Intro: DC Through Coil Motor
Dear visitor, let me show you and potentially discuss this concept of the electric motor. I will be really glad for all comments.
Ones upon a time my younger brother David came to me and told me that he sign him self for high school thesis to develop new type of electric motor. I was quite surprised because he has totally no experience with electronics and this stuff at all. Also sound like tough challenge to invent something as new type of electric motor. Then I told to my self lets listened to him, because thats usually place where new ideas are coming from, its from people with absolutely no knowledge about topic. He told me his ideas and we found some issues but the direction of thinking was set. After few talks we came up with functional prototype, then we made next improved version which I am sharing with you. We was not able to find any similar product or type name of such a motor. I call it "Through Coil Motor" (lets say TCM if you like abbreviations) because rotor goes directly through coils and not around like in conventional motors. This should bring some advantages and also disadvantaged, our learning from this research is that electric motors are a lot about compromises. Let me sow more in next steps.
Step 1: Basis
Basic idea is to take coil gun and bend it to the circle to have projectile speeding up round and round. Nice explanation about coil guns was made by electro boom channel https://www.youtube.com/watch?v=mdZo_keUoEs
My brother have little bit different thinking about this topic, mine explanation is: As you already know metal (or magnet) will stay at middle of energized coil, that means the biggest force is there just in center of the coil. Conventional motors never goes through the center, they are just passing it from the distance witch is space between rotor and stator allowing rotor to rotate and half of the coil length (also half length of the magnet, see picture attached). Thats why intention is to make length of the coil as small as possible. Problem is that with short length of coil, you have to wind more magnet wire, because length of the loop is increasing with all additional layers. For the coil: more loops = more force, more wire less efficiency.
Challenging part for this concept is to make rotor in coils, take a look on next section where is explained how we deal with it.
Step 2: Sketch Up 3D Model
3D printing comes really handy doing such project. You can download it from my thingiverse.Problem with the concept is that there is no possibility how to connect one output shaft directly to rotor. Please find SketchUp project attached to do your modification. Problem is that rotor must be inserted to already winded coils, because it will be impossible to wind it afterwards. Thats why this model have split rotor which can be glued after inserting to the coils. Its good to avoid metal parts, because rotor with neodymium magnets reacts to all nearby metals. From the firs prototype I had to use metal bearings this time because only 3D printed sliding mechanism was not good enough.
You will find also picture of first prototype attached, it was only two pole. Two pole means only one magnet on the one side of the rotor = balancing issues. Also two coils means there are only two places between to put wheels in, the rotor moves really unstable while fixed only on two points. The space between coils was also to big causing uneven movement of rotor. These are the points where we decided to make four pole as next prototype.
Four pole switches coils in groups, opposite coils are one group. Rotor contains two groups of magnets in opposite sides = perfect rotor balancing. Four coils also means four spaces between to put four rollers to hold rotor in place.
At the end it needs quite few gluing to make this happen.
Next part will show you how to build this up.
Step 3: Building the Motor
First step is to wind coils, we used 0,3mm gauge wire with 48V power supply targeting around 1,8A of draw. So resistance should be around 27ohms. Yey we used ohms law :) Than is good to know how many loops you should do to achieve 27ohm winding. R=ρl/S resistivity of copper is 0.0169x10-6 ohm to one meter, S for 0,3mm wire is 7,0686x10-8 m3 from that we calculate that wire should be 111m long rounded up to 120m. Circumference of our 3D printed core is 9,6 cm means we have to do 1200loops to one coil group, at the end we will finished with 4x 600loop coil. Glue coil lid to the coil before winding. Good tip is to use kapton tape. Cut 60 small pieces of kapton tape first and glue every 10 spins you made, that will help you to count how much you did according to missing kapton tape pieces. Also cover whole layers with kapton tape to be able to easily wind next layer. Huh.
We will use standard NO,NC micro switch. Please use high quality micro switch and connectors for it. Switch gets quite hard shocks from mechanical and electrical force, cheep switches will handle only few spins. Thats why I suggest to change this mechanism for optical or motor driver circuit.
Put neodymium 12x2mm magnets in magnet slots in both parts of the rotor, push paper to the half way between each magnet to make it round. You can full fill those slots by magnet fully, keep it in center when you put less magnets in. Glue magnets in place. Glue magnet cover on top of magnet slot.
Test coils and rotor parts to have them in correct direction, now its important to have magnets on both rotor parts in same direction. Poles of coils can be switch later to change direction of the coil to pull to push magnet in way you want.
Slide coils on rotor parts. Glue both parts of the rotor and let it cure.
Glue in center stars which will place coils in the position together with central spacer secured by screw.This is good to do really precisely.
Build up wheel mechanism, short tubes will come around wheel shaft to secure bearing, longer tubes are between center of star part and wheel holders, you can extend or shorten according to tolerances you got. Check my thingiverse parts are named there also with number ho many to print. Wheel parts will goes from both side of the bearing, problem is that it slips time to time, so its better to glue them between each other.
Attach switch arm with switch.
Wire according to diagram attached, it will be nice to have also fly back diodes in the circuit.
In first steps just put rotor before one coil and energize it to see if it goes to direction you want and mark wires as plus and minus. Then wire groups and then groups to the switch. With good luck it will spin from the beginning. Always touch your coil, do not connect it to the power source for long time, in common for the motor is only way to destroy by overheating winding, temperature should be as low as you can keep your hand on (<70 Celsius).
Step 4: Ussage
Idea here is to use planetary gear with planets on the wheels to make one common output. Planets can make supporting wheels itself running on teeth gear surface of rotor, so output gear can be hidden inside the motor. This can be neat piece of hardware with integrated gear.
Another application can be with totally enclosed rotor. It will just side in coils without bearings. This can be used as gyro stabilizer or such.
Step 5: Pros and Cons
More expertise and tests should be done to judge, we need more precise mechanism to achieve higher speeds. Also to use different switching mechanism like optical gate or motor driver circuit (like ESC) to prevent friction from the switch.
From now biggest issues are:
- Complex to build
- No possibility of direct output shaft
- Metal parts in frame
Advantages should be:
- New type of applications (for example without output shaft)
Challenges for next prototype
- more poles
- driven by ESC
- switch polarity of coils to not only pull in but also push out when magnet is released
- metal coil core
I will really like to hear your opinion about this projects in comments bellow. Thank you for wisting this post.
Step 6: V3 Work in Progress
Thanks all of you for feedback, I already started with V3 model.
- Planetary gear, rotor as sun (gear ratio for more torgue), planets and coils are fixed between each other to prevent collision
- 3 set of coils for smooth movement (textured by colours in picture)
- Herringbone Gears to be able to center rotor itself
- Driven by ESC (electric speed controller) - I will measure hobby grade DC outrunner motor and do same coil resistance for my prototype. I will be able to use hobby ESC then.
Again all suggestions are welcome.