Ace R/C Throttle question

Thanks Phil.

Hi Bernie,

Have  a lok on Roddie's thread about the Ace RC. He tested it and made some needles himself. He made the video above as well

https://www.coxengineforum.com/t5486-049-reed-valve-venturi-throttle?highlight=049+throttle

Lieven

I 3D printed one, with muffler on, it throttled quite nice.

In my long list of projects is to make a Bee throttle like Roddie did. But, as usual, if you make one at a reasonable cost, I'll buy a couple.

The B-Lister Mark

Not sure exactly how you plan to produce these Bernie.. but there are a few things I'd like to point out. It was designed for .049 Bee-type engines only.. which you probably know already. The Ace needle.. or "plunger" as they refer to it, is merely a piece of .062" music wire with a round taper ground on one end. This is the main part. The other two parts that Ace provided were a plastic "guide" and a short piece (approx. 5/8" long) of small silicone fuel line.. to provide an "adjustable" link between the needle and a servo linkage. The guide is thin.. for mounting between the engine and firewall. It is shaped exactly like a Bee-style backplate. It supports the needle and "guides it" straight into the venturi. The little round debris-screen must be removed for this. The guide has a nipple protruding from the backside. A hole is drilled in the model's firewall for the nipple and needle to pass through.

In my opinion, there's a few reasons why these weren't more popular. There was already a fairly effective exhaust-throttle available at the time.. and most people flying 1/2A RC didn't want the added weight of a throttle servo. Another consideration is the amount of RC kits available; having a built-up fuse with a radial-mount firewall design in order to mount a Bee-style engine. I can think of only one offhand.. and I think it's called the "Littlest Stick".. and I believe it's designed for the Pee Wee.

It should be noted that the needle; as designed by Ace, works with a stock Bee venturi which tapers down to .063" in diameter at the backplate.. which is why their needle/plunger is made from .062" music-wire. If the venturi is larger.. or drilled larger.. the throttle will not be effective.

Modern on-board radio gear is featherweight compared to just 10 years ago.. so it's a much more desirable option to run a throttle now.. even on a less powerful Bee engine.

I have put some thought into modifying the product-engine backplate (horseshoe) for a plunger-type needle. It would need an extension on the air-intake (not unlike the necessary guide required for the Bee..) The problem is.. the horseshoe has a spray-bar running through the venturi.. as opposed to the "spray-hole" in the Bee's backplate. With the Bee design; the plunger/needle will actually meter the fuel and air.

Ace recommends the use of a muffler to hold heat in the cylinder and keep the glowplug lit at low engine speeds. I would think that this is more the case for an aircraft application.

Here's a copy of the instructions that came with my Ace venturi throttles.




This is a more "solid" link that I made.. because I used a threaded clevice for adjustment.


You can see in this photo, that the plunger needle can pass all the way through the backplate. The primary needle's "spray-hole" is just inside the opening.. which provides for effective metering. Although "crude" it does work well.

I really need to apologize for that video. Idle speeds of 4k were no problem on the bench.. with the prop and fuel I was using. Sig 25% 1/2A fuel.. and the prop was a grey Cox 6-3 or 6-4. When you get down near 4K, you begin to hear the engine parts functioning, over the sound of the exhaust. That loud "shriek" diminishes rapidly when idling down.. and the engine also starts to 4-cycle because more air is metered than fuel. Watch the vid again if you didn't notice this. At one point, the engine was idling around 2500 rpm.. and you can definitely hear the piston reciprocating. It would be around 42 strokes/second. It's a "chirping" sound. At 15K.. by comparison, it's stroking 250 times/sec.

The muffler works well.. but I have ran the engine without it. I have only bench-run this throttle. I ran it for the first time in the kitchen of an apartment I had years ago.. That time I had a radio/servo connected.. the glow-driver "dis-connected" and ran what I think was a wooden 7 x 3 prop. Same fuel.. Sig 25.. and no muffler. The ease of installation combined with decent linear throttle-response was more than encouraging to me.

If you got creative.. you could build a 3-line 1/2A carrier model. The spring-type wheel retainers fit firmly on the plunger needle and provide for a "throttle-stop" for adjusting lowest idle. Connect a 90 degree bellcrank, linkage and spring-return.. and you have throttle-control. Maybe via a key-ring for your third finger. Pulling on the ring would close the throttle.

I believe that we could have a contest that would be fun and original. We could call it the "CEF Babe Bee MPG" contest! If Bernie sells the throttle.. Buy one for your Babe Bee and tune it to the lowest sustainable idle without a glow-driver attached.. and time your engine run until the tank runs dry. The longest time will win the prize!

This might be the ideal product to get into 3d print with. Small batch size so low inventory. I think there will be continuing interest at a low level because everybody wants more control even if they don't need it.

Phil

Jaspur X said that he made a needle/plunger for his Pee Wee. I don't have any experience with that engine.. but if you were to measure the hole size of the backplate's air intake, you could make a plunger to fit it. For instance; let's say the hole size is .047" (am I close?) I have T-pins that have a .046" diameter.. and they already have a taper. Just cut off the "T" end.. or devise a servo-link using it.

Making a guide is as simple as marking an "X" on-center with the radial mount holes on the backplate of either size reed-engine.. and drill a hole in your firewall for the plunger to pass through. The guide I used in my video is actually the engine mounting plate, and is made of PVC. It should be at least 1/4" thick to support the plunger and drilled with the next size larger drill than the plunger's diameter.

When tuning.. it's best to start the engine with the venturi "open" and adjust the primary needle for peak rpm. When you close the throttle, it will richen-up the mixture.

