SBS_Pilot

Last week I started a Cox engine for the first time in more than 30 years. Gee, guess if I felt nostalgic....

Today it was time to test the throttle tube (coxengines.ca/throttle-conversion-for-cox-049-engine.html) I've bought, but with very limited success. The engine did start allright (it was an other engine and an other prop than last week), but the throttle tube didn't act as a throttle - more lika an on/off-switch. When I turned the throttle lever the engine run with full speed until the airhole in the throttle cylinder was almost gone. Then the engine almost choked (well, somethimes it did) until I opened the throttle again, and then it was back to full rev. It was not like those videos I've seen on the 'tube where the engines throttle real nice with this throttle conversion kit.

1. Is there any way possible I could have mis-mounted the conversion kit and still get the engine to run?
2. My throttle cylinder have a little slop, approx 0.1-0.3 mm, from left to right when standing behind the engine. Is this normal?
3. If the slop (by the way, is that the correct term?) isn't normal: could it be eliminated by adjusting the hex screw at the right side of the kit? If so:what size is the correct hex key?(My 2mm key is too small, and the 2.5mm is too large.)
4. What else could I have done wrong?

Please excuse if theese questions have been beaten to death allready - I can't find any good search terms to come up with any answers.
/Stefan

dckrsn

Hi Stefan,
I'm not sure what glow head you're using.
I've never user the throttle, but Cox Int recomends
using a conversion head type "A" or "B".
Go here and scroll down to see them.
http://coxengines.ca/performance/
Hope this helps,
Bob

SBS_Pilot

Bob, thank you for your fast reply

Your post made me do a LOT of searching and reading, and I found this thread: www.rcuniverse.com/forum/m_10057797/mpage_1/key_/tm.htm

If I understand the text correctly, it should be possible to run the throttle with the stock glow head, but the two conversion heads gives higher top and low speed respectively. But your post also made me check which glow plug I used in my test, and I think Iused the one that sat on my Baby Bee from my childhood. The head actually works, but I'm not experienced enough to say if an old head degrades and affects throttling. Any experiences anyone? Anyway, the next test will be with a new head.

Is there anything else I might have done wrong?

/Stefan

Mr Cox

You might have too high expectations, it is not a throttled carb it is an adjustable choke, just like large engines would have for cold-starting. It only chokes the intake and that makes the engine goo very rich and the rpms drop.

Tee Bee

SBS Pilot, I've got a bit of experience with Bernie's throttle setup. I currently have 2 models that use it. As mentioned, it does have it's limitations but can be a useful and fun addition to a model given the right combination of parts, prop, etc. I've found the most linear of operation with the lowest idle to be with the Type B head. It's a low compression setup so high end performance is greatly affected with lower power output and rpm. But that setup gives a remarkably low idle. On a lightweight and slow flying model it can be very fun and effective.

Video of the throttle operating with a Type B head: http://www.youtube.com/watch?v=85ELhzP5Lp4&feature=plcp

Video of my Scoundrel flying with this setup: http://www.youtube.com/watch?v=Iq_Q1ODC8Ko&feature=plcp

Another video fo the Scoundrel demonstrating the throttle and a power on landing: http://www.youtube.com/watch?v=tAsJMY_KxEU&feature=plcp

My Minnie Mambo also has one of these Surestart throttle setups. Because the plane is so heavy(22oz!), it is set up differently. The Type B head provides a nice slow idle but not enough top end power for this plane to climb well. The Type A head provided more power but I had trouble with overheating and sagging performance after a few minutes regardless of how many head gaskets I installed. I ended up settling on a stock Surestart glow head with 1 gasket. This doesn't provide as low of an idle but gives decent top end performance which this heavy bird requires to fly well. It idles too fast to land on paved runways but does ok on short grass. A compromise had to be reached to give the airplane a decent performance envelope.

Video of the throttled Minnie Mambo flying with stock Cox head: http://www.youtube.com/watch?v=b6lb8UYmPBI&feature=plcp

The sideplay in the throttle tube is normal, not a problem. The hex screw in the control arm is for position adjustment. I mounted the arm upright on one model but down on the other. The screw is a standard size, not metric.

I've enjoyed tinkering with these reedie engine throttles and they are effective on the right airplane. I don't use them on any of my "speed demon" planes since they sacrifice top end capability to get the low idle. I hope I've helped you.

