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View Full Version : how to use variable pitch with a dd tail?


pmbou
03-21-2007, 12:29 AM
It's my first post. I have to say this is the best site I have ever seen for any hobby. Packed full of good technical info and good people too.

A little about me - I'm 31, I hadn't flown anything before, and my only rc kit was a turbo optima electric buggy I had when I was about 13. My wife 'doesn't get it' but I have 2 kids and they do, so we all voted and I get to be a kid all over again!!!

So I got a blade cp pro a month ago. The stock tail motor sucks, so I ordered the DD instead. I'm told that it will be great.

I narrowly avoided getting sucked into the hdx300 "upgrade". I thought it was a good way to fix the weak tail. I had the frame assembled before I saw the scathing hdx300 build thread. I turned around and returned the frame, and I'm sticking with the CP pro until I trex my way out.

I am also getting a gyro in this box of parts I ordered. Now, I was thinking... servos are cheap ($10). The plastic hdx300 variable pitch tail rotor is cheap ($13)... I like the efficiency of a direct drive tail but performance suffers since you can't power the nose left...

So, what if I use the dd motor to turn a variable pitch tail?
The problem I see is how to control the tail motor. In standard configuration, the 3-in-1 turns the motor off when turning nose left, while I want it to stay on at right or left and slow in the middle. I could simply hook into the main motor leads and bypass the 3-in-1 and gyro. I don't want keep the motor on full all the time if I can help it. Can I get a little esc and plug it into the separat gyro along with teh tail servo, and program it to do this? (but then both the motor and tail would respond to the rudder control and that might get real sensitive... oh boy)

Is this worth a try or not and any ideas how to do it for cheap?

Cheers,
Paul

Pinecone
03-21-2007, 04:45 AM
With a brushed motor you could just a add a resistor to get the tail speed you want. But with a variable pitch tail, you want the tail RPM to be pretty constant.

Rebuild
03-21-2007, 08:24 AM
You might consider a programmable heli Tx with Revo Mix.

pmbou
03-21-2007, 01:49 PM
I'm leaning towards getting a little esc for the tail motor that can be hooked into the throttle channel on my rx. That way I don't risk overdrawing the 3-in-1 as would be the case if I spliced right into the motor power leads.

I would love to get a revo mix tx, but I don't want to spend the money now while I'm playing aroudn with my blade.

I will get around to it a few weeks and post a pic.

eugeneo
03-22-2007, 07:10 AM
I've tried so many different combinations to make this heli stable. It now flies as good if not better than my Trex 450 SE.

1200 mah 20C 3 cell hyperion battery
370 brushless/ESC
Rear/Brushless with Trex 450SE tail (None of that belt drive maintainence crap)
Align gyro (upgraded on the trex..)
Metal swash
PCM reciever

Get rid of the PPM and 3-in-1, since you now have a high performace machine that will cause glitching no matter what you do.

The dual tail or direct drive are usless. Using a fixed pitch tail will never work well.

There's one thing that is tricky, you need to program a chip to read the pulse width from the throttle ESC and output it to the tail ESC with a linear rise to about 20 percent throttle. After that limit it at about 30 percent of the output. This lets the tail spool up and hit a constant speed.

If anybody is interested I will post a video

Buzzkill
03-22-2007, 10:45 AM
I'm interested. Please do! A Trex tail on a cpp?

pmbou
03-23-2007, 03:57 PM
eugeno,

This sounds like the hot ticket. I am a newbie noob so I have virtually no idea what you're talking about except the part about how well it works.

When you get a chance, pleae post more info with pictures. I am picturing a brushless tail rotor with variable pitch!! I did not know that they were already used by trex though.