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TOPIC: Lighting Rapiers on the Flying Field

Lighting Rapiers on the Flying Field 7 months 2 days ago #2074

  • Aquarius
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Igniter is as simple to build as possible. Just find a pipe (alu, PVC, paper, composite) with a diameter that matches the diameter of the cell. I can design 3D files and send them to you. 3D printing is not a problem today, the rest is simple.







B)
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Lighting Rapiers on the Flying Field 7 months 9 hours ago #2083

  • Terry Kidd
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This is my latest version. The box is laser cut from MDF. It's much the same as the version I put up a few posts back.
There's a cover, removed for clarity for the underside.
The cable to the right is the charging cable. One must disconnect the battery, connect the charging cable to the battery and the other end of the charging cable goes in a mobile phone charger.

The battery is a 3.7V 18650 Akku, 3200mAh which, so far seems to be adequate.
See below for battery link:

18650

The heating element is made from 'flat' nichrome 0.4mm wide by 0.1mm thick. This folds quite nicely into the familiar 'hairpin' shape. I start with a piece 65mm long and fold it in the middle. The two ends are each folded back 5mm or so and then mounted in the terminal block.
I found a German supplier:
Zivipf for the flat nichrome wire.



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Lighting Rapiers on the Flying Field 6 months 3 weeks ago #2088

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The 'bottom line' of the postings in this thread show that electric ignition of our one shot motors, whether old Rapiers or new TSP types is the favoured option. :)
And we are making progress towards having available an 'off the shelf' instrument that is attractive, as we hope our new 'Spectre' motors will be, to aeromodellers (and others) thinking about 'jet-propelling' their models.

Both the 'Bovie' type cauterizer tools and the cheaper 'Cord Zap' instruments are OK, but both types are limited by using only two AA batteries. Two cells are no more than adequate, especially in a breeze (which inevitably cools the element) or with old motors whose propellents needs s bit of encouragemrnt to fire up. :dry:

My most effective recent igniters were no more than three -cell and four-cell 'proof of concept' efforts (see earlier posting). Both work well, though the four-cell one has a tendency to melt new 26 SWG and 28 SWG elements! Note the cells are 1.2V rechargeable types and not 1.5V 'dry cells'. I favour the latter as these have lower internal resistance, and under load, the voltage is perhaps higher.



My most 'presentable' igniter was based on a reusable 'Bovie' tool modified to take three cells:



These instruments, though don't appear to be as easily available now. :unsure:

The very nice Cord Zap is much cheaper, and looks better, but is more difficult to adapt to three (or even four) cells as the electrical circuit is made through the adonised aluminium body.



Above: Rodger Wright's modified Cord Zap. Very effective (it is after all, four cells!) but it would be better if the battery could be hidden in the Cord Zap's body. Tricky!

I hope we can follow up on Rodger, Marcin's and Terry's work and make something commercially available ...... the search continues. B)
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Lighting Rapiers on the Flying Field 6 months 3 weeks ago #2089

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I use a 4 cell nimh pack with a futaba connector to the nichrome bit which I bought on eBay. The cord zap with only two cells doesn’t work. Such a shame. The push button is really necessary. I must investigate medical cautery products.
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Lighting Rapiers on the Flying Field 6 months 3 weeks ago #2090

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As I have written before, the Cord Zap, uniquely, completes its electrical circuit fia its aluminium casing. This gave me the idea of adding an extra extra one or two AA batteries and ensuring a good connection by addig a thin strip of metal on the inside of the casing, i.e. between the Cord Zap's body and the batteries. :unsure:



The extension is cobbled together from the casing of a spare Cord Zap I had by me, which I carefully cut to length. Three times :ohmy: The 'connector' is a 2-3 cm length of thin 4mm tin plate (see the top illustration where it is fitted in a spare Thread Zap body). This connecting strip is a very tight fit between the battery and the Cord Zap's body. This means, incidentally, that I had to use Duracell dry cells as rechargeable AA batteries are slightly wider and a very tight fit in the Cord Zap's body. :dry:

After I'd got the length right and ensured a good connection (a bit of twisting and turning did the trick) I was pleased to see a healthy orange glow from the 26 SWG Nichrome element. :lol:
It wasn't as bright as I would have expected with four cells, probably due to (a) the internal resistance of the cells and (b) the cord Zap's body is not, I suspect, that good a conductor. But the element is probably hot enough to light all but the most recalitrant (old!) motors. :S

I'll be trying it out at Old Warden at the end of the month. It seems robust, but we shall have to see how it does under fire. :unsure:
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Lighting Rapiers on the Flying Field 6 months 3 weeks ago #2097

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This is summary of my own efforts so far with igniters. I have 5 different igniters, 2 gas and 3 electric based units and each one has their advantages and disadvantages.



Gas
These can work brilliantly and reliably for a while, I have even ignited Jetex motors with them. However, you have to remember to turn off the gas before lighting up or you can ignite the model or melt it if it is foam! Bin there, done that, got the T shirt!
The converted soldering tool (below) is however cumbersome in use as you have to ignite it separately with cigarette lighter, but great if someone else holds the model for you while lighting up and passes it to you in time to launch. Unfortunately mine started leaking gas quite early on.



The converted chef’s blowlamp (top pic left) allows single handed operation and has been great. However, I have had two as the handy piezoelectric spark ignition for the gas fails after a while and the seals also leak eventually. I need to buy a third now as my totally reliable back up igniter.

Electric
The cautery tool can work well but the single cell is wimpy and needs adapting to two cells. It has the lasting problem of keeping the motor exhaust crud off the contacts of the igniter wire. I am going to revert to wrapped connections again to see if that is more reliable. Last time out, I tried bending the wire at 90 degrees to help keep the crud off, but that needs further testing.



As a result of only having 2 cells on my adapted the cautery tool I made up my own 4 dry cell unit from a Radio Spares 4 cell carrier. In fact I have made two but the second has to remain a work in progress. The first unit has proved reliable once set up with new batteries and clean connections, I estimate I have achieved about 50 ignitions per set of batteries but that may well be an overestimate. A revamp is called for with some better means of protecting the igniter wire contacts from the crud without going to bulky terminal connectors.
The wire i use is 15 thou 28swg Nichrome wire for the 4 AA dry cell units. I keep the length of the wire beyond the terminal grip as short as possible, i.e. like 8 – 10 mm terminal to tip. 15 thou has proved sufficient to become hot enough and retain enough strength at this length to remain serviceable for extended periods.



As well as the crud problem I must look into rechargeable 4 cells at some point, as for the ‘cord zap’ type, I haven't tried them so cannot add anything.
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