Monday, June 29, 2020

Tilt - A Balancing Robot (#1) - Thinking about it

Tilt will be my next robot with a focusing on implementing Dynamic Control in Robotics.

There are a good number of videos on YouTube from 2 years ago on how to build a "self-balancing robot". I do find these fascinating, and I would like the experience of building one - of course as cheaply as possible with as many reused parts as possible.  ;)

I am challenged by the engineering aspects of this type of robot.  Perhaps because ... that an inverted pendulum was offered as a senior project when I was an undergraduate. I passed on it due to the complexity at the time, and lack of good motors and controllers. Yes, I am a bit haunted that I *should* have done this project. So, I feel like I should re-live my Control Engineering days and build this robot! :)

I feel that these type of control will be standard in most future interesting robots. I sense that we are still at the early aspects even though Dynamic movement has been a part of the current stable of robots. we are starting to see combinations of quadrupeds -and- wheels. (Soon, I would not be surprised to find reaction wheels also included for more stability and agility.)  

However - after all that is mentioned, these types of developments are still very uncommon in the DYI Robotics space!

Moving forward with this robot, the numbers and types of parts are limited.  Here is what I am considering at this point:

  • 2 wheels, recycle, reuse, or print
  • 2 motors - 9-12v from a recycled printer
  • 2 belts - to drive the wheels and do some gear reduction/torque
  • 2 encoders - used to measure the output of the motores
  • 1 motor driver for DC brushed motors (L298N)
  • 1 micro controller - EPS32 or Arduino Nano or other
  • 1 motion sensor - MPU-6050
  • 1 battery solution - drives the motors, powers the electronics
What else would I need?

OK - Time to scavenge for parts!  and think about an encoder solution.

Thursday, June 25, 2020

Intergalactic Planetary (gears)!

Just doing some thinking and sketching on how best to use Recycled Printer Motors in my robots. 

One of the Totally Not Evil Robot Army motivations, is to make robotic creations by recycling parts from existing technology. To RE-USE, is the best approach to waste management. -- and also of course, because I am really, really cheap.  ;)

Recycled Printer Motors

Most computer printers have these nice (DC Brushed) Motors, but they tend to be too fast and with out a lot of usable torque for my projects. This would be expected, since the printers they come from have a lot of built in gear reduction.  For power, they typically require 12-18v. These are not light either, they have some weight to them. In order to utilize these printer motors, they will need a gearbox to both reduce speed and increase the torque - which is exactly what gearboxes do for motors.

The Planetary Gear is a good choice for a compact way of converting the motors output into a stronger more useful force.

The Planetary Gear is made up of 4 pieces, The Sun Gear, one or more Planet Gears, The Carrier (connecting Planet gears) and on the outside, the Ring.

Named Parts of a Planetary Gear Box

The configuration of a planetary gear box can vary based on specific needs. Any one part of the system can be 'fixed' which allows for the other two parts to become the Driver (input) and the Output.  

Example:  by fixing the Ring and attaching the drive motor to the Sun, it makes the Planetary Carrier to become the Output and move.  Likewise, you could fix the Carrier and attaching the drive motor to the Sun Gear, would cause the Ring to be the output and move.

Here is a quick 3D print or sketch of the Planetary "Wheel".  Here the motor and Carrier are the same part. This allows the motor to directly drive (input) the Sun gear.  Since the planets are fixed, the Ring will move. I have built the Ring gear to be the inside of a wheel.


Planetary Wheel
Motor Mounted on the Planetary Carrier

On the reverse side you can see the planetary gears encased in the wheel. The Sun Gear is removed.


