[Ken Currell]

Hi John

I will likely try the tubing for my 9 foot bow as it should be lighter than the wooden one and it won't warp.

I am particularly interested in how you secure the cutting wire to the 1/4 inch rods.

Do you use control line wire in both bows?

[moo]

Originally Posted by byrocat

Gee! A couple days away from a thread like this and it's growing like a weed!

I did some digging around on the INternet and found the website where I got my original meter design.
http://www.nsrca.org/technical/tip_t...wer_supply.htm

Wow, primitive. At least jam a 555 timer in there for some repeatability and linearity so that you can take out that wasteful long/short resistor.

[Vulcan1]

I secure my cutting wire by putting a couple of wraps around the end with the groove and basically tying a knot or similar. There are no connectors on the wire. The other end I use 14 guage extension wire and on the ends there are 12/10 guage yellow crimp connectors. I use a heavy soldering gun to solder the 1/4" ID connectors to the ends of the piano wire. All connections are soldered and the only place I ever use acid core is clip to the piano wire. It gives me a good connection but also has to be cleaned properly. I also use the U shaped clips on the other ends instead of banana plugs. My banana plugs are the type you unscrew and then can get a good connection. The jacks are the weak point if they start getting loose or warn. There is a pic of my vertical cutter also.
Make sure everything is taped and insulated with heat shrink when making these. Some pics of my manual setup.
John

[Vulcan1]

For any interest this is a couple of pic's of my CNC cutter. What is nice about this is you do not need a template and everything is adjustable for sizing on your cut. You can also adjust for the gap your wire leaves when cutting.
This is made with the Hobbycnc 4 axis board (not the foamcutter board) with the wire heat addition added. (4) 80oz. steppers and the screws are 3/8"/16 ready rod. The upright and bottom tracks are ball drawer slides which I modified and screwed on to 8"x4' shelving. This makes it so you can vary the length of cut or for storage. For setting up I clamp it to the bench. As usual it is a copy from the net with modifications so I can get rid of the play.
I used the 4 axis board as I am going to CNC my mill drill which is partially done at this point.
If anybody has any questions or interest you can pm me. I would only to happy to help.
John

[igor_throw_the_switch]

Originally Posted by moo

Wow, primitive. At least jam a 555 timer in there for some repeatability and linearity so that you can take out that wasteful long/short resistor.

The worst part of it is having that resistor immediately below the on/off switch (my stupid). It's not a problem if you remember to turn it off after each cut, but my dad cut out some styrofoam snowflakes a few years back and had it on for about an hour. Burned his finger pretty good when he tried to turn it off.

It's also very dumb to be cycling this circuit on the secondary side of the Tx. It takes a little while for the voltage to rise enough to trigger the gate on the triac - I have no control (read no current) between 0 to about 30% of the dial. When this sucker finally does kick in, I think it's a bit too hot for white beadboard. Not terribly hot, but I wish I had a bit better control of the low end of things.....Also, don't forget that the output of this circuit is *not* going thru a transformer (which would act as a choke and smooth out the waveform).

This is why I recommend doing the chopping (dimmer) on the primary side of the Tx. Smoother output, and more adjustment down low.

And yes, I should have said that you would need an *AC* ammeter to measure the current. It might not be accurate, but once you know the value for *your* system, then repeatability shouldn't be an issue.

The shunt I described I actually use to measure input (DC) current to my ESC's - not terribly accurate either, but it gets me into the ballpark, and that's all I really need as a sport flier.

I think I'll be fighting hi-tech all the way to my grave (despite my field of work) . I believe in keeping things as simple as possible.

Brad

[igor_throw_the_switch]

Originally Posted by Vulcan1

I secure my cutting wire by putting a couple of wraps around the end with the groove and basically tying a knot or similar.

I've found that knots in the cutting wire are weak points. I pass the wire thru a pair of eyescrews (one at each end of the bow) and then basically screw them down to the wood of the bow. I pass the wire around each screw that secures them a few times, and use a washer on said screw. When I tried using knots, the wire would break at those knots.

Brad

[Spitball]

One final word from me - I just found quite a nice article by Laddie Mikulasko at
http://www.emfso.org/electric_flight...oam_models.asp
He covers foam cutting nicely; not too deep but succinctly.
He should know if anybody does!
You sure opened up a pirates chest here, Benji!!

Edit: it won't d##m well print 'foam' right - I dunno?? Seems to work fine anyway!!?

[benjhind]

I didn't think there was enough chat about it here on RCCanada. A few posts about CNC jobs, but that is WAAY too out of my league.

I'm glad my post has gotten some people thinking. I do wish that I had a safer box though. Any thoughts on covering the "crate" design with screen from a screen door? Can I borrow your staple gun?

[benjhind]

Hey Spitball, just saw your edit. The software for RCC automatically shortens links. This works great for those links that are about 3 pages long, but looks strange when it only chops a bit out! Don't worry, the link works fine.

Ben

[Vulcan1]

I use a circuit that is not to hard to makefrom the web. From the diagram I use a Radio Shack 24 volt transformer with a bridge rectifier for input. I then use this circuit and it works for me. The LM338 will handle 5 amps and you very the voltage for the cut. You don't need 24 volts output but usually about half. The regulator does not get very warm for the amount of time we use it. The schematic shows -12 volt and +12 volts but it works with -0 and +24 volts. The idea is for me to be simple but have good adjustment and the resistors change there value with heat. I may be wrong but that is my thoughts for today.
John