I suspect that added rotational-mass in the way of a heavy spinner, flywheel or even possibly a larger prop having a low pitch might be helpful in maintaining low engine speeds and idling. If you know what a "hit and miss" type engine is, you know what I'm talking about. It would affect throttle-response, but this throttle design already has fairly decent response in my experience.

My dream is to install a Babe Bee in my Sterling DR-1 using this throttle and the now available nano flight-packs. A scale prop would be 8" diameter. I have run engines on models using 8" props. The DR-1 can be a handful running on the ground. I ground-looped my little Flyzone model after several attempts of r.o.g. take-offs. I broke the top wing loose from it's struts. It's so lightweight, that it doesn't track well and wants to torque-roll with the least amount of power input.

Thanks Roddie,

We have a sample here and are presently getting a quote to have them made in aluminum. Cognizant that the venturi holes differ on various engines, we will have the plunger made to an ID that matches up with the biggest hole.

$9.95 for the throttle, made out of aluminum should work? We could even get them oxided in black.

Put me on the list for one at that price.

Phil

We are sending our sample to the vendor for a prototype run; after which they will co into production.

Any idea what the largest venturi hole should be that we may encounter in backplates?

Essentially a simple slide valve carb nice I wouldn't mind one either.

COOL , I think .086 would bee the largest I just tried a 0.92 or 3 and the run was not good it had a #4cyl. on a BABE BEE Soooo My guess Eric

I drill the aluminum to 5/64 (pretty close to 2mm) if necessary.  I suspect 3/32 would be suitable and able to shut any engine down.

Phil

Bernie, if I may make a suggestion; I would guess that the majority of Bee-style engines have the standard .063" venturi that this throttle was originally designed for. The Ace plunger/needle measures .062" and will fit past it's taper through the backplate and into the venturi-tube. (with reed removed, it will pass completely through the tank and out the other side). A "larger diameter" plunger could get stuck in the backplate if inserted too far (i.e. beyond it's taper)

It may be better to duplicate Ace's specs on this.. at least for the first round.. and state in your specs. that it is made to fit Bee engines having the standard .063" venturi. If they sell well.. you can choose to offer larger diameter plungers to fit larger venturis. The throttle's "guide-hole" would need to be drilled larger.. but that's not a big deal. You could either have some drilled.. or the end-user could do it themselves.

I'm assuming that it's the "guide" that you're having made from aluminum? This sounds more expensive than the molded plastic design that Ace used. Have you consulted the people who make your props, about making a mold for a plastic guide?

We are planning to make the whole thing in aluminum. A mould would cost in the $5,000 range and, with a run of 500, make for a $10/piece mould amortization. Even with a run of 1,000, that's still $5/piece just for the mould. For that we can make the whole throttle lol.

Shall do some measuring on all the backplates we have but copying the Ace specs may make the most sense for starters; with perhaps a secondary plunger for bigger venturis.

I am curious as to why you're going with aluminum for the plunger-needle? I see this as being problematic for a few reasons. Forming the necessary taper on an aluminum rod that small of a diameter could be tough.. and some modelers may want the option of soldering a link to the plunger, which can't be done if it's aluminum. Ace used common 1/16" diameter music-wire for theirs.. which is a lot more rigid and durable.




I'm just trying to help you to foresee some issues before you commit.

I have one of these from ACE tucked away somewhere, and I only remember it as being totally from plastic, both needle-rod and the guide?

With metal there is always the risk of electrical interference to the radio, this can happen whenever to different metals are touching intermittently. Aluminium doesn't run well against aluminium either, brass would be better I think.

Personally I would much rather see a new backplate being made/offered. This could accommodate a proper carburetor while still fitting against the regular tank.

One thing to consider is that anyone can fabricate the things, all you need is the tapered needle-rod (can be shaped from a suitable rod) and a guiding hole in the firewall...

Can a surestart snorkel be fitted to a bee?

Phil

pkrankow wrote:Can a surestart snorkel be fitted to a bee?

Phil

Not really.

The reason for making all the parts from alu is cost-effectiveness. Of course, the plunger could be made of brass at increased cost.

There should be no issues when it comes to the taper; after all, we manufacture needle valves for engines as small as .010. Friction should not be an issue either as there is enough "play" between plunder and guide. Also, we can't see electrical interference being an issue, as our throttle for non-tanked engines has all moving parts made out of alu as well, and we have sold thousands of those.

A new backplate is, unfortunately, out of question due to a mould costing tens of thousands of dollars. Even if made on a CNC machine in quantities of 1,000, retail pricing would have to be in the $30 range.

That concern for noise arose out of the relative lack of immunity by older R/C systems. I could take two pieces of metal whilst rubbing them together to cause the servos to jitter on the old AM digital systems of the early 1970's. Engine vibration provided the source. Thus, one used nylon and plastic components against the metal to isolate potential metallic connections. Then, manufacturers started manufacturing wheels with plastic hubs instead of cast metal and a whole array of non-metallic R/C linkage components, and etc.

Bernie has already qualified that electrical EMI noise should not be an issue. Upon introspection, since this new throttling device is essentially an air restrictor, similar to Cox International choke tube throttle, if it were to finally make contact with the metallic backplate given the limited free play from the accessory plastic backplate guide would essentially shut the air off sufficiently to stop the engine. So electrical EMI noise should be very minimal at best.

I'm guessing the advantages to this type throttle is its lower cost over the choke tube throttle. Personally, I've have very good success with the exhaust restrictor throttle, which produces a reliable idle. However, I could see an advantage to this needle intake air restrictor throttle. One can use a fixed muffler, since some flying sites require .049's to muffled. I do like the choke tube throttle though, as it is a more elegant way of controlling the engine.

Bernie, will the new plastic backplate guide be drilled so it can be also used on the Sure Start backplate?