Progress of project for week 5 (10/06 – 14/06):
Aim for week 5 – Initial ideas
In week 5, we decided to branch our project into two parts: Retractable quad skates and wheel-locking inline skates.
Rough designs of the wheel-locking inline skates were drawn and discussed its feasibility. Toggle clamp was included in our design to lock the wheels with a 3D printed chock. We modeled and 3D printed the inline skate frame, which lead us to the conclusion that very limited space is allowed to insert a chock inside. This will be taken into consideration in future stages.
We also explored the possibility of extruding supports on sides of the skates to support walking instead of retracting. However, no good idea came to our mind to be executed.
The development of retractable quad skates was on hold until the skates arrive.
Meanwhile, we tested the feasibility of wheel locking on inline skates using wire straps. The walking experience was steady but a little uncomfortable.
Progress of project for week 6 (17/06 – 21/06):
Aim for week 6 – Procurement of materials and testing of wheel-locking mechanism
In week 6, we purchased many different items with the goal of extracting certain parts from the whole item. We plan to assemble the extracted parts together into a single product.
Overall, in week 6, we purchased:
- 2x skateboard
- 2x inline skates
The rationale behind purchasing 2 of each items is because we wanted to experiment with different types of inline skate frames (structure and materials) and skateboard trucks. Through this, we understood that the idea of incorporating a wheel-locking mechanism in a row of wheels (inline skate construct) is not exactly feasible as we were not granted the luxury of space for us to insert a wheel locking mechanism. We then decided on constructing a pair of roller skates instead of inline skates.
Apart from the procurement of items and deciding on the design of the construct, we further investigated on the different types of wheel-locking mechanisms that may be possible. In week 6, we tried to clamp the wheels with a wheel clamp attached to a servo motor. The wheels will be clamped when the green clamps swings down with the aid of the servo motor. We also realized that this method does not work out as the normal force generated does not provide sufficient frictional force to hold the wheels in place.
Progress of project for week 7 (24/06 – 28/06):
Aim for week 7 – Develop a strong proof of concept
In week 7, we aimed to develop a proof-of-concept of our concept and design. Following discussions held in past weeks and through numerous eliminations of unlikely designs and concepts, we have managed to settle on one that we feel confident in. In this week, we developed an electric powered pair of skates that is equipped with a wheel-locking mechanism. Pictured below are our prototypes in the intermediate stage of development, without the wheel-locking mechanism in place yet.
After successful attempts at running our electric powered skates, we continued to brainstorm for ideas on the wheel-locking mechanism. Our team was inspired by the wheel-locking mechanism of wheelchairs, and we attempted to develop one of our own through the limited materials available in the MnT lab. Shown below is our skate with the wheel-locking mechanism added into it. When the lever is pulled, the clamp eats slightly into the wheel, thereby locking it.
From here, we had develop a working prototype and a proof-of-concept. We continued and carried out different tests on our skates. We experimented with different electric power delivered to our skates and we intend to find out the optimum range of electric power to deliver to our skates. The electric wheel (orange) is capable of running on minimally 18V source, but the recommended voltage size would be 25V – 30V.
Besides testing the amount of electric power to deliver to our skates, we also held a simple and brief test on the amount of stress it can withstand by adding weight onto one side of the skates. There were signs of our aluminium frames bending when a load of 83 x 9.81 = 814N were applied. We plan to reinforce our skates with more screws.
Summary of problems faced:
- Constrained by the limited amount of space available around our skates, we struggled to find out a wheel-locking mechanism that could fit our skates.
- Our makeshift skate trucks, although sturdy, had showed signs of bending when placed under large amounts of force. Adding more reinforcements solves the problem, but also introduces more unnecessary load to our skates which will render it infeasible.
Progress of project for week 8 (01/07 – 05/07):
Aim for week 8 – Experimentation of different wheel-locking mechanisms
Week 8 was considered a lull week for us. The week was spent on waiting for the materials that we ordered previously to arrive, and also for us to pursue unreliable retailers for our items. Alas, certain parts failed to deliver and hence, we had to order from alternative retailers. This resulted in a waste of precious time.
While waiting for our materials, we tried to motorize our existing ‘wheelchair’ clamp by connecting it to a 3D printed accessory and a servo motor. This was a failed attempt. Our next source of hope lies in the ‘corkscrew’ locking method which we have not tried out yet. Another promising method recommended to us by Tony involves the use of gears that are rigidly fixed onto our existing wheels, and then chocking the gears with a gear stopper. This effectively clamps the wheels too. For simplicity, we call this the ‘gear’ method. For week 9, we intend to experiment with the ‘corkscrew’ and ‘gear’ method, if everything (delivery of items) runs in order.
Apart from the above-mentioned, Week 8 was also used to prepare for Progress Meeting 3.
The backlog accumulated in Week 8 will be pushed to Week 9.
Summary of problems faced:
- Items failed to deliver. We had to turn to alternative retailers for our materials. As a result, Week 8 was a lost week.
Progress of project for week 9 (08/07 – 12/07):
Aim for week 9 – Development of ‘gear’ and ‘wheel-clamp’ mechanisms
Week 9 was considered a fruitful week for our group. We managed to achieve not only the aim for this week, but also Week 8’s. Week 9 was mainly spent on developing 2 new mechanisms and then motorizing them.
