For the 2019 Coderdojo Belgium Coolest Projects fair, we built a LEGO Boost variant of Yoshihito Isogawa's Mindstorms pipe cleaner bending robot. He only published a Youtube video of his EV3 robot, so we didn't have any building instructions to start from. Building from scratch took several iterations before achieving a working robot, but we're thankful that we could borrow some of Mr. Isogawa's brilliant ideas nonetheless.
As always, every challenge has many possible solutions. We present solutions that were possible using our collection of spare LEGO parts. Your mileage, and your parts collection, may vary.
Please note that this instructable was documented by taking the robot apart. Building from scratch is far less linear than taking the final build apart...
Step 1: About the Components
We build the robot on two 8x16 stud, regular height plates. One is just for holding the Boost motor block, the other one holds the mechanism itself.
Every step will include pictures of the components used. Small details can make a large difference sometimes, so make sure to zoom in if you're not sure which type of Lego part we're using. Please don't ask where we got a specific part, as these all come from the "spare part" box, with no record of which set they once belonged to.
In the first picture, you can see the Technic parts on the left, and the regular parts on the right. This will not be a large build, as you can see. The Boost main motor block and the Boost external motor are in the middle. We didn't use the Boost color sensor in this build. The second picture shows all axles we used, with a couple of Technic beams for length reference. We tried to use the minimum length required for the specific purpose of each axle.
Step 2: Transmission Axles
At a height of two flat plates from the base, we mount two transmission axles that will take the rotation from the A and B motors in the Boost block to the two bender arms at the front of the machine.We need four 1x2 perforated blocks, four stoppers (half or full length doesn't matter) and eight plates to achieve the required height. Also, we need four bevel gears. It doesn't matter if you use the newer 12-tooth version or the older 14-tooth version, but make sure you have a matching gear for each one you use. The final build needs four matching pairs of these bevel gears. As pictured, we used three 12-tooth pair and one 14-tooth pair. The distance between the two transmission assemblies is 6 studs. This area needs to be kept free for now.
Step 3: Supports for Later Components
Using regular (non-Technic) Lego bricks, we build a couple of supports for the rest of the robot. Note that the perforated 2x4 plates in the picture will connect the two base plates together. There's no functional reason for those to be perforated.
Step 4: Walls for the Feeder
Using perforated bricks (mainly 1x6), we construct side walls to mount the feeder wheels between. The total height is a full number of regular bricks, but we split one into three plates, to push the two feeder wheels onto each other. That is also the reason why we have the perpendicular beam: without that beam the forces on the wheels push the wall apart.
On one row you can see two grey pins. The external Boost motor will connect to those, and the wheel axle driven directly by the motor goes in between the two connectors.
Step 5: Feeder Wheels and Rear Alignment Tubes
We chose Lego wheels that have a compressible rubber tire on a central rim. This allows for pressure to be exerted by pressing the wheels together a bit. The pipe cleaner will be fed between the two wheels, one wheel will be motor-driven, and the other wheel will be driven by its firm contact with the first wheel.
We use 180 degree axle and pin connectors as alignment tubes. The three rear alignment tubes are centered by pins on one side, and by axles on the other side. The axles protrude from the wall on the other side, which allows us to fixate them in a permanent direction. The only part that has three fixed axle attachments in a row was the grey egg-shaped part in the last picture. You could reduce the construction to two alignment pieces, and use a piece with two fixed axle attachments instead. Note that using pins on both sides would allow the alignment tubes to rotate. Also note that the space between the walls is one unit wider than the black tube parts. This is why we add half-unit spacers on both sides.
Step 6: Wall Assembly
The wheel on the longest axle is the one driven by the motor, so it is positioned between the grey pins that will keep the motor in place later. It doesn't need additional stoppers, as the connection in the motor is rigid enough. The other wheel is on the shorter axle, and is kept in place by two half stoppers on either side of the walls.
