Vertically suspended Mendocino motor

Last update:  5/21/2015 
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If you haven't seen the video of the motor running etc you ought to view it now so you will have an idea what this article is about.

Youtube link showing motor running etc

Overal Background:

Normally Mendocino motors are built as a levitated horizontal motor. I decided to build mine as a vertically suspended motor so I could test some ideas on magnet placement etc. I was able to quickly set up the vertical suspension system the same way I did my vertical pulse motor that I recently built. For this motor I used a two liter plastic soda bottle as the case and supporting structure of the motor. Motors can be built very quickly using a vertical suspension in a bottle instead of levitating the armature.

Please note that if you are building a conventional horizontally levitated Mendocino motor, the armature and ball point pen axle are made exactly the same as this motor.The only difference is that the magnets are used in suspension instead of levitation.
You will find that having the armature balanced is much more critical with horizontal mounting than with a vertical suspension system. Actually my armature is out of balance due to one of the solar cells shifting off center after the motor was finished. I didn't do any balancing on it for a test run and found that the out of balance doesn't really affect the running of the motor. The worse that can happen with my motor is that the bottom of the armature swings around in a small range of low RPM. On a levitated motor the out of balance can cause the armature to bounce out of the levitating magnetic field.  Also, a low power motor may not have enough power to speed up beyond the out of balance low RPM resonance speed.

Using field magnets on either side of the armature reduces the out of balance swinging to a minimum and this motor easily accelerates through the out of balance RPMs. So keep that in mind when deciding which suspension system to use. Or try vertical and then horizontal levitation with the same armature.

If you plan on building this motor please read this article several times until you understand what needs to be done.  Once the solar cells are mounted it is very hard to remove them from the armature.

Description and theory of the motor:

The motor takes very little light to run. I have the motor placed near a north facing window. With the curtain closed each night the motor is sometimes already running in the morning at a very slow speed due to the light leakage around the curtain. The motor normally still runs 5 minutes after the published "sun set" times while inside the house.

The design of the motor is a stationary magnetic field created by magnets attached to the side of the 2 liter soda bottle and a styrofoam armature with four solar cells and two coils wound on the armature. The timing of  the current flow through each coil is done by pair of two opposing solar cells that are mounted on the armature. The two coils and their connected solar cells are mounted 90 from the other set of solar cells and their connected coil.

Each pair of solar cells are electrically connected "back to back". That is; the positive terminal of each cell is connected to the negative terminal of the opposite solar cell of the pair. Each of the two solar cell pairs and their coils are not electrically connected to the other cells or coil.

As the armature rotates the voltage polarity applied to one connected coil is reversed every 180 of rotation. This reverses the direction of the magnetic field generated by the switched coil. The fixed external magnetic field surrounding the armature repulses the magnetic field generated by the coils. This repulsive force causes the armature to rotate.

The direction of rotation can be reversed by simply rotating the bottle ~180. Rotating the bottle reverses the external magnetic field polarity in relation to the direction of sunlight striking the solar cell in use as the armature rotates.

The CD is used to have a flat surface for the bottle to sit on. The bubble plastic foam is used as a shock absorber in case the armature drops away from the suspension magnets. The thin solar cells are very brittle and it doesn't take much to break them.

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The magnetic suspension system:

 show suspension setup I used the same suspension system for this motor that I had already devised to suspend my vertical pulsed coil motor. A flat disk magnet, two ring magnets and two ball bearings attract the ball point pen tip.

All the magnets used on the motor are Neodymium magnets.  There is one 1/2" diameter ring magnet (N42) on the outside center of the [now] top of the bottle. A 1/2" diameter flat disk magnet (N35) and another (N42) ring magnet are  inside the bottle as shown in the picture. I had to use three magnets to support the weight of the armature and it's components.

A 3/8" diameter steel ball bearing is magnetically attached to the lower ring magnet. A 1/8" diameter ball bearing is attached below the larger ball bearing. The ball bearings are used to concentrate the magnetic field towards the point of the ball point pen.
The idea is to have just enough magnetic attraction between the small bearing and the ball point pen to keep the armature attached to the small ball bearing. This will reduce the mechanical friction between the ball point pen and the small bearing.  A little Marvel Mystery oil is used to lubricate the ball point pen ball bearing.

By using the ball bearings, the armature can hang vertical even if the bottle is tilted.  If a flat disk magnet were used as the contact point for the ball point pen and the the magnet was not perfectly horizontal while running, the pen would tend to walk off towards the lower side of the magnet and eventually it would jamb on the side of the disk magnet which would stop the motor from running.

