New to electric

[david Osborne]

You've most likely heard all this before but here goes.

Just getting back into flying again after 20 years. The electric stuff has answered all my old complaints about fuel, smell and mess etc. However, a few questions about motors, ESC, LIPO and power requirements.

I recently acquired an Innovator by Seagull and had a bit of a discussion with the local shop. I went for a slightly larger brushless motor to help future proof myself a bit and came out with the following:

Tornado C3542 (thumper?)

3cell LIPO, 2200, 11.1V 3S1P 25c

Tornado 30amp ESC with BEC

10x5 prop (a bit small for the motor?).

I realise that the motor is a bit big and the prop a bit small but an 11x5 gave no ground clearance and I do not need to use all the throttle, please correct me if I am wrong, (go up in pitch possibly) but how do I work out the power / amps based on prop load on the motor?

The model also needs 5 servos and I have some Hitech HS-82MG items but how do I work out the radio gear power / ampage requirements? I am also concerned that the ESC / BEC is not suitable due to the large voltage drop and number of servos and will lead to a hot battery and wasted power. Radio gear is a Futaba 6ex 2.4GHz.

if I need a separate ESC and UBEC or separate batteries for motor and radio what do I need and how do I put it together?

Any and all advice is appreciated

Finally, is there a good book or website with info in one place for use electric novices!!?

Thanks Dave

[Bruce Richards]

David,

the only way to ascertain you power requirements is to measure the current with a meter. Most multi-meter will be capable of measuring the current draw of your radio gear but for the motor current you will need a specialist meter capable of measuring high current up to say 100A.

When you measure the current draw from you radio wiggle the sticks around on the TX and provide some resistance by holding 1 or 2 0f the control surfaces. Be careful not to brake anything. If  the max current drawn is much more than half the current rating of the BEC in your ESC I would suggest you get a UBEC. I think there are other threads on here talking about how to set up a UBEC.

 Hope this helps

Bruce 

[Former Member]

[This posting has been removed]

[Tom Sharp]

This motor is really best on four cells and a separate Rx battery. Also you need a separate Rx battery if using five servos.

[david Osborne]

Thanks for the replies so far.

I think it is becoming a bit clearer.

Not withstanding the fact that to get a true idea of the wattage for the motor / prop combination I need a wattmeter (what about the Banston Checkmaster or other recommendation), its looking like I will need either seperate batteries for motor and RX simply based on the five servos and the fact that the spec for the motor states 45A at max efficiency and a max power of 540 watts, although this is with the rec prop of 11x5 and above, so my slightly smaller 10x5 prop would need less torque resulting in less power or higher RPM?

from my reading so far I am thinking of a seperate ESC rated at 50amps but if I use a seperate battery for the RX the following questions come up:

1. can I use the standard 4.8v 700mah 4 cel Ni Cad that came with the radio set with a weight penalty?

1a. How do I wire the setup? Do I connect the RX battery to the reciever via a switch as per the glow plug days and disconnect one of the wires from the ESC to the RX throttle connection leaving me with essentially seperate battery supplies for motor and RX?

3. would it be better to use a seperate UBEC and ESC, and again how do i connect up?

4. what is the minimum recommended voltage level for a LIPO? I have read some stuff but still not sure, is it 3V?

Also looking at the parameters for the ESC I have can someone explain the less obvious ones?

Brake means electrically preventing the motor from spinning (windmilling) so I assume soft would be a good bet as this would apply the braking current progressively?

Protect value sets the voltage for a LIPO that cuts off the motor but keeps power to the RX?

Assuming the above is correct what is power protect? and what is the best setting, off limited or hard?

Start mode soft, medium or full defines how the power is applied to the motor at startup with soft being progressive and the best setting for long life?

What is the timing auto, low, medium, high parameter and how do I know what to use?

I presume PWM stands for pulse width modulation for motor control but how do I know what setting to use 8 or 16khz? I am presuming that the higher rating will give a higher degree of control over motor speed and thus finer throttle control but what is the trade off?

I would still like to read up on things through a good book, any recommendations (electric flying for dummies!!!!).

I dare say there will be more questions.

Thanks Dave.

[Ian Hoodless]

Hello there Dave, i too have 6ex 2.4ghz and a seagull inovator.I have not purchased the elec drive train yet, as like yourself i want the motor at least to be transferable to my next plane.      Please could you let me know how you get on ,especially with the batt to rx (seperate?) sounds logical but for the wieght. I am a total novice ,but a petrol head from birth and to be honest i don,t want to be sticking amp meters on wires when i don,t really know what i,m doin in that department!!.  I think i will be purchasing my drive from puffin models as everyone says the advice is so good,i will let you know how i get on.Thanks Ian.

