Using High voltage servos?

[Richard Harris]

Just trying to understand high voltage servos and how they are set up. I am planning a bit of a big build once all other builds are complete, for this I will be needing a couple of servos with a combined stall torque of around 60kg.

The servos I have been looking at look to be able to give me more than what I have calculated but most seem to be of the HV type.

This is something I don't really understand, do they have a seperate supply to give them this voltage or is there some kind of 'unit' that has to be used in conjunction with them?

Sorry if its a bit of a daft question, I just don't know!

Rich

[ken anderson.]

rich-why not have a look on the LMA forums.......they might use the 'heavy' stuff you are talking about..like here....

 

ken anderson ne..1 ...LMA dept.

Edited By ken anderson. on 10/03/2012 18:00:12

[Steve Hargreaves - Moderator]

No direct experience Richard so I might be wrong but my understanding is that you would connect them to the Rx just the same but then power the whole systems with a "high voltage" battery which usually translates as a 2S LiPo (8.4 volts). Most 2.4GHz Rxs are OK up to 9 or 10 volts input....

[Richard Harris]

Thanks for the helpful advice gents, I will take a look at the LMA site.

Its a bit of a daunting thought connecting a 2s Lipo up to my receiver

[Frank Skilbeck]

The Rx has an onboard voltage regulator for it's own electronics and as the power to drive the Rx circuit is very low the heat generated by dropping the volts is minimal, so if the Rx is rated for a 2s lipo (or 9v) then it will be fine. The servos are all powered off a common rail so the servo power doesn't actually go through the Rx electronics, for the same power using a higher voltage will require less amps so it's actually better for the cables and connectors, providing the servos are rated for the voltage. Quite a few recievers are now quoted as being 2s lipo compatible.

Don't try and use a standard servo on a high voltage supply though.

 

Edited By Frank Skilbeck on 12/03/2012 17:04:13

[ross blackwell]

Having just read the above notes re high voltage,I would like to know when my new servo info says "4.8v- 6.0v does that mean using higher voltage batterieswill damage? (my electric powered glider has 11.1 lipo through esc with BEC) Or does it mean that it just needs a minimum of those quoted voltages to operate correctly?

[ken anderson.]

ross it means thats the range that the servo can take/needs...the bec controller will look after the settings for the RX and servo's....

ken anderson ne..1 early morning reply's dept.

[Peter Beeney]

Ross - Just to supplement Ken’s early morning post, if I may, the 4.8 - 6V info means that 6 volts is a maximum that can be a applied to the servos but they will also accept 4.8 too, it’s just that they won’t be quite so fast or have quite as much power.

Having now said that, these voltages are nominal voltages, which simply means in this context it’s just the wording written on the label, there is a degree of inbuilt flexibility; a 6 volt battery in this case will mean a 5 cell nickel pack, and becoming more popular nowadays, a 2 cell LiFe. A fully charged 5 cell NiMH pack might be as high as 6.75 volts, tapering down 5 volts, fully discharged. So the servo will actually be ok working between about 7 volts and 5 volts. LiFe is from about 6.6 volts down. A 4 cell pack will vary from around 5.4 down to 4 volts.

It’s a bit like your car, this has a 12V battery and electrical system, but it’s rarely working at that level. From about 14 volts when it’s running, mine is 14.2, down to 11 volts if it stands with say the lights left on for a long time. If the battery is in good nick it will be around perhaps 12.7V when standing. All the equipment will accept these variations. As Frank says in his very user-friendly post above, anything that requires a precise voltage will be supplied by a regulator as part of the circuit.

The BEC on your ESC will simply supply a steady 5 volts to the radio and servos, or sometimes 6 volts now, I believe. So the servos will be fine either way. Connect up and go flying!

If it’s of any interest, and as you mentioned a 11.1V lipo, this is halfway voltage, between 12.6 and 9 volts, so that the watt-hours can more easily be calculated. It’s an average voltage over the discharge. The watt-hours give a more meaningful comparison between battery output, for instance, comparing a 10 volt, 1,000mAh and a 20 volt, 1,000mAh pack, they are both 1,000 milliamps capacity, but the 10 volt contains 10 watt hours and the 20 volt has 20 watt hours, twice as much energy.
Strictly speaking, 10.8 volts is the halfway mark, 3.6 volts/cell, this was the original level used, but then I guess someone managed to squeeze another ounce out of a pack and then said “ My battery is better than your battery!”. So everyone else had to follow suit!

Also just for interest, a servo will go on working down to about 2.7 volts; although it does tend to get a bit erratic at this point. Even down here the electronics carry on working though, the transistors switch the motor on ok but there’s not enough wellie to get it to start!

Hope this is not too confusing…….

PB

[ross blackwell]

Thanks for the advice Ken & Peter:I have a new E-flite 60 brushless which hasn't been given a home yet 400Kv up to1200watts 80amp esc reccommended:the info included with it says it must be used with sensorless brushless speed control"? Does that exclude my Turnigy 80amp esc with BEC ?Have been reading the arbout amps watts props & stuff;am trying to get it right first time. Boy, trying to get a prop adapter to fit a motor with a 6mm. shaft is near impossible around here as they don't have enough thread to safely lock the prop on.But I digress again.Look forward to your comments.

Ken,i find that 6a.m. is about the best time for P C to work without waiting 5-10 minutes to check mail.

[Peter Beeney]

ross, - I’m not into electric flight much, and I’ve very little experience of more recent up-to-date installations, but I think it’s possible you might need to stand a little closer to your figures; but as a start you can at least ignore the sensorless bit, all ESC’s are now sensorless, any that are not would be a special application, a motor with most likely it’s own ESC, perhaps.

