'unitepower.com' 48V 1800W brushless motor teardown

A friend recently acquired a '1800W 48V' brushless scooter motor and I decided to have a look inside, ostensibly for the purpose of doing thermal testing.

The rotor measures 63mm (diameter) by 73mm (stack height). This gives an air-gap-area*radius metric of 289 cm^3, which is not too shabby; for comparison, the Sonata HSG, which is a 60Nm motor, is 415 cm^3. The laminations are about .56mm thick, which is not great for high speed performance and is probably a huge reason why these motors are not very efficient.

The stator is surprisingly well-made. The fill factor is OK, and the concentrated windings mean there aren't a ton of end-turn copper losses. The stator also has a pretty high iron-to-copper ratio, which is good for peak torque and not good for efficiency. The large volume of iron in the stator is probably another contributor to the high losses - at peak efficiency, copper losses are less than half of the total losses.

The motor has hall sensors, installed using the standard in-the-slots technique:

The housing is mediocre. The end caps are cast aluminum, and the stator is pressed into a piece of steel tube, which adds quite a bit of weight. The motor is also much longer than it needs to be - out of the 177mm of total length, only 72mm contribute to torque production.

Motor specifications:

Type: Surface PM machine
Pole Pairs: 3
Resistance (line-to-line): 73 mOhms
Inductance (line-to-line): .415 mH
Flux linkage [derived]: 0.036 Vs

Back EMF:

Full of harmonics, but reasonably sinusoidal.

Thermal testing:

Thermal testing was done by passing DC current through a pair of phases while watching the temperature of the end turns with a Flir A65 thermal camera. We initially set a temperature cutoff of 110C, but backed down to 95C after noticing some degradation in the either the enamel or epoxy in the stator at around 100C (this is pretty terrible; good wire can operate at 200C!).

Performance with no additional cooling proved to be rather poor; at 28A (which is the RMS current at 40 peak phase amps), the stator hit 95C and started overheating.

Performance with active cooling (a Sunon PMB1297PYBX-AY 12V blower) proved to be much better; we were able to achieve 33Arms (46 peak amps) with a stator temperature that stabilized at around 90C.

Note that this is a best-case operating scenario; at stall, there are no iron losses. Further testing at speed is planned for a later date.

Conclusion:

This is "a lot of motor" - it can produce huge amounts of peak torque. Unfortunately, terrible efficiency, non-existent high-speed performance, and a dubiously low temperature cutoff all serve to severely limit its applications. Even for its advertised application (small electric scooters) it is a poor choice, as 70% peak efficiency means around 20% of the battery pack is wasted (versus a 90% efficient machine).
These motors are very close to being good - better wire and thinner laminations, both of which wouldn't drastically increase costs, would go a long way to making them more useful. Maybe in the future, we will see an updated version with these improvements, but for now, I would steer away from these motors.

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 carriers 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).