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General control line discussion => Open Forum => Topic started by: steve bittner on March 13, 2015, 04:00:23 PM
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Tom Lay told me he used electronic ignition with his Orwick engine he had in his Madman stunt plane, does anybody know what he used and how it was set up? I wish I would have pursued the info before he passed on. Thanks
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There are several ways to go with electronic switching on spark ignition engines. Some use just a single transistor, and others use a more elaborate small circuit board with a few components including a couple of transistors. There is also one designed by Don Hutchinson that shuts off the ignition when the engine quits. Both Don and Floyd Carter (Dr. Spark) have turned over theres to Larry Davidson if I am not mistaken.
By using electronic ignition you still use the points but not the condenser or capacitor as they are now called. It also saves the points from burning as there is just enough current going thru them to trigger the transistor. And, last but probably the most important, even when the points are a little on the oily or dirty side they will still trigger the transistor and produce a good spark through the coil.
Here is a simple circuit that really works pretty well designed by Bill Schmidt called the Schmidt trigger. For control line you do not need the resistor in the spark lead as that is only to keep interference from getting into the receiver on R/C planes.
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A couple of notes, from a circuit designer's perspective:
The transistor is a PNP. I'm assuming it's a silicon (i.e., plain ol') transistor. My favorite through-hole part is the 2N3906, but you might want one with a higher breakdown voltage (an expert could weigh in here and tell us what voltage that might be...). I don't see why the designer felt compelled to use a PNP here -- NPN's are generally easier to come by, but you'd have to reverse the battery leads to make it work.
That has got to be the worst drawing of a transistor that I've ever seen. Just sayin'.
A capacitor across the coil may still be a good idea. Without the cap, you're almost guaranteeing that when the transistor stops conducting it gets an overvoltage pulse -- at least, unless there's a healthy amount of self-capacitance in the coil. You wouldn't need (or want) a really high value of capacitance.
"Schmidt Trigger" is a horrible pun -- but only if you're a circuit designer. https://en.wikipedia.org/wiki/Schmitt_trigger (https://en.wikipedia.org/wiki/Schmitt_trigger).
Hopefully one of the ignition designers will get on this thread and correct any glaring mistakes I've made.
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I did the design of the auto cutoff circuit and gave the info to Larry Davidson and he is building and selling them. I knock one out on occasion but need to beg a few boards from Larry to make some more. Is there an error in your 2n3906 number? That is a small signal transistor. I have come to using the MJE5852G for the power transistor, it has a Vceo of 400 volts and Ic max of 8 amps. When the points open there is a -200 volt pulse out of the coil primary and this is the meanest one I could find. The TIP42C works OK but the Vceo on this one is only 100 volts and they can fail on occasion. As for the Schmidt circuit, it will work but with 18 to 22 ohms in the base one will only get about 160 mils of base drive and the power transistor will not be saturated (switched full on) thus less than max coil current.
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Thank you Don. Yes, the 3906 is only a small signal transistor -- I wasn't thinking big enough (and I didn't run any numbers: I tend to be lazy about that when I'm not getting paid!).
Why PNP?
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Electrical engineers know that "Schmidt" refers to the person who campaigned the single-transistor coil driver.
A "Schmitt Trigger" is a well-known monostable circuit having hysterisis. The usual configuration uses two transistors in a cross-coupled circuit with positive feedback. Doesn't operate anything like a Schmidt Trigger.
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Electrical engineers know that "Schmidt" refers to the person who campaigned the single-transistor coil driver.
I'm an electrical engineer, and I didn't know that.
If we were nice people we'd pause in our fascinating digression into circuits and terminology to stick in some links to some threads that answer the OP's question. If not the question "how did Tom Lay do it?", but "how should it be done?"
For me, the answer is to build the circuit given (after actually doing my job and figuring out the appropriate transistor to use!). But for someone who's not an enthusiastic electronics tinkerer the answer is probably a diagram and a list of vendors.
