Author Archives: stephen

Seeed Studio DSO nano oscilloscope review

I just received my Seeed Studio DSO nano oscilloscope.

I had difficulty justifying the purchase of this oscilloscope, as I had doubts on its usefulness and performance. However, the unit has such cool form factor that I just had to have it. The oscilloscope is modestly priced at USD $89. I justified buying it because, if for some reason the oscilloscope is not usable, then I still can use it as an ARM STM32 development board (Hey, this is the same CPU that powers Hexi’s locomotion engine).

DSO nano

The DSO nano is really small

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Go Hexi!!

Meet Hexi. Hexi is my new 6-legged robot (hexapod) family member. He is demonstrating the three standard walking pattern for a hexapod: wave, tripod and ripple gait. For now he can only walk in a straight line.

Body: Lynxmotion Phoenix
Actuator: Hitec HS-645MG servos
Processor: ARM Cortex-M3
Battery: 5 Sub-C 5000 mAh (

Hitec Servo

These are some of Hitec servos that I looked at:

Size Speed

(Time/60° (s))

Torque ( Price


Bang per buck (Torque/Time/Price)
HS-475HB Standard 0.23 4.4 15 1.3
HS-645MG Standard 0.24 7.7 34 0.9
HS-985MG Standard 0.16 9.6 58 1.0
HS-755HB 1/4 0.28 11.0 25 1.6
HS-805BB Mega 1/4 0.19 19.8 34 3.1


Micro 0.17 3.6 41 0.5


Standard 0.23 10.3 48 0.9

For standard size analog servo, the HS-985MG performs best. It is based on a coreless motor. It provides the highest torque as well as the fastest speed.

The HS-475HB is the best value servo. It has the advantage of using Karbonite (just like kryptonite 🙂 ) gears. Karbonite is supposed to be stronger than nylon but has less wear and tear compared to metal.

The HS-645MG has good torque compromise without being overly expensive. It uses mostly metal gear.

For a mega 1/4 scale servo. The HS-805BB looks awesome.

Hobby Servo

RC or hobby servos provide a convenient actuator to be used in a small-scale robotics project.

Inside a servo there are a DC motor, a gear reduction system, a potentiometer as a position sensor, and some electronics that control the motor based on the desired position.

A hobby servo is great, as it provides all the above in a convenient small package. Due to its popularity, hobby servo is quite cheap.

However there are shortcomings in using a hobby servo in a robotics project:

  • No position feedback. Once commanded to move to a target position, we don’t know when or whether the servo has reached the target position
  • No torque sense. We cannot tell if the servo mechanism is unexpectedly obstructed.
  • Sub-optimal control system. The servo manufacturer cannot know what load the servo will be connected to, so as a result the control system will not be optimal. The problem shows up as: overshoot, slow response, and steady state error.

My plan is to use all the mechanical components of a servo, but replace the electronics with one that I design myself to solve the above issues.