Complete "Planetary Wheel"


Gear Reduction with Planetary Gears


The actual gear reduction and torque increase can be calculated based on the number of teeth in the gears or the radius of the gears (given a specific modulus).  The equations are similar to basic gear equations, however there are differences due to the planetary gear set.  here they are:

For the gear ratio of a basic gear 

    i = Z2 / Z1 

where Z are the number of teeth on Gear 1 and Gear 2

For the Planetary Gear, we have the number of teeth - Zs for Sun Gear and Zr for the Ring. The number of teeth on the carrier does not matter, since it is derived and removed from the equations. (also, it does not matter how many actual planet gears you have).

the equation for planetary gear reduction is:

    i = 1 + (Zr / Zs)

Here is a nice little summary video of deriving the gear-ratios of Planetary Gears.


Testing the 3D printed gear box


I was able to make this wheel work pretty much out of the print.  I did have some difficulty in the motor shaft 'stripping out' the inside of the sun gear if the gears were blocked.  this is the same problem encountered on the Milli project.  I believe some glue may help hold the gear in place, but this does not seem to be a sustainable solution. I would have difficulty replacing the gear when needed.

As a result, The Sun gear would slowly lift off of the motor spindle when operated at full speed.  (A failure you would not want if the Wheel was part of an inter-planetary rover.)

Looking forward, at these brushless motors, I believe a belt and tensioner system may work best. Most of the motors I have, already have a nylon belt gear on the motor spindle.  I will try to use this combination in one of my next projects.


Postscript

Hi all, this post was somewhat delayed due to some personal health issues.  I am doing much better now, thanks!  I have some upcoming work on a balancing robot - using Printer Motors that I am currently considering.  More to Come!  Thanks! Doug

Wednesday, May 27, 2020

Two Year Anniversary

It has been an interesting year, who would have thought!

It is now Two Years since I started my Totally-Not-Evil-Robot-Army!  



For this blog, I have had over 14,500+ visits.  Hopefully, this is a sign of more Makers becoming interested in the building robots.  

However, I am savvy enough to understand that many (possibly evil - Internet software Robots) have driven some of my numbers.  Web-Crawlers and Search Engines regularly pass through the Blogger collecting information, pictures etc. I have been directly crawled from an Israeli base search engine responsible for at least 3k hits in the last year, by my estimates. Also, this humble blog had been the target of some Ukrainian SEO- Search Engine Optimization hackers, trying to make comments that cross link URLs and drive up results for their customers. I have removed their posts, but I believe I am still in *their* logs, which results in a lot of other victims in their bot army cross-linking to my site.  Thus, I have a lot of referrals from random non-robot, non-educational sites.  <sigh> unfortunately this is part of our modern Internet.  And, it also make the Ukraine the most popular country amongst our visitors.

The Covid-Crisis has also brought in a number of visitors. Perhaps people are building robots while in lockdown?  some of the most popular locations have been from Hong Kong - perhaps a future robot hot-spot?

The year in passing


Well, I did take a bit of a sabbatical for a few months. I had a lot of personal work in relocating to a new home, and even more effort in  starting a new software business.  I am still thoroughly enjoying robot building and will continue to post my adventures in robotics in a public journal. There are many many robots to be built. As we all know, the robots can't build themselves... until they can. ;)

This years robots include a new design for a Robotic Dog - Mojo3.  In addition (as a distraction?) I worked on a Millipede based robot call Milli (original, eh?).  Both of these robots are still in active design stages. Mojo3 is going through walking tests. For the Millipede, I am exploring better ways to drive the robot using recycled printer motors.

Let keep building!


Friday, May 8, 2020

Mojo3 - A Robotic Dog (#10) - New Video Out

 New Video Out

There is a new Video on YouTube showing Mojo3's first (stumbling) steps.  Check it out to see what it is like to try to tune this little robot in both physically and with software.


Only 9g Servos

The biggest challenge with this little robot is trying to only use inexpensive 9g servos.  These are great hobby servos, easy to use and code, and inexpensive if you burn one out. They do have their challenges in the amount of force that they have. I found this to be restrictive in my first attepts with the original Mojo robot dog design.

