 1:1 ratio. The frame is angled much differently from the front to the rear in comparison with Concept #1. Included with the new framework was the introduction to a new adjustment feature for the seat to help prioritize student experience.
Concept #3 includes some of the latest design ideas. The biggest idea being the hybrid transmission that includes a link drive, meshed to a gear on the rear axle of the bike. The capabilities of the hybrid drive allows the bike to roll freely when being pushed without a rider onboard. Our group considered potential safety hazards with Concept #2’s direct link setup, as the handlebars move back and forth in it’s rowing motion while the bike is being pushed. Frame updates include a new “swept” design that is much more considerate of student ride height, increasing safety for the rider. This concept maintains Concept #2’s cable steering system, only changing potential geometry of the cable setup.
Concept Design #3 is the most evolved in terms of safety, experience and portability. Our group has decided on Concept Design #3.
The selected design, Design #3, is considerate of many requirements for a bike that is easy to use, portable and enjoyable. It is also considerate of the cost and time constraints placed on the team.
The bike consists of the following features:
The rowing arm propulsion system was selected because of the effort-to-reward element, and the easy integration into the sandwich frame design.
The rowing arm runs from about the height of the riding child’s shoulders to the bottom of the frame. It is mounted into the frame with welded bearings. The bottom of the rowing arm is linked to the rear axle sprocket by chain. The chain design was chosen over the linkage design to generate a greater reward for the child’s rowing efforts through the gear ratio selection, and to minimize “dead zones” in the propulsion system dynamics. The rowing arm system components also fit flush and are easily mounted inside of the “sandwich” frame design.
In the interest of simplifying our design and decreasing lead time, we also elected to discard the steering system, since the ability to steer was an optional design parameter to begin with.
The bike needs a feature that can help the student caretaker move it out of tough to maneuver situations. For example, if the child rode the bike to a dead end, the caretaker has to able to remove it out of a jam. A caster system was chosen because of its simplicity. Other ideas that offered a greater maneuverability feature, such as freewheeling, required more technical work in the drivetrain. While these ideas were very much possible, it was clear to the team that the caster system idea removed a lot of work that would take up time during the short semester provided to deliver the bike.
The mechanics behind the caster system are straightforward. The system consists of 2 caster wheels. The placement of these wheels are centered between the bike wheel and the bike frame on their respective side. While deactivated, the caster system tucks up between the bike wheel and the bike frame, removing the caster wheels from contact with the ground. It can be activated via a cammed pedal, that props the wheels down and lifts the rear side of the bike off of the ground. The caretaker can now swivel the bike, while the front wheel acts as a pivot.
The plywood sandwich design was the obvious choice for frame design. The multiple benefits of the sandwich frame include weight of the frame, the cost, the lead time for manufacturing the frame, the time necessary to assemble the frame and structural support provided by the plywood material.
Initially, the bike was a steel frame. As previously stated, the team examined the frame and determined that it had weaknesses and concerns. Fixing the issues involved with the steel frame would require too much effort and time for the semester-long timeline. Taking the plywood direction for the frame removed a lot of cost (much less steel material required) and time necessary for completion. The plywood frame materials can be purchased locally with little to no lead time and can be cut in a matter of a day by the team, with the help of the shop engineers and their equipment. This greatly increases the chances of delivering a complete bike to the students.
The sandwich frame also enhances the safety of the bike. It provides protection from injury from the mechanical components by essentially housing the entire chain driven propulsion system. This keeps children from placing their hands and feet in areas where extremities could easily be caught and/or injured.
After receiving guidance from Jeff Randolph, we elected to use sections of 80/20-style t-slot aluminum rail as standoffs for the bike’s frame.
The adjustable seat feature is considerate of the height range, and arm length differences between the children that might ride the bike. It is a simple pin design that can lock into multiple position slots located on the bike frame. There are 5 adjustment settings for students that range in height from 4-1/2′ to 5-1/2′.
Analyzing the rear axle of the rowing bike was a necessary test to perform as it is the most critical for safety and performance reasons. The expected max weight of a child that will sit in the rowing bike’s seat is approximately 150 pounds. For assuring feedback, the applied load on the axle in this analysis is 300 pounds, which is double the expected weight of any child that will ride this bike.
The purple arrows in the analysis image represent the 300 pound force applied, and the green arrows represent components of the real axle that are statically determinate.
