2S Li-Po Hot Wire Polystyrene Foam Cutter

2 October 2018

My 'scroll saw'/'jig saw' type of hotwire cutter was simply the frame hotglued onto  a carton box. Yeah, well, it is easier and faster.

Then after playing for a bit, the guitar string broke and things went on hold until this arrives from Banggood yesterday:

Wire replaced, and plugged to the same 2s battery, the Kanthal wire sagged in the frame.
I took up the sag with the winged nut, and when cool, it was strung very tightly.
I don't know if this wire will be even shorter lived.
It seems this Kanthal wire runs hotter (that means I can lower the voltage? No point since I'm on 2S).

Physically, the wire is somewhere between the soft steel wire and the guitar steel wire. I think it is good enough to make pushrod wire ends. 

Next update will be for some control on the heat using these:

The female plug fits the adapter.

Don't like the smell of polystyrene. It seems this time it burns more polystyrene than the last time. Maybe that's because the cutting wire is now thicker.

12 September 2018

This setup limit my cut to about 10", but it should be enough for my purpose most of the time.
I am just glad I didn't buy a variable voltage DC power supply unit (about $100, 0-30V, 0-10A) because I have no alternate use for that and that will become clutter.

Here is the working combination. I tried it yesterday and all that matters is it worked:

Assembled from:

• Frame: Hacksaw frame (the tension of the wire is easy to adjust)
• Power: 2s lipo battery with balancer plug
• Wire: Fine Guitar string
• Miscellaneous:
• A matching battery plug (I don't like 'wriggly-iffy' contacts)
• Battery/Cell Checker that is plugged to the 2s lipo battery (to check that the lipo will not be discharged too low while under use)
• Bit of wire and soldering (for got electrical conductance)
• Velcro strap to secure battery to frame.

Apart from the guitar string and perhaps various bits which may not be re-usable or recycleable, the rest will revert to their original state and function on disassembly.

Transform it into a 'scroll saw'/'jig saw' type

Adapting the 'free-hand' hot wire foam cutter will need additional material:

1. Secure frame to edge of table at desired angle.
2. Small metal piece, perhaps a short length of wire or a useless key, can be fixed to the point where the wire touches the table will prevent the wire from burning the table's edge.

The table will double up as the foam work platform. The foam sheet rests on the table top as it is fed towards the hotwire. Although there is no platform extension to support the 'free' end, it should meet most of my needs. If I have to, I can go around this limitation by cutting half way and recommence cutting from the other end. To make 45 degrees cut etc, just secure the frame at the correct angle to the table.

This mode allows:

• consistent angle to cut edges
• using only 'top/single' template
• identical copies by cutting multiple sheets in one pass
• cutting in a straight line without template (use guides for foam sheets)
• making parallel cuts
• cutting cones and discs (think spinners and wheels)

Why do I consider carving foam planes?

1. Rounded or compound curves
2. Lesser glue is lighter
3. Lesser mass for small fuselages
4. Lesser work for small fuselages
5. Cheaper if foam is purchased (even though Popular selling polystyrene sheets at $10 which I think is strange)
6. Free if foam is sourced from throwaways
7. Strength and hardpoints:
1. tissue/paper/cardboard
2. wood/plastic rods/strips/pieces
3. glue/epoxy/tape
4. carbon fibre rods/strips
5. music wire
8. Surface Finishing: 
1. Bare (or with some sanding)
2. with markers or paint
3. Cover with tissue/paper/cardboard, markers and paint

SAFETY HAZARD

For safety's sake, it may be a good idea to do all foam cutting and sanding outdoors.

• heat can result in burns or fire
• toxic fumes

15 April 2016

(Was: Supplying power to Hot Wire Foam Cutter using a battery charger; Micro receivers and ESC)

My battery charger can power my hot wire foam cutter. This is the original IMAX, the one without the hot wire supply feature. I used it to charge my lipo batteries, thinking that NiCd, NiMh, Pb are legacy features and useless for electric RC. Glad I found a use for it, because now I charge my 1S lipo with a USB charger.

