Our goal is to construct an off-roading walker for a young boy with RTS syndrome. Rubinstein-Taybi syndrome in a genetic disease that affects mobility because of low muscle tone in the patients. Due to this, our client requires a walker to assist him in moving around.
For our project, we are creating a walker that has the ability to function on rough terrain such as grass, gravel, and tile. The walker also has to be adjustable height and width wise to accommodate his needs for a long time. We plan to make detachable accessories for the walker to help increase the comfort for him.
The photos attached show his current walker, which is a Rifton Pacer. We met with his father to discuss him and the design specifications for the walker. We still have to meet again to see the walker in person and also to see how he uses his current one. However, in our meeting, his father explained the following:
The Rifton Pacer 501 is a walker specifically designed to be customized to the needs of the user. In our research, we found that many of its features are customized through locking sliders, knobs, and straps that buckle. In the photos of the Pacer currently used by Wayland, it’s clear that he uses the chest harness, which straps around the user’s chest to give them more support. We found through multiple tutorial videos that it’s common for the chest harness to be positioned too high and too loose. These videos are linked below.
In the pictures, it also looks like Wayland uses the hip positioner, which acts as a sort of saddle for support of the hips. The straps connecting the positioner to the frame of the walker are extremely customizable and can be connected to pretty much any part of the frame depending on the needs of the user. A video explaining this in further detail is linked below.
Rifton Pacer: Tips on how to adjust a gait trainer
Modify his current walker
Pros: The frame is already built for us
Cons: He wouldn’t have access to his walker while we were working on it
Make a walker from scratch with 4 swivel-locking wheels
Pros: Design flexibility
Cons: We have to create the frame from scratch
Make a walker from scratch with 3 wheels
Pros: Cut down on the weight of the walker
Cons: It might lose some of the stability
After some research into the required materials and consideration of the timeline of the project, our final design became a hybrid of Concepts 1 and 2. We were able to procure a used Rifton Pacer model, which was larger than the boy’s current walker, to modify to his specific needs. This had a threefold advantage: solving a key design problem (a larger and more stable base than he can grow into), allowing him access to his current walker if needed, and avoiding the cost and complexity of creating a new frame from scratch.
Our main concern became modifying the new walker to suit the user’s needs. The key to maintaining off-pavement stability is the wheel base and size. We formulated an extension bracket to accommodate larger off-road wheels and increase overall stability through increasing width. The bracket arms also rotate to set positions, allowing the user to narrow the walker to fit through doorways or for transport. The Rifton frame we are purchasing already folds vertically for transport, fulfilling that design criteria.
We also plan to create/modify several accessories including a stability harness and custom cupholder to improve the versatility of the design. Use of another Rifton model also allows the family to use accessories from their previous walker, including a guiding handle and arm rests/support items.
Our first method of analysis was to replicate the motion of our design in MotionGen.io. Our design includes 3 bodies joined by 2 revolute joints.
Ignoring the locking pins, which rigidly lock bodies together, this gives the overall mechanism a mobility of 2. This represents the rotational degrees of freedom of the arm and the caster, with respect to the vertical axis.
The images shown include a top and side view of the walker with our modifications as well as a static analysis. These equations are variable based as we do not have proper measurements yet.
This image shows the stress analysis on the pin connections. However, the stress on these pins should be very minimal to where it doesn’t have any major affects
Our first priority was switching to the bigger wheels. Because the back wheels were already casters, it was very simple to swap them with the 7 inch ones that we ordered. However, the front wheels were not casters and were mounted directly to the frame. This made putting our casters on the front much more complicated.
To combat this, we fabricated an attachment piece that we could bolt the stems of our casters into. Starting with a piece of 1 ¼ inch steel tubing, we cut two two inch long segments. To attach it to the frame, we cut a piece of steel sheet that would weld to the tubing and bolt onto the frame. However, to ensure that the wheels would be perpendicular to the ground, we had to account for the angle of the frame with the shape of the sheet. After welding the pieces together and grinding down the sharp edges, we were able to successfully replace the original rigid wheels with the larger casters we had ordered.
This is where we ran into a problem we hadn’t really anticipated: larger wheels meant that the walker would be that much taller. We had a few options on how to solve this problem, but we ultimately decided on cutting the legs shorter and adding new holes for the telescoping parts to snap into. For front legs, this was as simple as taking out the telescoping tubing and cutting the outer tube with a hacksaw. We then shortened the inner tubing and moved down the leaf spring pin that allowed it to lock in place. After filing down the rough edges and drilling the necessary holes, this suitably reduced the height of the walker in the front.
However, the back legs of the walker were a different problem. This is because there were multiple pieces that were welded together, and we wouldn’t be able to weld them back together after cutting them. Furthermore, three different pieces of the frame came together at the bottom of the back legs, so to shorten the legs we’d have to cut all of those pieces.
In order to get access to these parts, we had to disassemble pretty much the entirety of the back of the walker, including cutting the welds that held the back pieces together. After it was disassembled, we cut each piece in iterations and checked how it would affect the walker as a whole. This process involved lots of taking the walker apart and putting it back together to gauge what modifications needed to be made.
The casters that came with the walker included a locking mechanism that worked by putting a pin through the wheel so it would no longer swivel. We decided to use this mechanism with our casters by welding a nut onto them that the pin could sit in. This was as simple as finding nuts that would work and welding them onto the prepped casters.
One challenge that we continually ran into while doing modifications to the frame of our walker was making sure our modifications wouldn’t affect its ability to collapse or telescope. To ensure this, we did lots of testing all throughout the process to make sure everything still worked smoothly.
