Radiolink R12DS & JX HV-6210-MG

[Mitchell Howard]

Hi all - building a new model and have been gifted some JX servos from a clubmate. They certainly seem to be of a decent spec, but they're high voltage. Normally I would have used the ESC BEC at 5.5V, 5A to run the receiver and servos, but the voltage is too low for these servos being rated for 6-7.4V.

 

Another clubmate recommended a UBEC, something like ZTW's 6A version for £15. I think this is the right idea.

 

Only problem I'm having is that I can't find any information on what amperage the servos will pull nor the receiver's max current per channel.

 

Can anyone help? Is there a standard current the receivers are built for? Can servo current be estimated?

[Frank Skilbeck]

Which servos are they? They will probably work OK at 5.5v, just that they won't develop the full torque or speed. 

 

Note servo plugs are generally rated for 6 amps and this is the typical max current per channel, if you are providing power to the receiver with a standard servo lead then this will be the pinch point. BECs or switches with higher max currents will often have two standard plugs to connect to the receiver and some large receivers (and power distribution units) have different power connections to handle larger loads imposed by multiple large servos. 

[Philip Lewis 3]

High voltage servo's are high voltage capable but they don't have to be used at the higher voltage, 5.5 volts will be fine they will just be a little slower and not quite as powerful.

 

A servo requires amps in the same way any electric motor does, it doesn't draw a certain amount of amps it draws amps in response to the resistance to positioning itself where commanded, (speed and size of control surface), the more they are stopped or prevented from attaining their assigned position the more they will draw.

 

Power in the receiver is just a BUS, i.e. the +ve and -ve are all connected on a rail.

[Mitchell Howard]

7 hours ago, Frank Skilbeck said:

Which servos are they? They will probably work OK at 5.5v, just that they won't develop the full torque or speed. 

 

Note servo plugs are generally rated for 6 amps and this is the typical max current per channel, if you are providing power to the receiver with a standard servo lead then this will be the pinch point. BECs or switches with higher max currents will often have two standard plugs to connect to the receiver and some large receivers (and power distribution units) have different power connections to handle larger loads imposed by multiple large servos. 

 

Hi Frank - models in the subject of the thread.

 

That's good to know, paralleling two smaller connectors to increase the max current to the receiver.

[Mitchell Howard]

6 hours ago, Philip Lewis 3 said:

High voltage servo's are high voltage capable but they don't have to be used at the higher voltage, 5.5 volts will be fine they will just be a little slower and not quite as powerful.

 

A servo requires amps in the same way any electric motor does, it doesn't draw a certain amount of amps it draws amps in response to the resistance to positioning itself where commanded, (speed and size of control surface), the more they are stopped or prevented from attaining their assigned position the more they will draw.

 

Power in the receiver is just a BUS, i.e. the +ve and -ve are all connected on a rail.

 

Hi Philip, thanks for the note about 5.5V. I want to plough ahead with using the UBEC solution if only to learn something new.

 

I've had a replay from Radiolink already - they've said;

"The R12DS receiver does not return overload. You can use it with confidence. The positive pins of each channel of the receiver are connected in parallel, and the negative pins are also connected in parallel. You need to be careful not to mix high-voltage servo and ordinary servo, otherwise it may cause damage to the normal steering gear due to overload."

 

I take this to meant the white or yellow signal wire is low voltage, low current and doesn't factor into the load calculation. Mixing HV and standard servos means you could overvolt the standard with a supply for HV. I'm not doing that, all servos are the HV type.

 

They're saying each servo is connected in parallel to common + and - rails. That means that while you're not pulling voltage/current through each servo in turn, you're still putting an increased load upstream of the common connection point, and the rail itself has to cope with that. Presumably the physical rail is just a printed track on a PCB. If each of the servos pulls 3A at the same time, the question I think I should be asking Radiolink is, "can the rails cope with 12A@6V".