I believe with good design and engineering, it should be possible to build a little quadruped robot with them. You can see in the video that my in my first tests, the rear servos were struggling to meet the position commands issued by the controller.  The front and back "hips" and "knees" were given the exact same position commands literally using the same computer array of positions.

Then I changed the rear "hip" leg gear positions. I rotated the rear/hind "hip" leg out by about 30-40 degrees. This was easy to do in my new leg design. I simply pulled the hip off of the mount, rotated it back and put it back on.  There are marks for calibration visible in the pictures. The result was a much smoother "hip flex" motion.



New Hind Leg Configuration

The next step in developing the walking gait is to explore how each leg should move to proppell the robot forward. I am starting with just basic movements of the hind/rear legs.  I have replaced the front feet with "training wheels" (like a kids first bicycle). Now the hind legs can attempt to walk without any resistance to the front legs.

More work to come! 

 
Mojo3 Robot Dog
Mojo3 with 'training wheels' for front feet.

 
PS:  Quadrupeds on Wheels is going to be a thing!!  Check out this video of Hybrid Locomotion by ETH - ANYmal.

Wednesday, April 29, 2020

Mojo3 - A Robotic Dog (#9) - Ready to Program the Step Sequence

Mojo3 is a 3D printed Compliant Quadruped Robot Dog

The 3D printing is done for this build. I am currently working on updating the Arduino software to control the robot leg sequence.  I need to add all the electronics and batteries as well.  More to come!

Mojo3 - Robotic Dog - ready for electronics

Mojo3 compared to Mojo2

Sunday, April 19, 2020

Mojo3 - A Robotic Dog (#8) - The New Alternative Leg Design

Mojo3 is a 3D printed Compliant Quadruped Robot Dog

The results of the last test (and blog post) were clear, the SEA design is not working as I had hoped. I maintain my believe that the compliancy in the SEA design is needed (superior) to a static approach. However, this current design will not work with the relatively weak pull of the 9g servos. At least not in the current configuration.

In my desire to move the prototype along, I have considered some other approaches. In my Mojo3 #6 blog post, I was considering using a hinged approach similar to a 4 bar mechanism. With such an approach this would allow for the servo to directly lift the 'arm' off the ground. This would provide the movement needed (ability to lift the foot when moving the leg forward), however, a different thought came to mind as I was adding the servo gear to the hip joint. 

Why not use a servo gear to raise the 'arm'?



Mojo3 - Robot Dog - Alternative leg approach (OpenSCAD)

The gear driven servo would provide small additional torque (without the servo horn) and less backlash. It will also be significantly easier to tune, being able to reset the location of the gear. Also, the Inverse Kinematics would be much easier to calculate. The downside is that I would lose the compliancy in the lifting mechanism. Compliancy would need to be moved to another location on the leg. (perhaps the 'arm' or foot). Note, the above picture uses "shorty" arm, just a very quick sketch to see if the concept was plausible.


Mojo3 - Old and New leg designs - "shorty" on the right side.


Testing the new design


Mojo3 Robot Dog - Test for Kinematic path

The new design proved to work well. It was easy to adjust and tune. Most important, I was able to get around 12mm of upward movement in the Kinematics.  With experimentation, I learned that increasing the delay or slowing down the motion, provided a very different Kinematic path. The servos had more time to get to their set points.


Mojo3 - impact of timing differences in the Kinematics


Putting all this design work together

I am pleased with the current design. This approach will be faster to get to a walking quadruped. The gear design will allow the robot to be adjusted much easier. I will need to have some compliant mechanism added to it in the future.  The new robot frame should look something like this:


Mojo3 - A Quadruped Robot Dog (OpenSCAD - exploded component view)

Tuesday, April 14, 2020

Mojo3 - A Robotic Dog (#7) - OK, One More Test!

Mojo3 is a Compliant Quadruped Robot Dog

Ok, maybe I should read my own blog posts. I believe I was supposed to do a new design. Instead I started the Milli - th WildWorm, but that is a different post.  Before I jump off to a new design, maybe just ONE MORE TEST?  I build the hip servo mechanism so that now we can see the actual distance traveled by the robot's leg.