If you are contemplating using a 3S lipo the 400 revs/volt figure seems low, 11 by 400 = 4,400 rpm, driving a 6 inch pitch prop results in a miles per hour figure of 25, flat out. Even a 12 inch pitch is only double that, 50 mph. Of course, I’ve no idea what sort of model you are thinking of, this may be imminently appropriate, it just seems slow to me. However, I would consider the BEC connection to be suitable.

If you doubled the battery number, to a 6S, we are now looking at 22 by 400 = 8,800, much better, now we’ve double the speed with a 6 inch pitch prop to 50 mph and and a 10 inch pitch to 83 mph. However, here I would think twice, or even three times, about using the BEC, a separate UBEC would be in order, but I would personally use a stand-alone receiver battery. The reason for using a separate supply of some sort is because the voltage differential, the volts in to volts out, is too great, and the regulator might get too hot; and that can cause extreme grief because ‘in extremis’ it will shut itself down, instant result, no radio, followed shortly by no model! If the instructions with the speed controller say that it’s ok to use the BEC with any number of cells, however, then I’m sure that will be fine.

I suspect that any information you have with the motor will give all this in much finer detail, such as number of cells and prop sizes. I have to say though, it can be confusing, I’ve occasionally looked at some motor specs and invariably at least they give you a current never to exceed. Then they give you some other data which exceeds this! The first one I looked at the other day gave a max current of 60A and then the prop test data, out of six results two exceeded this, one by five percent and the other by thirty! So it is a bit of a guessing game.

If you mentally derate all the figures you see, by say 20%, and then if you don’t have enough power you have to buy bigger, that might be the cheapest result in the end. The current, the all important thing to consider here, is directly related to the load, i.e. the prop size. The load directly controls the motor speed, for any given voltage, and if the motor goes too slow it will eventually result in everything getting too hot. I think in some cases it’s very easy to overstep the limits without realising it, until things stop working, or worse. Generally speaking, the faster it goes, the better.

Anyway, it’s maybe I’m now way out of line here with the O/P, so maybe I’d better stop before someone cuts me off at me roots…….

Good Luck.

PB

[ross blackwell]

I may have unintentionally misled you you Peter with regard the application of the Eflite mtr:its the first "bigger" brushless mtr I have baught that has had quite a bit of info enclosed & I'm trying to take all this "new info"seriously as I'm not that confident with figures.The article was prompted perhaps by" too" much information read by me.My previous digression was because of the non availability of prop adapters for the G60 brushless that have in my big Cub.I am robbing Peter to pay Paul;the Eflite mtr has a very nice prop adapter which fits the G60 nicely & of course I happened to read the info enclosed within the box as well. Have previously read advice on the afore mentioned Cub & have printed out all good advice so that I may use these"recipes" as required. I now have a watt-meter & a range of lipo batteries up to 6c 22.2v:just need to follow the best recipe for my particular application & perhaps sit down with pen paper & calculater & come to terms wth these dreaded figures.Mothers day here:don't forget to give your mum a hug.

[Alan Cantwell]

WELL  after many atempts to put a link on here, i have better things to do,  suffice to say, you need futaba heavy duty industrial servos, they have  what you are after,    but, just what needs the power you seek?  most intrigued,     slough models show them, but they are not in stock,    just google futaba industrial servos,  

Edited By Alan Cantwell on 13/05/2012 08:59:43

[Peter Beeney]

Thanks very much for your answer, ross, my humble apologies if I gave you any duff information; - or was indeed telling you what you already knew. I think maybe I really need to look into electrics a bit closer so that I have a better idea of what I’m talking about. … perhaps I shouldn’t really say too much about that which I’ve not been practising.

I think my own plan too, in similar circumstances, would be to have plenty of kit so that I could try various combinations to find the best one. A bit of trial and error should soon tell me if I was on the right track, or not. I’ve found with i/c engines, at least, I soon know instinctively more or less how one size of engine will perform with a certain size prop in a particular model, it just then needs fine tuning.

I also wish you well in any calculations you do, I think I shall be joining you in a few hypothetical ones myself, too, as a bit of much needed practise. I’m sure the more we kick these around, the more familiar they may well become.

Anyway, all Good Luck with your flying.

PB

[ross blackwell]

Welcome to the fray Alan:this column must be running short on space. I'm sure the learned contributors to the column will provide answers to your questions.My level of interest will never go much past what I'm trying to do at present. Way back when we had i c motors & a m radios I did lots of flying & lots of experimenting with little risk:getting into electrics is a whole new ball game especially for those of us who are not readily pre-disposed to the wonderfully challenging world of electronics.Ritchard is certainly aiming "big" to be using servos with 60kg torque; hope you enjoy the forum as much as I am.

[ross blackwell]

P.S. No need to apologise Peter: knowledge & enlightenment comes in many forms & to use a previous quote we must all find the "recipe for learning "that best suits us as individuals & my passage of learning is sometimes laborious & I'm gratefull for the indulgance of all those people who are willing to pass on thier experience/knowledge to others so this great hobby can continue to evolve & include some of our younger generation. But I digress.....again.

[Sigh]

Hi there;

I will be using the sbus and high voltage system and telemetry for the first time. I am going to use an evolution 10cc in a seagull texan. I Wanted to combine HV and telemetry because I will be flying with a single battery for the servos, ignition and the rx and be able to monitor the battery voltage. But the retract servo I want to use is 5V servo. Have you guys ever used regular servos in a HV system. I can build a small regulator to power the retract. But then the signal would be a little high.

Alternatively I may use an sbus decoder to run all three servos in the wing. And use the regulator to power the decoder thus the servos. But again the signal wire will be running on 2s lipo which is higher than the power supply. Is it a problem?