Quote from: Pikle6 on May 26, 2009, 06:23:25 PM
try using a voltage transformer which has amp adjustment and keep increasing the amps until you get the right amount of heat. increase amps slowly

Ok.. just to make it clear,... You cannot increase just the amps without decreasing the resistance of the wire (or) increasing the voltage. (I=V/R)... A wise man named Ohm discovered that long time ago!... . So, I would say you better increase the voltage until you get the right amt of heat. And make sure your transformer output current is rated high enough (~5A) for this kind of job..

i used a 12v 2amp transformer and no rectifier(diodes and capacitor) and the bought "e" string for guitar (which is the least dia string- so higher resistance hence heating takes place here). i had a 1.5" dia pvc pipe, fixed a 0.5 feet plastic rulers perpendicular to the ends of the pipe and fixed it firmly using tapes. then tied the string between these rulers as ends. result- i now cut thermocole as a cake

For a good variable heat foam cutter, here is a best link for scratch building...

http://www.instructables.com/id/Hot-wire-foam-cutter/

MEROG

Quote from: akash on May 26, 2009, 10:42:45 PM
i used a 12v 2amp transformer and no rectifier(diodes and capacitor) and the bought "e" string for guitar (which is the least dia string- so higher resistance hence heating takes place here). i had a 1.5" dia pvc pipe, fixed a 0.5 feet plastic rulers perpendicular to the ends of the pipe and fixed it firmly using tapes. then tied the string between these rulers as ends. result- i now cut thermocole as a cake

Can you post some pictures of the cutter, don't the wires also cut into the plastic rulers?

good question... the simple trick is to solder the wire with the string between the rulers(inside) and not outside. so the heating occurs between the soldered points. dont confuse with the 2 wires which i soldered, they are just parallel. i made this arrangement to allow more current to pass (as i dont have a bigger dia wire).

update,I have finished building the wing n covered it with cello tape plus added small pieces of fiberglass that i had at the wing center near leading n trailing edges to give it a better strength, i decided to use a readily available fuse that i built for a 1.5 HLG glider long time back.Change of plans the power setup will be a pull type with slight difference.

see pictures

guys, from now on the build will get slower sorry i want to finish the long pending rc project that i have taken up .

sahil

okay guys stay tuned i will be finishing the model today

sahil

update, i have decided not to use balsa fuse instead a EPP fuse  motor mount is fixed,servo press fit n receiver guard, antenna wire cover all done. Hopefully i will be finishing the entire model today and will be left with only the ESC part.

some pictures,

update, added rubber band mount

Quote from: sahilkit on August 19, 2009, 11:59:53 AM
update, i have decided not to use balsa fuse instead a EPP fuse  motor mount is fixed,servo press fit n receiver guard, antenna wire cover all done. Hopefully i will be finishing the entire model today and will be left with only the ESC part.

some pictures,

Hi, please confirm.......this is an actual EPP fuse of some plane or is some EPP packaging of DVD Player or something 

It looks like EPS  packaging of something to me. Clever use 

Rao

its EPP from packaging of a blue ray player 

sahil

Although you have changed your design, but if you were to use the balsa fuse you were better putting a block of wood to anchor the motor post as the pull from motor coupled with the leverage due to height would sure at some point of time yank the post off the base.
Also just wanted to warn you that you should consider appropriate up thrust on the motor at that height from the fuse, if the motor was mounted zero zero you would find that the craft will pitch down severely when you open up the throttle.   

Quote from: flyingboxcar on August 19, 2009, 09:26:18 PM
Although you have changed your design, but if you were to use the balsa fuse you were better putting a block of wood to anchor the motor post as the pull from motor coupled with the leverage due to height would sure at some point of time yank the post off the base.
Also just wanted to warn you that you should consider appropriate up thrust on the motor at that height from the fuse, if the motor was mounted zero zero you would find that the craft will pitch down severely when you open up the throttle.   

Could you pls explain the up/down thrust that should be used when mounting these motors. A bit of down thrust is what is recommended when mounting the motor on the nose, here we seem to need up thrust instead.

Quote from: sahilkit on August 19, 2009, 08:45:26 PM
its EPP from packaging of a blue ray player 

sahil

Another Eg. of "Best out of waste".........really appreciate    .
I will try to search some more for me

QuoteAlthough you have changed your design, but if you were to use the balsa fuse you were better putting a block of wood to anchor the motor post as the pull from motor coupled with the leverage due to height would sure at some point of time yank the post off the base.
Also just wanted to warn you that you should consider appropriate up thrust on the motor at that height from the fuse, if the motor was mounted zero zero you would find that the craft will pitch down severely when you open up the throttle.

yes capt. i had a similar issue with my air boat,can you explain the science behind it please and this whole process of changing design was to prevent damage to the prop/motor shaft but i have given up due to CG problems so i have changed it to ordinary front motor mount with prop saver n rest is in gods hand 

sahil

Hey Sahil...

Come on hurry up man, I wish you should fly first than I could, with my Scratchy 'Indian Trainer'!

Dying to see you fly.....//MEROG

QuoteAnother Eg. of "Best out of waste".........really appreciate   Clap Clap Clap.
I will try to search some more for me

well i had this lying around in my room, all of a sudden i see a potential pod n rest you know  

sahil

its raining like hell in hyderabad since last night n still raining........hoping tomorrow will be sunny,clear sky,clam no wind.....so that i can maiden the model.

sahil

update, had some problems with the ESC but got it working need to fine tune the LVC values and capt. can you please explain the motor angle thing 

The "motor angle thing"   

When you look from the back of the plane to the front, point the motor 2 or 3 degrees down AND to the right.

  anwar i was referring to this post by capt.

QuoteAlthough you have changed your design, but if you were to use the balsa fuse you were better putting a block of wood to anchor the motor post as the pull from motor coupled with the leverage due to height would sure at some point of time yank the post off the base.
Also just wanted to warn you that you should consider appropriate up thrust on the motor at that height from the fuse, if the motor was mounted zero zero you would find that the craft will pitch down severely when you open up the throttle.   

yeah the motor angle thing 

Sahil and Capt

I don't know whether it is right of me to interfere at this stage... Capt has to have his say about what he meant.

Sahil, I believe now you are not going with the post mounted motor concept right ? If you are not, then the motor thrust should be directed a few (2 to 3) degrees  down and to the starboard side (i.e. to your right as looking from the cockpit forward). This is to counter the reaction torque of the motor trying to pitch the plane to the port side ( opposite of starboard) and up

I could add the following in explanation of what I think Capt meant:

With the post mounted motor, the thrust line is above the wing. Since the wing is what is holding the whole plane, its cg point tries to act as a fulcrum and the moment (thrust x moment arm) tends to pitch the nose down. To negate this tendency, perhaps, Capt said that the thrust line should be modified to reduce the moment arm, by giving a certain amount of upthrust. (moment arm is the perpendicular distance between the line of force and the fulcrum point)

Saju

OK Guys,
How does one get to measure the 2 or 3 degree shift while mounting the motor? Its all good when its on a drawing board, but in applying the principle, what is one supposed to do?

Pankaj