Mojo3 - Leg Design with Gear Driven Hip and Bearing
The new hip design will be just a gear driven leg unit, and a gear on the servo - as the CAD picture suggests. This design should work, as the weight of the servo is now directly transferred to the Chassis through the bearing. This should remove the considerable load from the small 9g servos.

Mojo3 - Kinematic Motion Test

Here the test is set up, the leg is moving repeated through a single step. There is a 60 degree sweep of the hip section, and a 40 degree pull on the leg segment.  The results are (blurry) below.  In this configuration, the leg is only able to lift about 4mm on the return swing. (I will include the video in the future on my YouTube channel)

Mojo3 - Step Kinematic Motion Trace - Just Not Enough!

Only a 4mm lift on the return of the leg to the forward position.  I do not believe this is going to be enough to overcome the dynamic (tilting) nature of the gate.  Time to consider another design!

on the up side.  A shout out to Oracid1 on YouTube and his nice Inverse Kinematics Arduino code. It is a bit cleaner solution than the one I wrote for Mojo2. I have adopted some of the 'clean code' concepts for Mojo3.

Thursday, April 9, 2020

Milli (#8) - Rethinking the Motor and Spendel

Milli is a bio-inspired robot that uses a single actuator to create standing wave motion.



Where to go next on the design of the WildWorm drive and Milli??

As expected, the recycled printer motor that I am using (9-12v) powered by a 18v rechargeable drill battery, is too much for the little robot. (duh!)  When testing, the rotational speed of the motor is too much for the directly driven helix spindle.  After some testing this has lead to the helix base to be burnt out by the motor spendel.

Milli's WildWorm drive - burnt out helix mount separated from the motor.

What is needed is a gear reduction, to reduce the rotational speed, and increase the torque of the helix.  This is very similar to the gear reduction used for the same motors on the Wild Weasel track.  Here you can see the video of the gear reduction built into the track:



But Where to put this on the rather simple chassis of Milli?


Milli - Motor Mount

Actually, there is plenty of room.  With the next iteration of design, I will:

  • Add a bearing to the chassis, creating the mount for the helix.  this should reduce any load from the wildworm drive on the motor itself.
  • A shaft will connect the helix, through the bearing to a similar sized 3D printed gear.
  • The Gear train will consist of a small gear directly on the motor.  This will drive a large gear with coaxial small gear. this small gear will drive the helix gear.  (A quick estimate would have 18mm diameter to 40mm diameter gears. times 2 ~ 4.8:1 gear ratio)
  • If another gear set is needed, it can be added relatively easily.

Milli - Chassis with Recycled Printer Motor

Unfortunately, this is all conceptual at the moment.  It is not even in the CAD system just yet.  However - the thoughts have given me some new insight on Mojo3 - and there will be a new design blog post out shortly.


Stay Healthy!

Saturday, March 21, 2020

Milli (#7) - Update: Added Steering and Pede-Wheels

Milli is a bio-inspired robot that uses a single actuator to create standing wave motion.

Update: I have been somewhat distracted (as we all have been with this virus), but here is some progress made.  I have added a forward section of the frame to provide room for a steering mechanism.  For the first prototypes, I will use a set of wheels that can be turned to steer the 'WildWorm' in a new direction. This may look like a traditional vehicle, but all of the motive force propelling the robot will still be from the oscillating standing wave motion.  In order to keep the Millipede motif, the front wheels will be made of little feet!

Here is a CAD view of the current design:
Milli in CAD - Single actuator bio-inspired robot 20MAR2020 (OpenSCAD)


and here is the current printed version:
Milli 3D Printed - Single actuator bio-inspired robot 20MAR2020 


Next steps:

  • build a system to support a servo for steering
  • consider balancing the robot with a 'tail'
  • and it still needs a monster millipede head!

