In order to calculate your RC helicopter head speed, there are 4 things you need to know:

1. The number of Teeth (T) of your motor pinion. If you set up your RC helicopter yourself, you should know that by heart. If you bought the RC Helicopter RTF (ready to fly) or someone set it up for you, just count the teeth of your motor pinion. It is a lot easier than counting the teeth of your main gear.
2. The number of T of the main gear. This is easy to find – just count the teeth on your main gear. Well, not that easy – just try it, you’ll know what I mean. I get a different number every time I count it. Again, you may find the number of your main gear T on the owner manual.
3. Motor kv – the rpm (head Speed) produced by a motor per volt applied. You should be able to get the motor kv from the motor specification sheet.
4. Voltage: This is the voltage of your battery. You may get this information from your battery specification sheet or label.
5. Efficiency rate: This is the percentage of your RC helicopter motor efficiency when you are flying with your set up. It is the norm to use 80% (.8) or 90% (.9) depending many factors though you run 100% on your throttle curve.

As it was said earlier, the result would only give you a rough estimate of the head speed. A better way is to use a tachometer to measure your RC Helicopter head speed.

Estimate Head Speed = (Motor kv * Battery Voltage /(Main Gear /Teeth of Pinion)) * Efficiency Rate

I’ve decided to use William’s tricopter controller boards for my own copter.

Reasons being that I’m using 3 rotors, and that the code is written in basic, so that will be easy for me to edit.
I don’t plan on starting with the full IMU cube. Just 2 gyros will do for a start, and I will add on later. Probably a bad idea not to use the whole cube… should just bite the bullet, and make my life simpler, since the development of this copter is secondary to the platform I am after.

Also Will’s code will not dirrectly work on my machine, since I will be adjusting the pitch on the 3 corners, not the motor speed. And the servo that he controlls, will be used by me to control the main motor speed.
These modifications will be made to the code when I get to that stage.

UPDATE 01Feb2010: Kinda thinking I should spend my money on a Arduino controlled copter, mainly since that’s the direction I will be heading into in the future anyway, and this way I can totally reuse all the components in the future.

Cost breakdown for a tricopter from this thread:

This uses a Arduino CPU. The asselerometers and gyros are the expensive bits. Look for cheaper alternatives.

The Rec-Enc I can’t find. Look at this thread for a PPM converter. They use this converter priced at reasonable $25.

Read this for CCPM mixing on the Futaba 6ax

Tricopter build. Uses only a heli radio, and gyros. No control board. This is the one to try and build, since it’s simple. I can use the arduino board to do the CCPM mixing which the Tx would normally do.

Updated Cost breakdown:

DT 750 motor X3 http://hobbycity.com/hobbycity/store…utrunner_750kv
$10.95 total $32.85

The review on Hobbycity.com rated this motor at putting out 40oz thrust. 3 of these would put out 120oz or 3.4kg pf thrust. That’s HUGE! Should be more then enough for me.

You can use any motor in the 600-1000kv range. The lower the Kv, the more resolution each step of the speed control will give you. Motors over 1000 Kv are more difficult to make stable. That said, some have used ducted fans and made it work.

Speed controls X3
http://hobbycity.com/hobbycity/store…d_programmable)
$9.23 total $27.96
BEC X1
http://hobbycity.com/hobbycity/store…oise_Reduction
$7.83

speed control programmer X1
http://hobbycity.com/hobbycity/store…ogramming_Card
$6.95  This just makes things easy, its worth $7

Battery X? this battery works great.
http://hobbycity.com/hobbycity/store…00mAh_3S1P_20C
$10.99

3.5mm connectors X2
http://hobbycity.com/hobbycity/store…idproduct=4136
$4 Total $8

Gyro X3
http://hobbycity.com/hobbycity/store…Digital/Analog)
$24.79 total $74.37

Yaw gyro X1
http://hobbycity.com/hobbycity/store…zo_Gyro/Futaba
$23.95

Better and cheaper yaw gyro is the EK2-0704 from ebay. only $12!

Volt warning A must have!!!!
http://hobbycity.com/hobbycity/store…ery_Monitor_3S
$4

This is $185, you still need wire, battery plugs, a servo.

——————

May have just made the build a little cheaper. Only 2 gyros required, and one headying (yaw) gyro. Need a couple of V-Tail mixers which are dirt cheap at $2.95.
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6321

See diagram here: http://www.rcgroups.com/forums/attachment.php?attachmentid=2934020

This would bring the total down to $160 (plus materials to build the frame, say $30 in wood at the hobby store)

To do CCPM mixing, I could use one of these. It will eliminate the yaw gyro, so the price is right.

http://www.amainhobbies.com/product_info.php/products_id/27017/n/Ace-R-C-Heading-Lock-Gyro-w-E-CCPM-Mixer-TG6100M