Digital Futaba standard servos

[Graham Bowers]

I'm about to use the last of my small stock of new Futaba S3001's in a second hand Wot 4 Mk3 airframe.

 

The next projects  will be an electrified Seagull PC9 Pilatus and then a  Blackhorse Chipmunk, the 64 inch version, for which I have an RCV 91CD.

 

If I stick to standard Futaba servo's, and I probably will, it'll mean using a digital replacement for the S3001's, so most likely the S-U301.

 

For glow powered models I use 4 cell NiMh packs and I see the servo's are rated 4V to 8V. Am I going to need to up my game in receiver packs please? Any other "gotcha's" ??

 

Thanks

 

Graham

[Paul De Tourtoulon]

I just bought some U301's and mixed them with Futaba 3001, 3010  and some corona 939 analogic ones in my Seagull Seafire they all work well together.

[Nigel R]

25 minutes ago, Graham Bowers said:

Am I going to need to up my game in receiver packs please?

 

short version, no, as they're rated much the same torque/speed as the 3001 at 4.8V

[Graham Bowers]

Thanks gents. 

 

[Engine Doctor]

Just check the current draw . I see the other post refer to using the newer servos with the 3001's and seem to miss the bit about the battery. If the newer digital servos are like many others they use more current and its worth upping the battery pack to allow for this. Like changing from AA  cells to Sub C or C cells or even a  life pack.

 Are 3001 or equivalent no longer available ?

[Nigel R]

They've switched to the SU300 I believe. Futaba claim 3.5kg at 4.8V - not much different to the 3001. I'm guessing that was done deliberately to make it a drop-in replacement.

 

disclaimer: I'm only looking at futaba's ratings and I haven't measured one.

Edited December 5, 2022 by Nigel R

[Graham Bowers]

27 minutes ago, Engine Doctor said:

Just check the current draw . I see the other post refer to using the newer servos with the 3001's and seem to miss the bit about the battery. If the newer digital servos are like many others they use more current and its worth upping the battery pack to allow for this. Like changing from AA  cells to Sub C or C cells or even a  life pack.

 Are 3001 or equivalent no longer available ?

3001's no longer available - that's progress I suppose.

 

I'm not sure how I'd check transient current draw and voltage dip with the equipment I have available. And even if I did, am not sure how I'd evaluate the data, in terms of what's good or bad. I worked as a test engineer in a past life and had access to all of the toys .................................

 

There is a case for just playing safe and upping the battery spec. It would be nice to have facts and data as well as anecdotes, however anecdotes do have their place.

[J D 8]

      You do not say what capacity 4cell packs you use, but you could just move up to a 5cell pack of possibly larger capacity. 

[SIMON CRAGG]

I have used Futaba digital on all my larger models for many years without any issues.

 

Always used LifePo4 Rx packs in the model and TX.

 

All practical experience "up the field"!.

[Graham Bowers]

57 minutes ago, J D 8 said:

      You do not say what capacity 4cell packs you use, but you could just move up to a 5cell pack of possibly larger capacity. 

Good point.

 

Up to now, AA packs, so 2000mAh to 2300 mAh. 

[john stones 1 - Moderator]

If you're happy with standard servos, why not just buy another make of analogue servo ?

[Graham Bowers]

29 minutes ago, john stones 1 - Moderator said:

If you're happy with standard servos, why not just buy another make of analogue servo ?

Thanks, may well do that. It just seemed a suitable time to consider options. Perhaps one may anticipate other brands following suit at some time in the future.

 

[J D 8]

30 minutes ago, Graham Bowers said:

 

 

Up to now, AA packs, so 2000mAh to 2300 mAh. 

   Unless you are powering many extra servos I see no real need to up capacity. With the old nicads we used to be happy with 500 to  600mAh batts, An extra cell increase's capacity as well as voltage.

[Ace]

As you are a longstanding Futaba user it may be useful to ensure if you buy another brand they also have 25t splines making swooping arms easier. 

AA 5 cell works fine for me on up to 6 std digitals. If a long session I do a quick check with a loaded battery checker, 🤞 never been an issue for me. 

[Harry Curzon 1]

5 hours ago, J D 8 said:

   Unless you are powering many extra servos I see no real need to up capacity. With the old nicads we used to be happy with 500 to  600mAh batts, An extra cell increase's capacity as well as voltage.

No, an extra cell in series does not increase capacity, it increases the voltage.  The higher voltage drives more current so the battery does not last as long as one with fewer cells!

[John Lee]

8 hours ago, Graham Bowers said:

 

 

I'm not sure how I'd check transient current draw and voltage dip…….

