When I was in Junior High School, we had a set of World Book Encyclopedia's, circa 1968. There were about a dozen science projects in these books, and I built several of them. One of them was for an electric motor model. I kept this model for years, but eventually threw it out. Unfortunately, I never took any photos of the model.
I would like to make another model for my grandchildren.
I found where a a copy of this year was scanned in on Archive.Org. In the "E" book, there is an electric motor science project. It is not exactly like mine, but it is the same general concept.
It is interesting to note the 1967 book shows using 2 batteries to run the motor. In the text, it says you can experiment and run the motor from 1 battery, or from a train transformer. I ran my original motor on my 1965 Lionel train transformer (which I still have).
On my original model, the bearings never worked very well. I think they were pointed nails into wood. For my model, I am going to use real ball bearings from McMaster-Carr, which should work much better.
I think I used 12 gauge wire on my model, with 1/2" pipe for the 2 stationary poles and the 1 rotating pole. I am going to try 20 gauge wire and 1/2" solid steel bar for my model. I may also try heavier gage wire to increase the amps, which increases the magnetic force.
I added a wood fan to the model, so it does perform some function to make it more interesting.
I will try using a light spring to hold the contacts against the rotating shaft.
I bought three 1 ohm resistors, so I might set up the model so different speeds can be obtained by choosing how many resistors to use.
I don't have a good way to measure shaft RPM, which would tell me how well the motor is running.
My degree is in Agricultural Engineering, specializing in Power & Machinery.........basically the same as a degree in Mechanical Engineering. If I was a EE, I could probably express the motor design in equations that predict the speed of the motor.
The motor speed is a function of the load applied, and the design of the motor. I would predict the speed increases the larger the wire size, the diameter of the coil, and the number of turns on each coil. I first applied the classic EE equation that E=IR to the motor using the wire resistance of the coils.
First, I found the resistance of various wire sizes.......
I made an excel spreadsheet to calculate the Resistance of the wire in the coils.
I ended up choosing 14 gauge wire, so my wire resistance should be around 0.20 Ohms.
If I use my 16V Lionel train DC transformer, applying E=IR, then my amps would soar to 81 amps!! The max amps for 12 gauge is about 20, then the wire melts........so 81 amps would fry 14 gauge wire.
When I was a kid, I ran my motor at 16 volts and number 12 wire........and never melted anything.
I talked to some EE's and they said a back EMF is created by the current going through a coil, which effectively raises the resistance in the motor. I found a web page which says the motor resistance is the sum of the wire resistance plus the back EMF.
Using a VOM meter, I can measure...
1. Resistance of coils with no voltage applied
2. Amps when motor is running
So I can use E=IR and solve for the resistance if I know the voltage and current. If I subtract the wire resistance, then this would be the back EMF resistance.
My memory is a little vague, but I seem to remember, the more accurate the rotating armature, the better.
My plan to make as perfect as armature as possible is:
1. Cut 1.25" diameter dowel to 6 inches length
2. Mark centers in each end using dowel drilling fixture........that has screw in a half drilled depth hole, and you rotate the dowel by hand
3. Put 3/8" Forstner bit in tailstock of lather, slide tailstock until Forstner bit spur goes into marked hole. Tighten tailstock
4. Rotate lathe, push in drill bit by hand on lathe. Swap ends and drill other end as well.
5. Cut 3/8" oak dowels and install in each end. Make sure ball bearing slips over dowels before you glue on (can sand down if necessary)
6. Use special fixture to drill 1/2" hole for steel rotating armature that is 8 inches long
7. Saw 1/2" steel rod to 8 inches, deburr both ends
8. Mark 5/8" each way from center of bar, use those marks to align to wood dowel, epoxy steel dowel to 1-1/4" wood dowel
Everything seemed to work as I planned. Once I get the 2 end bearing supports done, I can check and see how freely it rotates.
About the only way I can think of to make a higher quality armature would be to turn down the two 3/8" diameter ends from the original 1-1/4" diameter dowel.