‘Gear’ mechanism
The ‘gear’ mechanism, first proposed to us by Tony, was developed by our group and it underwent certain load testing. We modified the existing servo motor that we had, and attached it to a clamp. This connects the servo motor and clamp together, and thus we had managed to produce a wheel clamping mechanism that is motorized. We 3D printed the gear (pink) and glued it onto the wheels. Shown below is the experimentation of our ‘gear’ mechanism.
We put this to the test with approximately 50kg load. The pink gear remained attached to the wheels although it was glued, but the black rubber fitting gave way and broke into two. This partial failure prompted us to alter this ‘gear’ locking mechanism. And so the ‘wheel-clamping’ mechanism was born.
‘Wheel-clamping’ mechanism
We capitalized on the existing servo motor that we modified, but we altered the rubber fitting and replaced it with a crescent-shaped metal object with tight rubber fittings. The engagement and disengagement of the new clamps are shown below.
Similarly, we tested this ‘wheel-clamping’ mechanism with approximately 60kg load. The entire structure was sturdy and it did not give way. However, we intend to improve the grip the clamp has on the wheel by increasing the normal force provided by the servo motor if possible.
Problems faced:
- The ‘gear’ mechanism was done up but the rubber fitting broke. This resulted in a partial failure of the ‘gear’ mechanism and prompted us to look for other solutions.
- The new ‘wheel-clamping’ mechanism works well and fine up till now, but we believe the friction force can be increased by enlarging the normal force provided by the servo motor.
Progress of project for week 11 (22/07 – 28/07):
Aim for week 11 – Motorization, and then finalization and assembly of final product
The first 3 days of Week 11 (22/07 – 24/07) coincided with CNYang’s FOP. This leaves one member available for the project. During that period of time, our group focused on the assembly of the final product. In between breaks during the FOP, we had some small discussions on the placing of the servo motors and we also decided to replace the external bracket fasteners with internal fasteners. Doing so reduces the space taken by the bracket fasteners, and thus leaves more room for the foot.
We also attempted to shorten the length of the our skates in order to shave off some weight.
The motorization of the wheel-clamps didn’t go as smoothly as intended. The aim was to control all 4 wheel-clamps with a central circuit. However, during the trial phase, the voltage regulator was burnt. We suspected it was due to a faulty motor which might have caused a short circuit. We changed the servo motors and converters and reattempted again. This time round, the motors worked, but the converters failed. One possible reason for this failure was that the current drawn was too high as the motors were placed in a parallel fashion. Over numerous trials, we concluded that the current peak for each motor is at 1.5A, which totals 6A for all 4 motors. Meanwhile, the LM2596 converter that we used has a maximum current tolerance of 3A. If the current reaches 2A, the power supply will be cut off.
The image below shows the 2 converters that were burnt during the trial phase.
We then devised a new mechanism to rotate the servo motor completely down and use the toggle clamp’s locking mechanism so that the servo motor doesn’t stall and current doesn’t exceed the converter’s current tolerance. We tested the mechanism using a power supply to determine the peak current and we found out that the peak current was around 1.6A which is still within the tolerance level of the buck converter. Below shows the video of our testing phase.
Past all the ‘electrifying’ stuffs, we went on to assemble the final prototype. The video below shows how the skates will be like when the clamps are engaged. We can see that all 4 wheels are successfully clamped.
The image below shows the final prototype.
Further more, taking the safety of the user in consideration, we 3D printed a bracing meant for the heels of the user.
Summary of problems faced:
- We encountered the biggest problem when dealing with the electronics. The trial phase resulted in the destruction of many electronic components, but as of now, they have been rectified and it has shown that it works.
- We also had to deal with space constraints (foot space). The external bracket fasteners was taking up too much space, and thus we decided to replace it with internal fasteners, which do not take up precious space as they are hidden within the aluminium profiles.
Progress of project for week 12 (29-30/07):
Aim for week 12 – ,Assembly, final testing, and preparation for presentation
The last day of MnT is finally here! Alas, it was a bumpy day for our group.
With the help of Tony, we managed to solder the wires together and connect them to the Arduino. With all the messy wires in place, we proceeded to heat shrink the bunch of wires. This leaves our final prototype with 2 heat – shrinked wires extending from each skate.
While testing, a few of the soldered wires tore off, hence we had to re-solder the wires back. We also realized that the two skates were moving in opposite directions even as a single command was given. This was because of loosely soldered wires in the heat shrink tubing causing the hall sensors to malfunction. This was rectified later on. All in all, our final prototype looks like this:
A snippet of the skates working is also provided below:
The initial part of the video shows the clamps being disengaged, and thus the wheels are free to roll. In the later part, with the clamps engaged, the user was able to successfully walk on it.
However, when we wanted to test out the locking together with the electric wheels while putting the circuits in a bag, the buck converter exploded again and we suspect it might have been due to short circuiting due to messy wires. As such, we decided to design and print a housing for the wires and circuits to stick the electronic components on and to prevent short circuiting. In order to avoid overloading of current, we also altered the code to lock the wheels one wheel at a time to reduce the current drawn at any single point of time so that the current doesn’t peak and cause the buck converter to overheat again. Finally we changed our buck converter to one with higher current tolerance to prevent any further issue.
The video below shows the locking mechanism with the new code. The wheels are locked one after another to reduce current flow at any one time.
Summary of problems faced:
- Some soldered wires tore apart during the testing phase, hence we had to re-solder them back on.
- The 2 skates run in different directions, so we had to re-configure the circuit.
- Messy wiring and short circuiting caused the buck converter to explode again, so we changed the code to reduce current draw, changed the buck converter to one with higher tolerance, and printed a housing to prevent short circuiting.