Conversion to Electric

[JayCee]

Ok Thanks

 

Prop at present is 12X6 as I have fitted slightly larger wheels.

 

JC

[Richard Wood]

With clearance to swing a 12" prop. you could try a slightly lower

kV motor still - say around 800kV.

The idea is to be able to turn a bigger, more efficient prop at slower

revs without drawing too much current.

Scorpion motors are also very good.Look on the Micron website for these.

 

Edited By Richard Wood on 28/09/2010 13:13:10

[JayCee]

Hi

 >>

I have a provisional shopping list and would be grateful if you would check it over and give me your comments and suggestions.

 >>

To recap: - Model HW Trainer weight 5lb 10oz

 >>

Motor: - E-Power BL3526/04 860kv Outrunner Brushless MotorV>>

Specification

No. Of cells: 5x Li-Poly ?          can I run this on a 4s 3700mah battery?
RPM/V: 860
Dimensions: 35x26 mm
Shaft diameter: 5 mm
Max Amps: 60A Weight: 250 g
Recomended model weight: 2500-3000 g
Recomended prop without gearbox: 13*6.5 14*8.5>>

 >>

ESC:- Hobbywing Pentium 60Amp Brushless Motor ESC Speed Controller>>

 >>

Size: 56mm x 28mm x 18mm
Weight (approximately): 63g with wires
Sustaining Voltage: (Li-ion/Li-poly: 7.4 - 18.5v) / (NiMh/Nicd: 6.25 - 18.75v)
Balance Discharge Protection: optional
Current (Continues): 60A
Current (Burst >10 sec): 80A
BEC Mode: Switch Mode
BEC Output: 5v/3A
User Programmable: Yes

 >>

The plane has clearance for a 12 inch prop 12X6?

 >>

Regards

 >>

JC

[Tim Mackey]

Well if the motor specs suggest a 13 x 6 to 14 x 8 prop on a 5s battery, then a 12 x 6 on a 4s will be underpowered. You can run the motor on almost any cell count you like, but the revs and power will alter accordingly. For 600 Watts, Im still inclined to suggest a higher Kv motor if you are sticking to 4s and a 12 x 6 prop.

Personally I would go bigger on the prop - 13" if possible - but otherwise increase the pitch up to around 8" or so?

The ESC is fine and should not need a UBEC if using standard non digital servos.

[JayCee]

Thanks Tim for your prompt response I have to be honest I'm struggling a bit with the maths concept

 

As the aircraft has a tricycle undercarriage there are clearance issues, checking again this morning I could possibly just get away with a 13 inch prop which leaves me with just under 1/2 inch clearance just about OK if the strip is nice and short <grin>

 

As far as Lipo's go there are cost considerations, as this is my first foray into electric flight.

 

 I was hoping to get away with 4s (4 X 4s 3700mah batteries from Hobby King £82 inc P&P) Obviously I don't want to compromise flight performance.

Could you suggest another set up with a links to possible products, I seem to be going around in circles

 

Thanks JC

 

 

[Tim Mackey]

Oh dear.... dont worry JayCee many have been in this position, its all part of the learning curve mate

Now first off I should remind you that my article suggested that starting with the prop size was only a suggestion, and applies to certain models only - particularly where I am aiming for a nice scale size prop to suit a particular model. As I did say, there many ways to skin a cat, and a was mentioned earlier in the thread ( Chris I think ? ) starting from one "fixed point" is a good way to go...be that battery, prop, or motor or whatever...then choose the other components to suit.

 

So, with that in mind, and your apparant restriction to 12" prop, lets try again.

 

Youre aiming for around 600 Watts, and  the next important thing is what cell count to use. 

More volts = more RPM and power, and less current for the same power ( a good thing generally ). However, a low Kv motor will need a largish prop to get the power up, and were stuck with a relatively small 12", so we may need to up the KV a bit, which means it will spin a bit faster and pull more current equaling more power.

MOTOR Now this is a 950 Kv motor and on a 4s with a 11 X 8 prop, showed  40A on someones rig. Now  40A X 14 V = 560 Watts.  About right for ya - however if you want even more power you put a 12 x 6 or 12 x 7 or so on it .

The motor is rated at 30A continuous ( 45 A burst ), but with adequate cooling should be fine at 40A.