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Solar cells used for my motor:

I bought a pack of twenty 78mm x 19mm solar cells through eBay. The eBay number if the listing is 350837537118.  My solar cells are rated at 0.5 Vdc no load and 0.5 amp when short circuited. These solar cells are very thin and brittle.  The main reason I bought them is for their light weight.  You can use thicker cells but you may have to use more or stronger magnets to support the heavier hanging armature.

Attaching the positive and negative voltage wires to the cells was the most difficult part of the project. I cracked four cells to end up with four to use on the motor. I was able to salvage a few pieces of the cracked cells that can power other projects. I used a temperature controlled soldering iron and a flat piece of hard wood to place the cells on when soldering the wires and tinning the negative voltage tabs.

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How to make the styrofoam armature coil form etc:

You may have to click on each of the following two pictures to see them properly.
End view of the Styrofoam armature

styrofoam armature

This drawing shows the shape of the ends of the styrofoam armature coil form. I made a hot wire foam cutter using a 3" length of bare solid #28 wire mounted on two insulated posts that positioned the wire 1" above an aluminum plate. Two 6" long thick insulated wires connect the ends of the 3" wire to a soldering gun as the power source to heat the wire.

By using the hot wire cutter I was able to cut out a 1" square length of Styrofoam and then cut it to the same length as the solar cells I'm using.

Do not touch the the soldering iron to the styrofoam when melting the wire grooves. Just bring the tip of the iron near the foam and it will melt. By moving the iron down the length of the armature you can create a shallow groove to wind the coils into.

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Connections for solar cells and coils

solar cell connections

This drawing shows the location of the electrical connections (solder tabs) on the solar cells and describes how to connect them when the time comes.

The next pictures will show the details how I connected the jumpers and coils. Most people route the solar cell jumpers towards one end of the armature and then attach the coil wires to the jumpers at the end. I positioned the jumpers to go around the top of the adjacent solar cells to lighten the armature.

Wind the coils before placing the solar cells on the armature. I used #36 magnet wire for each of the 100 turn coils. It took about 200 feet of wire for each coil. The resistance of each coil is ~65 ohms.

Instructions of how to build the armature are given further down this page.

Schematic of  the armature wiring:


The schematic shows S1B and S2B reversed to simplify the wire lead placement on the schematic. I wanted to show the solar cells in the order they are placed on the armature without the wires crossing in an X at some point.

The solar cells are mechanically placed on the armature so the jumper wires all point in the same direction before soldering to the other cell of the pair. The negative tab wire may leave the solar cell either to the left or right in relation to the axle. The S1 jumper wires may go to the left or right side of the S2 negative solder tabs. The S2 jumper wires will pass over the other side (right or left) of the S1 negative solder tabs.

I used #28 solid copper wire for the jumpers.  One of the reasons I used wire that thick was to help hold the solar cells in place on the armature with a girdle of wire around the cells. The disadvantage of using wire that thick is that you have to be very careful when you form it around the other cells so you don't break the thin solar cell.

As it turns out the #28 wire I used is really too stiff to easily form when soldered to the solar cells.  

If I build another Mendocino motor I will use thinner jumper wires for ease of bending them.

Perhaps #30 will be OK.  The #36 wire I used for the coils will electrically be OK for the jumpers but won't offer any support to hold the solar cells in place. The jumper wires could get damaged over time if they contact the solar cells of the other pair.  So use your own judgment how to wire the jumper wires and how thick they should be.

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Bearing end

This is the view of the ball point end of the armature. Wind 10 turns of #36 wire at a time on each side of the pen until you have 100 turns wound for the inner coil. Then wind the other 100 turn coil 10 turns at a time on each side of the pen.
Free end

This is the other end of the ball point pen armature.  You can see the solar cell jumper wires at the very top of the picture.  I positioned the start and end of one coil at the pointed end and the start and end of the other coil at the the end shown above.

Armature view

Notice the wrap of scotch tape at each end of the styrofoam armature to attach the solar cells. The tape is wound with the sticky side out so the cells will stick to the tape. The cells are purposely offset a little bit so the jumpers for each pair of cells will clear each other as they go around the armature to the other cell of the pair.

After I had the armature assembled I found my roll of double side sticky tape which would have worked better. Such is life .........

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jumper view

This view shows the overall view of the jumper from the negative tab of the vertical solar cell going over the top of the horizontal cell to the positive tab of the vertical solar cell 180 on the back side of the armature.

