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!

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