I was very curious how well the rotating poles would align with the 2 vertical poles.
The good news is I did a good job of gluing the 1/2" steel rod exactly halfway on the 1-1/4" wood dowel. I installed the first vertical dowel, leaving 1/4" gap between the vertical and horizontal pole. I then rotated the armature 180 degrees and still had the same 1/4" gap...........Hooray !!
Now to the bad news. I did not get the 1/2" steel rod exactly perpendicular to the 1-1/4" wood dowel. This must have been caused by my drill press table not being exactly perpendicular to the base plate.........and/or the bit wandered as it drilled through the wood. I think it will still work ok. How could I have done this better?
Well, I could have used a square to check the perpendicularity. If it was off, I could have Dremeled out the hole, then clamped it in the right position when I epoxied it.
I used a small metal square and checked the perpendicularity..........and I am off about 2 degrees to the eye.
With the ball bearings, the armature really turns freely and nicely !!!
I center drilled a piece of 1-1/4" diameter dowel in the lathe, then turned down 1 end to 1/2" OD. This small end fits against the bearing and only rubs the inner race [if it rubs the outer race, it puts friction the bearing]. I glued these onto the main center horizontal dowel.
I bent 3/4" wide brass strips and installed them on the 2 hinged pieces. I had some Ace eye hooks and bought a spring to put force on the 2 arms so the brass contacts will rub against the rotating armature.
I thought 12 gauge was too big and rigid, so I settled on solid copper 14 gauge wire. I bought 2 rolls, 50 ft each......so I will use 1 color on rotating armature and another color on fixed vertical poles.
I have some left over brass sheeting that I bought from mcmaster-carr or another project.
I roughly calculated it would take 80 feet of wire for the 4 poles, or 40 foot for each set of 2 poles.
I used the 50 foot of green 14 gauge to wrap the rotating armature with 4 levels and each level had 25 turns, or 100 turns per each pole. I had about 8 foot left over from the 50 foot roll, meaning I used 42 feet.
I will do the same 4 levels on the fixed vertical poles, since I know I have enough wire in the 50 foot spool.
I used the 16 volt DC Lionel train transformer.
It did not spin by itself :(
I made my gap between the brushes about 1/8 to 3/16". I don't think this is a big enough gap. I also had juice when the rotating pole was closest to the vertical fixed pole, indicating I was not breaking the circuit at the right time. I will try increasing the gap.
I studied the wiring diagram for another example motor. My rotating armature poles are wound in the same direction, and so are the 2 vertical poles.
On the other motor, the rotating armature poles are wound the same, but the 2 vertical poles..........1 is wound a different direction than the other. This makes sense because you are trying to attract 1 rotating pole to the vertical pole, and at the same time on the other pole, you are trying to repel each other.
I switched one vertical pole, and the motor would run briefly if I give it a starting spin........then eventually stop.
I tried moving the vertical poles out about a 1/4", made it worse......so keeping them close is the right thing to do.
I'm guessing the motor is extremely sensitive to where the start and stopping points are on the brushes. You want to be attracting right up the rotating pole is almost even with the fixed vertical pole, switch off briefly, then re-energize so you can repel. This is really hard to set accurately. Maybe I can draw up one piece in Sketchup, then separate the two pieces once they are in the correct position on the 1.25" diameter wood dowel?
You probably get all the "kick" in force when you are close to the pole contact spot, and not much force the rest of the time.
Nothing happened except the light flashed on and off.
Moved rotating armature so it was not making contact. Plugged into 110V AC outlet. Gave it a spin and it took off!!!!!!! Had lots of arcing !!
Went to do it again to video it, and did not make sure motor was in non-conducting position.......and tripped the breaker. Put motor armature at non contact position, plugged in, and it took off with lots of arcing. You can see the video using this link.
At some point between 16 and 110 volts AC, the motor will run with just 2 poles. I have no AC power source in between 16 and 110 volts.
The motor will also not run with 6 volt DC battery.
