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Mixing HDD And HD Servos

What happens if you mix HDD servos with HD servos in your robot? Will only the HD servos jump around or will others move inadvertently too? Thanks.

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That's correct, only the HD servos will move on initial power up the HDD servos will not move (they have a completely different internal electronic design).
What are  the  HD and HDD servos ? I only know usual servos .

HD is anologe and HDD is digital.
HD and HDD  don't help understanding . Both seem digital ("D" and "DD"). I never saw those  acronyms for servos.
#7   — Edited


I never saw those acronyms for servos.
They are used by EZ-Robot to describe two different servos:

User-inserted image

Left side: 2 x EZ-Robot HDD Servos (Digital)
Right side: 1 x EZ-Robot HD servo (Analogue)
Analogue x Digital servos:

There is no physical or main component difference between a digital servo or analog servo. The servo case, motor, gears, potentiometer all have the same purpose in both types., the exception is the PCB i.e. board.

The difference between the two is in how the signal from the receiver is processed and how this information is used to send power to the servo motor.

An analog servo controls the speed of the motor by alternating on and off voltage signals or pulses to the motor. 

A small microprocessor int the servo PCB analyzes the receiver signals and processes these into very high frequency voltage pulses to the servo motor. Instead of 50 pulses per second, the motor will receive upwards of 300 pulses per second. The pulses will be shorter in length, but with so many voltage pulses occurring, the motor will speed up much quicker and provide constant torque.
#9   — Edited


That's correct, only the HD servos will move on initial power up the HDD servos will not move (they have a completely different internal electronic design).
So the problems at startup are likely caused by power on and control floating for a few seconds, the analogue servo will interpret the voltage floating as impulses and will try to match with the feedback from the potentiometer, so you ll see the servos moving without "control".

With digital servos, they don't move until the controller sends pulses. 

It's possible to mitigate the problem (Analog servos) using a different power source (not from EZB vin), controlled by relay (a good one with enough Amps to support the servo inrush) and using the relay Normally Open position, so when you power the Robot, the servos will not get the power, then you have plenty time to EZB to boot, Windows, ARC, initialization script to initialize all servos to the initial position.
When you are ready, you enable the relay, so the servos will get power and logic control at the same time.
Thanks to everybody. I understand. HD and HDD  are used by ez-robot servos. "Heavy-duty" is used for  digital servos.
Hitec servs, for example, are simply  analog or digital, non such acronyms.
#11   — Edited
Not to be pedantic ... but "Heavy Duty" is the HD meaning, is common to analogue HD and digital HDD.

you gave a good example:
User-inserted image

If you look well the Hitec's model HS-322HD uses the same terminology.

The devil is in the detail:)

btw: the Hitec descriptions are misleading. Has 2 Karbonite and 2 nylon gears and in light use they both break easily. It's not a heavy duty servo by any means.  EZ-ROBOT should change to SHD Super Heavy Duty :), off course not all HITEC servos are equal.
#12   — Edited
ez-robot :HD =heavy duty , HDD=heavy duty digital 
Hitec : HD =it should be heavy duty but itsn't necessarily