The different colors throughout the rear axle component represent the amount of deflection due to the applied load. Blue represents the least amount of deflection, and red represents the greatest amount of deflection, at a minuet measurement 0.15 millimeters.
This test confirmed that our design will successfully maintain stability, durability and structure for proper functioning while the bike is being used.
For the rowing arm analysis, we have and are continuing to have great considerations towards the child’s overall experience. It is necessary to provide something that encourages physical exercise. The child must also be rewarded with a safe but strong enough propulsion for fun and excitement. Delivering a bike that is too difficult to row would exhaust the children too quickly, discouraging exercise, and would be boring to ride. It’s obvious but critical that the bike holds fun and exciting characteristics.
This analysis considers a pulling force that a child could apply to the rowing arm, which was determined to be 50 pounds. The influence behind choosing this force amount came from a study regarding how much force needs to be applied to a child-dimensioned bow to successfully fire an arrow.
Breakdown of Arm Analysis:
The first portion of this analysis positions a force up to the 50 pounds against tension felt in the chain:
After MATLAB computation, the max tension felt by the chain is likely an approximate 352 pounds.
For the second portion of this analysis, the max tension force of 352 pounds applied on the chain was placed against different potential lengths of the rowing arm component:
This portion of the analysis provides insight towards how the team should move forward when designing the rowing arm mechanism for an efficient effort to propulsion ratio when rowing the bike.
The MATLAB code used to compute these figures is linked below:
The third analysis performed had to do with the force required to prop the caster wheels into place and successfully lift the bike up off the ground.
The calculations above include estimations in regards to bike weight, max student weight and dimensions regarding the bike frame and caster component.
These calculations demonstrated that a force 75% of the total weight (bike and student combined) coming down due to gravity is necessary to activate the caster wheels and prop the bike up off of the ground.
The fabrication process took about 4 weeks. Fabrication activities included many hours of cutting wood and metal, welding components together and painting all sections of the bike. For cutting, a laser cutter was used to cut out the frame rails. Metal components were cut with a bandsaw, and modified with drilling, filing and welding. Altogether, the prototyping and fabrication process went very smoothly.
Assembling the bike was done with mostly bolts and screws. The frame rails were put together with bolts running through the stand-offs and mono-block, creating the sturdy and parallel stance of the entire frame. The real axle was put in place with mounts and bearings for it’s smooth revolution movement. The seat was bolted to its mount, which was then pinned to the frame, ready for adjustment if necessary. The front wheel and yoke run through the front monoblock, while the rear wheels are mounted on and kept in place by welded hubs. Brake lines run through the inside of the frame rail back to the rear control handle bars. And finally, the rear drive components rotate around the rear axle while the rowing arm mounts to the inside of the frame.
After completing the assembly process, the bike was tested by teammate Zach Hinchman and Dr. Canfield. The testing session demonstrated that the effort-to-reward target was hit, and that the bike reached a quick enough, but safe enough speed to really enjoy. Later that week after tests, the bike was delivered and was tried by a student. The student rode the bike and was left with a smile on his face. The bike is a true success.
** Hugo did manage to survive a devastating blow from Spencer.
Although the rowing bike was designed to take on more than the weight of most elementary school students, the teacher/caretaker should be mindful of who rides the bike. It is not intended to take on more than 150 pounds for long periods of time.
The bucket seat and seatbelt offer great safety features to keep the rider from falling off the bike. Be sure that the student is always buckled in before riding.
All mechanical components of the bike are housed underneath the rider’s seat, between the two wooden sandwich rails to protect against hands/fingers from getting caught, but the student and the teacher/caretaker can still interfere with the functioning if one was to reach inside the bike. Be sure to avoid sticking hands/fingers around the mechanical works of the bike.
This project has had struggles in past semesters due to the complexity of designing an all-around usable bike. Factors like weight, effort-to-reward ratio, safety, durability, cost and a few others create a tall task. This project was completed because of the ambition, shop experience and leadership displayed within the members of our group. Guidance from Chris Mills and Jeff Randolph was also necessary for our team to make the most of our time and deliver an operating bike. We are more than grateful for their contributions to our work. This project went through many design iterations before we were able to settle on a solution that met all of the necessary parameters. Adaptability, teamwork and investment of thought and time were needed to take the bike project from where it was, to it rowing down the halls of local schools. Team members were able to gain experience working with other members and also gained experience fabricating in the shop to bring the bike to life. Everyone in our group was an integral part of the effort; this project would never have been completed without each member’s contributions, and we are proud to deem this project an incredible success.