offGrid Systems website
Project duration: ~3 months
Projectvorm: Fixed price
Period: autumn 2015
Activities: Idea, proof of concept, design electronics and firmware, prototyping, production, support & warranty
Technologies: STM32 Cortex M3, OGS/CAN-bus, C, high-current, DipTrace, EmBits
Parts: STM32F105, MCP2562, BTM7811, BTN8982, FM24LC16, ITS41K0S

Description:

One particular feature of the OGS control® system is it's intended ability to perform a self-leveling of the device on unlevel terrain. Electrically, this means a control system to drive four 250 Watt DC motors. In addition to the self-leveling feature, the system may contain other motors, for example to adjust the rotation and extension of a camera mast.

Specifications:

Driver for 4 DC motors
  • Operating voltage 12VDC-33VDC
  • 4 H-Bridge drivers, 40A nominal, >100A peak each
  • 8 Digital 'direct-control' inputs
  • 4 Digital open drain outputs with diagnostics
  • Build-in auto-leveling algorithm for four adjustable supports
  • Accelleration sensor for precision angle sensing
  • Internal I²C connection for limited internal expansion possibilities
  • Customized Italtronics Railbox DIN-rail mounted enclosure
  • CAN-based OGS control® bus to connect with an OGS control® Master

Auto Level:

A (firmware-based) derivate of the motor controller is a dedicated 'auto-leveling' controller. That controller drives the motors of four adjustable feet under the system enclosure. The firmware contains an algorithm to perform a self leveling of the system to within 1/10 of a degree while retaining firm ground contact each support.

Brake resistor:

Braking an electric motor is essentially the same as using it as a generator. That is regenerative power, which is often a good thing. However, in this system, there are (ideal) diode arrangements on the battery outputs. That means that this regenerated braking energy cannot flow back into the battery. And when power is not absorbed, then the voltage will rise... It will rise to the point where current starts to flow and an equilibrium is reached. Obviously, that is not a good thing because that current starts to flow when breakdown voltages of capacitors and mosfets is reached, and we don't want to break those down.

Using some TVS diodes, we could clamp a substantial amount of the voltage peaking, but not enough. So we created a chopper braking resistor add-on module. Which is just a large resistor element that is switched in and out of the circuit using with a comparator. This brake resistor device is attached to the back of the motor module and managed through it's internal I²C connection.

Agentschap NL
Gerealiseerd onder het innovatieprogramma WBSO

ARM Cortex M3

'OGS control' is a registered trademark of Reijneveld Machinebouw B.V.