If you look closely you can see the #36 wire coming from the left side of the coil groove that is soldered to the vertical negative solar cell tab.

Close up view of the thicker #28 solar cell jumper wires and a #36 coil wire soldered to the solar cell negative tab.


You can also see two of the wire wraps around the coil bundle to keep it away from the heat of soldering the coil wire to the jumper. I wouldn't add any glue or thin paint to the wires to keep them in place because it might dissolve the styrofoam. 

Here is how to actually build the motor.

Preparing the solar cells for mounting:

Since the cells are very fragile I decided to not run the long jumper wires from each cell down to the end of the armature and back up to the opposite solar cell. Instead I wired the cells with the jumper wires going directly around the outside of the cells to shorten the length of the jumpers and perhaps provide a little protection to the cells. When handling the solar cells try to not get finger prints on them.

The jumpers should be pre-formed to pass over the adjacent cells without touching them before mounting them on the armature.  The following pictures will show the shape of the jumpers.

First problem:
The tab plating on the front and back of the solar cells is very thin and you can not use ordinary rosin flux cored solder to tin or solder a wire to a solar cell as you would ordinarily do. Perhaps solder with silver content will work OK but I don't have any.

Trying to use flux cored solder just coats the solar cell tab area with flux and for one reason or another the solder won't flow onto the tab. If you try rubbing the tab with the iron tip the tab plating gets ruined. I tried some pre tinned tab wire and it wouldn't stick either.

After thinking about why my solder wouldn't stick to the solar cells I realized that I have a very old 5 lb. roll of rosin cored tin-lead solder. New solder now days is usually made with water-soluble flux and doesn't use use lead (Pb).  My advice is to NOT use old tin-lead solder with rosin flux like I did!  But all my warnings about the cells being very fragile still hold.

I finally broke down and bought a proper solar cell flux pen through eBay which works fine.  It only takes the slightest drop of the stuff to allow you to solder the wires to the cell.  Don't apply too much of it because the heat of the iron causes the excess to form a very hard blob.  If you try to scratch or scrape  it off you will more than likely crack the solar cell.

My method of soldering jumpers to the solar cells:
If you don't have the proper flux pen try this:  place the tinned tip of a piece of ~2" long #28 or thinner magnet jumper wire on the rubbing alcohol cleaned cell tab and then apply a bit of solder to the soldering iron tip; wait until the smoke is almost gone (leaving a minimum amount of flux on the tip of the soldering iron) and then quickly place the iron on the end of the jumper wire and with luck the solder would flow onto the wire which in turn would transfer a bit of solder to the tab.  It ends up looking like a cold solder joint but it does hold.  But the solder flux pen is the way to go.

In trying to figure out the sequence of mounting the cells and attaching the coil wires I came up with the following method. Attach one of of the jumper wires to the positive tab point (on the back of the solar cell) near the edge of each cell. Position two of the cell jumper wires so they aim slightly to the right of the short axis of two cells and two more jumper wires to aim slightly to the left on the other two cells. Next tin the negative tabs on the top of the solar cells at the edge of the cell opposite the positive connection wire. The solar cells will be mounted on the armature so that as you rotate the armature the jumper wires alternate angling from left to right as they come into view.

Once a cell is mounted on the armature you will not be able to get to the positive tab to do any soldering so make sure the tab wire is really soldered to the cell before mounting it.  I checked them by very slightly wiggling the free end of the wire from side to side.

Since the silicon used to make a solar cell is a good heat sink you may need some sort of an insulator under the cell while soldering the tabbing wire. I used a piece of notched in the center of the long edge hard flat wood to lay the solar cells on while trying to solder the tab wire to them.  You need three hands to do this, one to hold the wire, one hand to hold the soldering iron and the last hand to keep the solar cell from moving. And a forth hand to apply the solder would help too.  Not having even the third hand I just placed a thick rubber eraser on each end of the solar cell.

Once you get the wire attached you have to be careful when you flip the solar cell over to tin the negative tab area so the blob of solder and jumper wire hangs over the side of the wood in the notch or you will certainly break the solar cell with any force you put on it.

Tin the negative tab area on the opposite side of the solar cell from where the tab wire is attached.  Place the cells aside for later use.

Remember to always hold the tab wires with needle a nose plier at the solar cells when bending the wires.