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Ah yes. Tim, I worked around engineers all my life and found that if you can do something only using one part, an engineer will usually figure out a way to use 27 parts. LOL. Not to say the 27 parts won't work better, but the one part will still get the job done. I won the ignition event at VSC 3 years in a row using the above lowly circuit, along with a good running Anderson Spitfire. I also had an old large Aero Spark coil that had 6700 ohms primary to secondary and would throw a really good spark. When I got the coil it was open at the primary. I took the end cap off and found it was broken right inside. I ran a new wire in and epoxied the end cap back on and have flown it for hundreds of flights since. I did use a large audio amplifier transistor, and in the hundreds of flights I have never had one go bad. I have also run Don's and Floyd's units and they work great. I really like Don's auto shut off unit as it saves batteries and maybe a coil sometimes.
Anyway, the above circuit may not be the best, but it still works.
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I use the same diagram Jim posted. I've got one setup in my Humongous, two more for bench running, and another in my Vampire. So far I haven't had any problems with the ignition system, just discharged batteries and faulty coils. Generally speaking, if the rest of the components are OK, the posted circuit works too.
From what I've seen of vintage ignition circuitry, modelers back then couldn't solder a good joint if their life depended upon it. I understand that vintage batteries were crap. Some ignition engines are not as well manufactured as others. My point being that with good joints, good batteries, and a good engine, ignition isn't that much more difficult than glow.
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I want to thank everybody for the input. How do I get hold of Larry Davidson? Thank you everyboy
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www.modelflight.com/larrydavidson.html This should get you there or just googl Larry Davidson model supplys.
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A real quick look at the Schmidt circuit changed to use a PNP transistor appears to me that the battery +3 volt lead would have to be connected to the engine crankcase instead of the - lead. Would probably work just fine, but different from the normal - to ground we normally use.
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Now to answer the question regarding Tom Lay's Orwick Madman plane. I built that plane for Tom. He drove from L.A. up to my place in Los Altos (no.Cal) to pick it up. I finished it through covering and a few coats of clear dope. Tom finished painting. In addition, I installed the ignition system. I used a Modelectric coil, three NiCd AA cells and my own TIM-4 transistor coil driver.
I understand that the engine bolts got loose and the Orwick fell out during a flight! Later, Tom sold that same Orwick 64 to me. It is a 4XXX serial made by Henry Orwick, probably in the early 1950's.
I don't know what happened to the plane.
Floyd
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Why not a modern Electronic CD ignition?
Replace the points cam with a flying magnet and the points timer with a fixed mount for the pickup?
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That would work well Doug, but the rules say the points have to be operational. It's an Old Time thing.
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That would work well Doug, but the rules say the points have to be operational. It's an Old Time thing.
Oh yeah, the OTS Overlords.
But if your not a competitor, it would be a nice project.
Our Sep. Contest has a nice system. It rewards engine originality (bonus points),
but doesn't penalize participation with modern engines (-0- bonus pts.).
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That would work well Doug, but the rules say the points have to be operational. It's an Old Time thing.
Depending on the magnetic pickup used, you might be able to replace the magnet and pickup with the cam and points, but still use the rest of the system. It'd take some tinkering to figure out what the sensor is "telling" the ignition module, but it might be a nifty way to get up-to-date electronics in your plane.
I have no opinion on whether the effort would be worth it.
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Ah yes. Tim, I worked around engineers all my life and found that if you can do something only using one part, an engineer will usually figure out a way to use 27 parts.
In my case, only if I get to count a quad op amp as one part.
I do have something useful to add to this discussion, though: Larry Davidson has the good Polyspan.
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Depending on the magnetic pickup used, you might be able to replace the magnet and pickup with the cam and points, but still use the rest of the system. It'd take some tinkering to figure out what the sensor is "telling" the ignition module, but it might be a nifty way to get up-to-date electronics in your plane.
I have no opinion on whether the effort would be worth it.
I guess I should have posted a better pic. Rcexl Ignition universal kit comes with a pickup and magnet.
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I guess I should have posted a better pic. Rcexl Ignition universal kit comes with a pickup and magnet.
But then you wouldn't be in compliance with the rulz. Hence the suggestion to still use the points.
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I thought about using some modern gear and just disconnecting the Hall effect pickup and substituting the points. I got as far as ordering the ignition module. I then lost interest, because the module was heavier than a Modelectric coil and transistor ignition board! The ultimate killer was it needed a 6v DC supply, so the NiCds were heavier too.
