fritzke

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See post 21 for "How To" pictures.

Here is the scoop on my little experiment to make a cheap and easy throttle for the
Cox "Product" engines we all seem to have...

2 18g. "Machine Bushings" washers from the hardware store (absolutely perfect fit on cylinder,
(Hillman Fasteners, 1" OD, 9/16" ID)
1 centimeter length of #1043 Aerotrend Ultra Blue Tuned pipe coupler
2 scraps of brass tubing

I used a SHARP Midwest Miter Cutter on the Ultra Blue, and a Harbour Freight punch
to make the just-undersize hole in the silicone tubing for the exhaust outlet.

"V" notch is cut with a Dremel disk.

Outer "slider" tube end plugged with 1/32 ply disk (the punch again) CYA into end, add a
woodscrew and some tubing to hold on to. Would be attached to the throttle servo of course.

Brand new engine, no break in, have not reset the socket yet. 25% nitro, perfect evening. See pix:


EDIT- Forgot to mention I had to cut a teensy bit off the front of the grey plastic "knob" on the top of the backplate
to clear the bottom washer.

I am very encouraged by my short test tonight!

Dave

fritzke

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Pix of it running. Note the "v" notch is partially open at 7k, closed at idle.
Not even hitting 13k yet, but it'll get better. And I think idle would be better
if I put everything together "sealed" with some hi-temp silicone. As it is, it's
all compression seals. (if I can get a 5000 to 15000 RPM range, I'd be very happy).
I await any suggested improvements!
Dave

combatpigg

My Feedback: (3)

Very clever DAVE.! Did you find the washers, or did they find you? I sure don't have any advice, it just looks to me that you have a working setup there.

meowy84

5400rpm at idle? I like it!

jboy381-RCU

i like it dave...i really like it...can you show pics of the parts to make it...i'm a little fuzzy on the washers... i guessing the slide is the ONLY part that moves...

thanks
john

fritzke

My Feedback: (1)

What RPM are you guys getting out of these engines typically?
And, what idle RPM can you get with a good fitting "ACE" or Cox throttle ring?
I want to know just to see how much this setup is limiting the top end and how
the idle compares to what else is out there.
It seems to idle well enough to land or at least do a touch-and-go on a "typical"
1/2a plane. (To me, that's a Mambo!) Not to many 1/2a's will stay in the air at 6000 rpm.
But if it's REALLY hurting the WOT speed, that's bad!
I am going to break it down and re-assemble all sealed up, and see if it
idles better. (I have to hammer down the ball socket anyway!)
Dave

fritzke

My Feedback: (1)

J-Boy,
I'll cobble up another one and take some pix. Costs $2 and 30 minutes of time!
I need to resurrect my Kyosho "Papillon" to try it out in the air!
Dave

mclintock

My Feedback: (3)

If nothing else, even without the throttle function, just having the exaust collected into one pipe so it can be put into a length of tube to direct the grease blast away from the plane is priceless! I need to slap one of these together in pee wee size to see how quiet it is. Maybe the baseball park can be a glow field after all?

jboy381-RCU

the old one i have runs WOT at 16K with a 6x3 cox prop...i haven't ran the NEW ones yet...

the washers,are they fender washers...i'm not sure what a machine bushing is...

sorry for my ingorance,

john

fritzke

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About 1/22" inch thick steel. Wish I could find
them in aluminum. A stack of 11 measures 1/2"...
Dave

jboy381-RCU

gottcha...i have seen the light[X(]

john

BMatthews

Dave, I think you have a very well equipped hardware store. I've never come across anything like that in my travels without going to an industrial place. I'll check Home Depot but I suspect I'll come up bust.

I suspect your 15K is only a larger exhaust outlet away. It's still pretty restrictive with that pipe. Perhaps a second V notch on the other side?

fritzke

My Feedback: (1)

I dont think I can put in a larger exhaust tube, I won't have any silicone left above and below it!
And notice that the top RPM reading is with the slider off completely, so adding
another "V" cut won't help. (It does not gain any RPM once the slider is halfway off, honest!)
I am thinking about how tiny the exhaust outlet is on the Cox annular muffler. The brass tube I used is
MUCH larger. I think my restriction is the area between the outside of the cylinder and the slightly "squished"
silicone tube. The ID of the silicone tube is 3/4 inch, only 1/16" bigger than the cylinder OD. However, I think adding any
volume around the cylinder will raise the idle RPM, so, like all things, probably a trade-off must be made.

