Background:
While there are lots of videos on YouTube concerning pulse motors I really haven't found a concise explanation of how to make a pulse motor drive coil. I finally found how many feet and what sized wire Lidmotor used from one of his YouTube videos. From that I made a coil that works very well. Thanks again Lidmotor.
This article will explain how I made the drive coil used in my low voltage capable motor.
The coil form:
The coil form I used was originally an empty magnet wire spool similar to the 75' spools of wire that Radio Shack sells. You could make your own out of some thin walled 3/4" PVC pipe by putting flanges on a short piece of the pipe. Do not use a metal coil form.
The dimensions of my coil form are 3/4" inner tube diameter by 3/4" between the flanges. The flanges are approximately 2" in diameter. I didn't want the length of the coil to be too long since I wanted to mount the coil under the rotor.
If your coil form doesn't have a hole near one of the flanges to allow the start of the coil wires to emerge from the bottom or side of the flange you will have to drill a hole so the wires can come out of the coil. Another way is to carefully guide the start of the windings up inside one the flanges and cover the wires with some tape so the insulation doesn't get chipped off while you wind the coil.
My coil form was originally longer and I cut it between the flanges to make the final coil form 3/4" between the flanges. I was able to hot melt glue it back together. My form had a piece missing from one of the flanges and I was able to fix it with a piece of thin plastic and some hot melt glue. That gave me a thinner place to make holes for mounting the connecting wires.
When the coil was completed I was able to make eight small diameter holes in the thin plastic surface on the flange to wrap each coil wire around two of the holes (two holes for each wire) as a convenient place to attach four wires that go to the drive circuitry. I used a thin scribe to make those holes.
Wire lengths & size:
You need a 200 foot length of enamal or polyuethan insulated AWG #30 copper wire for the oscillator feedback winding and 75 feet of enamal or polyuethan insulated #26 copper wire for the drive winding. The wire is commonly called magnet wire. My #30 wire came from an old sonar buoy and the #26 from a degaussing coil from an old TV set. (It pays to have a lot of "pre-owned" stuff around.)
These lengths and sizes aren't set in stone but since they do work I'd try to keep as close to those numbers as you can. The feedback winding has a lot of turns in comparison to the drive winding (a 2.7:1 ratio) which gives a good bit of feedback to the transistor blocking oscillator.
You need a high winding ratio to be able to run the motor on low voltages. If you plan on normally running the motor on more than 5 volts you could probably use less than 200 feet of the #30 wire. How much less depends upon the voltage you plan on running and other factors. Since these motors are a learning exercise you will have to experiment some if you want to optimize the drive circuitry. There are lots of schematics of pulse blocking oscillators on YouTube. Just pick one with a two winding coil.
Coil details:
While there are lots of videos on YouTube concerning pulse motors I really haven't found a concise explanation of how to make a pulse motor drive coil. I finally found how many feet and what sized wire Lidmotor used from one of his YouTube videos. From that I made a coil that works very well. Thanks again Lidmotor.
This article will explain how I made the drive coil used in my low voltage capable motor.
The coil form:
The coil form I used was originally an empty magnet wire spool similar to the 75' spools of wire that Radio Shack sells. You could make your own out of some thin walled 3/4" PVC pipe by putting flanges on a short piece of the pipe. Do not use a metal coil form.
The dimensions of my coil form are 3/4" inner tube diameter by 3/4" between the flanges. The flanges are approximately 2" in diameter. I didn't want the length of the coil to be too long since I wanted to mount the coil under the rotor.
If your coil form doesn't have a hole near one of the flanges to allow the start of the coil wires to emerge from the bottom or side of the flange you will have to drill a hole so the wires can come out of the coil. Another way is to carefully guide the start of the windings up inside one the flanges and cover the wires with some tape so the insulation doesn't get chipped off while you wind the coil.
My coil form was originally longer and I cut it between the flanges to make the final coil form 3/4" between the flanges. I was able to hot melt glue it back together. My form had a piece missing from one of the flanges and I was able to fix it with a piece of thin plastic and some hot melt glue. That gave me a thinner place to make holes for mounting the connecting wires.
When the coil was completed I was able to make eight small diameter holes in the thin plastic surface on the flange to wrap each coil wire around two of the holes (two holes for each wire) as a convenient place to attach four wires that go to the drive circuitry. I used a thin scribe to make those holes.
Wire lengths & size:
You need a 200 foot length of enamal or polyuethan insulated AWG #30 copper wire for the oscillator feedback winding and 75 feet of enamal or polyuethan insulated #26 copper wire for the drive winding. The wire is commonly called magnet wire. My #30 wire came from an old sonar buoy and the #26 from a degaussing coil from an old TV set. (It pays to have a lot of "pre-owned" stuff around.)
These lengths and sizes aren't set in stone but since they do work I'd try to keep as close to those numbers as you can. The feedback winding has a lot of turns in comparison to the drive winding (a 2.7:1 ratio) which gives a good bit of feedback to the transistor blocking oscillator.
You need a high winding ratio to be able to run the motor on low voltages. If you plan on normally running the motor on more than 5 volts you could probably use less than 200 feet of the #30 wire. How much less depends upon the voltage you plan on running and other factors. Since these motors are a learning exercise you will have to experiment some if you want to optimize the drive circuitry. There are lots of schematics of pulse blocking oscillators on YouTube. Just pick one with a two winding coil.