I use one of these

[Frank Skilbeck]

10 hours ago, Harry Curzon 1 said:

No, an extra cell in series does not increase capacity, it increases the voltage.  The higher voltage drives more current so the battery does not last as long as one with fewer cells!

True at max load or for a stalled servo, but work is power x time and power is volts x amps, so if the servo is only applying the same force it should draw fewer amps. The SU300 can generate 3,5kg/cm at 4.8v and 4.5kg/cm at 6v, but if you only need 1.5kg/cm the servo will only draw as much current as it needs to hold that position, the servo at a higher voltage may move quicker to the new position (depending on how quick you move the stick 🙂 ),

 

I use a mixture of 4 and 5 cell subC packs on my larger gliders and after a day at the aerotows I haven't noticed that the 5 cell batteries take more mah on recharging. 

Edited December 6, 2022 by Frank Skilbeck

[Engine Doctor]

17 hours ago, J D 8 said:

   Unless you are powering many extra servos I see no real need to up capacity. With the old nicads we used to be happy with 500 to  600mAh batts, An extra cell increase's capacity as well as voltage.

Yes we did however firstly the radio gear was far less sensitive to low voltage and responded to a drop in voltage by reducing range but it still worked . Unlike modern radio that shuts down / brown out . Also the servos were not so power hungry as modern equivalents. 

[J D 8]

               That is so, but the packs the OP is using are 2000mah one's. Same as what I use.

[Frank Skilbeck]

2 hours ago, J D 8 said:

               That is so, but the packs the OP is using are 2000mah one's. Same as what I use.

One thing to watch with high capacity AA packs is that they can have a reasonably high internal resistance, so if asked to deliver a large current they will exhibit a noticeable voltage drop, the old 600mah Nicds were often better in this respect. No problem if its a typical club size model with lightly loaded servos, but for larger models I tend to go with Sub C cells which hardly blink under load (in Peter Kay speak they are the Hob Nobs of the battery world 🙂 ) 

 

 

[Nigel R]

The low discharge nimh tend to have fairly low internal resistance. 

 

Eneloop cells will easily supply 5a before significant voltage drop. Plenty for a sport model if the size being asked about. 

[Nigel R]

Further to above.

 

I fly a 3d sort of hack, 5lb, 70 size four stroke, with four Futaba digitals driving four very large surfaces. RX pack? Eneloop 4 cell. No issues, uses around 100mAh per 10 min flight. Don't skimp on the brand! 

 

9 hours ago, Frank Skilbeck said:

high capacity AA packs is that they can have a reasonably high internal resistance

 

Eneloops do not have a problem with internal resistance.

 

I've copied some graphs below. Many discharge tests have been done on Eneloop cells. Similar results across the board.

 

The third curve up (purple/pink) from is a 5A discharge on an Eneloop cell. It holds up well even at that constant 5A load - that's around 4 fully stalled standard digitals. If that many are stalled you need a bin bag.

 

I am aware servo loads are not constant, digital are not like analogue, etc.

 

I also don't work for Panasonic. Other good brand nimhs are available. However, lots of RC places sell Eneloop packs.

 

 

 

13 hours ago, Engine Doctor said:

Unlike modern radio that shuts down / brown out

 

Sorry ED but I don't buy this.

 

Spektrum RX (I'm guessing its Spektrum we're talking about here - I've never heard anyone mention other brands in this context) operate down to 3.6V. 

 

Even the 10A discharge curve does not push the nimh enough to pass that threshold on a 4 cell pack - until the pack is flat.

 

10A would on a 4 cell nimh pack would risk melting the wiring. Heavy gauge silicone insulated servo wire is good for around 5A if memory serves. Standard wiring with plastic, about half that?

 

A badly chosen BEC? With too many servos? Sure. Might cause that problem... But. That's user error.

[Frank Skilbeck]

Nigel, that's useful information and backs up my experience with eneloop AA cells, but I do have some other non-eneloop packs which have a much higher voltage drop under load, never had a brown out, but did experience telemetry low voltage alarms, set at 4.5v, so I stopped using them and they are relegated to bench duties only. But maybe I should check that the packs in question don't have a faulty cell.

 

I'll also add badly chosen switch to your badly chosen BEC.

[J D 8]

            Eneloops are what I use in my club size models,

             Some years ago I helped rescue a club members 1/3 scale Cub that ended up in some tall thick scrub when control was lost. You would think a yellow cub of that size would be easy to spot, not so.

I then slowly drove my Land Rover into the scrub and by standing on the roof was able to locate and eventually recover the Cub with little damage.

  The power pack for this large model was a new 4cell sub C item with no markings that had just died.  Why????