Unlink WRO 2017 Junior Group competition, WRO 2018 Junior Group has versatile design solutions. In this post, I will introduce three representative models. Each of them is unique and has its own highlights.

The game description, rules and scoring could be found at WRO website: https://wro-association.org/competition/previous-challenges

Model 1

This model looks very compact. Its attachment is mounted at the rear side of the vehicle. From the video, we could see that the attachment is just like an automatic storage and retrieval device. When medium motor spins, it drives the gears and the two wheels which are attached at the bottom of the attachment. The friction of the wheels will slide the block into its storage slot. When the vehicle is going to dismount the plant blocks, the medium motor rotates in the opposite direction. The friction of the wheels will slide the bottom block out.

This robot model uses a color sensor mounted on the side to check the block color in Soil Quality Area. If you observe the video carefully, you will notice that it is not running straight strictly when passing the Soil Quality Area. The vehicle keeps a bit distance from the blocks to avoid moving them out of initial places. Luckily, since those blocks are just black or white, keeping color sensor a bit far could still recognize colors properly. If the blocks are colorful ones, such a simple method might generate wrong result.

In terms of route planning, you could notice that this robot model just picks up yellow and red plant blocks, without touching any green plant blocks. Does it violate the game requirement? Here I would like to mention a confusion point for the WRO 2018 Junior Group. In “Game Description, Rules and Scoring” document, it first mentioned that “green plants could only be planted in the green farm”, while in the following scoring table, it specified that “Place any plant completely within a grey area in the green farm, undamaged and in an upright position”. Therefore, the rule seems like that the green farm could accept plants of any colour. This rule has been interpreted like this and utilized by many teams.

When placing the plant blocks to the destination, this model will run over the wall of the farm area. It requires accurate positioning of its wheels, otherwise, the walls will be damaged. From the video, we could see that two colour sensors mounting in front of the vehicle are responsible for navigating. When crossing the farm area, the robot will ensure that both color sensors follow the black lines so that it could maintain accurate path.

Please note that the base of plant block is a 2*4 LEGO brick. This model dismounts the plant blocks with its long side of base consistent with the long side of the gray area. Therefore, there is more buffer area for the block to be put completely in the gray zone, which ensures to get full score.

Model 2

This model has a different design of its attachment, which could stick out and retract from the side of the vehicle, just like an arm. When it sticks out, the rail at the top will slide the plant blocks into the container at the bottom of the vehicle. When the vehicle is going to dismount the blocks, the attachment will push the blocks out one by one. From the video, we could not see clearly how the attachment realizes the functions. It should have two medium motors responsible for pulling and pushing actions, respectively.

When the vehicle checks block color in Soil Quality Area, the bumps on the side of the vehicle could be pressed a bit hard against the field wall, so the vehicle could run along the straight path without worrying of touching color blocks. Since the vehicle could keep close enough to the color blocks, the reading is more reliable than that of Model 1.

In terms of picking up plant blocks, this model uses the same method as that of Model 1 by only getting the yellow and red blocks. In this way, it could spend less time on picking up the blocks.

The design is really innovative and very efficient in collecting the plants. However, it has an issue on placing the plant blocks. The game requires all the plant blocks should be put completely within the gray area. Due to the existence of farm walls, the vehicle needs to run to the external side of the farm area to dispatch the plant block, but in this way, the long edge of the plant block is aligned with the short edge of gray area. It is possible for part of the plant blocks to fall outside of the gray area, losing some scores.

Model 3

This model’s design is different, too. It has a very long arm, which could be lifted and put down. There are three clamps positioned along the arm, corresponding to the positions of plant blocks in the farm area. Based on the scanning result in Soil Quality Area, the attachment will fetch the plant blocks at proper clamp position and then put them in the farm all at once.

From the video, we could not identify what is driving the attachment and how to control it. It looks complicated but delicate. The first two clamps seem to be controlled by one medium motor because their actions are synchronous while the third clamp seemed to be controlled by a separate motor. There should be a third motor to control the lifting and putting down of the whole arm.

Compared to the previous two models, this one has chosen to put green plant blocks in the green farm area. It follows a more strict rule, but if the game rule is that yellow and red plants could also be put into green farm area, such a programming design might put it at a disadvantage because it takes a bit more time to pick up green plant blocks.

When picking up the plant blocks, this model might not be the fastest, because it needs to turn to a proper position before fetching blocks, but it is very efficient in placing the blocks. If it could position itself accurately in front of the farm area, it is highly reliable that all the plant blocks are put in the gray area accurately.

Which model is your favorite? The best path to the success is to put it into practice. Come to design your own model and have fun!

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