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Blue Bird High Torque Servos

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Old 01-07-2007, 08:07 PM
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cleatis123
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Default Blue Bird High Torque Servos

There have been a few threads about the BMS-620 series servos, I just want to know if anyone has been running these high torque or high speed servos lately, and in what plane or vehicle, the guys at bphobbies said that they have made some changes recently?
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Old 01-08-2007, 02:27 AM
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Default RE: Blue Bird High Torque Servos

The 620 is a pretty good servo for the money but the 621 is junk -- slow (despite claiming to be faster) and lousy centering.

The ones I've looked at are actually OEMed to WayPoint and rebadged as 1620 and 1621 but they're the same basic servo. These may be the older ones because I bough them about 6 months ago.

The new 630 and 631 seem a lot better -- but not as high torque.
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Old 01-08-2007, 06:38 AM
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Default RE: Blue Bird High Torque Servos

I have been running the BMS-660MG for brake and throttle in my FG, works like a charm, but I expect they are not as fast as advertised.

I have replaced with Thunder Tiger ACE DS1015, as I want to try Digital Servos.
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Old 01-08-2007, 10:59 PM
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Default RE: Blue Bird High Torque Servos

Yep, Bluebird are incredibly optimistic when quoting speed figures. The 1621/621s I got were supposed to be "high speed" (around 0.1Secs or so) but they're about half as fast as the Hitec HS5925 servos I've got which also claim to have the same speed.

Even the 631s I got a few weeks back which claim to be 0.08Secs on 6V are *much* slower than the HS5925 which claims the same.

The reality is that you just can't get this kind of speed from a cored motor -- there's too much inertia in the heavy iron-cored armature and that means it can't start and stop fast enough.

The result is either a servo like the TowerPro MG995 which is under-damped and overshoots like crazy (the motor doesn't stop in time so it goes back past where it's supposed to be and has to back-up) or one like the 621 which is exactly the opposite -- they've overdamped it so that it slow right down before reaching the commanded position and almost crawls the last few degrees -- thus making for a *very* slow overall transit time.

Ther are some good hi-torque cored servos but no good hi-speed ones. For that you need a coreless motor and (preferably) a digital amp.
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Old 01-09-2007, 06:22 AM
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Default RE: Blue Bird High Torque Servos

In the large scale car circles the Thunder Tiger ACE DS1015 is thought to be one of the best. 14.5kg/cm and 0.108/60 (0.08 at 45) and Digital,
But price is at least twice that of the BMS-660MG and maybe 3-4 times the BMS-620/630 series.
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