Cogsy Builds Rupnow Engine

[Swifty]

Great job Cogsy, the sound of it running is certainly familiar.

Paul.

 

[Cogsy]

Thanks Paul. Yep, those miter gears are noisy little things aren't they. In the flesh the exhaust note stands up a little better though.

 

[Brian Rupnow]

CONGRATULATIONS!!!! You are now a member of a very select club. I think that is "Rupnow Engine" #5 to come on stream around the world, (I think) but I am losing track. there is mine, Swifty's, Gus's, and yours. I think I may have missed someone, but I can't remember who.---Brian

 

[Cogsy]

Thanks Brian. I will make it prettier than it currently is, but it sure is a nice feeling having it running. I hope I don't wear it out before I give it away, but I've got a feeling I'm gonna be burning quite a bit of fuel in the next week or two.

 

[gus]

Hi Cogsy,

I like the H&M Chimes of your engine which sounds sweet.th_wav

 

[Cogsy]

Thanks Gus. It's been a long time coming, but you're right, it sounds good.

 

[Brian Rupnow]

Cogsy--I have watched the video a few times now. Your (ahem) balls--should be moving up and down a lot more. This may require a bit of fettling on the levers which the balls are attached to, where they contact the top of the central rod, or it might be a matter of adjusting the length of the rod itself.The total movement between when the balls and arms are hanging almost straight down and the time when they have flow out fully under centrifugal force has a very great bearing on the number of miss cycles the engine goes through before it hits again.---Brian

 

[Cogsy]

I noticed that I wasn't getting much ball action either (I almost couldn't type that sentence ;D), and I will investigate it. I understand how the mechanism works, of course, but I can't get my head around how to optimise it.

Mine seems to be running almost in equilibrium where a very slight increase in engine RPM allows the balls to lift slightly, engaging the latch and making the engine miss, which then drops a few rpm, instantly disengaging the latch before the balls have a chance to sink much. This means I don't get many misses per cycle and not a lot of variation in engine RPM either. I know there is a lot more travel to be had for the balls to sink lower and raise higher. Everything is free and smooth.

One thing I have done is set up the latch so it doesn't quite hold the exhaust valve at full open, so the cam has a slight action on the pushrod each 'miss' revolution. I set it up like that so the latch couldn't jam in place and cause the engine to stall. I wonder if it needs a slight 'jam' so engine RPM can fluctuate more.

The first thing I'll try is to adjust the latch so that it engages when the balls are at the top of their travel. Maybe I missing some sort of variable force dependant on ball angle. Ok, I'm going to have to change to using the term 'weights'. The schoolboy in me keeps chuckling...

Anyway, I'll have fun testing theories and let you know how it works out.

 

[Cogsy]

I have more ball movement now. I adjusted the latch so that the balls fly out to nearly their maximum before it catches and that has made all the difference. Thinking about it in my study while reading a technical journal (ok, on the dunny playing Angry Birds on my iphone), I do remember high school physics and something about "conservation of momentum". If I remember correctly, when the balls are all the way out, for them to be drawn back in they need to spin faster to conserve their momentum. In reality or course, the mechanism slows them down but I believe they come down at a slower rate that they flew out, while trying to "conserve momentum". This gives the change in engine RPM. Anyway, even if I'm way off track, adjusting them has worked for me.

I tweaked the ignition timing a tad and I'm reasonably happy that's it pretty close now. I also changed out the spring on the governor adjuster as it was a smidge too soft and I managed to get coil bind at one point, sending the engine way over-revving.

I also changed out the carb to the one I built from Brians' design (the big bore one). Screwed the needle all the way in, then adjusted it out as I spun it over. It was running inside of 10 seconds. The new carb is a heck of a lot better to tune than the RC carb. Must be the fine taper on the needle but it's easy to get it tuned just right.

So with everything set, I let it go for it's first long run. I had to leave the shed for most of it, out of fear of CO poisoning (it's raining here today so I couldn't leave the big doors open). I shut it down after 15-20 minutes of trouble free running.

I am running into one potential problem with the engine though - I'm already foreseeing great difficulty giving it away to a new owner. Maybe I'll give it to him but tell him it needs to stay at my place...

 

[tms6401]

Well Done Cogsy ... The engine sounded good ... oh ya ... my bench is worse than yours!

TMS

 

[Brian Rupnow]

Cogsy--Sometimes it will bend your head a bit, trying to envision all of the sequences that happen in a hit and miss engine, and the effect that a small change to one of the components will have on all the rest.--Especially around the governor.-Brian

 

[Cogsy]

I have officially finished the Rupnow Engine! (sort of). In the end I decided not to polish it up, or paint it, but to largely leave it 'as machined'. I realise some people might not like this approach, but as it is a gift for my Dad, I wanted it to be 'approachable' - something he would feel OK about pulling apart and tinkering with and not worry about scratching it. I also wanted to convey some of the work that went into it and to show it's 'home made-ness'. Anyway, for better or worse, that's how he's getting it tomorrow.

I did make a rough base for it (I really don't get along with wood very well) and trim the fasteners, install pins, etc. Once it was all back together, it took hours to get running again. Getting the valve timing, ignition timing and carb settings to gel at the right time was almost as difficult as the first time. I did have it running better than it is now (before I pulled it apart), with a lot longer 'miss' cycles and more movement of the governor balls. The good thing is, I'm giving it to Dad tomorrow and staying at his place for a couple of days, so I'm sure we'll have lots of fun tweaking and tuning it until it runs perfectly again. Soon, I hope to get him to move off the farm and near me in the city (he is nearly 80) and I hope we can build something together for the engine to run.

Many thanks to Brian Rupnow for his excellent design and invaluable help, as well as the other guys who built this engine, and to all the members I've learned from Thm:Thm:.

Here's the final video of it taking me for a walk.

[ame]https://www.youtube.com/watch?v=MbaHs_UZiFc[/ame]

 

[Brian Rupnow]

Cogsy--A wonderful job, well executed. Thank you for finishing it, and I hope your father really enjoys it.---Brian

 

[Path]

Fantastic job ... glad I followed along.

Your dad will surely love it.

Great job.

Pat H.

 

[Swifty]

Great job Cogsy, I hope that your father gets many hours of enjoyment from it.

Paul.

 

[AussieJimG]

Good one Cogsy, and it looks great just as it is.

Jim

 

[gus]

Hi Cogsy,

Congrats. You done a great job. The Rupnow H&M Engine is not an easy engine to build and complete and getting the Hit & Miss going was very tough. I nearly gave up if not for the help,support from Brian and Paul and others.th_wav Think of it .Not too many in the world has built this engine. We are the chosen few.Ha Ha.
No worries about the carpentry,Gus is not good at it either.