CL Drive - STMicro Hardware Demonstrator - Oct 24

 

Video Clip 1 -

CL Power-up Calibration Movements

 

Video Clip 2

CL Auto Pilot Following Movements

 

CL Drive Hardware Migration

 

Before I stopped making cards in 2021 the Control Loader system was the most popular project on the site. Unfortunately since then the system has been effectively unavailable for home cockpit builders.

 

It was originally designed for home cockpit builders and I've been looking for some time now for a way in which the system might be made available again. Migrating to off the shelf drive hardware may be one way to do this....

 

STMicro's STM32 Nucleo-64 microcontroller development boards with their 3 phase motor driver expansion boards always looked like a potential route and recently, with the help of some well targeted embedded system engineering support, it has been possible to make good progress on a CL Drive demonstrator project using that hardware.

 

STMicro based CL Drive System Schematic

The STM32 Nucleo-64 evaluation hardware topology leads to a system configuration of one microcontroller board mounted with one 3 phase motor driver board to drive one

Control Loader axis.

 

UART is used as the comms method between the PC CL software and the STM microcontroller cards with a separate UART channel for each CL axis. Each UART connection is via a USB-UART isolated converter - this maintains full electrical isolation between the CL drive and the PC USB system.

 

The CL software running on the PC is a modified version of the original software (supports MSFS & X-Plane 12), and the 3 phase servo motors and flight yoke mechanics are the same as used in the original CL system.

 

The STM32 NUCLEO-64 boards used in the project are the NUCLEO-F446RE microcontroller board with the X-NUCLEO-IHM08M1 low voltage 3-Phase brushless motor driver expansion board (see right). I've been able to use the cards in their as-supplied configuration with only simple jumper settings used to make any required configuration adjustments.

 

The IHM08M1 can drive a single BLDC motor at up to 48V DC and 15A(rms) drive current, this makes it a good match for the range of servo motors used in the CL system and the F446RE microcontroller is a newer generation than those used in the original BLDRV3 cards and runs considerably faster and has more memory.

 

The project has involved re-writing the microcontroller firmware from scratch - although STM provide several motor drive sample solutions the encoder feedback, space vector modulation scheme used to commutate the motors in the CL drive meant no existing STM firmware solution is available for a CL drive.

 

The coding is now at a stage where the software structure is established and all the CL loading components are present and working (aerodynamic, fixed, weight, vibration, friction, damping, detents, A/P following etc), the PC comms via UART is fast and solid and preliminary card condition monitoring is in place (temperature, current, voltage). This has allowed me to spend some time flying with the new CL drive using both XP12 and MSFS (I continue to use FSX for some testing because it loads faster!).

 

Performance and Initial Thoughts

 

The CL drive runs very nicely and reliably, in fact you quickly forget that it is a new drive system when flying with the CL flight yoke. The motor commutation is smooth at the stalled/nearly-stalled motor conditions present in a CL drive so producing smooth force feel at the flight controls. The STL220N6F7 Power MOSFETs used on the IHM08M1 board warm only modestly when driving the currents used by the motors (typically < 10amps) making it likely that additional heat sinking will not be required.

 

Dual Axis CL driver setup using STM Hardware

The modified PC CL Software updates the 2-axis demonstrator drive with new loading data at about 60Hz and the cards update motor torque demand at 500Hz with on-board calculations taking place for the control lag sensitive load components to maintain output loading stability as before.

 

The motor drive is by torque demand for normal manual flying, and by position demand when Auto Pilot is engaged and the drive simulates the control actions of the A/P (see videos).

 

Similar power-up calibration methods are used as before with automatic power-up calibration movements the default. These require only quadrature encoder feedback and so the original requirement for hall sensor feedback has been dropped. The opportunity has also been taken to simplify the drive motor connections and the new drive adapts automatically to any encoder and motor phase connection wirings when calibrating.

 

Overall the performance of the 2-axis demonstrator drive is very encouraging, so I'll probably continue its development - further housekeeping coding is needed for error handling, full temperature and current monitoring and other card protection features.

 

The CL software also needs to be further developed to run with the new drive and some project documentation will be needed if there are builders out there who may wish to try it.... The comms data structures are much simplified from the previous system (partly because each card handles a single drive axis only) and I hope to be able to write a useable API for the cards. This would allow builders to use them with their own CL software.

 

Although the firmware development is taking place using the full STM32 Integrated Development Environment, flashing the microcontrollers with finished firmware can be done using STM's simpler STM32CubeProgrammer software directly through a USB connection to the cards. The NUCLEO-F446RE comes with a built-in programming link (ST_Link) and so does not need further separate programming hardware.

 

Looking further ahead, custom drive cards could be designed based on the STM evaluation board designs provided by the vendor and as such the demonstrator microcontroller firmware would port directly to those cards.

 

A Couple of Videos

 

One giving a quick overview of the demonstrator system and showing the automatic power-up calibration movements driven by the new hardware.

 

https://youtu.be/sx70I3Kg1Pc

 

This one shows the new drive in Auto-Pilot following mode - the flight controls are moving with the A/P flight control actions for a GA aircraft flying in a storm.

 

https://youtu.be/15OqcIkxt08

 

 

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