How much stuff I don't know

[davidk]

Amazing the amount of stuff I don't know. 

Disclaimer:  I'm going to be talking about 9g MG servos... in a reasonable price range... a "normal" price range.  I'm not talking about servos that cost $100.

So... I'm shopping for 9g metal gear servos and it's taken me a couple of days to understand that there really isn't any such thing as a 9g MG servo.  It seems all 9g MG servos weigh 12+ grams.  It is the physical size?  Nope.  All 9g MG servos are essentially the same size... and are the same size as 12g MG servos.  Are 9g MG servos weaker?  Less torque?  Nope... all about the same speed and torque.  So, why are they called 9g MG servos?  Because the original 9g servos were Plastic Gear servos... and as a class of servo, the name stuck even though they got upgraded to metal gears which adds 3g+ in weight.

Next, High Voltage servos.  I thought I couldn't use HV servos.  Many HV servos have the words "2S Lipo Ready" printed on them.  Yikes, what the hell is that?  Well, apparently "people" want to power their servos directly... and not with a string of 12lb NiCd batteries.  In the olden days (yes, I'm pointing to all of you reading this) servos were powered with NIMH packs.  No one wants to do that anymore... they want to use a 2S Lipo... which is 7.4V (8.4v fully charged)... which would blow up a normal servo.  HV servos and Spektrum Rx can handle up to 8.4V and 9V respectively.  So, todays HV servos and receivers can be powered by a 2S Lipo.  Well... that's just cool.  And, with a HV Servo, you get a bit more torque when directly powered with a 2S Lipo.

Again, I thought, I couldn't use HV servos... because... well... they're HV... but I can, I can.  HV servos can be powered "normally"... you just get a little less torque than reported in the servo specs.

So, there you have it.  9g MG HV servos are actually 12g servos than can handle a range of input power.

This has been... stuff I don't know.

[GuyOReilly]

Thank you for the information.
I never powered servos "directly" with NiCad nor LiPo, but interesting to know that one could for high power/torque requirements.
When I shop for servos, I prefer metal gears because I had many, many stripped nylon gears.
Have a great day.
Guy

[msatin]

Thank you for your post David!
I also have been confused by servo nomenclature.
Supposedly industry "standard" terms such as Micro, Sub Micro, Standard, etc. don't really seem to be standard.
Also - some manufacturers show their torque only in either metric or imperial. ARRGGHHH! 
Q. If you're powering HV servos with a separate battery, do you have to split the connector? i.e. 2 wires going to the battery, and the signal wire going to the Rx?
BTW - I have similar confusion with the terms re: motors such as "Park xx" & Power xx".
I found a pretty good cross brand reference chart. (They also have a good Glo to Electric conversion chart). If anyone is interested I can post the links

[davidk]

Thank you for your post David!
I also have been confused by servo nomenclature.
Supposedly industry "standard" terms such as Micro, Sub Micro, Standard, etc. don't really seem to be standard.
Also - some manufacturers show their torque only in either metric or imperial. ARRGGHHH! 
Q. If you're powering HV servos with a separate battery, do you have to split the connector? i.e. 2 wires going to the battery, and the signal wire going to the Rx?
BTW - I have similar confusion with the terms re: motors such as "Park xx" & Power xx".
I found a pretty good cross brand reference chart. (They also have a good Glo to Electric conversion chart). If anyone is interested I can post the links

I think it was all well meant many years ago, with somewhat defined standard, but because of marketing the water is now mud.  Same with motors... naming made sense at one point... but no longer.  I no longer care for the class name of a servo... I only care if it fits.  Better servos go to the rear, ok servos for the wings, don't re-use crashed servos, try not to use plastic gears.  The cost difference between plastic and metal is a billionth (yes billionth) the cost of the airplane that servo is keeping in the air.

Good question on the use.  If both the Rx and the Servo can take HV, the 2S plugs directly into the Rx.  If a normal Rx and HV servo then you need to share the ground with the Rx, the Servo and the battery.  Use a Y connector.  The end that plugs into the Rx will have the Red wire removed.  One splitter end, Red and Black, goes to the Battery.  The other splitter end, Signal and Black, goes to the HV Servo.