Coil details:
Please
note that my coil has no metal core inside the coil form.
This is
done to reduce the drive current to start and run the motor. With
a
metal
core the magnetic attraction between the rotor magnets and the core
causes the motor to require a higher drive power and it's harder to
hand start. And I suspect that it will demagnitize your rotor
magnets quicker since the magnetic field will be much stronger with a
metal vs an air core coil form.
The two wires are not twisted together. Just wind both wires at the same time and try to keep the wires parallel to each other as you wind the coil. It won't be easy but try. Guide the wire back and forth across the form as you wind the coil. Luckily by using a fixed length of wire you don't have to worry about how many turns you put on the coil. Just keep winding until you run out of wire.
When the shorter wire came to it's end I brought the wire out of the coil by running it up the flange where the terminals were to be located. I covered the wire on the flange with some clear tape so the rest of the winding wouldn't nick the insulation. I left about 4" extra wire to make connections to it later.
It took me about 8 hours to hand wind the coil. You could speed up the winding by using a small hand powered or a variable -slow- speed electric drill and some sort of a holding fixture to allow mounting the form onto the drill chuck. Maybe just cram a cork inside the coil form with a 1/4" diameter bolt through it? Then mount the bolt into the drill chuck.
It will be much easier if you clamp the handle of the drill to a table or in a vice so you can turn the handle of the drill with one hand and guide the wires with the other. You will have to have the two wires on a rotating feed bobbin(s) to try to keep the windings as smooth as possible. If the bobbins don't rotate as you pull the wire from them the wire will actually be twisted and will eventually ball up in a pretzel looking mess. To do it correctly you should allow the bobbins rotate as the wire is pulled off of them. Sort of like an old fashioned fishing reel.
I measured the lengths of wires I needed and rolled the wire up on a temporary bobbin made from a piece of PVC tube that was mounted on an old hard drive motor spindle. As I wound the coil the PVC tube rotated.
The two wires are not twisted together. Just wind both wires at the same time and try to keep the wires parallel to each other as you wind the coil. It won't be easy but try. Guide the wire back and forth across the form as you wind the coil. Luckily by using a fixed length of wire you don't have to worry about how many turns you put on the coil. Just keep winding until you run out of wire.
When the shorter wire came to it's end I brought the wire out of the coil by running it up the flange where the terminals were to be located. I covered the wire on the flange with some clear tape so the rest of the winding wouldn't nick the insulation. I left about 4" extra wire to make connections to it later.
It took me about 8 hours to hand wind the coil. You could speed up the winding by using a small hand powered or a variable -slow- speed electric drill and some sort of a holding fixture to allow mounting the form onto the drill chuck. Maybe just cram a cork inside the coil form with a 1/4" diameter bolt through it? Then mount the bolt into the drill chuck.
It will be much easier if you clamp the handle of the drill to a table or in a vice so you can turn the handle of the drill with one hand and guide the wires with the other. You will have to have the two wires on a rotating feed bobbin(s) to try to keep the windings as smooth as possible. If the bobbins don't rotate as you pull the wire from them the wire will actually be twisted and will eventually ball up in a pretzel looking mess. To do it correctly you should allow the bobbins rotate as the wire is pulled off of them. Sort of like an old fashioned fishing reel.
I measured the lengths of wires I needed and rolled the wire up on a temporary bobbin made from a piece of PVC tube that was mounted on an old hard drive motor spindle. As I wound the coil the PVC tube rotated.
Bottom view of coil form:
To see an
enlarged view of the pictures, left click on a picture or right click
and select "View Image".
Here is a close up of the bottom
of the drive coil
In this view you
can see the
hole inside the coil form where the start of my windings come out of
the coil. The two wires run over to the area where the makeshift
terminals are located. I put a little hot melt on the wires
so
they wouldn't move around and get broken. There is also some
clear tape over the two wires as they go to the terminal area.
You can also see the coating of hot melt I used where the wiring to the drive circuitry is located. The four pin connector is used for ease of changing coils etc for various experiments. The blue stripe on the connector is to mark the pin I used as #1.
The wires at the coil are arranged in this order, There is nothing special about the order I used, but it made it easier for me to remember which wire was which.
You can also see the coating of hot melt I used where the wiring to the drive circuitry is located. The four pin connector is used for ease of changing coils etc for various experiments. The blue stripe on the connector is to mark the pin I used as #1.
The wires at the coil are arranged in this order, There is nothing special about the order I used, but it made it easier for me to remember which wire was which.
- Feedback winding start. (Number 1 wire is on the right in the above picture.)
- Feedback winding end.
- Drive winding start.
- Drive winding end.
This picture shows
another view
of the terminals I made by wrapping the coil leads twice around each
pair of holes. I then used an X-Acto knife to scrape the
insulation off each wire and quickly put a drop of solder on the wires
to tin them.
This picture is an
inside view of the wrapped wire terminals.
If you look very
carefully you
can see the end of the feedback wire on the left side coming up the
inside of the flange and ending up wrapped through the two left most
holes.