For a similar motor with better current capacity maybe THIS

 

Stick to the 60A ESC , and as for batteries, you cant beat something like these from GC - you dont need to buy 4 of em, as they can be charged at 5C - assuming you have a decent charger.

HTH

[JayCee]

Thanks Tim

 

Your help and advice is much appreciated!

 

ESC and Motor now on order, Battery and Watt meter out of stock but plenty to get on with.

 

Thanks once again, will keep you posted!

 

Regards

 

JC

[JayCee]

Hi

 

Just like to say thanks to all who gave me help and advice on my first conversion project. a Calmato 40 high wing trainer... now Leckie powered!

 

First flight to day and was stunning, loads of power for vertical climbs and performed just perfect managed a full 9 minutes+

 

Watt meter reading showed 840 watts, 55amps on a 12X6 prop with a 4S 3700mah 25c

 

Those IC's might just have to go

 

Thanks JC

 

 

[Tim Mackey]

Good stuff JayCee - glad it went well, and we all appreciate it when someone comes back to say thanks

What motor did you end up with incidentally?

Edited By Tim Mackey - Administrator on 17/10/2010 21:37:55

[JayCee]

I tried two

EMax BL 2826/06 850KV
and
E-Power 2832 960KV

 

The motor in the plane at present is the EMax the spec only states 700 watts!

 

 As you know I am a novice in electric flight and was surprised to get readings of over 800watts (55amps) obviously still got a  lot to learn, going to use the larger motor on my next conversion........yes I'm hooked!

 

JC

 

 

 

 

Edited By JayCee on 17/10/2010 22:00:03

[Danny Fenton]

Well done JayCee, glad it went well. Keep a close eye on how much capacity you use, and don't take the cells too low or they may not last as you would hope.

 

 

Cheers

Danny

[JayCee]

Yes thanks Danny

 

Am I being naive, I thought the ESC made sure the individual cells didn't drop below a certain level!

 

JC

[Richard Wood]

Glad it went well JayCee - well done.

You're right about the ESC - it'll cut power when the voltage drops

to around 3V per cell if it's set up for LIpos, but it's perhaps better to have a

slightly shorter flight time initially  - say about 7 minutes or so and

then see how much capacity your batteries take on recharge.

You can then set your timer longer if there's capacity to spare.

As Danny says - best not to let them discharge to LVC too often

to help battery life.

 

 

 

[Tim Mackey]

Only the "guard" series of hobbywing ESCs monitor individual cell voltages - others just the whole battery level - either way, as the guys have said.... best to NOT let the electronics do the guarding - your Tx timer is your best friend, and should be set for a round 30 secs or so less than the maximum you can pull from the particular battery yet still have about 10 -20% capacity remaining. When the timer goes....get into your landing circuit.

Im surprised at the power figures on the lower Kv motor with just a 12 X 6 prop, which prop is that? and as its pushing the motor well up the scale, be sure to to not burn it out!

[JayCee]

Hi Tim

 

Thanks, as you know bit of a novice all round, but had a club member pop round and we did the tests together.

 

Watt meter (BRC) definitely showing in excess of 800 watts, drawing approximately 55amps, that is at full throttle.

 

The ESC 60 amp again from BRC I think it was from the pro series, the prop is an APC (E) 12 X 6 The motor is completely exposed (no cowell) so loads of air flow.

 

Also this is a high wing trainer and I'm still a relative beginner so although there were a few steep climbs and loops 80% of the flight was very sedate at no more than half throttle and a few throttle off down wind glides so I guess that would explain the longer flight times.

 

Anyway thanks for the tip I will keep flight times down and check the battery (cell) voltage at the end of flights.

 

Again thanks for all your comments!

 

JC

[Steve Hargreaves - Moderator]

Well done JayCee...you got it all working.....

 

Might be worth trying a smaller prop to reduce the current slightly......maybe an 11x6 might be better for the motor!!!

 

As we all know power become addictive & you might find yourself using full power more & more often & it would be a shame to melt something!!!!

[Steve Hargreaves - Moderator]

Just had a quick look at that motor....it recommends 45A max (for 60s) so I think you are definitely pushing it a bit at 55A but confusingly the recommended prop is a 13x6.5 on 4S!!!!

