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My Blitz Avro 90!

My Blitz Avro 90 flying in Windsor Great Park Flying in Windsor Great Park - November 2007

Heli Related Electronics Projects

High Performance 800 degree/s Gyro Project

The photos are of a prototype high performance helicopter tail gyro based on the Silicon Sensing Systems Ltd CRG20 sensor. This device varient used here supports a maximum pirouette rate of 800 degrees/second and features built in temperature compensation. It also has a fully digital interface implemented as an SPI bus (i.e. no explicit analogue to digital conversion is required).

Most of the required firmware has now been developed by Martin and myself, and we have just started flight testing. This is where we discover if our grasp of DSP, PID control theory and bearing tracking algorithms are actually any good! So far the gyro is working extremely well.

The "flying prototypes" are constructed on a small surface mount PCB - See the photos below. These prototypes are approximately twice the size as a Spartan ds760. Once the design is proven we'll shrink it down by about 60% and house it in a proper case.

Gyro Prototype

Various Mods

Flashing Firmware

Bug Fixing...

An Old Trex - Test Rig!

Partially Mounted

Flying Prototype #1

Flying Prototype #2

We're very excited about this project as it has been a lot of fun to develop, and we are expecting extremely good performance!

Various Gyro Test Videos

First Glow Powered Flight...

This video is of the first flight on an OS37 powered Century Hawk 30. We used this helicopter as it's old/expendable and no longer really flown, as such it has now become our dedicated test machine.

We'd not flown this helicopter for a while, and had forgotten how under powered and sloppy these old 30 sized helis can be when compared to 50s and 90s. Nevertheless it will make a useful test bed as so far the gyro hasn't been flown on anything that generates any real level of vibration.

Hawk Test Bed

The Prototype

Original Test Bed

450Pro Test Bed

The gyro worked extremely well, although it was slightly let down by the twistable torque tube currently fitted to the model. This need replacing with something more rigid as we could hear it winding and unwinding in flight!

CRG20/PinPoint 900 degree/s Update - August 2013

After a break of a few years we've decided to try and improve the gyro. This time round we re-wrote the firmware in C and have now incorporated many refinements to the original control loop.

It is now much improved as can be seen from the following test video!

We are only using the 300 degree/s variant of the CRG20 as we had accidentally damaged our 800 degree/s part! After this flying session we made a number of updates to the control loop as the gyro's hold wasn't as good as it should have been. Part of the problem was due to the sensor saturating at 300 degrees/s which is really too low for 3D flight with a model heli.

Bolstered by our success we've now redesigned the hardware to use a CRM102 gyro, a member of the Silicon Sensing PinPoint family. These gyros are related to the CRG20 range with the CRM102 and CRM202 having been specially vibration hardened and adapted for use in model helicopters (As used by Futaba, Mikado and Spartan in their fly-bar-less products).

Gyro v2.0


Flight Testing

As of the end of October 2013, the old CRG20 codebase has been ported to the new design. The CRM102 has been successfully temperature calibrated (via a dimmable Halogen lamp, fridge and freezer) and now works well, although it's not quite in the same league as the CRG20. We've done battle with gyro's SPI interface and the slightly odd but now understood relationship between its status byte and message checksum...

Our initial flight tests have been extremely encouraging. The gyro has an extremely consistent pirouette rate at low and high angular speeds. It doesn't drift or whip and appears to be well behaved across the various ranges of its control loop parameters.

The gyro and its current firmware is performing beyond our expectations and has since had many aggressive 3D wring-outs, we are very pleased!!

The DigiBar Flybarless Controller v1.0

Below are some photos of the DigiBar v1.0, it's a flybarless controller I'm developing with Martin. This hand assembled PCB is our first working prototype, future version will almost certainly change and will be considerably smaller. The firmware is written in C but needs to be debugged now that we have a flyable prototype.

The DigiBar is heavily influenced by our successful tail gyro design as described above. The hardware consists of three orthogonal vibration hardened PinPoint sensors (manufactured by Silicon Sensing) and is powered by a Microchip dsPIC33E processor.

The initial firmware will allow maximum yaw rates of 900 degrees/s and cyclic rates of up to 450 degrees/s. However the hardware supports rates up to three times these values should they be required. The unit also implements pirouette compensation for the cyclic controls so should fly extremely well.

Initial Prototype

Calibration #1

Calibration #2

The gyros need to be temperature calibrated in order to compensate for bias variation over temperature. For the prototype this was done using a dimmable Halogen lamp, a fridge and a freezer... This calibration was performed for increasing and decreasing temperatures in order to take account for any hysteresis (most gyros exhibit this to differing extents).

Ready for Testing

450 Installation #1

450 Installation #2

It Works!!

It works!! After many test hovers and tweaks to the control loop we decided to take it out to the flying field for some proper testing... It has a few rough edges to sort out but still flew extremely well! No unwanted high frequency cyclic oscillations, very stable and locked in! We are very pleased!

The above video shows the DigiBar in action with pirouette compensation enabled, improved cyclic lock and we've also added a pitch to elevator pre-compensation feature to smooth any elevator wobbles that can occur with aggressive pitch changes.