Monday, March 9, 2020

Milli (#6) - Many-Many New Feet

Milli now has many many new feet!

Milli is a sinusoidal, bio-inspired Millipede Robot.  It is completely 3D printed and is made of recycled printer parts and a metal cloth hanger.

Apologies for the delay in posting, it has been a busy month working on my startup (non-robot) business. However, this weekend, I booted up the 3D printer and created a whole new set of golden feet for Milli.  81 new feet to be exact! (not quite a "milli" but getting closer)


Milli - millipede robot track - new feet
Mathematically, the new feet should provide more distance ground traveled with the twist of each tread. This will result in an even faster robot!  The additional ground speed will also be enhanced by the additional grip (friction) with the ground surface, resulting in reduced slippage.


Milli Robot - Tread-Track with new feet 3D CAD design
Each tread now support either 3 or 4 feet.  The 3 or 4 treads are interleaved, to prevent the feet from colliding when they are traversing the rotating helix. The resulting sinusoidal motion will spread the feet as it comes to ground contact. Then contract the feet when lifted.  -- Video coming soon!


Milli Robot - close-up of the new track-tread-links
The result of the additional stretch between the expansion and contraction of the feet will result in a faster motion for the (standing wave) motion of the tread. Theoretically, the feet can be extended a bit further, this will be interesting to see in the future!

I am currently working on the 'head' of the Milli Robot. The new version will support axle and wheel-feet (feet-wheels?) to provide steering.  In addition, I need to create a place to stow the battery and controller.

In other news...
This TotallyNotEvilRobotArmy Blog has now had over 10,000 page hits!

Sunday, February 16, 2020

Milli (#5) - It's crawling now



The Prototyping of milli is moving - as well as Milli, its self!

The focus since the last post was to find and fix any binding parts of the tread tracks. I have located a specific tread that was not flexing properly, due to it being part of the v3 design and connecting to a v4 tread. I am using screws to act as 'pins' in the track to connect treads together. This is not a good practice as the tread of the screw can bind with the tread. however, if significantly bored out it is permissible at this stage of development.


Milli OpenSCAD - for 3rd prototype test 16 Feb 2020

The other change was to adjust the design of the horizontal stabilizing arm.  This arm converts the spinning helix motion to a moving sine wave. Thus it is essential to the design. Changes included shortening the arm by 8mm and increasing the opening by 4mm. I also noticed that the first tread was binding with the arm, and adjusted the tread to move more freely.


Milli - ready for static testing, full tread length, 18v battery, messy desk(!)

The result - the track moves freely!  At least in the initial trials when I applied 18V to the motor it worked well. I then removed the frame holding the chassis and a quickly put together a simple axle and wheels. This was made by a thin rod and some plastic gears salvaged from a printer. I used alligator clips to hold the wheels in place. I put the robot drive on some carpet for friction and Viola! - the worm drive works!!



Next steps:

  • Find that nagging binding point seen in the video
  • Thinking on the chassis and covering. How the heck am I going to get a battery on it?
  • New tread design with increased movement
  • Ability to move on smooth surfaces

Tuesday, February 4, 2020

Milli (#4) - Prototyping the Wild Worm Drive (New Video)

The Milli project is an effort to build a bio-inspired (math inspired?) robot capable of traversing surfaces that are problematic to other robots (such as loose gravel, shag carpet, and muddy bogs, etc).  And to make it look really cool. ;)

The results of the 2nd prototype are much improved, you can see from the video that the prototype has the correct motion and considerably less friction.


Currently, I have printed 23 links in the track tread.  There is an additional load to rotate the helix, but applying additional voltage the motor resulted in enough torque to spin the helix. (at 18V it is very quick).

Next steps will be to create a rear stabilizer to dampen the effects of the spinning helix.

Sunday, January 26, 2020

Milli (#3) - Making improvements

Milli is a bio-inspired robot that uses a single actuator to create standing wave motion.

