Market Review of Small Brushless Servos
Servos employing brushless motors won't fail from a brush failure.
So servos with brushless motors should be inherently be more reliable and last longer than servos with brushed motors.
Brushless servos tend to be larger high-torque servos when compared with servos with brushed motors.
They also tend to be completely digital devices and in most cases may be programmed to change some of their attributes, using simple USB programmers.
I sourced five different brushless servos from China to review and test. They were all the smallest brushless servos available in their range. They were all standard sized servos, with approximate dimensions of 40mm long and 20mm wide.
The desirable characteristics of a steering servo for a small long duration sailing drone:
- low idle current
- low operating current
- high torque is not important
- fast response is not important
The programmable servos could be altered to reduce their current draw, and hence reduce the torque they can apply. The primary attribute affecting torque and current draw is the maximum duty cycle.
My preferred servo at the time of writing is the Yipin X10.
Hitec HS-425BB - Brushed Servo - for comparison
Summary: This is a good standard brushed motor servo. Voyager sailing drones have sailed many miles with these servos and similar ones in the Hitec range.
Landed Price: AUD $25
Idle current: 9mA
Specified Torque: 4kg
Programmable: No
Spline: 24T
mass: 43g
Current measurements after optimum programming for reduce power consumption:
All testing performed at 5Vdc.
Idle current: 16mA
Step current: 1000mA
Sweep current: 100mA
9imod Brushless 20kg
Summary: This is good value for money brushless motor servo.
It is only slightly more expensive than brushed motor servo.
Landed Price: AUD $33
Specified Torque: 20kg
Programmable: Yes
Spline: 25T
Mass: 72g
web:
Programming software: http://gxservo.com/en/col.jsp?id=111
GXservo-v1.rar - ServoDebugger.exe, older version of software, but does work on my Windows machines.
GXservo-v3.rar - newer version, but crashes out on my Windows computers.
Current measurements after optimum programming for reduce power consumption with adequate torque of around 1kg.cm:
All testing performed at 5Vdc.
Idle current: 12mA
Step current: 360mA
Sweep current: 200mA
DS Power DS-B008-C 24kg
Summary: It sounds very smooth and quiet. Build quality is good.
But it not programmable, ands that means that it can't be optimised for a role.
Landed Price: AUD $49
Specified Torque: 24kg
Programmable: No
Spline: 25T
mass: 66g
Current measurements as supplied (programming is not an option):
All testing performed at 5Vdc.
Idle current: 40mA
Step current: 2000mA
Sweep current: 290mA
Yipin X10
Summary: This is my favorite brushless servo.
Possibly the best quality servo of those surveyed. The Yipin Servo uses the same PCB as the 9imod servo, but the build quality seems to be better.
They both can be programmed using the same programmer and software.
The Yipin servo comes with spare gears and pins.
Landed Price: AUD $81
Specified Torque: 10kg
Programmable: Yes
Spline: 25T
mass: 72g
web:
Programming software: http://gxservo.com/en/col.jsp?id=111
GXservo-v1.rar - ServoDebugger.exe, older version of software, but does work on my Windows machines.
GXservo-v3.rar - newer version, but crashes out on my Windows computers.
Current measurements after optimum programming for reduce power consumption with adequate torque of around 1kg.cm:
All testing performed at 5Vdc.
Idle current: 12mA
Step current: 450mA
Sweep current: 200mA
AGFC A73BHLW
Summary: This servo includes feedback in the form a 4th connection wire.
It is simply a direct connection to the potentiometer wiper pin.
This could be done on almost any servo without cost.
Landed Price: AUD $165
Specified Torque: 40kg
Programmable: Yes
Spline: 25T
mass: 79g
Current measurements after optimum programming for reduce power consumption with adequate torque of around 1kg.cm:
All testing performed at 5Vdc.
Idle current: 34mA
Step current: 390mA
Sweep current: 90mA
