Saturday, September 26, 2020

Milli (#9) - New Mount for Helix - and Crawling Video!

 Milli - a Bio/Math inspired crawling single actuator robot millipede - now with teeth!

Milli - Millipede robot - now with teeth

From the last post, you may have noticed that I had tried to print some "nodes" as a possible improvement to Milli the millipede. Well, that thought was not as successful as I had hoped. There turned out to be no flexibility and too much tension on the helix. With this in mind, I reopened the milli design and set to work on some design updates:

  • Offset the motor
  • add a gear reduction to the motor
  • add a bearing to main helix mount - to remove force on the motor itself
  • try out a new power source
  • Add teeth - because we need to add more Nightmare Fuel!!
CAD Design - new Motor Mount and Gear

The new design is a new motor mount, with drive gear, a bearing mounted main gear, and new 12V "shore" power.

3D printing gears remains a dark art to me, but here you can see that they are functional. In this print, I have used a larger Modul of 1.5, this makes larger teeth. I believe for my quick 3D prints this is a more accommodating solution (more tolerance for rough prints!).

I applied a liberal amount of hot glue to attach the pre-existing helix mount to the newly printed main gear. That may qualify this for a frankenstein prototype, no doubt.

Sloppy gears? certainly room for improvement - on the next iteration.  The thicker base layer print creates an uneven gear surface.

Another issue was the 'pede wheels' that I kept from the previous build. They function as wheels, however in the video you can see that the left wheel consistently unwinds and falls off, Doh!

Ready to Test!  Let's get crawling!

Milli - Robot Millipede on a colorful background

For this round of testing, I am using "shore power". The robot is tethered to a 12V DC source. I reused a momentary switch - also from a printer - in order to easily turn on and off the robot.

Testing goes as expected.  The motor gear hold, which is surprising.  However the front left pede-wheel falls off frequently.  The motion of the helix, continues to be smooth.  I believe the addition of the bearing smooth this rotation off, taking load off the motor.  

Video on YouTube:

Next Steps:

With this success, time to think of what would be in the next iteration.
  • Onboard 12V power supply
  • micro-controller with PWM output
  • Motor Driver board
  • remote or autonomous operation (Min1 project may come first)

Sunday, September 13, 2020

Current Thinking in the Robot Labs

These are things currently being thought about at the TENRA Robot Labs...

Late nights and early mornings in the lab!

3D Printing

Ah... the beauty of 3D printing for robots!   It is the magic of having an idea in your head, which leads to, a sketch on paper, a drawing in CAD, and then a solid print - or many prints:

1st - A quick sketch on paper

2nd - A quick draft in OpenSCAD

3rd - a quick print - a solid Object!

Finally - Repeat as needed

I really love this aspect of Rapid Prototyping. I find it one of the more enjoyable steps in robot building. At each step in the process, you can find opportunities or issues with your design. It is fantastically easy to go back a step or two and add improvement to the design.

A good example is in this very simple build of "Node", pictured above.  "The Node" is an experiment in the Milli Project. I wanted to explore the ability to move in two directions on the helix in order to improve the mobility of the millipede robot. 

At each step in the process, I found that new aspects of the build became evident.  Even in the first print, i realized that I need more of the 'feet' to touch the printer bed. A quick change to parameters in the CAD, and it solved the problem. Finally, a quick print of three copies of the nodes. I assembled them and was able to perform my tests. The result was that the solution would not work as is due to certain bindings. I was having a difficult time imagining this complex relation in my head.  The rapid development of the concept provides a fast path to success or failure, both are acceptable!

Min1 - what should it do at night? 

Min1 is the Minimal Viable Robot for the Totally Not Evil Robot Army.  But, I am just thinking, what can this robot do at night.  It is just sitting around, with nothing to do.  Idle cycles are the devil's playground, right? So perhaps it needs a few teeth and a sensor to seek things (like ankles) out and make stabby motions.  ;)

Min1 - outfitted with ultrasonic sensors and stabby teeth

Min1 ready to Roam - seek and stab

Min1 Robot - as a Franken-prototype ready to go


Tilt, the balancing - 2 wheel Robot, is sitting prominently in the TENRA Robot Labs. It is patiently waiting a more powerful power source.  Twelve Volts DC is not going to cut it, it needs more power to keep the recycled printer motors from stalling.  I have just recycled a 19V power adapter that I will use as 'shore power' for the next round of testing. 

I am really liking Tilts new 'eyes'!