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Teardown: HEBI Robotics Smart Brushless Actuator w/ Series Elastic Element
Product Description ● ● ● ●
Resear Rese arch ch an and d au auto toma mati tion on ap appl plic icat atio ions ns Mult Mu ltip iple le mo mode dels ls fo forr di diff ffer eren entt sca scale les s Appear App ears s to be mark markete eted d to res resear earche chers rs and and smal smalll busin businesse esses s Manufacturer cop copy:
“HEBI Robotics enables you to create custom custom robots quickly. Each module is a series elastic actuator actuator that offers control of torque, position & velocity, and is packed with sensors making it a self-contained unit that includes everything you need as a foundation for your robot.” -HEBI Robotics
8x Button Head Cap Screws Screws thread to tapped holes on opposite side
Two cap screws support the actual motor inside the housing
Note: The encoder magnet
Teardown
assemblies are not shown in these photos. The manufacturer was not
8x Dowel Pins
able to provide these components.
Top plate assembly
Enclosure ring Bottom plate
●
Dowel pins (yellow); why?
Teardown Machined notches Top plate Machined core affixes to output rotor with 8x screws; rotates independent of gear
Machined bosses to match notches in output rotor. Self-adhesive tape on bosses: why? Large output rotor bearing
Teardown
All output torque must be transmitted through this plate… what does it do?
Notch and boss interface; same idea as previous slide
Teardown
Metal plates
Natural rubber between plates
● ●
What does this element do? How was this part made?
Why have an elastic element? ●
Passive compliance - safety
Why have an elastic element? ● ●
Passive compliance - safety Measure forces with position sensors: F = (θ1 - θ2)*k
Why have an elastic element? ● ● ●
Passive compliance - safety Measure forces with position sensors: F = (θ1 - θ2)*k Increase the time constant of the system ○
Makes it easier to control applied force without a super-fast control loop
Why have an elastic element? ● ● ●
Passive compliance - safety Measure forces with position sensors: F = (θ1 - θ2)*k Increase the time constant of the system ○
●
Makes it easier to control applied force without a super-fast control loop
Disadvantages?
Teardown ●
A quick manufacturability note
Notched plate is affixed to output ring using screws
Why do this?
Teardown
Housing ring - how was this made? Why all those ridges?
Bottom plate with PCB and geartrain
More dowel pin holes
Teardown
● ●
Geartrain contains four reductions Note increased tooth pitch closer to the output; why not use one tooth pitch all over?
●
These are really big gears (high tooth count) - why?
Teardown Anything that might be wrong with the gearing here?
Teardown
Gears are cut brass with pressed-on steel. Why make compound gears in this way? Any other observations about gear manufacturing? What is the impact of gear quality on product quality?
Electronics
Current sense resistor Interface connectors Motor MOSFET gate driver
Motor
why two Ethernet ports?
Microcontroller Power connector
Three plastic balls sit just proud of PCB surface
Switching-mode voltage regulator circuit for electronics?
Big capacitor… what for?
Electronics
MOSFETs (three more on front of board) - where are the flyback diodes?
Inertial measurement unit (what’s with the foam?)
Ethernet switch Absolute encoder chips mounted under nylon balls
Components Used ●
●
●
●
Controller: STM32F427VIT6 ○ ARM Cortex-M4 ○ Probably intended for industrial UI ○ Lots of good real-time control features too Motor amplifier: TI DRV8303 w/ Infineon MOSFETs ○ MOSFETs good up to 80 V ○ No special thermal mitigation; all gate driver and MOSFET heat is going into the PCB. Positional sensing: MPU-6500 Inertial Measurement Unit ○ Accelerometer is mounted on a second PCB and sandwiched in vibration-damping foam. ○ Hebi has to calibrate accelerometer position after the device has been assembled. Encoders: AMS AS5048A Hall Effect absolute position sensors, 14-bit resolution. ○ These absolute position sensors measure the angular position of a magnet sitting just above the chip, using hall-effect sensor arrays. ○ Nylon balls are supports for encoder magnets.
