Theme: Save Our Planet!
Rules: 50% of the project MUST be Lego, Lego controllers only.
Team members: Chung Ngin Zhun, Abel Chai, Richmond Choong
In 2008, I was the president of the newly-formed Robotics Club, and the school contingent leader by default. I participated in the regular category of the National Robotics Competition, not the open category as it has less workload, making it more suitable for my final and busiest year in secondary school. However, I was the mentor for the team and was directly involved with this project. Many aspects of the design and building received direct input from my previous experience. This was the project:
MV Patrick is a multipurpose river-cleaning machine. It deepens rivers, cleans and collects surface rubbish and reduces the acidity of rivers autonomously without human operation. It can navigate through rivers on autopilot, without having the risk of crashing into riverbanks. The prefix “MV” denotes motor vessel, which is what it is. It is an actual floating robotic ‘ship’.
The main parts are denoted by numbers 1-5.:
Do note that the robot in the picture is not the final variant we built. This robot is similar, but not exactly identical to the final product, as we made numerous adjustments and improvements soon after the pictures above were taken. The final product may be seen in the video at the bottom of this post.
Parts 1-2: Dredging system
This is the heart of the whole ship. During the design phase of the project, the team members and me debated on the type of dredging mechanism to use. The first type was a grab dredger mechanism, basically a claw lowered into the riverbed to ‘grab’ material up to the surface.
The second was a bucket dredging system, based on the tin dredgers used in colonial Malaya for tin mining. This utilized a moving series of scooping buckets to ‘scoop’ sediment up:
We determined that for the claw dredging mechanism to be effective, we either need to submerge a motor underwater, or link a driveshaft from a motor mounted on the surface to the claw. Both were unpractical. The former meant the risk of a shot motor and the latter required a very delicate mechanism. Thus, the bucket dredging system was used. It came in 2 parts: Part number 1 (shown without metal buckets) was basically a motor driving a chain with buckets attached. The end of the part had lead weights attached, and was meant to sink to the riverbed. Part number 2 was another motor that lifted or lowered the dredger, which had to be brought up for the ship to sail freely.
Part 3: Propulsion system
These are basically paddles that allowed the ship to move in the water. We experimented with propellers, but they required additional parts and motors for rudders, meaning more weight that might cause the ship to sink. Paddles were good in the sense that they meant more effective steering (especially in a narrow waterway), and were simpler in design.
Part 4: Material collecting platform
This was basically a collecting area for the collected surface rubbish and riverbed material.
Part 5: Surface trash collector
These are lifting ‘filters’ that scoop rubbish from the river surface onto a conveyor belt. After this photo was taken we added wire mesh as filter material.
From the photos it can be seen that the distribution of parts on the ship is rather uniform, and the ship had a large surface area. That was to allow more floatation material to be attached on the bottom of the ship. We initially used plastic PET bottles, but they were difficult to attach and provided too much buoyancy for too small an area, which resulted in instability. In the end, we attached polystyrene foam to the bottom of the ship.
The ship also had a small dispensing mechanism that dispensed calcium carbonate at regular time intervals. Unfortunately I don’t have any detailed pictures.
Here is a video of the robot that was presented during the competition:
The video has pictures of the final variant of the robot. There were ultrasonic sensors mounted onto the sides of the ship to judge the distance from the riverbanks. If the ship drifted too close to the riverbank, the ultrasonic sensors (which detect distance) would sense it, and the information sent to the NXT controller would adjust for the paddles to steer away from the riverbank. To prevent water from getting into the NXT, they were put into solid Lego brick enclosures, with a waterproof lining. The ‘failure’ in the video was actually the ship on the bottom of a shallow artificial pond. Our initial tests using PET bottles weren’t successful, and resulted in quite a few minor disasters.
The ‘river’ and ‘riverbanks’ were made from plywood pieces hammered together. A plastic sheet lining was used to prevent the water from leaking out. The riverbanks were made with play-doh, and the river bottom sediment was actual river sand and soil, resulting in a murky river that is all too common nowadays in some parts of Malaysia.
The sad thing was, during the competition, the project and presentation by the team failed to impress the judges. I would say we went for a less risky design, one that presented few winning points to the judges. However, one of the winning teams in the national levels of the National Robotics Competition that year had a robot that was very similar to ours (it was a floating river cleaner as well). It was however, more refined and possibly more complex in its design.
So much for failures. On the next installment in this series of blog entries, the mood will be better, I promise!
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