Monday, April 22, 2019

Centi (#5) - New Leg Design is Printed


Here is the latest print and video of the Centipede Project.

moving from OpenSCAD to print went fairly smoothly.  As you can see, I have enclosed the main rotating mechanism that moves the chopstick legs.  In this design in OpenSCAD, I have rotated everything along the Z axis, to make it easier to keep centered. The covering socket cap and ball all align, as well as the cam. You can also see holes along the structure, so that small screws can be used to assemble the leg segment. I am reusing screws from recycled printers that are used to bind plastic parts together.

OpenSCAD design
At the 'base' of the leg, I have created a hexagon. This seems to me to be 'self-bio-inspired'. I have not used hexagons in previous designs, so it is novel to me. More importantly, it fits the nature of the leg, as there is no specific 'down' or 'up.  One the walls of the cam base, I have added two small holes for M3 bolts. This allows me to connect two or more legs in sequence... thus forming the multiple legs of the Centipede.

New Print
At this time there are only two leg segments connected.  The M3 bolts are not visible, as they are inside the cam housing.  Note: I had a near-fail as I forgot to leave clearance between the cam housing wall and the bearing mount.  There are many issues to design out when doing project like this. This is why physically making the prototypes is very important to realize assembly issues.

New Gears to connect to Drive
At the base of the Cam Housing are two gears attached to the cam itself. The cam shaft runs through a bearing and then is connected to the gears.  The gears are "kegelrad" from the OpenSCAD library "Getriebe Bilbiothek für OpenSCAD".  The kegelrad could give me an ability to mount the drive gears at an angle different from the cam housing.  We shall see!  ;)

Saturday, April 13, 2019

Centi (#4) - Design Video


I have published a video of the initial design and 3D Printed "drafts" of the Centipede leg mechanism.  You can find the video below on my YouTube channel.

From a design perspective, the drafts have served their purpose. It is now a good time to take what we have learned and start a new draft.  

I like the concept of making each leg of the Centipede to be a "module" that can be replicated and connected together.  I am also realizing that I don't care much for the 'rectangular' frame that was in the drafts.  The legs may need to be moved around.  Honestly, the rectangles do not seem to match the aesthetic of an bio-inspired robot.

Here is my new concept that I am working on ...

Centi - a new aesthetic! - CAD in OpenSCAD

Saturday, April 6, 2019

Wild Weasel - Tracked Robot (#3)

I have just posted a YouTube Video of the assembly of the Wild Weasel track.  You can find it here:

Wild Weasel a completely 3D printed Tracked Robot.  I wanted to build a tracked robot, due to their stability, and at the same time use some motors that I had recovered from recycled printers.

The project went very smoothly, a lot of CAD work was need to design the treads, chassis, and gears used.  The robot uses a Raspberry Pi and an L298N motor driver. This was my first time to use a Tallent Cell power bank, which provides 12V and 5V power - great for RPI and the motors.

Saturday, March 9, 2019

Centi (#3) - The next iteration of design

The bio-inspired multi-leg walking robot!

It seemed that the main sprocket is capable of turning the chopstick legs, and the ball & socket were going to work.  This is the working theory, i will not be able to test a load on them until much later in the development.

The next iteration of the design of the motion mechanism was to start to incorporate a gear into the drive in order to turn the sprocket.  I did a number of changes in the CAD design.  I increased the size of the frame (height) and added M3 holes on the sides.  I updated the socket top to take recycled torx screws from a printer. 

Centipede next iteration of design

For the main design, I have added a 22x7mm skateboard bearing (red) to take the load of the leg (also red) and provide rotation. I extended the cam shaft to hold a gear.  Most important, I designed two gears, one to turn the sprocket, and the other to drive that cam gear.

Close up

The new print has noted improvements. Also, a number of issues that will have to be tweaked in the next iteration

Full View, new iteration on the left, original prototype on the right. 
 Together, the assembly will start to look like 1/3 of the walking mechanism.

Sunday, March 3, 2019

Centi (#2) - A Bio-Inspired Centipede Robot


a little more drafting of ideas around the mechanism.  

Draft of the first test
I drafted out a simple test mechanism to see how well the ball rotating in the ball mount would work with the circular motion of a wheel.  Also, the end of the leg would have to fit inside this wheel as well.

Print of the "minimal viable test"

building the Wild Weasel helped me understand how the bearing and gears could be used to transmit the mechanical energy and absorb the weight of the robot.  I think I will mount the main "sprocket" with a bearing.  After all, the weight of the robot will be directly on this wheel. 

In addition, I will need to add some teeth to the sprocket so that it can be turned with a motor. Finally, it is not too soon to start thinking about how this could be made into a modular component where it can be attached to other legs in the Centipede!