Menu
The goal of this project is to redesign an existing hand trike from a previous project. The input source for the motion of the trike must be through the handles and not through foot pedals. The general idea of the existing model will be used as a starting point for our project and we intend on making improvements and modifications based on recommendations from the family.
The child we are doing this project for has limited use and sensation in his lower extremities, so he needs a trike that he can operate without using his legs. The trike we are working on will be powered through the handles much like a rowing bike. The trike will require both seat and foot straps to support the child while he is using the trike.
– Buckling system to strap in upper body while in use; i.e. some sort of seat belt
– Straps or supports for feet to keep them in place while the trike is in use
– Movable seat to allow for future growth of the child
– Power input through handles
The hand trike that we received from the previous group was very similar to the current market for hand trikes. We will keep the seat belt and foot straps to keep Dakota secured in the seat.
Concept 1 is very similar to the original trike design with some key improvements. The two main design changes are a rerouting of the gear and chain system. In the old design, the gear and the chain were coming into contact with the child’s legs and making it difficult for him to operate the trike. This design elongates the handles and moves the chain away from the body of the trike to allow more room for ‘rowing’ the trike to get it to move. Another main design change is raising the seat and the addition of a rail for the seat to slide on so that it can be adjusted to better fit the child’s height. Lower arms on the seat will allow for easier arm movement. This design will connect the buckle to the seat and improve the foot support.
This design will keep the original shape of the trike, that being two wheels in the back and one in the front. In this design, the classic crank and chain will be taken out and replaced by a crank and connected to multiple links which will be mechanically powered from the wheel.
Concept 3 design follows the original design of the trike, with some improvements. This design will need the frame to be chopped and extended to give room for the main changes. Those being, a bigger diameter front tire, wider body in the rear, adjustable seat, adjustable footrests, adjustable handles, and a lap belt.
We used a Decision Matrix to compare the three concept designs.
The selected design will be a combination of all three designs, where we will take good components and features from the three designs and combine them to make the best trike possible. This includes, a chain guard, new metal bars, new tires and wheels, bindings for the foot rests, sliding seat, extended frame, and brake.
This design will have a bigger diameter wheel and tire compared to the rear wheels and tires. It will also allow the seat and foot rests to be adjustable. The foot rest will also have more of a binding style so they can be slipped into and out. The gears and chain will need to be replaces as they have rusted. Since we are doing this we will use a bmx style brake either on the front tire or rears. The handle bars be made of full metal and have actual grips. To do all this the frame may be extended a little bit.
The goal of the first analysis was to examine the reactions and stresses on the beam that holds the seat. To do this, the machined connections were treated as walls on either side of the beam. A total weight force of 60 lbf was used to account for both the weight of the child and the weight of the seat. The seat is in the middle of the beam; therefore, the force acts in the middle of the beam. The reaction forces at either end are R1=R2=30 lbf. The maximum moment in the beam was found to have magnitude 60 lbf-in. The max bending stress was found to be 62.5 psi and the max shear stress due to bending was found to be 20 psi.
For Engineering Analysis 2, we decided to do a stress analysis on the seat. In the event that the trike is tipped back due to the weight being all in the rear and easy to pull up on the front, we wanted to make sure the seat would not break. The seat was made in Solidworks and a load was apply at the top of it, this being the most critical point if a load was applied. The trike probably weighs around 20 lbs so the applied load was set to 60 lbf. The seat did not show much deflection or stress.
This engineering analysis was used to show the stress on the crank arms for the pedaling. They rotate in two directions, the first direction will drive you forward, the opposite direction will apply a brake. When applying the brake the crank arms will recieve the most stress, also since when released it kinda kicks back a little. An applied load was added to the end, no more than 30 pounds. The analysis showed that the crank arms were fine, the delfected very little and didn’t have enough torque to snap the mount.
To build the new trike, we first completely disassembled the old one. The old frame was in good condition so we decided to reuse it. From a new youth bike, we took the gear train system as well as the back wheel and pedal system to use for the trike. The bike frame had to be cut apart so that we could access the chain. We then mounted the pedals to form handles on the trike to drive the front wheel. This was done by welding. New rear tires were also added. We decided to 3-D print a guide for the chain as well as a guard. The footrests are also 3-D printed. To attach the seatbelt we drilled it into the frame and wrapped it around the seat.
Ensure the seat is properly attached to the frame by inserting both pins through the holes in the bottom of the seat and the frame. Note that the pins will need to be inserted in opposite directions to ensure they go all the way through. Buckle seat belt before use. Make sure feet are secured on the footrests and legs are not in the path of the chain.
