Solar Commutated (Mendocino) Motor

A project I completed for the enjoyment of designing and building. The motor will silently spin when placed in sunlight or under an artificial light source.

The motor utilizes a few basic ideas. The solar panel facing up will deliver a larger voltage potential than the one facing down as it is receiving more photons. The direction of current flowing through the motor coil is then determined by the upward facing panel. If the panels are wired in such a way as to deliver opposing potential to the coil, on average the electromagnetic field will have a fixed orientation. This field will try to orientate with the horizontal field created by the permanent magnets resulting in the rotor tilting over. As the rotor tilts, the electromagnetic field decreases, as both panels now having similar amounts of light. The forward momentum swings the other panel up, reversing the direction of current through the coil and establishing the same vertical electromagnetic field. The process repeats from this point allowing the motor to spin in one direction.

A better explanation involves the Lorentz force, but this site is about creating, so I will focus on that!

Step 1: Materials and Tools

Materials

(look at provided drawing to determine needed material dimensions)

• Material for frame:
  1. 1/2" aluminum bar or plate
  2. 1/4" aluminum bar or plate
  3. Hickory wood 4/4" for base
  4. (2) 1X1X2" C8 ceramic magnets
• Material for rotor:
  1. 1/2" PVC plastic sheet
  2. 4.9mm OD X 2.8mm ID pultruded carbon fiber rod (4" length)
  3. 36 AWG magnet wire for armature
  4. Hook-up wire (~22 AWG)
  5. (2) Solar panels 6V 0.6W 80X55mm
• Hardware:
  1. (12) #6-32 1" stainless round head
  2. (6) #6-32 1/2" stainless button head
  3. (2) #6-32 7/8" stainless cap screw
  4. (2) #6-32 thumb nut
  5. (10) #6 stainless washers
  6. (2) 1/4-20 3/8" stainless set screws
  7. (8) 12X3mm 4mm hole countersunk neodymium ring magnets
  8. (2) 1/8" ball bearings

Tools

1. CNC milling machine
   • 3/8" end mill with a depth of cut 1/2" or larger
   • 1/8" end mill with a depth of cut 1/2" or larger
   • other tooling to use the mill (mill vise, tool holders, parallels, ...)
2. Drill press and drill bits
3. #6-32 tap and handle
4. Table saw
5. Glue gun (hot glue)
6. Super Glue
7. Soldering iron
8. Screw drivers
9. SAE hex key set
10. Fine sandpaper for smoothing ends of set screws

Step 2: Part Drawings

The provided drawing is for size reference and material selection. The drawing dimensions are not fully defined as the parts were CNC milled. The SolidWorks design files are attached and should be used when machining (STL files are also provided but untested).

Step 3: Magnet Support Arms

• Generate CNC tool path from provided solid model using 3/8" diameter end mill.
• CNC mill two support arms from 1/4" aluminum bar or plate.

Step 4: Rotor Supports

• Generate CNC tool path from provided solid model using 1/8" and 3/8" end mills and #36 drill bit.
• CNC mill two rotor supports from 1/2" aluminum bar or plate.

Step 5: Rotor Frame

• Mill rotor frame from PVC using the provided solid model as reference with 1/8" and 3/8" end mills.
• Drill the center hole matching the diameter of carbon fiber rod.
• Drill offset holes on one end large enough to pass magnet wire to center of rotor.

Step 6: Drill and Tap Aluminum Parts

• Mark hole locations using solid models as reference.
• Drill all #6-32 holes with #36 drill bit.
• Tap holes with #6-32 tap (remember to lubricate tap).

Step 7: Set Screws

Flatten and smooth end of set screws on a lathe or by hand using sandpaper.

Step 8: Hickory Base

• Cut base to dimension.
• Surface top and bottom.
• Drill #6-32 clearance through holes.
• Drill counterbores on backside to recess screw heads.
• Apply oil finish.

Step 9: Attach Magnets and Support Arms to Base

• Using the #6-32 1" screws with washers, loosely attach the support arms to the wood base.
• Slide the ceramic magnets into the support arms so they are attracting each other.
• Center the magnets and secure using the #6-32 1" screws with only enough force to keep the magnets from moving. Do not over-tighten as the magnets can break.
• Tighten the screws attaching the support arms to the base.

Step 10: ​Assemble Rotor Supports

• Look at first picture for placement of parts.
• Mount two ring magnets to the support arms using the #6-32 1/2" stainless button head screws with the countersunk side out.
• Mount a single ring magnet to the support arm over the slot using the #6-32 7/8" stainless cap screws with the countersunk side of the magnet facing out. Secure the fasteners using #6-32 thumb nuts and washers on the back side.
• Partially insert the 1/4-20 set screws with the flat side facing the magnets
• Attach the rotor supports to the base using #6-32 1" screws and washers with the ring magnets facing the center.

Step 11: Rotor and Armature

• Cut the carbon fiber rod to 3.92".
• Tap both ends using the #6-32 tap.
• Measure the output of the solar panels to verify the marked polarity (I discovered one of my panels was improperly marked after assembly).
• Attach about 2" of hook-up wire to the positive and negative tabs on one of the solar panels.

• Hot glue the panel with wire to the rotor frame.
• Hot glue the carbon fiber rod centered in the frame.
• Wind about 200 turns of 36 AWG magnet wire around the outside of the frame, (approximately 70 ohm) with the beginning of the wire passing into the center of the frame through one of the small holes. Leave a few inches of wire on both ends to work with.
• Pass the other end of the magnet wire into the frame through the other hole. Secure both ends of wire as they enter the frame with a small amount of hot glue.
• Attach the other ends of the hook-up wire to the opposite polarity on the second solar panel (+ to -) along with the magnet wire.
• Adjust the wiring to fit symmetrically into the frame in order to maintain balance.
• Hot glue the second solar panel onto the frame.

• Mount ring magnets to carbon fiber rod using the #6-32 1/2" stainless button head screws with the flat side of the magnet out.

• Glue the 1/8" ball bearings to the #6-32 screw heads using Super Glue and some tape to hold the bearings in place while the glue cures (short sections of graphite from a wood pencil will also work in place of the bearings).

Step 12: ​Position the Rotor

• Place the rotor in the center of the ceramic magnets being careful not to dislodge the ball bearings.
• Thread in the set screws until the rotor is centered and floats on the magnets. The smallest disturbance should shift the rotor from resting on one set screw to the other.

The rotor play between set screws should be as small as possible while still allowing free rotation.

Place the solar motor in the sun or a brightly lit room and let it spin!