DIY Motion Platform Servo Drive System - 64SPU-2 Card

 

UPDATE March 2015, the 64SPU-2 card replaces the older 64SPU-1, 12ADC-1 and I2C Isolator cards in a single card.

 

INFORMATION: for an excellent example of a drive system build using the older 64SPU-1 and other cards please see Roland van Roy's write-up here -  http://simprojects.nl/electrical_drive_iv.htm The wiring is slightly different for the 64SPU-2 but it still gives relevant examples of good practice.

 

Roland has helpfully provided advice and his technical wiring diagrams for his system on the page.

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The NEW 64SPU-2 card works with the BFF 3 DOF Motion Driver and  BFF PID Servo Controller software to provide cost effective DIY 3 DOF motion platform drive system control for flight simulation.

 

It combines the functions previously provided by 3 separate cards to simplify system wiring and operation.

 

The main features of the 64SPU-1 are:

• Fully isolated I2C data output for use with Devantech MD03 motor speed controllers.

• Smoothed 12 bit potentiometer position feedback via built-in ADC circuit.

• 2 or 3 channel output for 2 or 3 DOF motion systems.

• Built-in "Drive Enable" trip loop.

• 64MHz operation giving up to 70Hz refresh rates.

• Direct connection to PC USB via included FTDI chipset USB/TTL cable.

• Included external DPST (double pole single throw) card logic power switch to power-up card and isolated I2C together..

• LED status indicators, screw connectors.

• On-board 20X2 microcontroller re-programmable in-situ for firmware upgrade.

Illustrative system wiring:

 

 

For 64SPU-2 use with alternative Dimension Engineering Sabertooth / SyRen controllers see here...

 

The main components that make up the DIY motion platform servo drive are:

• The 64SPU-2 64MHz Signal Processor Unit card - see the order pages here.

• Devantech MD03 Motor Speed Controllers - 24V 20 Amp DC controllers delivering up to 480 Watts of electrical power per controller.

• 24V DC PM Motors to suit the DIY platform project. The MD03 controllers will support up to a maximum 20 Amps rating, sustained currents above this level will cause overheating and current limiting by the MD03's.

• Position feedback potentiometers. (Pots/encoders fitted to the drive actuators or elsewhere on the platform to report actual platform position.)

• DC power supplies for the drive motors and electronics.

• Actuator travel limit switches, fuses, cables and wiring.

PLEASE NOTE - I do not supply all of the above hardware, just the 64SPU-2 card (with USB cable and switch), and the motion software. If you want to build the servo drive for your own project then you will need to source the motors, controllers, potentiometers, switches etc  yourself.

 

 

IMPORTANT - The 64SPU-2 card is part of a closed loop position feedback servo drive. The position feedback potentiometers/encoders shown on the wiring diagrams MUST be fitted to the drive motors/actuators to report platform position to the 64SPU-2 card. Without this the closed loop position control can NOT operate. If you are not sure what a closed loop position control servo drive is then I recommend you try and read-up a bit before attempting to use this hardware. It is very important to understand that this is not a "plug and play" system intended for consumer use - it is intended for use by informed DIY system builders. Read both the motion software user manual and the 64SPU-2 data sheet before using the hardware.

 

64SPU-2 Card - The new 64SPU-2 signal processor card is at the heart of the servo drive and acts as the communications bridge between the MD03 motor controllers, feedback pots/encoders and the BFF PID Servo Controller software running on the PC. It also acts as a system monitoring and information feedback unit - it monitors for communications interruptions and stops the motor drives when required and also feeds back MD03 current and temperature information to the Servo Controller software.

 

The 64SPU-2 is available to buy as a ready-to-connect card (80 mm x 80 mm) and replaces the older 64SPU-1, 12ADC-1 and I2C Isolator cards as a single board.

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For full details read the 64SPU-1 data sheet -

 

64SPU-2 Data Sheet

 

The card is available to buy on its own or bundled with the V2 Motion Driver software - see the order page here.

 

 

SERVO SYSTEM OPERATION

 

The servo system hardware works in conjunction with the BFF PID Servo Control software running on the PC.

 

The servo software receives platform position demand information from the BFF Motion Driver and also receives actual platform position feedback data from the position feedback pots/encoders connected to the 64SPU-2 card. Using this data it calculates motor speed demand outputs which control the direction and speed of the actuator drive motors to drive the platform to the demanded positions. The motor control commands are sent to the MD03 motor controllers via the 64SPU-2 signal processor card.

 

The servo control loop can run at up to 70Hz (PC and connection dependent) - ie the speed and direction of each motor is adjusted by the system up to 70 times each second and this makes for an effective system response under most platform motions.

 

The servo software uses a PID (proportional - integral - derivative) control algorithm and the PID parameters that define the control response can be set through the BFF Servo Controller GUI. This makes tuning the servo system easier as small changes can be made to the control algorithm and the resulting effects on the motion assessed immediately.

 

Actuator limit switches and an Emergency Stop switch should be wired in series in the 5V supply line from the 64SPU-2 to the MD03 motor controllers to cut the drive to the motors to prevent damage if the actuators over-stroke.

 

Motor controller "live" current and temperature data is continuously fed back by the 64SPU-2 to be displayed on the PC by the BFF Servo Controller software. This makes for interesting viewing, however it can also be of significant assistance during platform set-up work as it provides a direct indication of the system electrical loading. The servo software also includes a virtual oscilloscope to view demanded and actual actuator positions and motor speed demand.

 

For the best performance of the servo drive built-in 12bit ADC is used for the position feedback.

 

Overall the 64SPU-2 and associated servo software can provide an effective servo drive for DIY motion platforms at a seriously low price. The 64SPU-2 is however a relatively simple card and although it contains a number of safety features such as comms time-out monitoring, some feedback error detection and feedback limit detection the price does not allow the types of system monitoring capabilities that can be found on much more expensive commercial motion controllers. You must take care to ensure the platform drive is properly protected by over-travel limit switches and an accessible Emergency Stop button.

 

If you wish to buy the 64SPU-2 please read the data sheet carefully and follow the installation and use recommendations.

 

 

 

 

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