The Evolution of a Winter Stove – Part 3

> Presumedly, you have put a defect in the publicly released version that will cause it
> to explode occasionally.

Yup. Embedded quantum-spin-based microprocessor chip with an encrypted WiFi link to the BPL membership database. As long as you have a valid membership, the chip stays quiescent and the 2 grams of C4 remains inert. However, if the chip fails to get a valid membership reply about 3 times, it becomes a temperature sensor. When it detects body heat in close proximity …

Cheers

>>>> Your valve seems very clever
>>Um … I am going to guess here that you are referring to the shut-off valve in the canister connector, not the one in the stove body.

The shut-off valve is a clever feature for remote stoves with the main control at the burner, but I was mainly referring to the ability to cope with both screw-on and camping gas cartridges. This would seem useful on any commercial stove, even remote ones with conventional heat adjustment at the cylinder end.

Thus the multfit connector would seem worth making available to others/manufacturers: on terms acceptable to yourself.

I have decided remote stoves are better: and have merged my can-top with a brunton stand, however, I still like meths :-).

I see that you have upgraded the stands. Great News! I was sort of wondering about that. Stainless is heavier but not really that much stiffer (unless well tempered.) Stoves like the Simmerlight/Windpro didn't seem all that floppy. But, I am guessing this add-on bit will require occasional adjustment, and/or loctite. Lighter is usually better when well designed.

I was thinking about the brass nut locking the FM-300T burner on. A small seat could be milled into the body letting you remove it. A fairly precise distance between the jet, air inlet holes and seat could be maintained that way and it might save a few grams of brass. This might require some clearance for the bottom of the threading on the burner body/mixing chamber though.

Well thought out!

Very nice work Roger, I particularly like the versatility of the canister connector. Availability of canisters in small villages in the remoter parts of Europe is a bit of a lottery.

Great work, Roger!

Your stove looks like just about everything I've looked for in a remote, inverted canister stove.

The one place where a more traditional upright canister stove would seem to have an advantage is in its ability to convert into a hanging system for use inside a tent.

Looking at your design:

1) Is the fuel tube long enough to reach a canister hanging just below the pot legs?
2) would it be possible to add notches or something similar to the underside of the pot legs such that they could retain the rolled lip of an inverted canister? (A wire "basket" anchored off the legs would likely be simpler, if less elegant. Or maybe a rubber/silicone ring that could slide over the inverted canister with small holes that would allow clips to connect it to the legs…)
3) If you tried to suspend the setup by running your suspension wires to the outermost cutouts on the legs (likely using a spreader bar or two on the wires), would it be stable enough if you had the weight of canister hanging below it? (Worst case would obviously be a full pot and empty canister, and I suspect that it might be too unstable.)

This may be a level of flexibility beyond your interest, but it intrigued me, so I thought I'd ask.

Thanks!

Hi James

> I am guessing this add-on bit will require occasional adjustment, and/or loctite.
In theory, no.
The nut which clamps all this together is done up tight against the end of the leg pivot. This means the nut should never loosen, despite the legs spinning wildly. There are low-friction brass shim washers to cut the friction and prevent galling, so there is negligible torque on the nut anyhow. The stainless steel grub screw which holds the nut is jammed in place rather tightly – it does its own thread forming in fact.

> the brass nut locking the FM-300T burner on.
Yes, I wondered about this too. But the weight of the nut is actually very low, and it serves TWO purposes. First of all it locks the burner onto the stove body so it does not accidentally unscrew and fall off. In addition, it allows me to align the pot supports on the burner with the heat exchanger coming up from the stove body. In theory I could adjust the start angle of the thread to do this by itself, but if they change the start angle on the burner column with respect to the pot supports during manufacture I would be in trouble. In practice, I don't think that angle is even controlled during manufacture.

The change in position of the air holes with respect to the face of the jet would be at the most slightly under 0.2 mm for the worst case alignment. The distance between the air holes and the jet is around 7 mm. Methinks I will not worry.

