[NSRCA-discussion] JR Servos of choice these days
Bob Lavey
bob.lavey at cox.net
Wed Jan 7 09:27:32 AKST 2009
Wow... That's a lot of great information, Dave. Thanks!
> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org
> [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Dave
> Sent: Wednesday, January 07, 2009 12:11 PM
> To: 'General pattern discussion'
> Subject: Re: [NSRCA-discussion] JR Servos of choice these days
>
> Ok....here goes...
>
> My "standard" servo package for many years has been:
> 9411sa on ailerons
> 8411sa on rudder
> 8417sa on elevator
> 3421sa on throttle (better yet, Castle 85 HV <G>)
>
> As FYI for those not familiar with JR servo nomenclature -
> - DS prefix indicates digital.
> - MG indicates metal gear.
> - SA indicates metal and nylon geartrain (generally metal
> pinion on servo motor, with metal output shaft, and 2 or 3
> intermediate gears are nylon).
> - 4 digit number indicates coreless motor.
> - 3 digit number indicated cored motor (3 or 5 pole).
> - 1st number indicates general case size (ie, 8411 and 821
> share same mounting pattern).
> There are some exceptions, but the above is applicable to
> most current and past JR servos.
>
> Speed and torque generally increase proportionately to
> increased voltage, and I have always run relatively high
> voltage to improve servo performance.
> In my glow days, I used 5 cell unregulated Nicd or Nimh to
> power the receiver and servos, and "bump" charged every
> couple flights to keep the battery voltage high. When I
> converted to electric powerplants, I started using (in
> parallel) 2 sets of TP 2s1p480 lipos regulated to 6.53 volts
> through Tech-Aero Vregs.
>
> 8417 - is only available as a MG servo. The 8417sa is an
> 8417 that has had the 3 intermediate metal gears replaced
> with the nylon gears from an 8411sa or 8231 (buy the 8231
> gearset, it is all nylon, and costs less). 8231 gear ratio
> is slightly slower than the 8417, so an 8417sa at 6.5 volt is about
> 0.09 sec and 130 oz/in torque.
>
> 9411 - I don't know of a midsize JR servo better suited for
> ailerons (save running 6.5 volts instead of 6 volts, which is
> good for about 0.01 sec on that servo).
>
> 3421 - I've used this servo a lot (including pairs mounted
> horizontally on the engine mount for the Webra 160MC), but
> never in pairs on elevator as I prefer a single servo.
> However, the 3421sa is a good choice (in pairs) for elevator
> @ .015 sec and 75 oz/in torque @ 6v. The 3517 is another
> option - slightly faster (and less torque) - 0.09 sec and 51
> oz/in torque @ 6v.
>
> 8411 - this servo is close to 200 oz/in @ 6.5v. Several
> years ago, I ran the 8411sa and 8611 back to back in my EMC,
> and I couldn't tell the difference between them in flight, so
> I've stayed with the 8411 as it is lighter (and the rudder
> size has not increased on the majority of planes since that
> time - but the fuses have!).
>
> Brief sidenote about metal / nylon gears. Metal gears are
> for strength (especially when space is at a premium), but are
> typically manufactured with small clearances (slop) to avoid
> binding. Nylon gears can have zero clearance without binding
> (gears flex instead) have better wear properties.
> I find the nylon gears ever so slightly more accurate for
> very fine control inputs ("leaning" on the stick, without
> actually moving the stick).
> However, the nylon stuff will deflect ever so slightly under
> load, whereas the metal gears do not flex under, so the
> "personality" of the servos at
> center and just off center can be slightly different.
> Linkages/control
> surfaces with any flex or slop will hide 99% of the
> differences in comparable servos. And, typically, all metal
> gear servos will weigh about
> .1 - .3 oz more.
>
> Regards,
>
> Dave
>
>
> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org
> [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf
> Of Jon Lowe
> Sent: Wednesday, January 07, 2009 8:56 AM
> To: nsrca-discussion at lists.nsrca.org
> Subject: Re: [NSRCA-discussion] JR Servos of choice these days
>
> 9411SA's (mid-size) on aileron, 8611a on rudder, 3421sa's on
> elevator (or my new choice, 3421's with the JRPSG3025 gear
> set middle two gears.
> Much faster, and plenty of torque, particularly on 6+ volts.
> On throttle, I use a servo mounted sideways (output shaft
> horizontal) directly on the engine mount, Hitec HS-56HB.
> Very tight and fast. I change the throttle servos out after
> a year of use.
>
> I hope Dave Lockhart chimes in here. I'd like to find a
> faster alternative to the 9411sa's in the same size package.
>
>
> Jon Lowe
>
>
> -----Original Message-----
> From: Woodward, Jim (US SSA) <jim.woodward at baesystems.com>
> To: NSRCA-discussion <nsrca-discussion at lists.nsrca.org>
> Sent: Wed, 7 Jan 2009 7:19 am
> Subject: [NSRCA-discussion] JR Servos of choice these days
>
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> Guys,
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> I’m finishing a pattern plane for a friend. He needs
> to know what the choice of JR servos are these days. I need two
> aileron servo
> choices, 1 rudder servo, 2 elevator mini digitals, and a mini for the
> throttle. Any recommendations would be great.
>
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> Thanks,
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> Jim W.
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