[scott cuppello]

"The motor is really a bit big".........no offence, but that's breaking the first rule of electric flight....keep it light.

When choosing a motor, firstly, power/weight is the first consideration, if your model weighs 4lbs, and you want decent power/weight, you need a 400 watt motor MINIMUM. Next choice is RPM...which is the motor kv rating....which in reality is the prop.

Now, if your back-ground is IC, you won't realise yet just how essential prop choice is on electric flight models, I am not familliar with thast motor but my immediate concern is you have added to the AUW......but will not be able to make use of the extra amount of power [watts] available for it because you are going to have to "down" prop.

So really, the smaller/lighter motor choice with the right prop would be the way to go? If the motor states 540 watts max with the 11x5 prop....which is the max....nearly always not what it will actually produce [there are a lot of factors involved here].....and you reduce the prop [which will have a signifcant effect most likely]....to 10x5....and you started with 500 watts....now down to 400 watts....on a 5lb model....it's going to be under-powered, duration will be short as you will be flying flat chat all the time.

This is why you need a wattmeter if you are going to mess with the standard set up, you may be able to get the wattage back with a 10" prop, but slightly deeper pitch....and so on.

My next concern is the Lipo, 2200mAh, which even at supposed 25c, is rated at 55A discharge....so, if you are producing the kind of wattage you are talking about, then we are going to be into VERY short flights....and a pretty useless battery in a short period of time. That motor sounds as if it's really designed for 4s, as to produce 540watts on 3s, that would 54A......Not good, on 4s....37A.

So now we have to question the ESC.....is it going to fry itself very quickly because of the potential current draw?

To sum up, a 2200mAh 3s Lipo and a 30A ESC the most "power" you would be wanting from a set up like that is around 25A.....250watts-ish....which is basically a 450 class motor, which depending on the KV....would be ideally suited to a 10" prop!

RX is a good question, as the model uses 5 servo's, the whether to use BEC or not is partly down to the rating of the BEC. Personally, I don't like them on any application that is A - Over 3s, B - over 4 servo's. ......BUT.....there are plenty of people out there that do, it's also partly about what you are using, 5 pretty standard servo's on a 3A BEC are probably fine....5 digital high torque MG servo's.....er, no. So, the weight saving option, is a OPTO ESC [you can convert a BEC ESC by simply cutting the red power supply wire from the ESC/BEC to RX] and fitting a higher rated BEC, which are tiny and light, and are available up to 10A rating, they simply tap into the flight battery supply, and plug into the battery "channel" on your RX, or an Aux channel.

RX reciever packs are weight, ideal in a 0.40/0.60 IC conversion, as you nearly always need the extra weight for C of G.....so, they plug straight into an off/off harness, and straight into the battery "channel" of your RX.....BUT....if you have a BEC ESC...you must cut the red wire going to the reciever to stop it supplying power to the RX. Otherwise, if you decide to use BEC, the obviously you don't need an RX Nicad, or a harness, as everything will be powered up once you connect your flight battery.

Hope this helps, hope it is simple enough, hope it's not patronising! You combo sounds, in short....not very good, you need to start from basics, starting with the AUW of the model...and go from there.

[Steve Hargreaves - Moderator]

Blimey Dave....so many questions.....where to start!!!

If we start with the definitions of the ESC parameters cos we can put those to bed straight away.

Brake...yes you are correct...basically shorts out the motor to prevent the prop windmilling....set whichever suits you...some say a windmilling prop is good as an airbrake...others say a windmilling prop is more likely to break on contact with the ground.

Protect...again correct...if yer Lipo battery drops below 2.75volts per cell you will likely kill it. This prevents you getting into the danger zone. The various modes are how this protection kicks in...some just chop the power to the motor (not good if you're low & slow) whilst others just spool the motor down slowly so you have to land. Personal opinion...you can usually tell when the battery is going flat so land once the sparkle goes out of the performance.....pushing batteries right to their endurance limit just reduces their life.

Start mode...again correct (you are going to earn a few chocolate drops at this rate!!!) soft is often used with gearboxes to prevent full load torque damaging them at start-up...not really relevant here...again set what suits

Timing...refers to the phase angle of the rotor vs the stator...of no interest to a beginner or indeed most people....leave on default setting

PWM...yes pulse width modulation...ESCs reproduce a quasi sine wave as the AC output & this is basically built up using lots of pulses of varying DC voltage....again leave on default setting

On to the more practical stuff.....yes you can use a standard Rx battery. In this case you would use a conventional "ic type" set up with a switch between the Rx & battery to power the servos HOWEVER you must not connect the positive wire from the ESC to the Rx (usually the red one) either snip this just above the plug or carefully remove it from the housing & tape it back against the cable. This prevents the ESC from powering the Rx. You MUST leave the negative wire connected as the electronics use this as a reference point.