SBS_Pilot

Mr Cox and Tee Bee:Thanks to both of you for your replies

I guess I just have to spend some more time to learn to use it correctly. I haven't even flown a Cox powered plane yet, the closest I've come is my electric powered Grassna (Grace fuselage with Cessna foam wing). My expectations in the throttle is to get some kind of get-out-of-trouble-by-reducing-speed device which - given my qualities as a pilot - is something I'm quite convinced I'm gonna need....

Also thanks to both of you for your video uploads - I have watched quite a few of them with great pleasure. Keep 'em coming!

/Stefan

Cox International

My Feedback: (10)

The most common cause is modellers not realizing that it takes very little movement between full-tilt and idle (or cut-off for that matter). The trick is to use the innermost servo arm hole and also set the servo throw to limit it before crossing into cut-off zone (usually done with the TX trim switch).

Bernie
www.coxinternational.ca

SBS_Pilot

Thank you

That is probably what I did wrong. I manouvered the throttle by holding a pushrod in my hand. Next time I will try using a servo which I'm convinced will enhance the control of small movement.

Thanks

/Stefan

Tee Bee

Bernie's right. It takes some time to set up the throttle for best performance. Sorry I failed to address that in my long-winded post above.

Cox International

My Feedback: (10)

Yes, Stefan, ahand-held pushrod is difficult to micro-manage. Try it with a micro-servo set up to minize throw and you should get good results. We have sold 1,000's of them .

The throttle does not replace a true carburetor but it is a decent low-cost solution. A "real" carb would run $30+, more than the current cost of a basic engine.

Bernie
www.coxinternational.ca

049flyer

My Feedback: (18)

I've had good results with the old exhaust restrictor type of throttle. Not much of a hit on the top end and still a low idle for a 1/2a engine. Cox International sells them and they are very reasonable. I think if one could rig up a linkage between the exhaust restrictor and the choke tube throttle his efforts would be well rewarded.

BMatthews

SBSPilot, you'll likely also get better results with a new glowhead. You mentioned that it was a very old head that you used for the trial. Older heads with many hours of operation seem to lose the platinum metal plating on the wire. And that platinum is essential for good operation. A fresh plug could well make a big difference for you along with the information mentioned already.

jaymen

Well, at Cox we all knew the exhaust throttle sleeve was an on/off proposition, basically two speeds. The secret was to have a real tight fit between the sleeve and cylinder, this gave a lower idle speed. To mellow out the transition, we cut a tiny slit one one edge of the throttle sleeve. This slit then would open before the large ports of the throttle sleeve aligned with the exhaust and give you a more progressive throttle response. We refined the slot by making it transition into a "Vee" shape that blended into the full height of the exhaust sleeves port. Some guys just cut the edge of the exhaust sleeves slot at a 45 degree angle to make it open more progressively, but the slit cut sleeves worked better. These mods all came from my late dear friend, Dale Kirn.

GallopingGhostler

One can also help to linearlize it by how the pushrod end is mounted on the servo. Instead of say, position from -45 degrees to +45 degrees, where 0 degrees is to the right when looking at the engine from the rear of the plane, position it in the servo wheel to +90 degrees and 0 degrees. (This is where 0 would be maximum throttle, +90 is idle.)

Then the opening of the throttle is more gradual. At half throttle (+45 degrees), it is 1 - 0.707 = 0.293 = 29.3%, versus 50% using the other method.

If forward is full throttle and back is idle, then it would be 0 degrees to -90 degrees on the servo wheel.

GallopingGhostler

I also wanted to add, back when I was using an Ace Pulse system with KRD sequential throttle (Hi-Med-Lo back to Hi), after careful measuring and calculating, I drilled an inner hole in the servo wheel. This was to control my throttle sleeved .049 RC Bee engine. The servo wheel always rotated in one direction, so forward (+90 degrees) was medium (slit open partially), center (0 degrees) was full throttle with sleeve fully open, rear (-90 degrees) was idle (sleeve pushed past full to partially closed).

(Please note, I am going from memory, it could be the other way around where full forward was idle.)

This setup provided full throttle with a decent half throttle and idle on the non-linear throttle sleeve.