 

Frank - if they're each rated to 6A and Radiolink have factored that in to the design of the rails, then presumably a 12ch receiver can handle 72A... which doesn't seem likely, so there must be a lower value.

[Frank Skilbeck]

The power supply connector is only rated 6A, if you double it up then 12A, it's the connectors not the common rail on the circuit board that are the limit. But if they were pulling 12A then this would put quite a load on the supply battery.

 

The servos are quite powerful so that must be a very large model to need them, as Philip notes the servos will only pull as much power as they need to move the control surfaces, so it's only when they are required to deliver their maximum torque would they draw their maximum current. I couldn't find anywhere where JX quote the stall current. But a similarly spec'd Hitec servo has a stall current of 2.6 amps.

 

If you model has large enough control surfaces, e.g. large flaps, to require very high torque then a separate supply battery with a power distribution unit (e.g. powerbox) would probably be the way to go. But if all you are doing is using over specified servos then the actual current draw will be much lower. My 1/4 scale ASK-11 on a 4s and aerobatic model (Dynam Smooth) using a 6s setup run on the ESC UBEC, but my Towrag on an 8s runs on a separate Rx/servo battery, but here the maximum load is the tow release servo.

[John Lee]

If you want to check how much current your servos are actually drawing you can use the handy little Safety Master widget. Obtainable from several suppliers, eg https://www.robotbirds.co.uk/safety-master-on-board-servo-power-analyser-rb408036-4460470.html.html 

I've shown it here on my bench where you can see real time voltage & current draw. In addition you can install it in a model & then after you land you can then see the peak current drawn by a servo during that flight.

 

[Mitchell Howard]

3 hours ago, Frank Skilbeck said:

The power supply connector is only rated 6A, if you double it up then 12A, it's the connectors not the common rail on the circuit board that are the limit. But if they were pulling 12A then this would put quite a load on the supply battery.

 

The servos are quite powerful so that must be a very large model to need them, as Philip notes the servos will only pull as much power as they need to move the control surfaces, so it's only when they are required to deliver their maximum torque would they draw their maximum current. I couldn't find anywhere where JX quote the stall current. But a similarly spec'd Hitec servo has a stall current of 2.6 amps.

 

If you model has large enough control surfaces, e.g. large flaps, to require very high torque then a separate supply battery with a power distribution unit (e.g. powerbox) would probably be the way to go. But if all you are doing is using over specified servos then the actual current draw will be much lower. My 1/4 scale ASK-11 on a 4s and aerobatic model (Dynam Smooth) using a 6s setup run on the ESC UBEC, but my Towrag on an 8s runs on a separate Rx/servo battery, but here the maximum load is the tow release servo.

 

It's not a large model, it's a Wot4, but having been gifted the servos I'd like to use them. They're better quality items than I was planning to buy.

 

I'm thinking about a 6V output from a ZTW 6A UBEC will do the job.

 

I'm happy with the technical principle that a motor will only pull the current it needs to. I don't have any idea what kg loading the control surfaces will need in the worst case. The servos are 9-10kg stall at 6V, so judging by the hitec spec, if they're all stressed at once (2* aileron, 1* rudder, 1* elevator) then we're looking at 10.4A. The engineer in me is saying, "make sure you've got enough current for that condition"!

 

[Frank Skilbeck]

Unless you have badly installed the control linkages and they are stalling because they are jamming I can't see any reason why they would ever need to generate anything like the full torque, my Wots Wot uses standard Futaba 3003 servos (3.3kg torque) and I have never noticed any control deflection problems with it. My 72" Astro Hog has a single 3003 servo driving both ailerons via bell cranks, as did my kit built WOT4 with Laser 61 a couple of decades ago!

 

At 9kg torque you are more likely to rip the control horn off the control surface ? 

[Frank Skilbeck]

Edit - the Wot 4 was some 30+ years ago and used a single Fleet servo (FPS-12 or 16?) to drive the ailerons ☺️

Edited June 1, 2021 by Frank Skilbeck