A UBEC is a regulator that drops the battery voltage to a steady 5V or so for the Rx. You would connect the input side of the BEC to the battery input connectors on your ESC (solder then on & then make a nice job with heatshrink tube. the output side goes to yer Rx. Again you need to disconnect the positive Rx feed from the ESC. For more than about 3 small servos or more than 3S LiPo a UBEC or separate battery is probably best......

Just another small point....be very careful with the contacts in the Rx plug of the ESC...if you start removing them from the plastic plug you can weaken the contact retention system so should you replace the contact in future so you can power the Rx from the ESC you can suffer contact pushback which at worst means an intermittant power contact to the Rx...if this fails you lose all power to the Rx....not good......be careful here....

[Steve Hargreaves - Moderator]

Contd from above....... 

Onto the power of the set up & how to achieve it then I think we should go back to basics.....

It is widely accepted that about 100 watts per pound gives reasonable performance whilst nearer 150w/lb is good for high performance & aerobatics.....so start with the weight of the model...lets say its 4lbs all up weight....you would be looking for 400 to 600watts.....working back from there you have a 3S battery which under load will run at about 10 volts. Power equals Volts x Amps so you will need 40-60amps to achieve a good power to weight ratio. Note if you went up to a 4S battery your input voltage would be higher (14.8v nominal about 13v under load) so your current could be lower.

be aware however that electric motors have an RPM per volt or kv figure which is basically fixed at the design stage & refers to the number of coil windings etc etc etc. A kv of 1000 means the motor wants to spin at 1000 rpm for every volt applied...in our example above on a 3S pack therefore the motor wants to spin at 10,000 rpm, (10 volts). At 13volts ie on the 4s pack it wants to spin at 13,000 rpm. If you stuck with the same prop guess what would happen to the current.....yep it would increase massively & something would probably melt so to achieve the same current at the higher rpm you would need to prop down.

The other thing to consider is your battery.....this needs to be able to supply the current comfortably. From your opening posts you have a 25C rated 2200 mah battery. This will nominally supply 55amps max (25 x 2.2amps). However if you do this you will find two things happen.....1, you will have a very short flight (2.4 minutes) 2, your battery will not last very long before it needs replacing (because you are pushing it to its absolute limit). IMHO you wouldn't want to pull much over 35-40A out of yer battery giving you a max power of about 400watts. Of course we rarely run flat out all the time plus the static current is a good bit higher than in the air when the prop unloads a little so this will all help your battery (& increase your flight time!!!)

So how do you know whats going on......?? From the above you can see its mainly down to prop selection & you can increase or decrease the power simply with a different prop. Your starting point should be the props recommended by the manufacturer. Once you have this fitted YOU NEED A WATTMETER!!!! Why the capitals??? 'cos you really do need one!!!! They cost about £35-40 (BRC/Robotbirds/West London Models all have 'em). A wattmeter goes between your battery & your ESC & will tell you the current the motor is drawing, the voltage of the pack under load & the watts consumed. Without one you are completely in the dark & you will either not have the performance you could have OR you will melt the motor, ESC, Battery or all three......ask yourself how much that lot costs to replace & then tell me you can't afford £40 for the meter!!!!!!!

A lot to take in there but it really isn't that complex.....think about what you want to achieve...think about the numbers & then check it all with your new wattmeter & adjust as necessary.

Final point....safety.....don't put the prop onto the motor until you are ready to test the set up. a 10x5 spinning at 10,000 rpm WILL injure you. Electric motors have two little tricks up their sleeve compared with IC....1, they can start without warning. They shouldn't but they can!! 2, Unlike an ic engine, when your bloodied hand or whatever stopped the prop from turning is removed from the propellor it will start turning again!!!!!!!

Hope all this help you make sense of things......keep posting if you need more info!!! 

[david Osborne]

Many thanks for all the replies, Most useful.

I must admit when I started reading up a bit more it become obvious my set up was not right - so much for advice from the model shop! I suppose most are good in that department.

After a bit more research I have eneded up with an AXI 2814/12 with a 9x4.5 prop. I used the Puffin / model motors calculator on their website to help with the descision. The ESC is an eflite 60amp with a switch mode BEC capable of handling six digital servos, a bit heavy but the model comes in at about the right weight using my old scales and has growth potential for later models. I now have a 3 cell 3300mah lipo. I have done a static test on my work bench using a stand I built with a wattmeter and at max I am using 35 amps giving about 350 watts.

Now all I need is a code book to decipher all the different terminology / connectors types / adaptor cables / different size this to that adaptors / lack of clear instructions etc. I hate to have a little moan here but for a beginner the large variety of different sizes and shapes in this area is a real minefield with limited info on the various retail websites. If there is one thing that will put beginners off it is total confusion that leads to wasted time, effort and money. I am also into astronomy as a hobby and I thought that was bad for beginners but.....!!!