The Frankenstein prototype was successful enough to indicate that the concept is feasible. The next step is to take the learnings and iterate on the next design as well as create new pieces to replace the Frankenstein parts.

New in this build are:

  • a motor mount, with a frame to hold the Horizontal Stabilizer
  • a single piece Horizontal Stabilizer
  • upgraded tread-tracks (version 4)
  • new Helix mount for motor spendel

WildWorm Drive - iterative design (OpenSCAD)

The Frankenstein prototype was becoming 'stuck' due to two combining factors. An astute YouTube viewer pointed out that the Horizontal Stabilizer was twisting which caused the treads to bind on the helix. In addition, the pin in the Horizontal Stabilizer was crudely glued and would obstruct the rotating helix. The new design uses a single piece Horizontal Stabilizer, pictured above in light blue. In addition, the new motor mount will more tightly secure the stabilizer and position it in line with the centerline of Helix's rotation.

The Tracks have been updated to use a screw as the henge pin between the treads. This design, I hope, will create more fluid motion. It will also be easier to assemble and reduce the failure rate the track becoming disconnected.


WildWorm - Underside view (OpenSCAD)

The underside view of the next design iteration shows the base of the motor mount. As you might be thinking, the helix will not be well exposed to ground contact with this design. This is true, it will be addressed in future iterations. For now, I need to verify the easy rotation of the helix. For this, I will need more track links and a smooth stabilizer. 



WildWorm Drive - 3D printed, the new design works much better

[later today...] I have printed the new design and put it together.  The single piece Horizontal Stabilizer was a significant improvement. With a some additional filing on the parts, the WildWorm drive rotates as planned.  I will update with a video of the new design.


Finally, for the Robot Lovers out there.  Ninety-nine years ago, On January 25th, 1921 the Czech play Rossum's Universal Robots premiered, entering the word 'Robot' into the English Language.

Tuesday, January 21, 2020

Milli (#2) - FrankenWorm (with Video!)

Milli is a bio-inspired Millipeded Robot and today's blog entry is titled:  FrankenWorm!

Rapid Prototyping
The best way to "learn quickly - fail quickly" is to using rapid prototyping techniques to test out ideas quickly and identify potential and real points of failure, design needs, and radical improvements.  Three-D printers are great for taking ideas and making them solid. An even faster way of rapid prototyping is "Frankenstein Prototyping", where the initial prototypes are built by using parts from other projects. In many cases, you just grab the part that is close to what you need and fasten it to the build.

Frankworm! Franken-prototyping the WildWorm Drive

Today, I am Frankenstein prototyping the WildWorm with 3D parts left over from previous projects. I wanted to quickly see if the rotating helix is going to be able to move the track treads of the WildWorm drive.

what is in the discarded print bin?

  • Motor frame - one of the chassis from the original Mojo
  • Battery holder - from an old RC car and RC Rover project
  • Motor holder - initial WildWeasle tests - holds a 'recycled' printer motor
  • Motor spindle adapter - from initial Centi tests
  • Helix Mount - Cam variation from the Mojo2 (he walks!) project
  • Horizontal Stabilizers - linkages from original Mojo project
  • Stabilizer linkage - v0 print of WildWorm track
...and this is why I don't throw away old 3D printed parts.

After finding the parts in the bin, I connected them all together to set up my initial tests. I just used quick fastening methods, tape, hot glue, twisted wire, and screws. It is meat only to learn what works, and what does not!  

Can you identify the parts in the picture??

WildWorm prototype test - Franken Prototype
Test Results
I ran the first tests with a weak battery pack, just under 5V DC. This was attached to a recycled printer motor that is rated 9-12V (I believe). I thought the motor had plenty of torque to rotate the helix without beating the assembly to pieces. -which was important at this stage.


The video shows the results of my initial testing.

First of learnings, yes this worm drive concept is feasible. The underpowered motor is just barely turning the helix, but the rotation is consistent enough to move the treads. The stabilizer will need to be tightened up to keep the tracks in a steady horizontal position. and the helix will need to be smooth, as well as the inside of the treads, in order to reduce the internal friction and sticking.

