I just got my Fluke 17B multimeter yesterday. I bought it from DealExtreme for USD $92 delivered. I’d like to use this multimeter instead of my Fluke 77 III for my everyday electronics at home.
This Fluke model is only for sale in China, however you can easily get this model from Ebay or DealExtreme. Given that it is only for sale in China, there aren’t many in depth review of it. My concern is that this model may not be of the same quality as the other Fluke’s model.
This meter has a sister model, the Fluke 15B which does not measure frequency nor temperature.
For more information, calibration manual of the meter is avaliable from Fluke China website here. Continue reading →
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).
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 (cheapbatterypacks.com)
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.
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.