Hey, I've got a question that's kind of weird. I'm not completely sure how to phrase it, but I'll try my hardest.

I was looking at the Futaba 9001's and noticed it said 72oz-in of torque. I was looking at stats for other servos that said they had 114oz-in of dynamic torque and 228oz-in of holding torque. Is the 9001's torque rated as "holding" or "dynamic" torque? I'm not sure which two numbers to compare....whether to compare the 72 to the 114 or the 72 to the 228. Any help would be truly appreciated. Thanks!

I have searched the Futaba servo web site and they do not say either holding or dynamic torque. Holding torque is the maximum restoring torque developed by the servor when energized. The dynamic torque is also called running torque or pullout torque. As a rule of thumb, the maximum dynamic torque is about 70% of the holding torque.

At 4.8v the S9001 is rated at 54oz-in and at 6.0v is is rated at 72oz-in.

The Futaba S9001 is a coreless ball bearing servo and can produce high-current draw from your batteries. If using NiMH or LiPo batteries, make sure they are capable of delivering sufficient amps.

Personally on a GP Giant Super Sportster, I use S9001 with 6.0v batteries and I am very pleased.

Okie-dokie....thanks!! Finally a halfway coherent answer! Everyone else that has responded has told me that holding torque is LESS than dynamic torque...even though all of the specs I've found show differently. Another common response is "It depends if you're running 4.8V or 6.0V" and "What plane is it going in?"

I guess that answers my question...I'll just wait to see what Bax says before I make my mind up completely. If he doesn't know for sure...I'll go with your answer, I guess. Thanks!!

Futaba servos are tested using a torque meter. This tests the servo at the maximum possible torque it can develop to move a control surface. If the servo cannot move a surface or function, who cares how much it can hold after it gets there?

I guess it wouldn't really help much at all unless you're wanting to advertise the higher torque rating. Unfortunately, marketing these days has gotten to the point that people will use almost false numbers just to sound better. I mean, in this case, if the Mfg (Futaba) wanted to show that their servo had a higher torque rating...y'all could publish the holding torque. Yeah, that's technically not lying....but once there's a standard set you're almost lying to use other stats without saying otherwise. Unfortunately, that kind of number-play is all too common. I'm glad to see that it's dynamic torque that we're talking about (even if I'm a little sad that my $40 servo didn't have 228oz-in of torque and a .13s speed rating...that would've been something else!).

Thanks Bax. As always, very helpful!!

One might care about the difference, since torque is a component of velocity. If, for instance, you crowed the ailerons / flaps on a glider at a certain velocity during level flight, it would require a certain amount of servo torque.

However, if the glider decended rapidly with the servos still locked "on crow", the likely increased velocity would cause an increase of force on the control surfaces, which could overstress the servo(s). Perhaps "Holding Torque" helps one determine if that's possible.

But what do I know?... I'm in Marketing (with an engineering degree)... lol

Best... Roger

If the servos get overstressed at any point for any reason, you have the wrong servos. In the above case, you didn't choose servos that were strong enough, regardless of how they're rated. Also, since nobody really knows the force that different control surfaces really need, you can only estimate which servo to use and then try it out to see if it does the job.