Wednesday, January 9, 2019

Feiyu Tech A1000 Gimbal Teardown

The Feiyu Tech A1000 is a midsize handheld gimbal for compact cameras and small mirrorless cameras. I recently acquired one and took a look inside, with the ultimate goal of operating the gimbal without the handle, which contains the batteries and some electronics.

The gimbal consists of a "main unit", which is attached to a handle by the means of a threaded collar. The handle contains the controls for the gimbal, as well as the batteries; it is not possible by default to turn the gimbal on without the handle.

The first task was to disassemble the handle. My hunch was that the handle suppled 7.4V (2S Li-Ion) to the inverters in the main unit, and sent pan and tilt commands via serial to a microcontroller in the main unit that ran the stabilization loop and talked to the inverters and IMU via I2C.

The Feiyu gimbals are remarkably easy to take apart - everything was held together with screws with not a plastic snap in sight. Removing the four Phillips screws from the top of the handle released the connector board:

The contacts for the spring-pins on the main unit are just pads on a matte black (!) PCB; the top board is just connectors with no active components.

Removing the four socket cap screws on the side of the handle reveals the bulk of the circuitry:

The module is an NRF51822 carrier module...with some sort of bonus wire on it to act as an antenna. Completely not OK - the reason manufacturers use carries is to avoid having to undergo additional FCC certification, and adding the extra antenna defeats this. The chip below it (next to the USB port) is a Silabs USB to UART bridge. This is a notable difference from the smaller Feiyu gimbals, which put the UART bridge inside the USB adapter and run serial over the physical USB connector.

The backside isn't too exciting - a buck converter provides power for the electronics on the board (and possibly logic power for the inverters as well). The connectors are all neatly labeled, a nice touch.

Moving on to the inverters (we look inside one motor, but the other three are nearly identical):

The microprocessor is an STM32F303, an popular choice for gimbals. Two shunts are present - no cost-cutting one-shunt techniques were used here.

The power stage is an MPS6536 integrated brushless driver IC. The position sensor is not on the board; presumably, it is on the other side of the motor.

The connector board on the main unit reveals something surprising: unpopulated pads for a NRF51822 module are present.

Presumably at some point during development, a handle-less version was in fact planned, but was aborted before it reached full production.

Some further analysis:

The handle does have an microcontroller in it - it is possible but unlikely that the NRF51822 (which contains a Cortex-M0) is used for the stabilization loop. However, the only data lines running up into the main unit carry 115200 baud serial on them; standard async serial is not easily daisy-chained, and very few IMU's speak UART. Most likely, one of the inverter microcontrollers also does stabilization (this is the case on the Feiyu Tech wearable gimbals, which have no handle).

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