About two weeks ago, progress on my current engine project practically stopped when the motor on my bigger lathe died (well, actually my Dad's lathe...). While I was waiting for spare parts (which ended up being a whole new motor), I started playing around with the ignition system for the engine and built a simple ignition circuit that is triggered by a hall effect switch. I have only tested this board with a battery and multimeter, but it seems to be working as it should.
The next obvious question was "what coil am I going to use"? I didn't want to use automotive parts, because of the size, so that left model coils. These coils generally sell for around US$45, which isn't too bad, but since I had the time to waste, I started looking into what it would take to wind my own. For US$45 worth of copper wire, I can probably make several coils anyway. After a fair bit of reading and a combination of rough sketches and CAD drawings, I started to build a coil winder. The only coil winder information and pictures I could find on the internet were for guitar pickups (which apparently don't require 'orderly' winding, while ignition coils do), so the majority of my winder is designed and built the way I think it should be.
I thought about using 2 stepper motors as has been suggested before, but without readily available software (which would take a while for me to write and debug) and the added cost of the steppers and drivers, I decided to go the good old-fashioned mechanical route. The winder is human-powered - hence the crank handle. I will only be winding the secondary coil on this machine (about 15000 turns ), as the primary coil can easily be wound by hand (only about 200 turns).
I designed the gearing so that the ratio can be changed if necessary, however this would obviously require more gears to be machined and it is currently set for the wire size that I plan to use. The mesh is fully adjustable on all but one gear so that it can be setup 'just right' and reset for different size gears. I also included a 'simple' reverse mechanism for the leadscrew.
As you can see in the photos, there is still a bit more work left to do until I can test it, but most of the hard stuff is out of the way. I still need to make the second centre, the wire tensioner (which has potential to be troublesome to set up properly), as well as the wire guide. Hopefully I'll be able to do a bit more on it tomorrow.
Once the winder is finished, I will probably get to go through a steep learning curve on coil winding. Should be fun!
I have been tinkering with a CDI ignition but put it on the back burner till my RC project is done. Couple of questions with yours. 1. Are you winding a coil for stepup on your board or the ignition coil. 2. What supply voltage are you using?
For line tension one article I read was to use something built like a cloth's pin with a bolt for adjusting and a spring for spreading.
Will probably have more later but I was winding a small torroidal transformer for step up. Pain in the butt when putting on 450 turns on 1/2" id.
I'm going to be winding the ignition coil. From what I've read (for one design anyway), it seems that the primary needs to be around 200 turns of 20 SWG copper wire, while the secondary needs to be around 15000 turns of 40 - 42 SWG copper wire. I don't think it's going to be a two minute job to wind it...
I am planning on using somewhere around a 4 - 6V supply.
Kipper, i had a look at the eBay auction. You'll notice that the main difference between that winder and mine, is that mine has got a leadscrew. I was not keen to try and guide 42 SWG wire onto a mandrel and keep it neat and orderly. The leadscrew will hopefully fix this problem and ensure that the wire is guided on smoothly with each turn neatly stacked next to its neighbour.
I sorted out out a counter yesterday. I simply modified a tachometer that I had built to count. It uses an Atmel MCU and LCD to display the number of turns. Looks a horrible mess, as it is assembled on a breadboard, but it works!
From your info you will not be using a step up transformer with an oscillator as is usually done for the model systems. The system I have has a coil that you can get from CH ignitions who sell to the hobby guy's.
The one I am working on has 4.8v nicd pack which has to be converted to ac for the transformer. At least this is my understanding as I am self taught as an amature to electronics but like building projects.
My system is not a CDI unit. It is basically the same as a simple points/condenser ignition system, except that the points have been replaced by a hall effect switch and a couple of transistors, resistors etc. The board is called the TIM4. http://www.5bears.com/tim4.htm
I know very little about CDI units, but would like to learn more. It seems like they are capable of a stronger spark than 'normal' ignition units, but it also seems they are not well suited to multi-cylinder applications (from what I've read anyway).
I'm quite interested in making an auto advance/retard unit for my ignition using an 8052 MCU. I'm also self-taught when it comes to electronics and it is probably fair to say that I am still trying to learn... I'm alright with the software side of these 8052 MCUs, but I do struggle a bit when it comes to the hardware and trying to make the circuit do what i want. I guess I have to keep reading...
What CDI unit are you building, John? Is it your own design?
I am playing with what I have found over the net and trying to make it simple to start. Where I am having a few problems is the step up transformer and still doing a bit of research. Then I want to program a pic for the auto advance which I also want to learn. This to me is what it is about, learning and making things.
I have been tinkering with a horizontally opposed engine that I am going to modify from weed eaters(2/30cc's). Want to get rid of the flywheels and the rest of it to keep lite for my model. With an opposed engine firing at the same time I don't think there will be a problem using one Hall. For inline or multi-cylinder firing at different timings I was thinking of a Hall for each cylinder with the magnets at different locations. With the magnet for one cly. you could mount it in the hub close to the edge and for the other move in 3/8" or so and mount the Hall's to match. With the CDI this small especially the voltage(4.8) you have to give it a bit of time to recharge the cap. Lots to still learn but it is coming.
I am going back to it next week as my model is almost finished and going to try it with a Poulan 42cc modified chain saw engine to start. If I get it right I will let you know.