Futaba Brushless Servos

[MikeV]

Futaba has recently announced new Brushless servos. With one being designed specifically for use as a helicopter tail servo. According to Futaba these new servos are 30% faster than digital servos. They're less susceptible to vibration and shock. They run cooler, last long. The gear trains have been treated to reduce slop and backlash. They have increased resolution, dual ball bearings, and the same power consumption and centering as brushed digital servos. The case sizes are also standard so that they'll fit most helicopters with ease. The BLS251 is designed specifically for use as a tail servo. It's compatible with the GY401 and GY611 Futaba gyros. Look for this new servo, along with the BLS351 (hi-torque car) and BLS451 (high-speed car) to hit the fields this month. The BLS251 will have a street price of about $140.
www.futaba-rc.com

[Shawn K]

Unofficial word from some people I've heard of who are already using them, is that they center very well, transition very quickly, and seem to run cooler than brushed servos. These should be a real boon to the market. I'm considering putting a few on the cyclic of my machine.

Futaba is also releasing a new servo (brushed digital, not brushless) to compete with the JR 8611. It should crank out about 320 oz./in. at 6 volts!

I'm anxious to see when/if the Big 3 (Futaba, JR, and ATX) develop a good contactless feedback pot. Coupled with a brushless motor, those should make for some incredibly consistent servos!

It's a great time to be in the hobby. :p

[AaronS]

my thoughts exactly Shawn, what about stepper motors?

[Shawn K]

Couldn't tell you. I'm not that familiar with them, but what little I know makes me think that you'd have to have some very fine resolution in them to make them worth anything for R/C use.

I would think that the limiting factor in a stepper motor would be in how fine a control you could maintain between the motor steps. For example, let's take an "old school" 1024 PCM system, which would divide the full Tx stick motion into 1024 discrete control "chunks". Let's also assume that we're dealing with a fixed 60% servo wheel rotation (I'm not going to include the variations in rotation that would come about with changes in EPA).

So now, we're talking about being able to break down 60 degrees of servo rotation into 1024 individual positional changes. That corresponds to each step of the stick movement affecting the servo rotation .058 degrees (we'll call it .06 degrees). That would equate to having a stepper motor with 6000 individual "steps" in it's 360-degree rotation to be on par with Tx resolution.

If you look at the new 2048 resolution radios, you'd need a stepper motor with roughly 12,000 individual steps around the motor to maintain the resolution that the radio could provide. While not impossible, I'd think that the cost would be prohibitive (.03 degrees per step is some mighty fine control!). Like I said, though, I simply don't know what's available and what the current state of stepper motor technology is. These are just SWAG figures off the top of my head.

The nice thing about brushless motors and contactless feedback pots is the analog nature of their operation. The motor simply spins until given a command to stop spinning. If you remove the brushes and the contact points of the feedback pot, you remove the wear associated with them.

Anyone else have any insight? I'll freely admit that I'm out of my league here... I'm just trying to reason my way through it.

[freakyreef]

Any word on how fast these things are going to be?
320 oz/in. :eek: This could really change the way heli's are designed with that much torque. CCPM is pretty much the standard since three servos share the load, but with that much torque a standard mix design may be feasible again. Just imagine the speed and low servo loading of a eCCPM without the interactions.

[Shawn K]

About .15 sec./60 degrees (at 6.0 volts), or something like that. It's not one of the new brushless ones, though, keep in mind.

Mega-power servos aren't that new an idea. JR has had the 8611 for over a year now, and the 8711 peaks at over 400 oz./in.. R/C car guys have been playing with Big Torque longer than us heli guys have.

[Shawn K]

but with that much torque a standard mix design may be feasible again.

I don't know why anyone would think that a mechanical mix design is unfeasible. I can point you to some mechanical mix machines from pilots that I know personally that would change your perceptions about mechanical mixing. In fact, I have an R90 SE that I'd place against any machine out there in terms of control purity and straightness.