Category Archives: RC

Calculate RC Helicopter Head Speed

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


Going to put together a list of what I would need to build a quad rotor that can do some lifting. Quad built using motors on each corner.

Inspired by the stability of this quad. Video showing AP stability shown here.

LED Strips from HK to light the 4 corners.

Motors (listed in this post) Turnigy 2209. Going with this 20L-22 motor

Turnigy 18A speed controller from HK.

3.5mm plugs from HK

HK450 heli tail booms. Carbon Fiber ones, and Aluminum ones.

Boom holder.


Props. Get them here?

Some more details.

Tricopter controller

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.

Variable pitch Quad copter (was tricopter)

After starting a few threads on RC Groups forums, and giving the design some thought, I’ve decided that the way I will be starting is with a quadcopter (was tricopter).

Change to a quad was dictated by the design of the frame. I couldn’t come up with an elegant and simple solution to design a body using few fabricated parts. A quad design uses much fewer fabricated parts. So far I only have to drill some holes in some aluminum angle. Simple enough.

I will use 3 tail rotors (HK-500GT Metal Tail Holder (Align part # H50073)) since they are pretty cheap, at $13.  That’s about the cost of one good prop.

Using HK450 tail units instead of the hk500 tails. The 450 has cheaper components.

One central motor will drive the whole system, which will be located in the center of the craft, and will drive the rotors using the belt system that comes with the tail rotors.

No rotation mechanism will be used on the rear rotor, as I will use a few vanes, and adjust their angle to direct the thrust. This should simplify my build considering, and it won’t interfere with the belt drive system.

I will eventually duct the props, for increase efficiency, and safety (so failed blades won’t kill anyone). Speaking of ducting, there a great thread here on construction of a ducted propeller build. Need to finish reading.

Found some interesting info on propsizes and thrust produced here. Need to give it a look.

Interesting: variable pitch heli tails not as efficient as a prop…here.

Another interesing post to read here, regarding variable pitch rotors.

Another Hong Kong shop for heli parts, here.

Forum post on SAFE lifting weight of different sized RC helicopters. Did a plot, and the trend seems to be exponential.

No 205mm blades, but from this, I’d estimate a safe lifting weight of 0.42lbs (190g). Not quite what I expected.

Servo choices: I looked at the recommended servos for a 250 and 450 sized helis. They seem to recommend similar size servos for both copters. 1.8Kg-cm servos seem to be recommended.  So 3 servos should be able to put out 5.4Kg-cm of torque. I am also looking for a digital servo, so that raises the price a little, but I think I found a 3.5Kg-cm digital servo at just over $11. Less torque, but I think should be adequate.

I should use this servo torque calculator to estimate a torque, to see if my choice is correct.

Torque tube upgrades: Tarrot Torque tube upgrade

Tricopter with full collective on all corners

For the version 3.0 of the copter, I am planning on getting 3 sets of the HK-T250 CCPM Electric Helicopter Kit which are only $30 each.

I will need 9 servos (3 servos per rotor swash plate) , and these look great value at $9 per pack and had great reviews. Turnigy 1800A SERVO 8G/1.7KG/.10SEC (3-PACK)

The microcontroller will have to control the speed of 3 motors, as well as 9 servos. Initial thoughts on this seem to tell me I may need 1 processor per rotor (controlling one rotor motor and 3 servos).

So 3 processors (one per corner) and then a 4th processor collecting data from IMU, and giving instructions to the other 3 controllers.

Or maybe use an ATmega1280 (Arduino Mega) which has 54 I/O channels, 14 of which can drive PWM. I would only ned 12 PWM channels.

Tri-rotor cost brakedown

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:

Item Amount Single [Euro] Total [Euro]
Arduino Pro mini (m328p, 5V 16 MHz) 1 16 16
Accelerometer Breakout Board ADXL322 1 25 25
Gyro Breakout Board ADXRS610 3 54 162
TriGUIDE PCB (DIY) 1 11 11
Motors FC28-22 3 4 12
ESC (I²C) 3 40 120
…or standard ESCs in combination with my I²C->PWM converters
Props EPP0845 2 3.2 6.4
Servo Bluebird BMS371 1 6.1 6.1
USB -> serial converter 1 12 12
Rec-Enc (recommended) 1 30 30
Frame 1 ? ?
Lipo battery 3S 2200 mAh 1 ? ?
TOTAL: 400.5

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…utrunner_750kv
$10.95 total $32.85

The review on 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…d_programmable)
$9.23 total $27.96
BEC X1…oise_Reduction

speed control programmer X1…ogramming_Card
$6.95  This just makes things easy, its worth $7

Battery X? this battery works great.…00mAh_3S1P_20C

3.5mm connectors X2…idproduct=4136
$4 Total $8

Gyro X3…Digital/Analog)
$24.79 total $74.37

Yaw gyro X1…zo_Gyro/Futaba

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

Volt warning A must have!!!!…ery_Monitor_3S

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.

See diagram here:

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.

GPS based Camera Tracking

The camera (on a gimbal) will need to track  a subject some distance away.

The subject will have planted on them a GPS receiver with a XBee radio, and the camera will have a GPS receiver with a XBee radio, and controlling the camera rotation.

The sender unit (on the target subject) will be powered by a Arduino Pro microprocessor, sending GPS data through the XBee radio. an XBee radio hooked up directly to a GPS unit. Here’s how it’s done. Very slick.

The receiving unit (mounted with the camera) will also be powered by a Arduino Pro microprocessor. Using it’s own GPS unit, and the signal from the target GPS unit, a direction will be calculated and used to aim the camera, and constantly update the direction it is aimed so it always points towards the target. The receiving unit will also need to power 2/3 servos to rotate the camera and keep it aimed properly.

Parts List in order of purchase:

First, need just an Arduino board with one GPS. Learn how to control the servos and how to access the GPS data. Build a rig to allow the

Arduino Duemilanove USB Board : CND$31.77
Antenna GPS Embedded SMA
: CND$12.68
Venus GPS with SMA Connector
: CND$52.99

Total : $97.44 +S/H

Then get the other GPS unit and 2 XBee units.

Antenna GPS Embedded SMA : CND$12.68
Venus GPS with SMA Connector
: CND$52.99
XBee PRO radio
: CND$27.30

Total : $120.27

Bookmark list:

List of good sites to keep bookedmarked for future reference.

How to hook up a GPS to an Arduino unit.

RC stuff

OSD for RC aircraft.

Cheap 2.4Ghz radio

Control RC from PC

Comparison of Quadcopter control boards:

UAVP Platform

UAVP Flight Controller + 5 Sensors (ADXR) : US$407.50

UAVP Flight Controller + 5 Sensors (MLX) : US$405.50

Arduino Platform

This is the current shopping list for the Quaduino:


Sum: $51.90


Sum: $313.75


Sum: $6.40


Sum: $132.40

Total sum: $504.45

RC Gear

  • 1x PPM compatible receiver
  • 1x Tramsmitter