The electronics of the gimbal system is being designed with considerations for how it should connect to the main system (the drivetrain Ebox). This documentation is aimed at justifying the decision to design the Gimbal subassembly (includes overall telemetry and Camera gimbal) as a fully integrated subsystem with a simplified electrical and controls interface that communicates with the main software architecture.
Concerned developers: Yuchen Lin Vedha Mereddy
Defining a fully integrated Gimbal Assembly
A fully integrated solution for interfacing with the gimbal system will effectively simplify the overall architecture of the mechatronic system and split the development of the system’s fulfilment into better sizeable tasks between the electrical, firmware and software subteams.
The connections between the gimbal system and the Ebox are defined below:
Required direct connections:
2x VectorNav GPS antennas - Coaxial
Intel Realsense D415 (Gimbal Camera) - USB A 3.0
Wave Nano - Ethernet
915 Mhz Sik Radio - USB TTL
Control Electronics
Camera Gimbal Electronics:
1x 5V pitch servo - PWM position control
1x 5V cooling fan - Speed / State control
1x 24V BLDC Gimbal motor for camera yaw
1x 5V Gimbal motor encoder - SPI
Wave nano antenna gimbal electronics:
1x 5-7.5V yaw servo - PWM speed control
1x 5V 14 bit absolute encoder - SPI
Note, a 14 bit absolute encoder is required for the position control of the Wave nano gimbal. as the continuous servo that was spec’d for the project only enables speed control
The control of these electronic components can be implemented with of the following architectures:
Option 1: Aux board control Harness
A single control harness will incorporate all the connections for the electrical components on the Gimbal subsystem that will be split in the Ebox
Includes:
1x SPI +5V to aux board
2x Servo 5V + PWM to aux board
1x 5V high power PWM to aux board
1x SPI + 5v to ODrive V3.6
1x 3 phase to ODrive V3.6
Option 2: Integrated system CAN Harness
Single source power delivery 24V
CAN communication with
Option 2 Control System Detailed
All control electronics for the Camera and antenna gimbal will be contained withing the space shown below according to the architecture below
Option 2 System Tasks Architecture:
Gimbal board is developed by electrical team member
Electronics enclosure and mounting is fulfilled by mechanical team member
Gimbal system controller firmware running on the gimbal board is developed by firmware member
Tracking antenna GPS feedback control and user interface camera gimbal control software on Jetson
Justification
This is all to justify the purchase of an ODrive Micro for camera Gimbal motor control, the scoping of Vedha Mereddy 's general purpose DD-Current sensing board to an additional version that implements the additional features required on the Gimbal board, and to define the project of integrating this mechatronic subsystem.
The proposed connection, Option 2 is comparatively less cheap that the intial option, assuming that the team already has access to ODrive V3.6 motor controller, as well as considering the development time and cost of a Gimbal board that incorporates the specified features.
The preference of option 2 is justified by the following
Current ODrive V3.6 available to the team are limited, with three being required to be used on the arm. In the case that we are short of ODrive V3.6 in the bay, a similar cost purchase to the Odrive Micro will have to be made but for a legacy device
The selection of the ODrive Micro over any other low profile motor controller is justified by its seamless integration with our current electrical (CAN TTL / frequency) and software architecture (CAN driver)
In the case of a system fault, it will be easier to isolate and troubleshoot problems in the proposed architecture. It also enables the gimbal subsystem to be completely separated from the rover base by unplugging 5 instead of 10 separated connectors with unnecessarily independent power delivery lines.
The current DD-current sensing board being developed by Vedha Mereddy and Yuchen Lin can be scoped to include a revision that provides all the required features
Relives the space for electronics incorporated in the drivetrain Ebox, etc.
Final Note:
This is being proposed this early due to the predicted unavailability / short supply of the ODrive Micro before SAR. Pre-ordering one right now would mean receiving it at the beginning of the W25 term.