RC10Talk - The Net's Largest Vintage R/C Community

As part of my learning in the last year on lipos, brushless technology, and other advancements in RC since I left in my teenage years (early 90's) I have another question. What are "digital" servos and how do they compare to the traditional servos I used in the 80's?

And while I'm posting this, I see some other brands out there I was never familiar with as I was a Futaba loyalist. I think I've seen Hitec and some other brands especially with modern radio gear that I never knew about. Is Futaba radio gear including servos still well regarded?

yes futaba is still great gear. probably a little pricier then the equivalent competition, so that is why you see many more vendors.

digital servos are exactly like analog servo in the primary drive side, so motors, feedback, gears, etc is all the same.

the difference is in how accurately the servo can hold position. analog servos basically used the control signal from the receiver to determine how fast to update the servo motor feedback, so there is a larger 'deadtime' between servo corrections. this means that you will see a larger jitter in a servo arm. this is typically around 60 corrections a second.

a digital servo has a much faster control loop and therefore a much smaller deadtime between corrections. so the jitter and error is much smaller. a typical one might have 1200 samples per second.

this is analogous to a standard esc vs. the 'high frequency' esc's. same control loop changes.

there is some general goofiness between different vendors in regards to their specs, so it's generally a good idea to keep brands together between receiver/servo. 95% of the time it's not an issue, but just be aware......

Another brand of digital servos to check out are Savox, you have a choice of Titanium and also steel gears....for the money they are fast and very torquey. they run the same spline pattern as Futaba. I have used just about all the other brands and these ones gave me that same impression when KO first released their FET servos back in the 80's...'Dayum thats fast!'

uzzi wrote:Another brand of digital servos to check out are Savox, you have a choice of Titanium and also steel gears....for the money they are fast and very torquey. they run the same spline pattern as Futaba. I have used just about all the other brands and these ones gave me that same impression when KO first released their FET servos back in the 80's...'Dayum thats fast!'

Dayum, I probably shouldn't have asked this question then. Did you say TITANIUM? (hah, see my signature link). Wow, that thing is badarse. But from what has been said I'd need a completely new/modern radio system to use something like that (the model #SC-1257TG Standard Digital "Ultra Speed" Titanium Gear Servo).

Thanks for the heads up, seriously. Very cool.

I forgot to mention the titanium geared ones are also slightly lighter as well (even with the heatsink body). The downside is you do need to upgrade your radio to the newer digital radios to take full advantage of the specs these servos produce. If you are using them for 1/8th buggies try the 1267 in steel gear at 7.4 volts (yup lipos w/o the regulator) they pull 20plus kgs of torque!!

A further advantage of digital servos (depending in the manufacturer) is they can be programmed, we run Hitec digitals in large scale aerobatic models with great results, you can program direction, end points, speed and other parameter direct into the servo, great for matching multi servo control surfaces.

One thing to note most metal geared servos regardless of the material have a sacrificial plastic gear to protect the motor so they are not completely resistant to stripping, it's always worth running a servo saver on the steering and that being the case it might not be worth spending the extra on metal gears.

bumping this because I have a follow-up question. What's the advantage of brushless servos? Is this level of technology REALLY necessary or is digital good enough for most hobby racing?

The brushless technology in the servo world makes the resolution finer still, and then adds increased speed and less battery draw-

I also race the futaba BL/Digital line- but it's not a factor for running/bashing

flipwils11 wrote:bumping this because I have a follow-up question. What's the advantage of brushless servos? Is this level of technology REALLY necessary or is digital good enough for most hobby racing?

I think mostly just efficiency. Some 8th scale truggies and monster trucks demand a lot from such small devices. Relatively small voltage can only produce so much power and the less resistance those volts meet, the more power they can produce. It would be real hard to sell me on the idea that expensive servos can improve the driving skills of amateur drivers...and I am ABSOLUTELY included in this reference so no offense to anyone please.

titanium is lightweight, but that isn't necessarily same as "strong" for a given mass
... some plastics are stronger imho

i have read some problems with savox with regards to the Titanium gears as compared to the metal gears. its a bit heavier but its negligible. nothing beats a servo saver onto the servo. I my self has a 1251MG low profile servo and its fast.... faster than my hands, hahahaha..... i really need to improve on my driving skills...

hahaha....

I ordered the Savox and have a Futaba 3PM-x coming in the mail so I'm excited to try it all out!

Nice transmitter! and I have heard good things about the Savox line as well!!

Charlie don't surf wrote:Nice transmitter! and I have heard good things about the Savox line as well!!

I should have clarified, I didn't order a new one, I bought the one bearickster had for sale recently. I did order the Savox servo new though.

I got my 3PM-X the other day and hooked it up. Lots of menus and things to learn on it. I set it up with my standard analog steering servo and it worked fine. Last night I got my Savox digital servo and hooked it up but there's a problem.

When I turn the steering wheel on the transmitter, the servo activates for a split second and then stops. The receiver led goes from green to red for a second like it's tripped some kind of fault protection and the servo won't respond. Then it goes back to green again and the servo will again barely move before "tripping" the receiver again.

EDIT: Got it. Savox support got back to me that the low voltage trip is coming on from the Futaba receiver because of the current the savox requires. I have one of these Novak glitch free capacitor things to try so hopefully that stops it.