Yeah, I'm lucky to have really good hobby shops and good hardware stores in St. Paul MN!
7 Corners Hardware is unreal. They had 1/4-32 taps in stock when I need one about 25 years ago!

http://www.7corners.com/7c_store/

And Hillman Fasteners Website:

http://www.hillmangroup.com/fasteners.htm

And a couple good reference charts from them:

http://www.hillmangroup.com/misc/Fas...0Chart%20A.pdf

http://www.hillmangroup.com/misc/Fas...0Chart%20B.pdf

Dave

Clean

Instead of a V cut, can you drill the inner and outer tubes, put an arm on the outer tube and then just rotate the outer tube opening or closing the holes?

epilot

Is anyone intersted in a helping me out? I plan to make some alu mufflers but I need a product engine to make sure I get the measurements right. I will make a small batch of mufflers for sale if there is interest. If anyone has an engine to spare I would offer you two mufflers in return for the engine. They will not have throttle (for the time being at least), just a plain muffler with a "gunk redirector"

TIA

Michael

g-rock

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Hi,

Dave this is very nice work. I have been a little fuzzy up till now on this subject. Your endeavors have made it clear for me as to how to throttle the Cox engine. The use of the silicone tube forces compliance, brilliant!

For those of you that do not know, Dave is getting married in about a month. It must have been Does night out when he made these parts.

Gene

cortacesped

Good Idea Dave !!! Not only for the throttle , also helps to take the oil out off the engine area. I think that somebody could cut some aluminum washers for you.
Good Luck with the marriage (It´s not so bad !!! ) I got married two months ago and yesterday I start building again. (JR Falcon). Regards

Claudio

fritzke

My Feedback: (1)

Clean,
I thought of drilling the holes and rotating the sleeve, but then you need some way to retain the outer
brass tube. I like the idea though! Any ideas on how to do it SIMPLY? How's that for throwing it back in your court?
(I am trying to keep this thing as SIMPLE as possible, but I did just think of a way....)

G-Rock:
Yup, May 7th is the day. Guess I won't be at the flying field that Saturday,
no matter HOW calm and beautiful it is! That would be a MEA (Marriage Ending Action)
before it ever starts! I'll just wear my Sodbusters club hat during the ceremony!

Cortacesped:
2 months and back in the shop? That's encouraging. My Sweetie knows I
have a lifelong model airplane monkey on my back. (35 years and counting...
easily since I was 10 years old)

Mike in DE:
Why not incorporate a gizmo like this into your muffler? (as an option, of course..)

Dave

newtech

Just always be aware of AIDS. Aircraft Induced Divorce Syndrome Very real for full size Experimental airplane builders and probably applies to model builders as well.

DICKEYBIRD

That's funny but unfortunately true! Fortunately, I met my 3rd wife at the flying field and she's a keeper.

Clean

Make the outer brass tube shorter than the inner brass tube, slot the inner brass tube and put a c-clip on the end of it to hold the outer brass on. Cap the inner. Probably need a washer to keep it from wearing through. Shouldn't add too much weight.

fritzke

My Feedback: (1)

Thanks Clean! Here is what I came up with, and some "How To" pix:
Picture #1, I had to clean up the hole in the washer to get it to fit on the shoulder of the crankcase.
And since it sits lower, I had to razor-saw clearence in the backplate. This makes it easier to assemble
everything though.

fritzke

My Feedback: (1)

More:

fritzke

My Feedback: (1)

And More:
Photo #1 shows a snap-ring on the outer sleeve. I replaced it with a
drilled out 90 degree bellcrank arm.
Photo #4 is the Seganku Werks (since we can't use "Skunk Works" I hear...)
Performance tests to follow...
Dave

jboy381-RCU

dave,
thanks for the play by play...the twist barrel is very nice...

john