.098 V twin using 2 Cox .049 Cylinder assemblies.

[mu38&Bg#]

When all nine plugs have a common "ground" you don't have many options. One option is to drive two plugs from one circuit by connect current to two plug center terminals. However if one plug burns the circuit is open. We had some discussion on RCG There wasn't much of a solution there either.

 

[petertha]

I'm no electrical expert but wouldn't you have to somehow insulate the glow plugs from the cylinders to connect them in series?

DOH! Exactly right. This should teach me to type when its already long after my bedtime. I started out wondering if any newer '1S' Lithium type cells were nominally close to 1.5-2.0v plug requirements. And then my brain slipped into series voltage sharing. But the common ground through the engine is not like a string of christmas bulbs on a wire, is it?
LifePo4 is 3.2v/cell, LipO is 3.7v/cell, Lto is 2.4v (dont know anything about them)

Without a resistor or regulator to knock back source voltage, I guess the cheap solution is back to plan A: dedicated Ni* cell per plug, maybe a bigger C or D size for longetivity & current rating?
http://www.batteryspace.com/ni-mhbatteries.aspx

 

[DICKEYBIRD]

We need Greg to get on board as a project consultant. I'm sure he can show how to convert all nine cyls. to diesel and be free of the need to light up those plugs.

Steve's sturdy crankshaft design and the inherent smoothing effect of the progressive firing impulses from the 9 radial cyls. will eliminate the obligatory crank failures of dieselized Coxes...no?

 

[mu38&Bg#]

I don't think i want to adjust 9 compression settings.

 

[petertha]

I'm not an electrical guy, so please don't chuckle to hard. My googling for low voltage regulators stumbled me onto this parametric product spec-er tool.
http://www.ti.com/

I assumed (1S min, 2S max Lipo battery) input voltage of 3.7v, 7.4v respecively, 2.0v output voltage & 4A output. ie one regulator thingy per cylinder driven by a single Lipo pack.

You push the red Start Design button & it then spits out parts that fulfill the criteria in kind of a dashboard tool where you can further compare/refine. Not sure if the resultant little black bits would actually do what we want, but the 2-3$/per looked appealing.

And thats the end of the road for me, maximum limit of electrical engineering incompetence achieved! Anyone else with knowledge know if a board/circuit could be built around this?

 

[cidrontmg]

James Engines was probably the last source that stocked those taps. Might as well to a couple practice pieces on the lathe for that price. Internal threading isn't that complex. Buy a carbide internal threading bar and it will be fine.
Greg

Well, it's an excellent plan. I have 12 Cox cylinders + pistons + glow plugs, but no 17/32" - 40 taps or dies. I have a 1/2" - 40 tap - close, but no go. I tried twisting (with a big enough wrench) the threads into ali, brass and steel. Ali and brass mangled the thread, and steel mangled the cylinder :rant:. Not a famous result.
http://coxengines.ca or James Engines don't have taps or dies, so no one are available. Special taps are quite expensive ($200? of one each ), but if you contemplate to think about selling taps/dies, with a moderate cost, I'm willing. And I think there's many more who would buy it. *discussion*

 

[mu38&Bg#]

I've done all sorts of special threads on the lathe manually. I did several 2 1/16"-24 internal and external last year. I can also CNC thread mill so that's what I'd end up doing in this case, but the hardest part of threading in the lathe will be mounting the crankcase to the spindle.

Greg

 

[deverett]

After failing miserably to source the 17/32-40 tap, I wondered about making one. For four holes into a bit of ali, I reckon a mild steel tap case hardened would do the job.

However, I've had brain failure. How do you calculate the depth of thread to cut the tap (Crest to Trough)? I've looked through Machinery's Handbook - 21st ed, 1979 - there are loads of formulae, but can't find the one needed.

Someone put me out of my misery, please.

Dave
The Emerald Isle

 

[barnesrickw]

As a side note to this thread, I don't think Cox realizes more people are likely to buy more parts, for more projects, if they would sell a tap and die at reasonable price. I may suggest they scan the internet for threads tagged 17/32-40 tap for Cox .049.

 

[barnesrickw]

The response I got from Cox International.

Hello Rick

We do not have any plans to carry the tap and dies at this time, but I will keep your suggestion in mind when adding future products to our line up.

Many thanks!

Theresa

 

[mu38&Bg#]

Don't let the lack of a tap stop you. Single point threading not as bad as it seems.

 

[barnesrickw]

I just inherited a lathe that will do threading. I'll give it a try as soon as I get it.