OK moan over, hope to up and running this week end weather permitting.

Thanks Dave.

[Steve Hargreaves - Moderator]

Sounds like you have an ideal set up there David.....you haven't told us what the model weighs yet though (all up weight including the battery obviously!!)...350watts will give good performance on a 3.5-4lb model. You also have plenty of "headroom" in your ESC & battery to increase the power by fitting a bigger prop say a 10 x 5 or such, provided the motor will take it.

Totally agree about the various connectors etc....have you looked at LiPo balancers yet?? Another minefield sadly as they all have different connectors!!!!!

Like so many things there is no substitute for experience & a half hour chat with one experienced in all things sparky can save you ££££££££'s & a lot of frustration.........suppliers like BRC & Puffin are a good source of advise as well as bits & there are some excellent contributors to this forum...(have you met Timbo yet?? A Modelflying Deity he is!!!!)

Best of luck with the first flight.....

[Steve Hargreaves - Moderator]

PS Just looked at the AXI catalogue & at 35A you are running the motor flat out...best performance comes at 20-25A with a 60second rating @ 35amps.

Hate to say it but the motor might be a touch under-rated here.....

[david Osborne]

The model weighs in at 3.1 lbs and is a trainer, 55 inch wing span.

According to various motor calculators (including the model motors one), and advice regarding power requirements from this forum the motor should be perfectly OK. 350 watts should be plenty. The model motors calculator advised that the motor prop combo should pull an 1800g trainer around ok. The motor should only need to run at around 20 amps for level flight. On the bench the motor was pulling 20 amps at a just over half throttle (not that it means much on the bench).

No I have not conversed with Timbo yet but I have read much of his advice on the forum.

Thanks Dave

[Tim Mackey]

Now you have

PS I have nothing really to add to what the above excellent answers have already provided.

I would like to reinforce the message about keeping things light! IMO many perfectly well designed and capable electric models are ruined by "boy racers" blinging and beefing them up to the point where they have to use larger than designed powertrains.

This also of course is a nice introduction to our old friend the PWR cycle.

More power=more weight=more power needed....and so on

[david Osborne]

Hi Timbo

Thanks. Coming from the aircraft industry I fully appreciate what you say regarding weight!! The main weight gain is in the larger battery. I went for the larger battery to get a reasonable flight time, and it is within the spec for the model. I know the ESC is a bit on the heavy side but I was finding it a bit confusing first time out. Having looked around a bit more I realise I could have got a lighter one / setup but I do not want to spend any more at this time. 3.1 lbs is the upper end of the recommended weight for the model.

Thanks Dave.

[Steve Hargreaves - Moderator]

Ahhh Timbo there you are!!!! I was getting worried..... David, the AXI should serve you well provided you're not flat out all the time....IMHO AXI motors are top drawer kit...expensive but top drawer. They also tend to be under-rated current-wise & have a higher "safety factor" in case of over current. This is in contrast to some of the cheaper motors which can rapidly release the magic smoke if you go only slightly over their maximum rating.... Best of luck with the first flight.....

[Tim Mackey]

Hi Steve, yes, still here, butmissed this particular thread somehow, until yesterday

No matter, you guys are just as capable if not more so than me to resspond to David's queries and have excelled again

[Steve Hargreaves - Moderator]

I did wonder....usually anything with "new" & "electric" & you're all over it like a rash delivering your usual pearls of wisdom!!!!!

Did you get the Pink Floyd CD OK????

[Tim Mackey]

Ah yes, many thanks, I apologise for forgetting to acknowledge it must have been "brain damage"

[Former Member]

[This posting has been removed]

[Tom Sharp]

Timbo couldn't find where the postie had left the Pink Floyd CD. He looked around "The Wall" but it was "Obscured by Clouds" so he asked "The Piper at the Gates of Dawn" and he replied that it had been left on "The Dark Side of The Moon"

[Tim Mackey]

I am NOT going to get drawn in to another one of these

[David Aston]

I have been an oily flyer for 30+ years but now am wondering about going electric, but wondering if I can afford all the different equipment on a pension. What will I need? I have the radio gear, with Rx, servos etc.A wattmeter seems important, a charger/balancer-what else? and how much do I need to budget for before I go down this route?

David

[David Ashby - Moderator]

Hi David and welcome.

Are there certain models you prefer? It can be done for very little say -

GWS foamie fighter - £25

Budget ESC and motor combo, say £15

Small Li-PO, say £15

A decent charger, say £50

Fit a handfull of £4.50 servos and away you go............

The skys the limit of course so it depends what you want to fly.

[David Aston]

Thanks David, thats a good start.  I'll look into it further.

David