RC India

Hi everyone,

Senior members, DON'T laugh!
My first entry was a chuckie (INDORE TLG1)
This, my second entry, is a DIY homemade tool.
A Lipo powered hotwire foam cutter.
Will try to graduate to an RC airplane build before May deadline  ;D

Ever since I lost my hotwire cutter
(probably went to member Ashok Baijal who rescued/ restored all my junk when i was posted abroad in 1992)
Been wanting to make a new one, but without long leads from car battery
Never had guts to try a lipo for fear of fire/explosion
My multimeter couldn't tell me the specific resistance of a guitar E string. Neither could Google!
Then i remembered i have a Wattmeter...
Showed 2.6 amps at just under 12v for about 24" of guitar E string.
My lipo can easily take that without exploding.

So here goes.
Forgot about newspaper as busy supporting RC Aunt standing on a chair to take the pictures.
But believe me, it is today, and it works. Amps drop to 2.4 as wire gets hot.

Will post video with newspaper tomorrow...

Materials required:
Some 1"x1/4" baton, some nuts, bolts, washers, an E string from a guitar, drill for making holes, 2 cycle stand springs. And a Lipo and leads!
Construction is self explanatory.

Lipo connected.
11.84v, 0 amps before start

Thereafter 11.6v, 2.4amps, 27.9 watts

Iyer sir....
one quick question...

what is the length of the bow.. ???

7 views even before i could upload the second post!
Wow!
Length of wire in bow 24"

So what if it is not the greatest invention of the year?
It is Desi Jugaad. And it works!

www.youtube.com/watch?v=Ot5nQf1o0zk&feature=youtube_gdata_player (http://)

@anwar sir,
Due to lack of response
Presumably due to entry being stupid and uninteresting
Kindly allow me to withdraw this entry from sweepstakes.

But, like Arnie says
I'll be back

Great info! I use normal steel wire connected to 5v output of a atx power supply. .5mm steel wire of 15cm length. Gets pretty hot... if using the 12v output you can get red hot at 30cm and medium hot at 40cm.. I use it to cut coro sheets and hd thermocol. :D

I use a guitar no 1 string along with a variable solder iron output something like this
http://www.ebay.in/itm/Max-Technologies-Micro-Soldering-Station-Max-550-/161198186453?pt=LH_DefaultDomain_203&hash=item2588291fd5&_uhb=1 (http://www.ebay.in/itm/Max-Technologies-Micro-Soldering-Station-Max-550-/161198186453?pt=LH_DefaultDomain_203&hash=item2588291fd5&_uhb=1)
does the job nice and easy, and you can control the current for the string size.

Ashok.P

Pms exchanged with b4ggu sir may be of interest to others too.

"Are you using any voltage reducer? I use the servo tester and an old brushed esc."

"The whole point was to have an independent bow not depending on cables from car battery or power supply transformer"

"So are you saying it does not need any fan regulator or resistor...doesnt that bleed the battery quickly??"

"Yes, it doesn't need any regulator or resistor.
No, it doesn't bleed the battery quickly.
At 2.4amps, the 2200mah 3s lipo should last at least 15-20 minutes.
Each cut takes only a few seconds.

Got fed up of going down to the parking bay to connect 3meters of wire with croc clips to the car battery etc. Needed a simple portable tool.

Putting our pm exchanges on the main thread as it may interest others too. Hope you don't mind.
Regards."

Very informative KK.. Nice jugad..worth copying, might try it one day. By the way guys, Vivek from Sharma Model Aero sells the Nichrome wire..I got mine from him a few years back with other bits..
Cheers
Deepak

You stole my post b4ggu. Nichrome is an excellent wire for foam cutters. I'm using a wire leader for deep sea fishing. Made of Nichrome and very robust. Not too much stretch and very thin. Please be careful when choosing guitar strings. Many strings are Nylon wound to reduce the harsh noise generated by fingers running up the string when played. This nylon will burn off when used for foam cutting and will affect the actual cutting. Plus they will tend to stretch more when heated and after prolonged use.

One small tip when using Nichrome. Be very careful when handling it when tensioned in a bow. I built a bench type cutter and the wire is so thin it's almost invisible. I brushed the back of my hand across the wire when reaching for something on the bench top. It excised a very thin few layers of skin from my hand. Apart from being very painful for a long time, it literally took years for the scar to vanish. Definitely not a good way to lose weight.