The alignment tubes are mounted in the dark grey brick in the example. You can see the egg-shaped fixating piece on one side, keeping the alignment tubes oriented correctly.
For the type of wheels we chose, the one plate below/two plates above positioning of the dark grey brick aligns the tubes with the contact surface between the wheels.
Step 7: Main Beam and Transmission Gear Prep
At the front of the robot, one long beam (15 holes) supports the front alignment tube, the bender axles and the transmission gears. Three 1/3th height beams are added to either reduce the freedom of movement of the axles, or to fixate the orientation of an axle. They are held in place by pins. Many of the other holes in the beam will be used in the next steps, so if you use 1/3th height beams of different length, that may cause issues later.
Step 8: Main Beam Axles, and Bender Arms
In this step, we assemble various items that go into the main front beam. The first is the front alignment tube. It consists of two axles, an alignment tube identical to the ones we used at the back, and a single-ended connector that keeps the pipe cleaner precisely centered. This one goes into the central hole of the main beam. In the previous step we already added a piece that prevents rotation in that position.This is crucial for the alignment tube.
Secondly, we assemble the benders. One bender arm consists of 4x2 elbow beam, a connector, and a small rim. We make two arms.These go one long axles, and into holes two steps away from the central hole.
At the bottom of the bender axles, 24-tooth gears are attached. The short axles from the previous step get 8-tooth gears, and a matching bevel gear for the transmission axle. Note that the 1:3 gear reduction provides extra force for the bender arms. Two 16-tooth gears cover the same distance, but didn't bend the pipe cleaners reliably during testing.
Step 9: Main Beam Attachments
Using two pins, an axle pin, a perforated 1x2, and a piece called "Axle and Pin Connector Perpendicular 3L with 2 Pin Holes" on each end, we make sure the beam is firmly attached to the rest of the structure. There are perpendicular attachment pieces with only 1 hole. Those will work as well, but we've seen that the movement of the bender arms exerts a lot of force on the construction, so we prefer using the 2 pin hole variant.
Step 10: Upper Beam
The movement of the bender arms is crucial, and a lot of force is transferred onto the axles and their support. Therefore, we mount an upper beam that provides an additional pivot point for the bender axles. We used a 9-hole beam. Holes 3, 5 and 7 are occupied by axles. This leaves the outermost two holes for mounting the beam. We used a part called "Axle and Pin Connector Perpendicular 3L with Center Pin Hole" on one side. On the other side this would interfere with the external Boost motor, so we went for the shorter "Axle and Pin Connector" and a 1x2 perforated block instead of a 1x4 perforated block. You could use the shorter version on both sides.
Step 11: Mounting the Beam and Bender Assembly
The main and upper beams can now be mounted onto the existing structure. Careful alignment of the bevel gears is needed, so the transmission axles don't block each other. Horizontal alignment of the bender rims with the feeder tube is also needed.
Step 12: Reenforcing the Structure
At the four attachment points of the beams, we add reinforcement using regular bricks. We take care not to hinder the movement of the axles, wheels, and bender arms.
Step 13: Attach the External Boost Motor
The attachment points for the external boost motor are already in place, so attaching it should now be straightforward. The motor can be added in four different orientations. Functionally for the motor itself it doesn't matter, but we prefer the orientation that leaves the most swing-room for the bender arm on that side.
Step 14: Attach the Boost Motor Block
We build two hind legs for the Boost motor block, and attach bevel gears on short axles on both A and B motors. We mount the front of the motor block on the second base plate. This leaves the battery compartment reachable at the bottom. After joining the two base plates, align the bevel gears so the A and B motors drive the transmission axles and the bender arms.
Step 15: Create a Program in the Boost App
Once the robot is finished, it is time to fire up the Boost app. Start experimenting with the feeder speed, the bender arm range, etcetera. We created programs to bend a 5 point star, a heart, a circle, a plus sign, and a diamond shape. We used pipe cleaners of 6 mm diameter and 30 cm length.
Have fun and good luck!