This test only proved that the motor with stabilizer will move the track in the correct motion. There are a lot of design learnings available, now I can iterate on these ideas and go for the next set of testing.

Sunday, January 12, 2020

Milli (#1) - A Bio-Inspired Millipede Robot

Next in line for bio-inspired robots is the Millipede.
(I know, I know, I am starting a new project without finishing the last ones. But, this one is interesting! ;)

Millipede design that I am looking at is the concept of having many many feet on the ground for the robot.  Similar to the Centi robot concept, I will use a mechanism to transfer the rotational motion of the motors to the feet in contact with the ground.

For this robot build, i am focusing on the work of David Zarrouk.  Zarrouk's SAW robot is a Single Actuator Wave-like robot.  The design uses a single motor that is spinning a helix twisted rod. The rod moves a linked set of treads in a way to create an advancing standing wave.


SAW robot from David Zarrouk

  This is best viewed in his video, from Zarrouk Labs:




For my build, I will start with the wave mechanism to provide the motion for the Millipede robot.  There is a published paper which describes the math put into Zarrouk's robots. I am using this as a starting point in my design. Using this as inspiration, I will first try to replicate his work, then extending on it. I will attempt to use this wave motion, as the driving actuator on the robot.  I am calling this my Worm-Drive, the WildWorm, for Milli the robot.

Initial Design:

The Track - The most complicated part of the worm drive is the tread design. The tread is conceptually the same as a crawling tank caterpillar tread. The only exception to a tank tread is that these treads will not be moved by cog wheels.
Each tread must have a pivot point so that it can be linked with the next tread. When linked together in must be very flexible. The joints must have low friction.  
Part of this design has the helix is spinning inside of it. The inside slot must have clear running path as the helix will actually slide along from side to side. But, as you will see it is not the helix that is moving, but the treads wrapped around the helix.


WildWorm Track design version 3

For this first set of designs, I am using nails to act at the connection axis.  They will be positioned between two pin holes. the inside hole is small and will hold fast to the nail. The outside has a larger radius so that the part rotates around the metal nail.

Finally I have extended a 'tread' to the track link, so that it can directly interact with the surface.


WildWorm 3D printed Tracks
v1 - top left
v2 - top right
v3 - bottom
It might be obvious, the track linkages will need to frictionless. It occurs to me that low friction will need to be designed into the treads. The next iteration of the design will perhaps use a metal washer between the tracks to reduce the friction. Lubricant will also be helpful. Ultimately, the series of track will need to be nearly fluid when shaken.

WildWorm - Helix and Tracks - 1st prototypes

The Helix - The helix is the part in the middle of the assembly that drives the mechanism. There are not a lot of details about the construction of the helix. I have started by using a wire from a coat hanger. I have wrapped the wire around a metal pipe and adjusted to create a consistent helix.  The helix should be smooth to reduce the friction of the track that slides around the helix. It may be possible to 3D print a helix, this would ensure the precision of the design and centering of the motor axis. However, a 3D printed helix may not have the strength needed to support the track linkages.

First Prototype

The first prototype assemblage of the WildWorm, has yielded a lot of insight. That is a nice way of saying, it did not go very smooth as I hoped. There will be a lot of tension between the helix and track. Perhaps this can be relieved by increasing the period of the helix. My first attempt was a 7.5 cm. I see that it should be much longer, maybe 10-12 cm.
WildWorm - 1st assembled prototype of the helix and track (5cm period)

Next steps will be to increase the length (period) of the helix. I will also design the motor housing, stabilizing arms, and a mount for the helix.  The helix will be easier to test, once I can mechanically stabilize (hold horizontal) the tracks.

[UPDATE] Extending the helix out to 10cm period, length of one full cycle, solves many issues. The track slide smoother, and there is significantly less binding.