The DigiNav Controller v1.0 (Auto Pilot)

Gyro Calibration

Finished Assembly


Now ready for flight testing!

450 Installation

Up Close

GY401 to 9251/9256 or BLS251 Adapter

I designed this unit to sit between the GY401's output and the tail servo. The unit simply converts from a 1.52ms to a 760us centered pulse stream, with an output frame rate fixed at 333Hz.

The converter does not expect any particular input frame rate so could be used with many other gyros that support standard pulse width servos.

The unit also provides a means to set each travel end point for the tail servo, a feature missing from the GY401 (it only has the facility to either increase or decrease the overall travel, so with asymmetric tail setups one direction often doesn't get the maximum throw that it might otherwise achieve).


Assembled PCB

Open Case

Finished Unit

With Gyro

Circuit Diagram

PCB Top Layer

PCB Bottom Layer

Setup mode is entered by powering up the device with the push button held down. Maximum mechanical end points can now be located by using the rudder input in combination with the push button. As the rudder stick is operated, the servo will slowly advance or retreat in the particular stick direction, with centre stick causing it to halt at its current position. The software will force you to set each end point independently. Once a given limit has been found operating the push button will store it permanently. After the second end point has been stored the unit exits setup mode and begins operating normally.

If during flight the unit suffers a brown-out it will flash the LED, or if the unit is reset as the result of a software problem the LED will illuminate permanently, this second type of reset should never occur! Errors are persisted across power cycles and must be cleared by operating the push button.

Installed (R50SE)

Just Flown!

The unit is based on the 16F628A PIC microprocessor and the software has been developed in assembler using the free MPLAB development IDE from Microchip. The complete assembler source and MPLAB project files are available here:  62k

In circuit programming is achieved via ISCP (4 pin header on top left of the PCB). Power from the programmer is also required and needs to be supplied to the unit via either the servo or gyro connector.

A full parts list is available here: parts list 2k

The Gerber files required to fabricate the PCB are available here:  5k

How to Dye Your Main Gear Black

Black gears don't get dirty!

To dye Nylon or Delrin gears you can use Dylon (UK) or Rit (US/UK) powdered dye. When using Dylon, only use the "Multi Purpose" dye, the other types will not work!

To carry out the dyeing I used a cheap slow cooker (Argos in the UK sell the one shown below for ‎£9.99). Or alternatively you can just use an old sauce pan. I decided to use a slow cooker as I expected the dyeing process to take a long time. Simmering a sauce pan on your cooker for 10 to 12 hours is probably going to get you into trouble...

$15 Slow Cooker

After 20 Mins

After 12 Hours

An Original

The dyeing solution in the slow cooker consisted of 10g of Dylon and 120g of Salt added to 1L of boiling water (as per Dylon's instructions).

The gears were then submerged in this solution and stirred/flipped every 30 mins. The Nylon gear shown below (an Auto gear taken from a Century Radikal) was given a total of 12 hours to dye.

Simmering your gears for 12 hours will also de-stress them and improve their mechanical properties. Plastics can be annealed just like metals, well sort of...

12S Trex 550 (VBar, Savox Servos)

Custom Motor Mount & Pinion Support

Custom Mount

Assembled #1

Assembled #2

Between Frames

Tray View

Side View

Gear Modifications

All Finished!

My Awesome Blade Helis

Various Photos of my mCPX-BL & 130X

130X at Windsor

KDE 130X Gearbox

KDE 130X Mount

Lynx Head Block

Stock mCPX-BL

Rakon Upgrades!

Blitz Avro (YS91, 30% Coolpower, GY611, TJ Pro)

Maiden Flight at Northolt

Waiting to fly

Tentative inverted

Down low...

Flying in Windsor Great Park

Low Autum Sun

Up Close

One Sleek 90!

Ticking Over...

In the Hover

Me & my Avro

Pie Dish?

Low Turn...

Raptor 50SE (OS 50 Hyper, 30% Coolpower, GY401)

Back in the summer of 2005

Raptor 50SE

Getting Ready...

Early Inverted

Windsor Great Park, Summer 2007

New Canopy

Inverted #1

Inverted #2

Strimming at Windsor


Mid Roll

TT Yellow Canopy

A Dim Saturday

Action Shot!

Mid Tic-Toc

Up Close!

The Platypus!

JR/Spektrum Receiver Installation

Front View

Left View

Right View

Century Radikal (Wally 21 Hyper, Total-G, Savox Servos)

Various Build Photos (Now Sold)

LHS Rear Frames

RHS Rear Frames

Completed Frames

The Wally 21 Hyper

Upgraded Clutch

Pinion Assembly

Upgrade Clutch Bell

Flybar-less Head

Dyed Main Gear

Dyed Auto Gear

Dyed Tail Drive

Sprag Oneway

Finished Hub

Engine In (Front)

Engine In (Back)

Fury 60 Expert (Webra 61, 20% Coolpower, GY401)

Original Form

At the Scrubs

Low Shot

New Canopy

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