Modeltech .25 Extra 300 conversion
 

Guys


Here are a few pictures and notes on my Extra 300 conversion using the smaller Modeltech version.

Jeti 30-3 motor Direct Drive
Jeti 70 Amp Speed Controller w/bec for 12 cells
9x7.5 and 10x6 props
12 cell 1800 mah Hecells and 3S1P 2100 mah 20C Kokam lipo
Standard servo in the wing for alierons and elevator
Bluebird Micro servo for rudder

StephenT

RE: Modeltech .25 Extra 300 conversion
 

Since I had worked with this plane before I knew I had to start the conversion with making the motor, engine mount and cowl line up correctly.

To do this I first removed the wooden firewall extension.

RE: Modeltech .25 Extra 300 conversion
 

Next you need to center a Great planes .40 MM over the hole in the remaining firewall. The Jeti motor is then strapped inplace with a hose clamp. The back of the motor is one inch from the MM base with the adjustable mount closed all the way. The motor can be slid fore and aft to get the alighment you prefer. This will center the motor with the cowl when you attach it. Consult the airplane's manuel for cowl attachment.

RE: Modeltech .25 Extra 300 conversion
 

Flip the fuse over and remove the throttle servo mounting tray and cross brace. This reduces a small amt of wt. and makes room for the battery.

RE: Modeltech .25 Extra 300 conversion
 

This pic shows the prop, prop adaptor speed controller and some of the batteries used to power the plane.

RE: Modeltech .25 Extra 300 conversion
 

This pic shows the canopy painted yellow and mounted in place. The plan was for a yellow canopy and spinner. Can't find the right size yellow spinner yet so I will use a red one for now.

RE: Modeltech .25 Extra 300 conversion
 

The rest of the plane is built following the included manuel with the exception of using a micro servo for the rudder. The listed CG is met with the Hecell pack all of the way back to the rear of the cockpit. Cinch it in with velcro like strap. Place the Kokam pack behind what is left of the throttle tray fuse brace. Strap it the same.

RE: Modeltech .25 Extra 300 conversion
 

Ready to fly, the plane fits fully assembled in the back seat of my Sport Trac. More later. I gotta fly before the post Frances winds pick up.

RE: Modeltech .25 Extra 300 conversion
 

Battery placement.


here are some battery placement pics.

RE: Modeltech .25 Extra 300 conversion
 

Couldn't get any inflight photos this wknd. I used up all the memory taking pics of my son flying. When it came time for him to be the photographer, the memory was full.

RE: Modeltech .25 Extra 300 conversion
 

Hurricane morning at the Flying field.



Go Extra. Go fast. Very fast. Wrong setting on camera.

RE: Modeltech .25 Extra 300 conversion
 

Guys


I found a new power source for the Extra. A ten cell Nimh 1950 mah battery good to 40 Amps continuous draw. I wanted a 12 cell pack but, it was not available. Great climb, very fast with same weight as 12 cell Hecells that only handles 26 amps. Vertical is limited. Great inverted flight. Loops, rolls, very fast landings though.

RE: Modeltech .25 Extra 300 conversion
 

Guys


Tried my E-Magics 4S3P pack in the Extra. Verticle was just a hair shy of unlimited. Way to fast. I need a flatter longer prop, but that would mean longer gear. Maybe later. I am going to stick with NIMH packs with this plane for now.

RE: Modeltech .25 Extra 300 conversion
 

Guys

My plane always seems tail heavy; so, I moved the Battery forward a little. It actually flew worse. Some times it snap rolls when I try to loop. Low rates are better. I am putting the battery back to the original place.

RE: Modeltech .25 Extra 300 conversion
 

Guys



I am going to go to a 11x6 yellow prop to see if I can slow this thing down.

RE: Modeltech .25 Extra 300 conversion
 

Keep up the good work and keep us informed, I like these electric conversions.
Joe

RE: Modeltech .25 Extra 300 conversion
 

Joe

Thanks for the comments.

I have reduced the throws on the Extra and moved the battery forward. Jim at the LHS said that extreme throws cause this snap effect when trying to loop. He said to move the battery forward also. I'll test it on Wed or thur. It's back to work tonight for 12 hours of healthcare fun.

RE: Modeltech .25 Extra 300 conversion
 

Guys

I moved the Battery even futher forward. The front of the pack is to the front of the wing craddle. There is no snapping in a loop now. Landing are still too fast for me. Good inverted flight.

RE: Modeltech .25 Extra 300 conversion
 

Guys

The Extra seems to be balanced and trimmed out well now. It is my new windy day flyer. On a calm day it uses up too much runway. Of coarse that may be the pilot.

RE: Modeltech .25 Extra 300 conversion
 

I have done about all I can with this set up. I am thinking of putting in the brushed Endoplasma system from my Avistar to see if it will work.


It will be something to do at low cost. I will use what I have. A seven or eight cell 3000 nimh weighs about the same as a 10 cell 1950 nimh.

RE: Modeltech .25 Extra 300 conversion
 

Help


Can some one run the numbers in Moto Calc

Endoplasma motor
10x8 prop
2.5:1 gearing
7 cells GP 3300
8 cells GP 3300

RE: Modeltech .25 Extra 300 conversion
 

exelent thread! lot´s of info and pics :) nice plane too

RE: Modeltech .25 Extra 300 conversion
 

guys



I was flying the Extra yesterday when I had a hard landing that knocked the wing out of the saddle. The plane was ok. I taxied it wingless back to the pilot station, got the wing, flew again.

RE: Modeltech .25 Extra 300 conversion
 

guys

About a year ago I bought a twin geared speed 400 drive from Dymond. When it arrived I couldn't find anything to use it in. Now I want to try it in my Extra. I static tested it w/10 cells and got 250 watts w/11x7 prop. The Extra weighs 3.25 pounds. Testing it tomarrow. Posting pictures before also. Will it fly or burn up on take off?

RE: Modeltech .25 Extra 300 conversion
 

Motor: Kyosho EndoPlasma 16T; 3785rpm/V; 2.5A no-load; 0.022 Ohms.
Battery: Gold Peak GP3300; 7 cells; 3300mAh @ 1.2V; 0.005 Ohms/cell.
Drive System: APC 10x8 Electric; 10x8 (Pconst=1.08; Tconst=1) geared 2.5:1 (Eff=95%).

Batt Amps = 40.0
Motor Amps = 40.0
Motor Volts = 6.9
Input (W) = 275.3
Loss (W) = 71.4
MGbOut (W) = 203.9
MotGb Ef(%) = 74.1
Shaft Ef(%) = 60.6
Motor RPM = 21650
Prop RPM = 8660
Thrust (oz) = 34.9
PSpd (mph) = 65.6
Time (m:s) = 4:57


Motor: Kyosho EndoPlasma 16T; 3785rpm/V; 2.5A no-load; 0.022 Ohms.
Battery: Gold Peak GP3300; 8 cells; 3300mAh @ 1.2V; 0.005 Ohms/cell.
Drive System: APC 10x8 Electric; 10x8 (Pconst=1.08; Tconst=1) geared 2.5:1 (Eff=95%).

Batt Amps = 46.0
Motor Amps = 46.0
Motor Volts = 7.6
Input (W) = 350.8
Loss (W) = 96.0
MGbOut (W) = 254.7
MotGb Ef(%) = 72.6
Shaft Ef(%) = 57.7
Motor RPM = 23319
Prop RPM = 9328
Thrust (oz) = 40.4
PSpd (mph) = 70.7
Time (m:s) = 4:18