Building the armature:

The sequence of how I built the armature is as follows;
  1. Install axle:  After I cut the 1" square styrofoam armature out I drew cross lines on each end from one corner to the other to find the exact center at each end.  I then used an ice pick to make a hole down the length of the armature form so that the point of the pick came out at the center of the other end of the armature. I enlarged the hole with various diameter Phillips screw drivers until the ball point pen would fit snuggly into the armature. Do this slowly so you don't split the foam. Leave the pen in the foam from now on as a handle to hold the armature.
  2. Make wire grooves:  I used a small soldering iron to make the wire grooves down the length of the armature.
  3. Draw a marker line around the armature at the mid section of the styrofoam. Use your soldering iron to make a shallow pit in the styrofoam where the jumper wires will leave each positive cell connection so the wire will have a little clearance to the styrofoam.  If you don't do this the solar cell is likely to crack when you press it in place on the scotch tape.
  4. Winding the coils: I wound the coils so the start/end end wires come out at one end of the armature and the other coil start/end wires come out the other end. I did this so it wouldn't get confusing which wire goes with which coil. Leave 2" to 3" of  wire leads on the coils to make the connections later.  After the first coil was wound I wrapped the extra wire around the pen and used a piece of scotch tape to hold it out of the way while winding the 2nd coil.
  5. After both coils were wound I wrapped short lengths of the thin wire around the coil bundles to keep the wire bundle together in the grooves.  I used 4 wire ties on each long leg of the coils. The tie wires are not electrically connected to any part of the motor.
  6. Pre bend the jumper wires so they will end up over the proper tinned negative tab point of the opposite solar cell before mounting the cells. 
  7. Hold each solar cell in turn on the armature, cut each jumper so it can be soldered to the opposite cell's negative tab. Tin ~1.8" of the free end of the jumpers.
  8. Apply tape to hold solar cells:  Rather than try to find a glue which wouldn't dissolve the foam I just wrapped some scotch tape around each end of the armature with the sticky side out to hold the solar cells in place. It would probably be better to use double side sticky tape to do this.
  9. Carefully mount the solar cells.  Offset one pair of solar cells to the other pair about the width of the negative tab width.
  10. Solder each free end of the jumpers to the tinned negative cell tab of the 180 offset solar cell.
  11. Attach each of the solar cells to the sticky tape with the jumper wires aimed so that they are aligned Left-Right-Left-Right to the negative tab area of the cell they pass over. Use extreme care so you don't break a solar cell!  Once mounted it is almost impossible to remove a cell without breaking it.
  12. Pick one of the solar cells to be S1A. This will automatically determine the part symbol numbers for the rest of the parts. It really doesn't matter which end of the pen you use as the reference direction. But do remember which cell is S1A for the next steps.
  13. Position the coil wires so they can be soldered to the pre tinned negative area of the proper cell.  
  14. Cut the start wire of coil L1 to length, tin it and solder it to the negative tab of S1A.
  15. Cut the end wire of coil  L1 to length, tin it and solder it to the negative tab of S1B.  Trust me on this.  ;-)
  16. At this point the motor should run as a one coil motor. I would test it to make sure you have this set of parts wired correctly before connecting the L2 wires. If the motor doesn't run check the trouble shooting paragraph for help.
  17. Cut the start wire of coil L2 to length, tin it and solder it to the negative tab of S2A.
  18. Cut the end wire  of coil L2 to length, tin it and solder it to the negative tab of S2B.
The motor should now start by itself and run much faster than when running a one coil motor,  Have fun with your new toy!  ;-)

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Trouble shooting if the motor doesn't run:

If the motor doesn't run you will have to use standard electrical trouble shooting tests. Check that the solar cells and coils are wired as shown on the schematic. Each coil with one lead disconnected reads ~65 ohms. The solar cells are more difficult to test when wired back to back because of the affect of any lighting on them.

If the motor ran as a one cell motor but not as a two cell motor you may have coil L2 wires reversed on the solar cells. I would disconnect one lead of coil L1 and get coil L2 to run in the same direction as coil L1 ran when looking down on the motor. If you get the motor to run on L2 but in the opposite direction of L1 then reverse the coil wires of one the coils to the negative tabs of solar cell pair of that coil.

If none of the above works then check the coil connections with an ohm meter. Each coil measures ~65 ohms when tested with my low applied voltage DVM before connecting them to the solar cells. But when connected to the solar cells they read about 26 ohms with the probes touching the negative tabs of opposing solar cells. This is due a combination of one of the solar cells acting as a diode wired in the reversed direction due to light shining more on one of the solar cells of the pair with the actual resistance of the coil in parallel while making the ohm measurement.

Check that you don't show continuity between the two sets of solar cells. That would be a sign of a incorrectly wired motor.  That's a no-no.

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