Introduction: Simple Dc Motor With Forward/reverse and Self Starting

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Grandson Nicholas and I developed this simple motor for his school project. We checked the web for ideas and then evolved this motor that has a number of unique features that make the motor easy to start and run.  The motor also features a forward-reverse and speed control.  

The motor armature rotates due to magnetic pulses created by a pulsating current that flows through the armature coil - these electromagnetic pulses interact with the rare earth neodymium permanent magnets (the "field" of the motor) and cause rotation to take place. The neodymium magnets are mounted on the sliding "direction and speed control" bar. Sliding the magnets under the armature gets the rotation started. 

Step 1: Video With Operating and Build Info

Step 2: Materials and Tools

Materials used
  • paper towel
  • paint can stirring stick
  • 2 solid brass ceiling hooks 2-9/16 inches
  • D battery - used for wire winding form
  • 6 feet #22 enamelled magnet wire 
  • 3/4 inch thick soft wood base approximately 3-3/4 x 12 inches (pine works good)
  • 4 neodymium magnets approximately 3/4 inch diameter
  • double sided tape
  • 4 AA alkaline batteries 
  • battery holder - connects 4 AA batteries in series for 6 volts
  • 4 push pins
  • 2 plastic beads
  • small piece of plasticine (not shown) 
Tools used
  • paper stapler
  • pencil
  • small awl or small Philips screwdriver (a drill and bit would work as well)
  • wire cutting pliers
  • utility knife
  • speed square or plastic triangle 

Step 3: Winding the Armature Coil and Stripping the Enamel Insulation to Form the Commutator

  • string out and cut off about 6 feet of magnet wire from the spool
  • wind the wire around the D cell leaving about 2 inches of wire on either end of the coil
  • wrap 2 to 4 turns of the beginning and end of the wire tightly around the coil to keep the coil snugly together making sure that the resulting "axles" are directly opposite each other.  Shift the wire axle wraps as needed to get a balanced feel.
  • use the utility knife to "strip" the enamel insulation from both axles as demonstrated in the video and shown in the illustration here - be careful not to nick the wire during this procedure
When the armature coil is mounted on the brass ceiling hooks,  current will flow through the coil only when the bare copper part of the "half-stripped" axle is in contact with the brass ceiling hook (the other axle is always in electrical contact with its hook).  Therefore the armature coil might occasionally require a little bit of influence with your finger to get it going.  If this continues to be a problem remove a little more than half of the insulation from the axle.

The armature coil, and coil ends serve as axles,  bearings, and commutator.

The armature is also the electrical ON and OFF "switch" for the battery - it must be in place on the ceiling hooks for ON and completely removed for OFF.

Step 4: Installing Ceiling Hooks, Battery Wires, Magnets, and Making the First Test Run

Solid brass ceiling hooks are commonly available in hardware stores.  But steel and plated steel hooks are also available.  Solid brass was selected for this motor for two reasons:
  • brass is a non-magnetic material so you don't have to worry about the strong neodymium magnetic jumping and attaching to the ceiling hooks
  • brass is a pretty good electrical conductor
The brass ceiling hooks become bearings, "brushes" and mechanical supports for the armature in this simple motor.

To let the hooks comfortably cradle the wire axles of the armature, the hooks are screwed into the wooden base at about 60 degrees to the horizontal.  It's best to first create pilot holes for the two hooks by forcing an awl tip or small phillips screwdriver tip into the wood with a twisting motion. The pilot holes make it fairly simple to get the hooks screwed in at the right angle. We then removed the hooks and poked the bare ends of the battery wires in the holes and once again screwed the hooks in to secure the wires in place.

Many alligator clips are made from magnetic material so that's why the battery wires are connected directly to the brass hooks rather than making the connection with alligator clips (we don't want the powerful magnets jumping after the clips!).

The magnets are stuck to the control arm with a small square of double sided tape.

Once the battery is hooked up the motor is ready for the first test run.  You just have to set the armature coil axles gently on the ceiling hooks and  slide the magnets towards the coil (make sure the spacing beads are installed on the axles first.) Sometimes a little jerking motion of the control arm is required to get the armature turning. If necessary give the coil a little help with your finger to get some action (see Step 3).  Either way, the motor should run at varying speeds as the magnets are moved back and forth under the armature. The armature will reverse direction at some point along its travel.  There's a good chance the armature will pick up enough speed, and vibrate enough, to cause it to jump off the hooks.  Step 5 shows how this problem was resolved.

Step 5: Plasticine to the Rescue and Some Refinements

Even with the ceiling hooks angled to give a good cradle configuration for the armature axles the armature often danced around and jumped clear of the hooks when it was rotating rapidly.  This is due to the armature being unbalanced (it's difficult to get it perfectly balanced) and perhaps also due to the magnetic pulses that drive the motor. The video gives a good demo of the armature breaking loose.

That's where plasticine comes in.  A couple of small rolls of plasticine formed around the axles and pressed in place does the job of keeping the armature from jumping clear.  The plasticine should not contact the axles when resting in the cradles. When the motor is rotating the plasticine also catches a lot of the carbon particles (generated due to arcing between the wire axles and the ceiling hooks).  But you will still need to do periodic contact cleaning to keep the motor operating smoothly (see Step 6).

Nicholas came up with the idea of placing guides to keep the direction and speed control arm centered between the ceiling hooks. Four push pins work well here.  The guides would be pretty well essential if the ceiling hooks are magnetic material like steel (see Step 4).

Good idea to staple the two battery wires to the base to keep the wires from being pulled out of place.  An ordinary office stapler works for this.

To finish up building the motor the direction and speed control bar was labelled to clearly indicate its function.

Step 6: What to Do If the Motor Is Not Starting or Running Properly

Like any piece of electromechanical equipment a little bit of maintenance is necessary to keep the motor in peak operating condition.

If the motor is not starting and running properly take a look at this set of checks and adjustments to help resolve the problem:
  • build-up of carbon on the electrical contacts - clean with a paper towel
  • armature becomes mechanically unbalanced - adjust wire axles until the armature turns smoothly
  • battery voltage too low - replace batteries
  • poor electrical connections between battery wires and ceiling hooks - twist ceiling hooks a few times in the wood base
  • if the motor has been running off and on for a long periods of time check the insulation on the armature axles to see if the insulation is damaged (Step 3) - wind and prepare a new armature if necessary
Always remove the armature from its mounted position after you finish a motor test - otherwise current might continue to flow through the armature and drain the batteries.

Step 7: Further Suggested Experimenting

Here's some ideas:
  • increase (suggest maximum 9-volts) or decrease battery voltage
  • change the number and/or the size of the magnets
  • reverse the polarity of the magnets on the control bar
  • reverse the armature on the holders (this will change the polarity of the electromagnet)
  • make more or less turns of wire on the armature (suggest minimum of about 10 turns)
  • include a scale and pointer on the base to indicate speed and direction
  • measure battery temperature
  • do a long term endurance test to see how long the motor will run before batteries are depleted (rechargeable batteries might be worth buying if you do this test)
  • try simple paper fan on the end of the armature "shaft"  - this would be a motor "load"
  • explain how this motor works 
The photo shows the setup for one endurance test that lasted about 12 mins.  One of the axles broke through the plasticine at that time and the motor stopped. The control arm was left in one position for the entire test.