DS620 vs DS650 tail servo

[Trailryder42]

Hey all,
I don't understand, in these Trex 600 kits I'm looking at, why they are touting the DS650 servo over the DS620 servo for the tail rotor. The 650s torque rating is half what the 620 is and is also heavier and has "metal" gears compared to the 610s and 620s titanium gears.

What am I missing?

[Bob O]

The DS650 is the fastest of the three, which is what you want for the tail. You don't need a servo as strong as the DS610 or 620 for the tail.

With the T-Rex 600N I had, I used the supplied DS620 servo for the throttle.

[Trailryder42]

I see. Thanks.

[paulmedford]

yup, i had the ds 620 for my tail and i always had a wag, switched to the ds650 and that settled it. As stated above i used it for throttle servo too, The ds 650 is the better servo for tail control

[Trailryder42]

But why use a servo that needs the voltage stepped down instead of one of the same like servos on the cyclic, that don't? Example, the DS650 and DS610 servos in my Trex600E Pro.

From the servo charts it looks like those servos come in both a 4.8V and 6V versions. So I'm guessing the 650 used in the kit is the 4.8V version.

Is it because the tail doesn't require quite as powerful a servo? Does 3 - 4 one hundredths of a second difference to make a 60* arc between the 610 and 650 servos really make that much difference? If so, then the 6V 650 has a .01" sec faster time. Why not use it instead and eliminate the need for a step down on the tail?

Can't be to try to save a little receiver pack voltage, since the stepped voltage is being wasted as heat anyway.

Even the 5.1V stepped voltage is over the rated spec of a 4.8V servo.

So how much safe overhead of the max rated voltage is there, and not with just servos, but all of our components?

Is there a % figure for safe overhead of max rated input voltage?

[Bob O]

Originally Posted by Trailryder42

But why use a servo that needs the voltage stepped down instead of one of the same like servos on the cyclic, that don't? Example, the DS650 and DS610 servos in my Trex600E Pro.
SNIP

All three have specs listed for 4.8V and 6.0V, as those are likely what people will run them at. There aren't two different versions of the same servo with voltage being the only difference. The DS650 should be the first choice of those three servos to use on the tail.

From what I've read on HF, lots of people have used the DS610 servo on unregulated 2S LiPo for hundreds of flights without any problems, despite not actually being rated for that voltage. I always ran all three of those servos at a regulated 6.3V.

[Superior]

No stepdown is needed for the 650 I've been using the 650 on 6volts on my 500 helis for about a year now with no problems

[Trailryder42]

Originally Posted by Bob O

All three have specs listed for 4.8V and 6.0V, as those are likely what people will run them at. There aren't two different versions of the same servo with voltage being the only difference.

Ok, thanks for that info. If these servos will run at either 4.8 or 6 volts, the Align B6X regulator regulates the 7.4V receiver pack to 5.8V, so I see no need to step the voltage down for the tail servo to 5.1. Seems running them at the 5.8V straight from the reg. would get you closer to the 6V specs of speed and torque than getting 4.8V specs at 5.1V.

[Bob O]

Correct.

They supply that step-down in case you're going to run a tail servo that is spec'd at 4.8V only. Or if you want to run a 6.0V rated servo at 4.8V.

[MrHeliNewbie]

The DS 650 is a great cheap tail servo.... BEST bang for your buck !
Plays well with a lot of gyros too......

[slamdance]

What happens if there is a little friction or bind on the servo linkage train? Faster/weaker servo not so fast!!! Right? Enough to take away .02 seconds? You bet. Especially, since align tail link design is not known for being "super slippery". Also, don't forget resistance due to harmonic vibration of the tail rod. (it wobbles like a guitar string unless you have carbon fiber rod). I will take the DS-620 over 650 or 615 anyday! Ofcourse, I have this tail servo mated with the bulletproof Futaba Gy401. Absolutely, zero tail wag issues.

[Gladius]

Well that was unexpected...

[TR450ZS]

Originally Posted by Gladius

Well that was unexpected...

[ticedoff8]

I will take the DS-620 over 650 or 615 anyday!

That would put you squarely in the minority.

The global RC heli community wants the fastest tail rotor servo possible.

And, the trend is towards higher voltage servos.
The old flight packs / servos used a 4-cell NiCad pack (4.8v).
Then they went to 5-cell NiCad (6.0v)
Now, you want to run 2S LiPo (8.4v)

I've used the DS-650 on my 700N and it works great. The DS-655 is slower than the DS-650.

But, look at the BL DS-7005HV tail rotor servo:
http://www.amain.com/rc-helicopters/...FUNafgodZaEAwA.
It runs any input voltage between 4.8v up to 8.4v
When I needed a new throttle servo, I moved my DS-650 to the throttle and now use the BK DS-7005HV on my tail
There is only a $20 difference between the Align DS-650 and the BK DS-7005HV.
How can yo beat that?

I have used DS-650 and DS-655 for throttle on my 700 / 600 nitros.
I never used a DS-620 - the specs are not up to par with anything I like.