The charger was set to NiCd charge mode and between 3A to 3.5A. If I set any lower, my hot wire cutter doen't cut foam, whereas if I set it to 4A, I find the hot wire cutter goes through foam too quickly. When I set to low 1-2 A, the voltage displayed was about 2 V; 3A:8V; 4A:10V.

Whilst in use, the charger would sometimes go down to 0V and I have to wait with the cutter in the foam but not moving anywhere. I can continue only when the charger goes back to charging. Charging was terminated once when the charger thought charging is complete. The alligator clips, the pins and connecting wires were warm at 3.5A.

My hot wire cutter is a hacksaw frame, it is not all-metal, the handle being plastic. I like the winged nut very much, because I can attach/detach and tension the wire easily. The two connection points are at the handle so I don't need to cut my leads.

I used the thinnest guitar wire because it is suggested on the internet and is available here. I strung the wire tautly, until it gives a high pitched sound when plucked. I like to think that doing this prevents the wire lagging behind when cutting foam causing scalloped cuts. The cutting length of my hot wire cutter is short, but it is convenient to use, and when not using, to store out of sight.


My hot wire cutter can cut through denser blue foam and the kerf is small as can be seen in this intricate jigsaw test piece in compressed foam/depron.

14 April 2016

I was de-cluttering my room the night before last ("Need Space") and found some small lipos. I have had them for some time now and wondered if they are any good. So I connected them to my blue IMAX copy charger, the one with hot wire output, and after a few lipos, smoke came out of the charger. Too bad but I have to threw that charger away.

My two other chargers do not have this hot wire output feature. The last time I tried, using Pb and Lipo didn't work, but this got me thinking that there must be many others like me attempting to supply power to their hot wire cutter using their chargers for that purpose.

I did an internet search and it seems that you can do so in NiCd-Charge mode. An article by Flite Test wrote that the author did just that by setting up the Amp at 2A and it was about 10V.

I think I will try that with my remaining IMAX charger.



Tito brought this small 0.6gm Flysky receiver to my attention. I don't know if I should choose the 8 channel or the 7 Channel PPM version. I know my Flysky transmitter is 9 channels, but I don't need so many channels, however the board is cheap, about $15.

Using this board (instead of the all-in-one WLToys receiver board) means I need an external esc for motor control.

I am ambivalent to the choice of brushed or brushless motors. My criteria for choice is availability and affordability. So what if the 8.5mm coreless motor needs replacing? So far I haven't needed once. My main consideration is whether I can find small ESCs for my purpose.




From Banggood, this is the smallest and lightest brushed ESC that I can find. It is only 2 grams. If I were to use this, say to power multiple brushed motors since it is 5A rated, I still have a big problem here, I can't imagine using this car/boat type of ESC on a plane because I don't want REVERSE!  I asked around my friends for a workaround. It is possible if you have a programmable transmitter, nobody has a simple solution to modify the ESC.

The smallest and lightest brushless ESC I have is 3A from Hobbyking and weighs 1-2 grams, but I am wary because I have already burnt out one such ESC. And it wasn't cheap.







In the quest for cheap and good brushed esc I did an internet search and found an article posted in 2002, the author modified a servo board and used mosfets and resistors to make an ESC: http://trebor69.tripod.com/speedcnt.html
Now this seems to be ideal because it is for forward use only as highlighted by the author. I hope it is proportional though and not a switch type.

I found my Walkera V120 helicopter has brushless main and tail motors, it has two ESCs to power the motors. I have not 'touched' the Walkera helicopter for years, because my helicopter flying skill then was quite bad and stopped trying when I got my first WLToys V911. Maybe I should try again? I remember I paid about $200 RTF, this price included a fancy transmitter.

For convenience though, I would use WLToys' components.