 

What sort of current would trhat pull then???

[JayCee]

Yes it's all very confusing for a newbie to electric.

 

When the plane landed the motor was cool to the touch as was the ESC, the battery was slightly warm....very 'Heath  Robinson' I know but didn't indicate that the power-train was struggling.

 

When I arrived home and charged the batteries they both showed a start up voltage of about 15 volts!

 

Time will tell I guess as I gain more experience..........at the moment I'm just having fun!

 

JC

[Tim Mackey]

'fraid to say that this is not the first time that data supplied with a BRC motor was way off the reality.

In fairness, they are not the only company to do this, relying as many do on data supplied by the manufacturer - errors can creep in, or the sometimes the wrong data sheet accompanies the contents so the box etc.

That why I like to use a wattmeter and selection of props to find the right set up.

If the components all felt cool, thats a good sign, and of course, the current will be quite a lot less in the air than on the bench.

[NigelH]

Posted by JayCee on 17/10/2010 21:58:39:

I tried two

EMax BL 2826/06 850KV
and
E-Power 2832 960KV

 

The motor in the plane at present is the EMax the spec only states 700 watts!

 

 As you know I am a novice in electric flight and was surprised to get readings of over 800watts (55amps) obviously still got a  lot to learn, going to use the larger motor on my next conversion........yes I'm hooked!

 

JC

 

 

 

Edited By JayCee on 17/10/2010 22:00:03

BRC reckons that you'd get only 510W with your 12x6 prop, with even a 15x8 only giving 710W.

I wonder why your figure and their own are so far apart.

http://www.brchobbies.co.uk/?page=shop&action=additem&item=671

 

[JayCee]

Nigel

 

Yes a bit of mystery, unless my new watt meter is faulty! But I can't believe it could be that far out.

 

I used it on my Wot 4 Foam-E and the readings 350 watts at 30 amps tie in with readings from other Wot 4 users (Wot 4 Foam-E thread)

 

But on that thread some readings are as low as 218 watts up to a whopping 375 watts all on a stock ARTF! how do you explain that?

 

Back to my conversion, I had other more experienced flyer's fly my plane that day and they all commented on the power and climb rate, may check it again with another Watt meter.

 

Will be interesting because I am just starting a second conversion with a similar set up on a low wing Calmato which is a bit heaver, it will be interesting to see the results.

 

JC

 

 

 

[Richard Wood]

JayCee,
Current delivery from different Lipos can vary quite widely.

A new, latest spec. 35- 40C rated one for example will be

able to deliver much more current than a tired old 15-20C

rated one of the same size.

This might explain those different power readings.

 

It wouldn't do any harm to double check your power readings

on another Wattmeter if one is available - just for reassurance.

 

Cheers

 

 

[JayCee]

Yes I will do that just to be sure, but even ohms law appears to verify the figures.

 

Even if the battery voltage drops to 14 volts P=I x V     55 x 14 = 770 watts! or am I doing something wrong?

 

JC

[Richard Wood]

Your power calculation is about bang on for a 4S at 55A.

The voltage will be a bit higher when the battery is only partly

discharged - up around 16V or so & will drop towards 14 V & lower

as it discharges through the flight.

The thing you might want to check with another meter is the current

being drawn at WOT (wide open throttle) on a fresh battery.

55A is quite a high reading.

 

Out of interest try a smaller prop - the current should drop quite a bit.

Different makes give different readings too.

The current will also be a lot less at half or part throttle when flying.

As you say though ,motor, ESC & battery are staying cool which is good.

 

 

 

 

 

 

Edited By Richard Wood on 19/10/2010 10:46:09

[Tim Mackey]

I normally work on around 3.5 to 3.7V per cell when the battery is under a decent / high load. This does vary from battery to battery, with higher capacity, and higher C rated ones holding up best of course.

A 4s lipo under a 55A load - which is pretty high - is likely to show around 14V+, so I agree, your figures look about right. If you dont have another wattmeter, just hook a normal voltmeter across the battery terminals whilst running your test, or a lipo monitor unit connected to the balance plug....and see if at least the wattmeter voltage figure is correct.

As I said earlier...not particularly surprised to see conflicting data as supplied by errr...the supplier .