Since our MSTs ended in Week 8, Weeks 9 to 11 was our prime time to work on our project in order to have something ready for the Technical Prototype Review in Week 13.
Unfortunately, we were all very busy with our own commitments (CCAs, events, etc) that we were unable to meet up or get anything done. However, discussion in our WhatsApp group carried out as per normal, and we did as much as we could at home.
The very first thing we had to do was decide on the design of our entire vessel. With what was taught previously throughout Term 3, we learned how to calculate buoyancy of a vessel and also how to design very streamlined vessels. This came in very useful in our design as we had an idea of the frame and pipe network we would end up using. It made use of the catamaran hull concept and also was of a hexagon-diamond shape, as shown below.
Next, we had to think of how we should control the water container. The water container would be controlled with a 12V solenoid valve and would be lowered using a scissors linkage system or a simplified version of it. When we hit the drawing boards and started brainstorming possible methods of lowering the container, we had to take into account a few things:
- If we were actuating the container’s sealing mechanism by electrical means, we have to ensure that the wires are able to connect from the headquarter to the container properly without entangling
- Intended motion
- The objective is to collect water from a certain depth below the water surface. This is a very simple linear up-down motion, and as such, in theory, we only need 1 motor to achieve this motion as it only involves 1 degree of freedom.
- The mechanism which lowers the container will be fighting against the force of buoyancy. Gravity is acting in its favour, but buoyancy acts against it. If the container is filled with air without any way of escaping, the container would simply float on the water surface and never submerge without any force actively pushing it down. However, if the container is open and allows water to flow in, the overall buoyancy of the container is far lesser as the whole aspect of trapped air is eliminated.
With these 3 factors kept in mind during brainstorming, we came up with a number of possible ways to lower the container:
- A single rope
- This is the simplest idea in concept but difficult to implement as the rope can only provide an upwards force to reel the container up. In order for the container to submerge, it has to be either heavy enough or lack buoyancy such that it sinks instead of floats. The rope would be unable to provide any downward force to submerge the container. We would control the reeling mechanism with a servo motor or a DC motor.
- Scissors linkage
- The huge benefit the scissors linkage would bring is that it naturally provides a downwards force, not only from gravity but also because the force is transmitted from one end of the link to the other, hence being able to push the container downwards into the water. Although it may look simple, fabricating linkages is complex and ensuring durability is a whole different story altogether. The links, if laser cut, would not be strong enough as they would’ve had to be very long. We would control this by mounting one end of the link and controlling the other end with a servo motor.
- Modified scissors linkage
- This is essentially half a scissors linkage controlled by 2 DC motors with cables, relying on the weight of the entire system to submerge the container sufficiently. Again, the complexity comes with fabricating this. The pieces themselves aren’t the problem – despite their glaring weakness of not being durable enough – but the real problem lies in the joints of the linkage. Obtaining proper link joints is expensive as the parts are not available in the workshop, and also need to be very carefully selected.
With that, we decided to go with the modified scissors linkage concept.
We then met Mr Tune to consult him about our project’s progress. He gave very valuable feedback as he pointed us in the right direction to find out how to control the linkages properly. He felt that the modified scissors linkage idea was doable (still complex) but he challenged us with achieving the motion with only 1 motor. As, again, we only had to achieve 1 degree of freedom of motion, it could be done with 1 DC motor, we just had to figure out the best way of achieving that.
He told us to look up bridge-laying tanks and find out how their mechanism works. We did some research and found that they are controlled by hydraulics, something we unfortunately is not easily available. Of course, it is within our capabilities to prototype the hydraulics by using a tube, water and a syringe.
Other than that, he suggested to us a sort of gear mechanism which would cause the angles shown in the picture below to be equal at all times. With his advice and setting us on a more doable path, we then came up with an entire vessel design.
With that, we came up with a design of how we intended Imp Bot to look like!
Above was the first iteration of the Imp Bot’s design, and after some further refinement and trying to incorporate the arm idea from Mr Tune:
This design, we felt, was doable with what we had, although the point of complexity came with fabricating the link joint.
And thus we began laser cutting! We laser cut the top platform pieces, which turned out to be very big and just snugly fit the acrylic available in the Fabrication Lab. We also cut out the 2 sets of arms (with gears) out from 10mm thick acrylic, while the platform pieces were cut out from 3mm acrylic.
At the same time, we bought the pipes necessary for our vessel from Sun Hee Hardware Store. We designed pipe brackets to secure the acrylic pieces to the pipe network.
All seemed to be coming along very nicely! We are indeed very excited about what’s next!