Cheers

Did not see this in the thread so far but was wondering if an upside down Coleman canister with adapter will work with this stove… Or is that just crazy thinking…

"The nut which clamps all this together is done up tight against the end of the leg pivot. This means the nut should never loosen, despite the legs spinning wildly. There are low-friction brass shim washers to cut the friction and prevent galling, so there is negligible torque on the nut anyhow. The stainless steel grub screw which holds the nut is jammed in place rather tightly – it does its own thread forming in fact."

Yeah, I can see where that would work. It occured to me that the Simmerlite pot stand was actually connected at the top, too. This adds a considerable stiffness, overall, to the stove. I am sure you have it well in hand.

Yeah, the alignment could get to be a problem around the heat transfer bar. Not as clean as I thought. Thanks for pointing that out. How do you align the Fm-116 burners? I am guessing the upper nut on the FM-300 is adjustable, also.

> wondering if an upside down Coleman canister with adapter will work with this stove
There are two sorts of Coleman canisters: screw-thread and Powermax. BOTH work without any adapter being needed.

The hair-spray style with a spray jet on top does not work, but they only have butane in them – not suited to winter use.

Cheers

> How do you align the Fm-116 burners?
I only have a few of them, so I took some care with the CNC and the start angle for the thread on the stove body. A very thin shim can also be used.

> I am guessing the upper nut on the FM-300 is adjustable, also.
It is usually done up tight. It holds the pot supports in place. Best to leave it done up tight. I guess you could spin it off, machine a gram or two off it, and replace it.

Cheers

"The hair-spray style with a spray jet on top does not work, but they only have butane in them – not suited to winter use."

But, the boiling point is 32 F or whatever. If you put it in your pocket you can warm it up and use below 32 F. With your stove you don't get evaporative cooling so you should be able to use it as long as contents are above 32 F.

If a canister is 2 ounces, fuel 2.75 ounces, your stove is 3.5 ounces – total 8.25 ounces – enough fuel to boil maybe 11 pints. That could be a good option for many trips.

> the boiling point is 32 F or whatever. If you put it in your pocket you can warm it
> up and use below 32 F. With your stove you don't get evaporative cooling so you
> should be able to use it as long as contents are above 32 F.
True, and if it's a Ronson lighter with iso-butane you could be on a good thing.

You can use n-butane (which boils at 0 C) at sub-freezing temperatures IF you use all the tricks, but it's going to be more tricky. It's not something I would recommend to a novice, but an experienced winter walker could do it OK.

Cheers

Hey Roger,

With the new design tripod design is the plywood board and micro-stakes (what are these and where do I get them by the way?) still needed?

Cheers.

Jerry, if it is not at or above the boiling point, then little pressure is generated in the canister.

I hadn't really thought about evaporative cooling, but you are right. Very little.

"I hadn't really thought about evaporative cooling, but you are right."

You obviously haven't used upright canister in cold weather : ) It always gets covered with frost. I bet it gets 10 degree F colder than ambient or even more.

Hi Robert

> With the new design tripod design is the plywood board and micro-stakes still needed?
The plywood base is nice to have when camping on soil or rock. It is essential when camping on snow.
The micro-stakes are useful, but not essential.

> (what are these and where do I get them by the way?)
Plywood base – that's an MYOG thing. Artistic licence allowed. I recommend ply rather than any sort of craftwood: the latter goes soggy rather quickly. Metal is a bit slippery.

Micro-stakes – hum, yes. I use Ti welding wire. Maybe you can find a welder who can give you one, or maybe you could use some stainless steel MIG wire. Or you could use high tensile bicycle spokes from a bike shop – you can even get Ti ones. The stakes don't have to be very long – under 10 cm.

I am sure creative minds will come up with all sorts of variants in time. Please let us know about them!

Cheers

> I bet it gets 10 degree F colder than ambient or even more.
10 C or more.

Cheers

You obviously haven't used upright canister in cold weather : ) It always gets covered with frost. I bet it gets 10 degree F colder than ambient or even more.

For an upright I can see that. I thought the discussion was for Roger's stove.

