Cirrus Vrs. Hitec micro servo's - RC Groups
Thread Tools
Oct 15, 2002, 10:22 PM
Registered User

Cirrus Vrs. Hitec micro servo's

I am going to buy 2 or 3 small servo's (not HS-81 small)

more like HS 55's

so I was comparing the HS 55 to the cirrus servo's....

this is the HS 55=

Torque: 4.8VDC: 13oz-in.

Speed @ 60 Degrees: 4.8VDC: 0.17 seconds

Bearing Type: None (Case serves as bearing)

Case Size: 0.9"x .46"x .95"

Weight: .32oz

Wire Length: 6.5" (Includes plug)


this is the Cirrus CS 21BB=

Torque: 19.0 Oz per inch @4.8V

speed: .09 sec @ 60 deg.

Bearing: ball bearing

Case: .86 x .43 x .77

weight: .32 Oz

Wire length: unknown

it would appear the Cirrus servo blows away the Hitec as they are the identical weight and the cirrus is actualy a bit smaller, and has WAY more power and Torque.

does any one use cirrus servo's?

how do they operate, any problems?

do they center well after much flying time?

Do they get sloppy?

are they jitery?

any and all opinions are much appreciated.

Sign up now
to remove ads between posts
Oct 15, 2002, 11:03 PM
Acme Powered!
Joe Elston's Avatar

Cirrus 21bb

Well I have some Cirrus 21bb servos and they seem to work very well for me. I am planning to install two in my T-33. I dont think that I would install them in my Jepe F16 But they have their place and work well when not put into super fast planes. That's just my opinion. But when I need really good servos like for my F16 I bought Volz Micro Maxx X's for the tailerons. Try em they work well.
Oct 15, 2002, 11:18 PM
rpage53's Avatar
Performance always has a cost. The high torque and speed of that Cirrus servo requires a large current. 3 of them have overloaded the BEC on small ESC's. Some people have added a resistor to slow them down.

Oct 15, 2002, 11:27 PM
Senior Member
sguty's Avatar
The one problem I've had with the CS-21s is that they can draw a lot of current when working hard--that power and speed has to come from somewhere, right? Can be a problem if you're using a BEC circuit that can't keep up/is at the max cell count count. I had some thermal cutouts when using them in a Ky F-16 with the max cell count for the ESC (Dragon-35). Going to a separate Rx pack (and checking the charge before every flight) fixed the problem.
I've heard reports that they can draw up to an amp apiece when stalled, though if you're stalling them with flight loads you need to be looking at a higher torque servo anyway...
Oct 16, 2002, 12:27 AM
drbird's Avatar
When speaking of micro I don't think the Cirrus are a slight bit smaller but rather a great deal smaller! I use to use nothing but Hitec HS-55's but since discovering Cirrus servos I will never go back! Just my opinion mind you!

Oct 16, 2002, 04:34 AM
smug in granny panties
monkamarm2000's Avatar


Cirrus is a good servo for a great price.And actually were all suckers cause were paying for a name!LOL Cirrus is Hitec. Break one sometime and call Cirrus customer service,you'll get Hitec on the phone!haha And break aprt a Hitec feather sometime then put a Cirrus MX-4 next to it and laugh at the similarity.
Oct 16, 2002, 09:04 AM
Big gov never Works
St. Martin's Avatar
I have the cs 21bb & cs20bb, ben using them since there intro.
I have the cs20's in my t-33( one in each wing panel) and have no problems to date. My balsacraft sea fury has the cs21's no problem. I would stress free moving surfaces, as much as possible
to lower current draw as much as possible. This is I feel relevent in all RC applications. Steve
Oct 16, 2002, 10:54 AM
Registered User
wow, over night it would seem that every one realy sems to think they are pretty good servo's!

I guess I have to order a few and see how it goes!

I have a Hobby People catalog, is there any other shop or online store that you all use to get these servo's....?

thanks ,

Oct 16, 2002, 11:01 AM
Big gov never Works
St. Martin's Avatar
Get mine at the LHS. I try to use the HS whenever poss. Steve
Oct 16, 2002, 01:08 PM
drbird's Avatar
You might try - I think thats where I got mine but I'm not for sure?

Oct 16, 2002, 01:30 PM
smug in granny panties
monkamarm2000's Avatar

You got it

St.Martin hit it on the head. Free surfaces. Heck I'm running about a 90 mph plane with GWS micros on it and i just did the surfaces correct, kept linkage at proper angles and no slop and this thing does snap rolls at speed like you wouldn't believe. When your dealing with mechanical leverage on short arms every degree of deflection counts. I'd like to do a test sometime to see on an average, how many of the advertised ounces in torque actually ake it to the surface in average applications.
Oct 16, 2002, 01:46 PM
Registered User
I have 8 CS-21BB servos. The youngest is three years old, the oldest is more than 6 years old. All have been in all manner of planes from little HLGs to a monster 6-foot 4-lb electric. And all have been through crashes that I figured shoud have been the end--but they're still running strong.

In my opinion, these things are among the best servo bargains on the market today. I *WILL* be buying more (as soon as I've laid aside enough spare change)!
Oct 16, 2002, 04:38 PM
Senior Member
sguty's Avatar

servo load worksheet

Totally agree that energy lost in mechanical binding helps no one, but do wonder how well those GWS micro servos are going to hold up in a 90 mph plane with any serious control area or deflection. There was an article in RCM back, I think, in April 2000 or thereabouts, on servo loads with a full blow-by-blow on the equations. Author said he'd created a worksheet in Excel to do the calcs. In one of my geekier moments I tried recreating his results, came up with the following worksheet:

You need to know the area of the surface, location of its centroid (center of area) from the hinge line, desired deflection, and the moment arms of the servo arm and control horn--those are the fields in yellow--and it gives you servo force required for a variety of airspeeds.
Last edited by sguty; Oct 17, 2002 at 01:07 AM.
Oct 16, 2002, 09:25 PM
smug in granny panties
monkamarm2000's Avatar

cool spread

I like that program. Gives you a second opion at the least to make dure you've got the math right.