When the motor was running with 110 volts, it did not blow a fuse. I have a 15 amp fuse on that circuit..........so E=IR.........R=E/I.........R=110/15 = 7.3 ohms. So the "effective resistance" of the motor is greater than 7.3 ohms.............while the wire resistance is less than 1 ohm.
Can I downsize the motor so it will run on a 6 volt DC battery?
I need to get the rotating mass greatly reduced to make this happen.
I reduced the shaft side from 1-1/4" down to 3/4". It will use 1/4" instead of 1/2" steel poles. The rotating pole is 4 inches long, or 2 inches on a side. This should dramatically reduce the rotating inertia of the motor. I don't know what wire size I will use yet, might try 20 gauge first.
As I built the mini motor, I noticed my ball bearings have quite a bit more friction than what I expected. I learned on the big motor project that the rotating mass inertia, including friction is a major factor whether the motor will run or not.
If this mini motor won't spin by itself, I may try another type of bearing design, maybe a finishing nail in a hole, or a dole in a hole, to reduce friction.
Sadly, the motor would not work with a 6 volt DC battery, a DC transformer, or 16 volts from my Lionel AC transformer. The big model ran 40 seconds with 16 volts DC, but this model would not run.
I need to make a table with my design and the results, to remember what did not work and what did work.
My $5 Harbor Freight VOM meter did not give reliable results, so I bought a $30 VOM meter from Ace.
Checking resistance, I found I was not starting and stopping the current at the optimum points on the brushes. I am going to try to fine tune them so they stop and start closer to the fixed poles. This is where you get maximum "Kick" in force.
I optimized the brushes as best as I could, and would still not run on 16V AC. Going to have to give it more windings.
I have a 3/4" diameter permanent magnet, with the motor energized, I could move the magnet around with my finger and feel the force from the electric coils. I was surprised how far out they were from the poles!! I could also coax the rotating armature to turn using the permanent magnet to attract it.
I added more turns to the mini motor, and it still would not run.
I thought bearings would reduce the friction to almost nothing, but that is not the case.........I still have a lot of friction. Maybe I should do like the Youtube guy, Callinan, and use plastic pipe. I checked and 3/4" PVC has an ID of .824 and an OD of 1-3/64 or 1.046875 and 1" PVC has id of 1.049 and OD of 1-5/16. Since 1.046875 is slightly less than 1.049, it should work as a bearing.
Was going to buy plastic pipe from mcmaster-carr, but it had $25 shipping on $25 worth of materials, will try Fairbury Ace first.
I wish I had a better brush design. The ideal design would minimized the angle the power is off, and have minimum rotating friction.
I had no idea how difficult it would be to build a simple DC motor !!
I went to my Fairbury Ace Hardware store. I bought a scrap piece of 3/4" PVC pipe about 24 inches long. Their 1" pipe did not fit over their 3/4" pipe, so for bearings I bought 2 couplings, 3/4" size. I put the couplings on the lathe, then with lathe stopped, I Dremel drum sanded the ID larger. I used a piece of 3/8" dowel with a slit to hold 220 grit sandpaper to sand the ID smooth. I did trial and error until I got a nice slip fit with almost no friction.
Got it built ok.
Got 80 turns of 26 gauge magnet wire per layer, and did 4 layers, so 320 turns per pole !!!!!!!!!!
Using new VOM meter from ACE, DC transformer put out 18 volts DC with no load, when I made load by rotating armature until it contacted, dropped down to just 4 volts.
My old Lionel transformer put out 16 volts AC.
Neither transformer would make my 3rd motor go.....................RRRRRRRRRRR.................it made sparks at rotating armature contacts but no go, even with spinning it by hand!
Boy, this is discouraging.
I think I have slightly less friction with the 2 plastic tubes as bearings, versus the steel ball bearings.
I could reduce my force on the 2 pivoting contacts, using a rubber band right now.
It takes a lot of friction to make the contacts. I don't have anything thinner to use for the contacts on the armature diameter.
So, right now, only thing I know to do is:
-reduce force on 2 pivoting contacts
-can I beat out brass sheeting to make it thinner with hammer?