review: MICRO SERVOS by LBRC

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LBRC
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Post by LBRC » Sun Jul 10, 2005 4:07 pm

Image
From left to right:

Blue Bird BMS-303
Size: 19 x 15.5 x 7.5 mm
Torque: 11 oz.in at 4.8 volts
Speed: 60° in 0.11 sec.
Pot: 5K surface mount.
Expensive, but the smallest and with a coreless motor it’s also the strongest and fastest in its class. Unfortunately the surface mounted potentiometer makes it a real bugger to modify for use with an Iwaver or Mini-Z circuit board.

Interflite Mega Micro :-o PN: MMIC43
Stock: 19.6 x 19.6 x 8 mm
Torque: 5.5 oz.in at 4.8 volts
Speed: 60° in 0.12 sec.
Pot: 10K ohm
Best fit for a ZZMT primarily doe to feed horn position but also width, it does however need a 10K ohm resistor to match an IW or Kyosho circuit board, and a ZZ 22K (red) motor for more torque.

GWS PICO+F/BB
Stock: 22.8 x 19.8 x 9.5 (PICO = 22.8 x 15.8 x 9.5)
Torque: 11 oz.in at 4.8 volts
Speed: 60° in 0.12 sec.
Pot: 5K ohm
Very strong and smooth however it ends up being awkward to install in because the feed horn sits all the way to one side while the larger motor ends up being very long on the opposite side.

HiTec HS-55
Stock: 22.8 x 24 x 11.6
Torque: 15.27 oz.in at 4.8 volts
Speed: 60° in 0.17 sec.
Pot: 5K ohm
Strong but slow and too fat for most micro work. For larger cars though this servo has real modification potential it’s torque comes from gearing so adding a high speed Bit or ZZ motor can have dramatic results.

All of the servo’s shown have or are being modified for use with Mini-Z/IW or Epoch circuit boards but since the new Iwavers appear to be using a 3 wire servo arrangement (the driver CB in the servo) I should mention that the larger GWS and HiTec servo’s are more stable and accurate than the smaller two and that will become a factor when we get access to these new circuit board, although I was looking at that odd chip on the IW-02 CB and it’s small but interesting outputs :???:.

Currently the Interflite Mega Micro is by far my favorite at $9 to $14 US the price is right, it’s exceptionally easy to modify, and holds up well. The one in the photo may look larger but that’s just because I have put a micro connector on it for easy installation and removal in a ZZMT. See my gallery for details.

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Post by ph2t » Sun Jul 10, 2005 7:24 pm

excellent work man. I found the ges pico servo to be too slow. It's more for electric flight setups. I had to remove 2 of the 5 reduction gears just to get it up to speed in my digimasta. In the end it just wasn't worth it. I was going to go with the hitec but it looks a little big. Thanks!

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Post by betty.k » Mon Jul 11, 2005 2:49 am

thanks for doing that! :-o

and if anyone else has something to add on the subject then feel free to speak up. :-)
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Post by Tuner1989 » Sun Jul 09, 2006 7:29 pm

It looks like from your listings that the Blue bird is the easiest to swap without motor or Resistor modification correct?

Excuse my ignorance but what do you mean by surface mounted pot? How does it have to be modified to work?

And when you say the smaller ones arent as stable do you mean servo play or it does not center properly etc?

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Post by LBRC » Sun Jul 09, 2006 8:42 pm

Depends what you want to use it in.

If for example you want to hook it up to a Mini-Z or Iwaver 01/02 circuit board it is the hardest because of the surface mounted potentiometer (pot). A surface mounted component is one that is made to solder directly onto the paths of a circuit board, there are no legs or feet for wires to be connected to. Unlike the others the pot on the Bluebird is soldered directly too the circuit board so you can’t just remove the CB.

If you where using the new (not yet released) IW-02M circuit board it could be the easiest due to the smaller size. But even then there can be problems, notice that the feed-horn is all the way over on one side so even though it is smaller you might have to offset it when mounting to get full servo throw.

By stable I mean less prone to jitter and wondering under a heavy load, the larger servos have stronger driver circuits and bigger motors.

When this was written it was assumed that the fist new Iwaver-02 circuit boards would be like the 02M is again supposedly going to be not the in-between 4 wire version that was actually released. Problem is that when choosing a servo for a car it’s not just speed and torque that need to be considered it’s stability under load. If for example you tried to use a Bluebird in a 1/28th scale car you would have weak, jittery, unstable steering, that is until you stripped all of the fine tooth internal gears then you would have no steering. Which I assume is part of the 02M delay Iwaver has never really understood steering servo power requirements. If you look closely at a Mini-Z you will notice that the steering servo driver H-bridge amplifier circuit (the FET’s) is identical to the drive motor H-bridge amplifier, they certainly didn’t do that because it was the cheapest route they did it for stability. With an external servo you don’t’ have room for the high power amplifier or hulking big high torque servo motor, you also loose a little speed due to extra circuitry involved since the steering signal needs to be converted into a serial output sent to the servo then decoded and reprocessed to drive the servo motor. The short of it is that a smaller race car needs faster response times and proportionally more steering power.

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Post by Tuner1989 » Sun Jul 09, 2006 9:06 pm

Very good info as always LBRC.

What i'm looking to do is swap out the old xmod servo in my Xmod-Z to a upgraded servo. 1. for more travel and 2. for more accuracy and speed.

What would you reccomend for this application. After reading your post the bluebird seems to fly out the window.

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Post by LBRC » Sun Jul 09, 2006 9:19 pm

Definitely not the Bluebird, out of the servo’s above definitely the GWS ball bearing pico.

What circuit board?

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Post by Tuner1989 » Sun Jul 09, 2006 9:21 pm

LBRC wrote:Definitely not the Bluebird, out of the servo’s above definitely the GWS ball bearing pico.

What circuit board?


Its a MR-01 Board with a Nelly Deluxe and Etec 700's as a powersource. The car competively races on large tracks.

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Post by beanoman » Mon Jul 10, 2006 2:18 am

The interflite mega micro appears to be a Blue Arrow 4.3 servo. I have a bit of experience with these since I do parkflyer planes, and I am pretty sure they are the same thing under different names.

Also, for 1/28, I think that a BMS-306 would be very good- They are 6 gram servos, much more compact thana hs55 with TONS more speed. The hs-55 is pretty sucky IMHO, especially for 1/28. It is .17 sec for 60 degree rotation at 4.8 volts, while the blue bird is .11 with similiar torque. I have one hs-55, have had 2 Blue Bird 6 grams and plan on getting another pair. I also have BMS-371 servos with are 9 gram servos, similiar positive results from this company :-o.

The BMS-303, Blue Arrow 3.6 gram are considered delicate and generally crap servos in aircraft circles; Blue arrow 4.3 grams are considered ok and BMS-306's are loved by all for their cheap price and good preformance.

Another consideration for micro stuff is Falcon stuff- they make 1.6 gram servos for $35, but may be too delicate.


www.bphobbies.com has a good selection of servos, at great prices.

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