I know I can use a LiPo but I have plenty of 3 NiCd packs and I am in no hurry to change them. I am also a touch suspicious of LiPos on an Orwick 64 powered plane, which vibrates! Try an OK Super 60, that makes a ST 60 feel lick a Rolls Royce
Floyd recommended a transistor which had a much higher reverse breakdown voltage than the ones normally used. I found a dozen in a concern sourcing obsolete transistors. I have used these with complete success on an Orwick powered Madman and other OTS stunters.
As far as using modern engines and electronic ignition modules is concerned, you miss the point completely. The fun is getting the old systems working, not winning pots! If you have never tried it, then you should, it is great fun!
Andrew.
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Remember, also, a spark ignition system gets extra points in an OTS contest. No-flaps also gets a bonus. These are "free" points, so why not get them?
Modern glo engines converted to spark ignition, no matter how its done, have been ruled non-compliant in OTS rules.
Floyd
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Now who would do a thing like that??
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Sounds like fun. If starting from scratch where does one get a reliable, legal spark engine for a Nobler?
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Sounds like fun. If starting from scratch where does one get a reliable, legal spark engine for a Nobler?
Snerk. I wonder if it was ever done, back in the day.
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I am in the corner of Jim K, Andrew T and Andrew H, in that just running the old Sparkies is just so much fun! As Jim K told me, run the engine on the bench and work out the starting and running settings. This makes it so much easier when it comes time to put in flights! If you take the time to do this, it isn't really much harder to run a sparker than setting a glow engine!
BIG Bear
RNMM/AMM
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Now who would do a thing like that??
Oh gee, I don't know, but I heard his initials are Don Hutchinson. LOL. The problem is that yours worked so well that they had to make the rule. You are a victim of your own success. LOL.
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Yeah, it did run like a Rolex but no better than any other good spark engine. I replaced it with a Torp 32 and got the same results the next two years. I see a bit of fussing in here over the Viking OTS model. Anybody interested in how it came to be?? I may have the answer.
Don
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Yeah, it did run like a Rolex but no better than any other good spark engine. I replaced it with a Torp 32 and got the same results the next two years. I see a bit of fussing in here over the Viking OTS model. Anybody interested in how it came to be?? I may have the answer.
Don
Hi Don,
Sure, would love to hear it!
Thanks
Bill
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It is a fairly long story, I will have to type it up and then I can e-mail copies to any interested parties. Goes back to 1948, actually 1947. I have planned to do this for some time, just haven't gotten to it but will now that there is some interest.
Note: To anyone planning to make a transistor circuit like the Schmidt circuit shown, I would recommend a 1 watt resistor. When the engine quits with the points closed the resistor is dissipating a good 1/2 watt and can get very hot.
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Hey Don;
I would like to have the story on the Viking also. You and a few others have way more knowledge on what went on back in the day than most. I loved reading your story's in Stunt News several years ago of your early days of building and flying.
Also, thanks for the info on the 1 watt resistor. I still run a few of those circuits in my free flights with a radio, and I think I am only running 1/2 watts. I do have a micro kill switch on the firewall to kill the engine with a servo, so they do not have much time to heat up as I do kill the engine before it runs out of fuel anyway. The thing that degrades the spark on those is that 10K ohm resistor in the spark lead to take interference out of the radio receiver. I guess the new 2.4 radios get by with less that my old 80,s JR PCM antiques.
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Don I would definetly be interested in the story also. Thanks
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It is all typed out but has a file ext of docx and I can't attach it. How do I change the docx to doc??
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Inset in circuit has transistors P/N.
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Open your document in Word. Go to the menu and choose "Save as" then choose "Word 97-2003 Document".
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Let us see if this will attach, then watch for the fur to fly!!
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Thanks, Don. If I were a betting man I would say your buddies model was the prototype for the Viking! I got to get going on mine so that I can have it for Huntersville in May! All traditional construction and materials with a Super Cyke .60. I am really looking forward to my first "Sparkie"!
Bill
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Thanks Don;
All of your story's are always interesting. I am betting that your Buddy's plane was the forerunner of the Viking. That is cool that the Orwick from then is at VSC now. Some old engines have a story all their own. I have Dale Kirns Atwood Super Champion that he flew as a kid on an Overeasy. Thanks again for the write up and story. In my mind I will always believe that the Viking got its start in Minnesota.
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Tried to down load the story. Would not down load as I don't have the program required and they won't me down load the program as the last it tied up the computer and had to boot every thing.