A tip for a power supply is to use one from a computer using the 12 volt Positive rail. Add a simple light dimmer and it's continuously variable.  Stu

@propfella sir,
There are of course any number of homemade hotwire foam cutters.
In the instant case:

Metal High E guitar string used, which is bare, not nylon wound.
Lipo held on the bow with Velcro.
Power regulated by using 2s or 3s as reqd, and sliding the clip to adjust length of heated portion.

Intended for small pieces less than 2ft long.

This canopy cut freehand, holding foam in one hand and bow in the other.

And thanks for bumping this thread back to life  ;D

Which key would you recommend using when stringing your bow? Personally I find Z Flat Major to be useful but not overly taut..

Haha. If i knew that i'd be another Tommy Emmanuel!
(I just fiddle with the bow  ;D)
Used a spring from a bicycle prop stand on each pivoted arm...

Iyer sir,

how do you control the temperature ?

It will be great if you can post some pics...

planning to build one soon (:|~

madaquif, A light dimmer is a good adjustment tool, they are easily mounted, compact and inexpensive. I've even heard of one being removed from a touch lamp which gave the user 3 different settings. A model train controller was another but definitely not portable. I think the best in any portable unit would be the light dimmer, it would certainly look the part and do a very good job. Please excuse me for answering Iyer's question.   ...   Stu

Voltage reducer setup as mentioned above by Iyer sir is for heat adjusting (More the voltage, more the heat). For an easy setup, one may also use 2S and 3S LiPo - no too much options to adjust heat, but you definitely get 2 levels of control !

with few parts and little soldering, one can make a simple variable voltage regulator circuit which will also do the job (No need of investing in a Servo tester and brushed ESC If you are on a low budget :) )
I will post the circuit if anyone is interested.

I've played with various forms of foam cutters over the years and found my table cutter to be the best to use. OK it's not portable, but if you have the room a table top model gives many advantages. I find it allows a much straighter cut over a longer distance. You can use what's known in the woodwork business as a "fence" Basically something to guide the foam to ensure a perfectly straight cut is performed. It's much easier to cut a perfect circle or bend, you can leave it running for those bigger jobs. They make it easier to handle things such as wings and fuselages. They will also handle much thicker pieces of foam and even allow a 10mm board to be cut into two 5mm boards. It's biggest advantage is being able to use very cheap  power units such as Computer power supplies which usually end up at the local garbage tip. It's construction is whatever your mind can dream up.

A good friend of mine attached a large cuphook in his ceiling and hooked the Nichrome wire to it and heavy household wiring to power it. All driven by a computer power supply through a standard light dimmer. He could handle any length and thickness he could get through his door. He made a lot of money by taking orders for any thickness foam hobbyists asked him for. I certainly wish I knew where he purchased the massive sheets he uses, 50cm sheets are hard to find :) At least we discovered why he always hooked up his trailer whenever he drove the 450km to see his girlfriend.

I must admit the smaller hand held type cutters are far better for fine, shorter cuts. Also, if you can find out what the wire is they use which can be made into any shape and hold it whilst cutting, the hand held would be ideal. Very handy for cutting troughs in wings to run cables etc. or for cutting neat and clean holes in wings to place servos and other small items.

Unfortunately my swivel workbench with built in foam cutter I spent a week designing and building was relegated to the storage room downstairs when I was away in hospital. My wife informed me she needed more room for shelving for the numerous boxes of spare parts I've collected. I wasn't too happy when I arrived home and found it gone. I grew attached to having it rolled across my bed so I could use it for building models. Try manipulating 2 meter wingspan planes whilst laying flat on your back. It's somewhat restrictive, believe me. Possibly had I been mobile I would have designed a portable unit myself. Until then I'll stick to my bench model, if ever I manage to get it back where it belongs :(   ...   Stu

@madaquif sir,
Sorry for delay, was not at home.

With due respect i do feel that many of the responders to this thread have missed the heart of this bow!
There are dozens of designs on the net, that can do many things. Mine is not for 2m cores!