 

[MCRIPPPer]

very cool motors.

why not just use a few D cell alkaline in parallel to get it going. those things store quite a bit of energy so should last a while. they can also supply pretty good current.

or you could make a low voltage transformer by winding the secondary with only a few turns of big wire, and get about a volt at hundreds of amps capability.

 

[stevehuckss396]

very cool motors.

why not just use a few D cell alkaline in parallel to get it going.

Tried it on an inline 4 cylinder and the 4 D cells drained in about 5 minutes.

 

[petertha]

Tried it on an inline 4 cylinder and the 4 D cells drained in about 5 minutes.

That doesn't surprise me Steve. Typical alkalines appear to have high nominal maH capacity, but that also presumes low current load. Great for LED flashlights, not so good for resistance heating elements. At increased current draw, alkaline capacity goes to pot in a hurry.
These performance graphs show the relationship visually.
http://data.energizer.com/PDFs/e95.pdf
At 100mA load, capacity = 100 hrs. But increase the current to 1000mA (1 Amp) and capacity goes down to ~1 hr. Its log scale so at target 3A plug load, capacity degrades to mere minutes like you experienced. In fact their scale doesn't even exceed 1 Amp, because it's getting outside recommended limits.

That's what cell C-rating is all about. Other chemistries can offer much higher current delivery capability due to lower internal resistance & other factors. In this Alkaline example: C = 1 A-hr / 1 Amp = 1C ("one C"). Compare that to Lithium batteries that will do 45C continuous & 90C burst. Even low grade LI will do 25/50 continuous/max these days.

Unfortunately the issue with all these great (& cheap) Lithium based cells is not their ability to deliver current, that's fine. Its that their nominal cell voltage is too high, in the +3v range. Whereas glow plugs are designed around 1.5v range. So what is required is a regulator circuit to step it down. That's essentially what the commercial glow drivers are all about +/- some other fancy features. But they are orientated around typical single plug applications. The multi plug application requires a different solution. But hopefully someone out there that can figure this out.

 

[derek999]

Hi, I'm new here but have been reading your thread with great interest as I plan to build a multi cylinder engine using Cox or similar cylinders and pistons.

The required starting voltage of around 1.5 Volts would be easy using power diodes in series with the positive line from the cell. Each diode would drop the voltage by around 0.7 Volt, so 3 would reduce a 3.7 Volt cell's output to around 1.6 Volts.
Diodes of about 50-100 Volts & 5 Amp capability would be suitable, but in use could get a little heated so they should be insulated.
Almost any electronics component supplier should have suitable diodes for pennies, and they should be wired in series to give the required voltage drop.
As they only pass current in one direction, test for correct function and reverse the direction if no glow achieved.

I found this to be a reliable and economical answer to the problem.
I hope it halps.

Best regards

Derek
St. Andrews, Scotland (Golf City!)

 

[pacomb]

There's also http://www.jamesengine.com ,especially the HEX-2, HEX-4 and Cox V-4. Drawings are included (free!), and there's also HEX-2 plans, published in Model Engine Builder Issue #9, HEX-4 plans were published in Model Engine Builder Issue #14.
There are also Italian designs, 3- and 5-cyl. radials, but I don't think there are drawings, or plans, just the fully and ready assembled engines. Nice interesting engines.

That nice 5 cyl radial, should be easy to take it apart, and do reverse engineering to take all the dimensions. As it is a 2 stock engine, you have so many little parts compared to a 4stroke radial.

 

[pacomb]

Hello,
maybe an old thread, but maybe someone who participated on the thread can help.
I and a friend are with the idea of building a radial engine using cox .049 engines.
We are stuck with the 17/32-40 tap, cant find a source for them. Does anyone know actually who is selling the tap?
If we are not able to find a source, maybe someone who has it could lend us his tap to make the threads?
regards
paco

 

[barnesrickw]

Hello,
maybe an old thread, but maybe someone who participated on the thread can help.
I and a friend are with the idea of building a radial engine using cox .049 engines.
We are stuck with the 17/32-40 tap, cant find a source for them. Does anyone know actually who is selling the tap?
If we are not able to find a source, maybe someone who has it could lend us his tap to make the threads?
regards
paco

They can be found but are expensive. It's prevented me from making anything from my cox parts. I'm planning on selling the parts on eBay and just make my own cylinders and pistons.


Sent from my iPad using Model Engines

 

[pacomb]

Newman tools sells it for $140, not cheap!
http://www.newmantools.com/price/taps_ns_pr.html

But what I see is that when ordering 6 units, the price drops to $50 which is more convenient.

For you north americans, it should be easy to join 6 and buy the tap cheaply!

Is there any interest to joing a group??