Our group was tasked with creating a bicycle adapted for a child with a condition that causes muscle weakness.
Our child has a rare condition that causes her to lose strength in her muscles after prolonged exercise. She has wanted to be able to ride a bike for a few years now, but due to her muscle problems, they need an adapted bicycle to accommodate. She needs a bicycle that can move without her pedaling a lot and can hold her up in her seat so that she does not fall over while riding. An IV pole would need to be installed near the seat to hold her backpack to feed nutrition into her stomach bag. She also experiences drastic growth in a short period of time. To ensure the use of this bike for longer than a year, it will also need to be able to adjust to allow for comfortable riding when she grows taller.
For our design, we decided that electric tricycles or quad cycles were the best way to give stability and allow movement without tiring the child. For our background research, we looked at several bike manufacturers to see if we could find a base for our design that we could modify. We looked at drift trikes, LEV Manufacturing, bikes on amazon, and more. We also looked at recumbent trikes as an alternative to peddling or electric trikes. One manufacturer that had a lot of options was Worksman Cycles. We got into contact with them about possibly getting a work order and if we could get it within our time constraint. Thankfully, they are willing to work with us and gave us some input on our design ideas. Along with our base trike research, we looked at several different types of seating attachments to help with picking a comfortable seat that can keep her secure while she rides. M2 cushions were recommended by her mother; however, we also looked into racing seats as a possible alternative.
For this design, we would need to replace the seat with something more comfortable and create a sort of railing system to allow for adjustments to account for her height. It would also need to have the straps to allow for stability when riding. The IV pole also needs to be added to the rear of the trike.
One of the parent’s primary concerns for the bike is its safety. For our second concept design, we decided to use a quad-style bike to offer more stability than a three wheeled trike. Like the other concept designs, this bike will have lap/chest belts as well as an IV pole. This design has a basket behind the seat to hold the nutrition backpack and any other cargo the child may want to carry. On this design, the chair does not adjust forward/backwards. Rather the distance of the pedals can be adjusted in/out of the bike frame. If the distance of the pedals is adjusted, there is a tension pulley that will have to be adjusted as well to take the slack out of the chain. The rear suspension allows a more comfortable ride if the child chooses to ride over uneven terrain.
For concept design three, it shares many similarities to concept design two aside from a few differences. The biggest difference being this design is a recumbent style trike which is less stable than concept design two but is more light weight and less complex. Another difference is the bucket style seat with the four-point harness. This design also has the fixed seat with the adjustable pedal distance, the IV pole, as well as the basket behind the seat for the nutrition backpack.
We selected Design Concept one as our main design, as it had the best score on the decision matrix. It allows for less complex fabrication/modifications to ensure it works as expected. It also will allow for all design specifications to be met, without cutting any corners. This design is more cost-effective solution without compromising the child’s safety.
The selected design is a electric tricycle that will need a tall and comfortable seat that can support the child, as well as straps along her lap and chest to hold her up while riding. The seat will be made adjustable so that it can move forward and backwards to account for her height changes over time. An IV pole will be installed on the back of the tricycle for her backpack and a foot rest will be added near the pedals for when she is not pedaling.
For our seat we chose to use a go kart/racing seat as it will provide some back support while being tall enough for straps to be installed around the chest area. It will be attached to rods that will act as tracks for it to move forward and backwards so it can be adjusted for her height. We were also asked to keep the seat cleanable in case a bag were to pop. We will get a leather seat to ensure it can be wiped and will not soak in any accidents.
For the IV pole, we plan on removing the basket from the back of the tricycle and attaching a vertical metal rod in its place. We will then put hooks near the top for the backpack to hang as well as hooks lower down for the tubing to be set to ensure it does not get caught by the wheels.
Using the SolidWorks model of the seat, we ran a stress analysis to see if it could replace the factory seat by simply placing it on the single bar. We put a small rod on the bottom of the seat to act as the connection to the frame, as well as a distributed load of 400N along the top of the seat for the weight of the rider. Using this, we found that the seat had high stress on the connecting frame rod. This could cause the frame to wear over time and possibly bend and break. It could also cause the bike to be unstable.
We did the same stress analysis, but this time with a plate instead of the rod. This kept the stress off of the connecting point (the plate) and in the seat.
Using the SolidWorks model of the IV pole, we ran a stress analysis to determine how much stress it will be under with the weight of a backpack hooked on top. We applied a 15 lbf on to the hook, and ran the analysis and found that it bent quite a bit.
Using this, we can determine how long and thick the hooks need to be to decrease deflection and stress to the members.
For our third engineering analysis, we used a simplified motion problem to calculate the power required to accelerate the bike, as well as the duration it can run using the battery from our chosen design.
Assuming no aerodynamic drag and on flat pavement, we used force equations to calculate the force needed to accelerate to 10 mph in 5 seconds, thus giving us the power required as well. We then used the friction force to calculate the power required to keep the bike running at 10 mph. When assuming a 100% motor efficiency, with the 48 V 13 Ah battery on our bike, the total idealized time of usage was found to be 13.19 hours. While the realistic value would be lower due to motor efficiency, drag, and other forces, this value shows us that plenty of power is present to meet our child’s needs.