The USP of this one is simplicity, portability, and lack of dependence on anything external, like power supply wires or voltage regulators. I just didn't want (or need) them.
All i need/have is some 1/4"x1" baton, a few bolts&nuts, two springs from a bicycle stand, one used guitar E string, an old/puffed/retired lipo, a bit of velcro, a pair of 1' wires with a Deans/XT60 on one end, croc clips or bananas at the other.

Draws about 2.5amps if 3s connected to the terminals. I understand this is about correct for foam. If you need more heat, just hold the banana plugs closer together on the wire!
(Varying the wire length between the banana plugs is, by definition, a rheostat)

If its too hot, replace old 3s lipo with an old 2s lipo, i guess. Will try.

Thank you so much for responding Iyer sir.... :bow: :bow:


I have a request....please please don't call  me sir....m half your age and hardly have fraction of a percent of aero modeling knowledge that you have....

.....still learning    (:|~

That's noting to be ashamed of Madaquif, we all have to start somewhere. You just happened to start at the best time of all. So much is happening to our hobby and so fast as well. You may be a newbie today, but within a few years us oldies will be asking you how to use all that new fangled equipment.

Without newcomers any hobby will eventually die. It's people like yourself who will keep it alive. Happy flying to you.   Stu.

Hi Thanks for your information

May I know where I can get this nichrome wire

Thank you

Ashwath

No need for nichrome wire.
Its a guitar E string.

To answer your question digitalgowda. A good place is a fishing tackle shop if you happen to have one close by. It's used a trace wire in fishing. They use it on the end of fishing lines to stop the fish from biting through the nylon line or having the line part due to chafing against the fish itself. I'm a long way from the coast so I buy it from Ebay in 10 meter lengths.

I've had one length connected to my bench cutter and it's been under tension for 3 years and I can still get a tune out of it by plucking and putting pressure on the support arm :) Guitar strings are nowhere near as strong and Nichrome can be much thinner than a guitar string, this gives you much cleaner and quicker cuts, plus draws less current. But if there's nothing else available go for guitar strings, just make sure they aren't nylon wound or even wound strings, just plain solid strings, just don't over tension them.

Good luck and happy cutting. :)

Iyer sir ibuilt foam cutter with nicrome wire of 0.5 mm and use 3 to 12 volt dc transfermor as a powersupply but my wire dont heat more i use 90cm wire so ehat can i do to more heat 90 cm is to big?

@gaurang.1972
Your transformer may be too weak.
See the label. How many volts and amps mentioned for output?

You may have to reduce the length. Shorten it little by little while testing with a piece of thermocol.
Be careful not to burn your hand, as you cant see how hot it is.

Do you have a wattmeter?

Iyer sir it is 12 volts and 2 amp and sir ihave only multi meter no wattmeter

@gaurang.1972
Sorry for the delay. Was looking up nichrome data.
The wire i am using (60cm) needs about 2.4 amps at 12v.

Your wire (if it is 0.5mm) should have resistance of about 4.8 ohms for 90cm length.
About 2.5amps is required to heat it enough.
So a 12v supply should be enough, provided it has the capability to supply 2.5amps.

I suspect that your transformer is too weak for this. With a 2amp rating it may actually be capable of only 1.5amps or so. This cannot heat it enough.

Even reducing the length may not work, as this will reduce the resistance, and so it will try to draw more current, loading your transformer even more.

I think a larger transformer of say 5amp rating may be required.

Alternatively, like me, you can use a 3s lipo of say 2200mah, that can easily provide 2.5amps at 12v.

Thanks iyer sir i will try because i am going to build wing of guppy

I think my warning about use of LiPo batteries for a foam cutter is quite a bit late.

Yet, I feel it is relevant.

If you use an ESC as part of the wiring, it adds some measure of battery protection. However, in case of an accidental short circuit (Crocodile clips promote this) the ESC and battery are both at risk.

If you do not use (should I say misuse?) the ESC for this, the risk is of the battery getting over-discharged. If the voltage of any cell drops below 3.2 V, the battery is useless and possible dangerous.

Instead of LiPo, I would use an old car battery or even better, an old motorcycle battery (or two if 6 V). With some home-made fuse protection, this is cheap and safe.

Most battery dealers will sell an old battery for you at little more than the rebate they paid for, when they got in exchange when selling a replacement battery to a customer. Just check or get them to check that each cell is not totally gone.

Regards