No, I havent used a canister much below 40F, if that. I usually use WG on longer trips or alcohol for short ones.

> With your stove you don't get evaporative cooling so you should be able to use it as
> long as contents are above 32 F.
Entirely correct.
But young novices do some strange things…

Cheers

Update 1

I was sitting there in the evening playing with a stove on my workbench, thinking vaguely about the leg stability problem, when I actually SAW what I was looking at. That is, I actually looked closely at what the legs were really doing – and it was not at all what I had been assuming. I went to bed thinking about what I had seen, and in the morning I shot out to the workshop to make some replacement parts.

To cut a long story very short, the replacement parts made the standard tripod legs much stronger and more stable. The whole idea of a centre support is fine, but if the tripod is stable enough it is not needed for a little stove like this.

A longer story is that I had been slowly upgrading the legs from a quite different titanium version which combined the tripod with the pot supports. There are some photos of these in Part 2. But I had not gone the whole distance.

The new legs look like this. Well, OK, you may not even see any difference at first, except that the outer end of each leg now has a stylish tilt to it. The critical difference is at the pivot, where the rather small 14 mm shim washers which I had been using have all been replaced with much larger 22 mm Ti washers and brass shim washers. This has made a huge difference. (Anyone want a large supply of brass shim washers 14 mm diameter?)

There is one other small change in the leg profile: the small tab at the outer corner. This merits an explanation too. I machine each set of three legs together. That’s a bit slow, but it makes for a much nicer set when they are folded together. The trouble was when the legs were all folded together they were packed really close together, and it was hard to separate them out. You could be sitting there at -20 C trying to set the stove up with gloves on and be cursing me for making the legs so hard to open. Not good enough.

The tabs on the two outside legs in the set are given a slight bend outwards, while the middle leg has a straight tab. Now it is easy to separate the legs. I should have forseen this as well, but I didn’t.

The older tripod legs have been withdrawn and scrapped. The centre-support legs have also been withdrawn, although if anyone really wants them I can supply them from the existing stock. All stoves have been upgraded to the new improved legs.

Cheers

The 116T RC has just arrived at my place.
Unfortunately I am almost packed up (moving house) so no tests for about 1 week.
As first impression feels incredibly light (90g on my =/-5g scale) for what it is.
My other two stoves of this type are almost twice and over twice that weight..
It holds a heavy pot with 2 liters of water and that is more than I need.
There is a bit of flex when you put that weight on but still sits nicely as you see in the photo.
Must remember (same as with my Kovea) to check that the arms are correctly open.

Roger – testing published here on BPL in the past showed remote canister stoves having lower fuel efficiency on average than top mounts. Now that you have a remote with the identical burner head as a top mount, I'd love to see whether there is a difference in fuel efficiency between the two configurations when the burner head is identical. If you have the time.

Hi Paul

> testing published here on BPL in the past showed remote canister stoves having lower
> fuel efficiency on average than top mounts.
Um – got a URL for that? I don't remember publishing that sort of data myself. Could be failing memory of course.

On the other hand, people using a remote are often starting with colder water, and may run the stove a bit higher in power because of the cold. Both of those will certainly affect the fuel used.

I'm prepared to stick my neck out and say that there should be no difference in fuel efficiency provided that all other factors are equal. After all, how far away the canister is should not really affect the result – should it?

Cheers

http://www.backpackinglight.com/cgi-bin/backpackinglight/canister_stove_efficiency_p2.html

Scroll down to "Analysis" and "Uprights vs. Remotes"

So here's our chance to see if it's all about burner size/design or if there is something more mysterious going on. And for even more fun, you could run the remote version in canister inverted and canister upright modes and see if that makes a difference.

technically, the liquid feed could be sucking heat from the burner zone to vaporize the liquid, where a normal cannister feed can be using more ambient air heat. Or maybe not.

but the heat of vaporization has to come from somewhere, all depends on how heat is retained by the windscreen.

When somewhere around 1/2 of the heat of combustion is lost to atm anyway instead of going into the water, its easy to either creaste false small differences in efficiencies, or hide them.