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Overlander motor/esc set up problems

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Tim Hickey14/05/2018 10:40:49
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Hi Gangster,

Yes..was a disappointing response.

Possibly even more worrying is the fact that having looked more closely at the leaflet that came with the motor, the dimension diagram is clearly for a different motor. The diameter is shown as 27.8mm not 42mm. I have a couple of other Overlander motors and the leaflets seem to match those. Something has gone wrong with published data on my T4250/06 800kv ???

Think I will get another motor. I can't justify the price of the E-flite Power 46 (670kv), so having looked around, think I might go for a Turnigy G46 670kv. Seems to have reasonable reviews.

Specs are 4-5s lipo, 12x8 to 14x10 prop, max 40A (55A-15 seconds) (900W +)

Any suggestions/comments appreciated.

Thanks.

Tim

Biggles' Elder Brother - Moderator14/05/2018 11:10:22
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If you are in the market for a new motor, then let's start from stratch.

You want 900W from a 5s. Nominal voltage of the 5s is 18.5v, so that's going to need a current of 900/18.5 or about 50A.

Target prop speed should be around 8,000rpm or so, allowing for Pat's fudge factor call that 10000rpm then divide by the battery voltage to get the desired kV. 10000/18.5 = 540.

So, we looking for a motor that can handle 50A, a 5s and has a kV of around 540.

This would seem to fit the bill very well? Or something similar spec.

BEB

PS the only real issue with the motor you propose is that 40A from a 5s won't get you up to 900W! It will get you reasonably close - say 700W. But if you want 900W then you need the bigger current handling capability of the motor I propose.

Edited By Biggles' Elder Brother - Moderator on 14/05/2018 11:14:21

Nigel R14/05/2018 11:13:18
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I would hazard the guess that the EFlite motor and the Turnigy motor are the same thing, badged differently.

Also worth looking at the Turnigy Aerodrive motors.

https://hobbyking.com/en_us/turnigy-aerodrive-sk3-4250-500kv-brushless-outrunner-motor.html

57A max, happy on 5S lipo

listed weight 269g, so within the real rough yardstick of "target max power divided by 4".

Or what BEB suggested. Very similar size/spec.

Edited By Nigel R on 14/05/2018 11:15:52

Tim Hickey14/05/2018 12:08:12
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BEB/Nigel,

Thanks for your replies.

Have had quick look at your suggestions, all look good at a reasonable price.

Looking at BEB's PS...I have had a bit more of a think about the power requirements for the model.

Its a scale(ish) Seagull model of the current RAF primary trainer Grob 115 so only needs to be capable of mild aerobatics, no 3d stuff. Given a maximum weight of 9lbs and allowing say 85W/lb, that suggests a power rating of around 765W, somewhat less that my original thoughts (100W/lb).

I think the Turnigy G46 550kv could be a good option for this model.

Given BEB's example (round up 765 to 800 for safety) 800W/18.5A = 43A (well within spec of my 60A ESC)

Think we are getting there. All started off with duff suppliers motor spec info.

Thanks again chaps.

Tim

MattyB14/05/2018 13:34:07
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Posted by Tim Hickey on 14/05/2018 09:52:04:

Hi Gangster,

Just spoke with a chap at Overlander... may as well no bothered.

No helpful information just said they may have to look at the prop size specs for that motor and suggested I buy a different motor. All I got was "ooh, not sure about that...don't know what to say."

As you say, in testing, the setup is way too powerful for the 60A ESC but this is what Overlander recommend for that motor. Not being an expert on electrics all a customer can go on is the published data when buying. May have to buy another motor.

Am I missing something here? If you consulted with them on your requirements before buying and they recommended this setup yet it cannot deliver the performance stated / the numbers they quoted are wrong, why not demand a refund or a replacement motor/ESC? Or is it that you did not realise that the headline wattage figures could not be realised with any battery within the usable range?

Tim Hickey14/05/2018 13:54:45
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Hi MattyB,

I bought the motor and ESC from different reputable sources but based on the published figures on Overlander's website. I have another couple of Overlanders and the info provided seems ok. They have obviously got the specs for this particular motor wrong.

Those specified figures seemed to give me the power setup I needed. Sure I can find a use for the motor elsewhere.

Will get a new motor based on suggestions made in this thread (thanks guys). I can then at least use the same lipo and ESC.

Tim

gangster14/05/2018 14:08:31
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Tim Are there any numbers on that motor. I thought the first two numbers were the diameter in my. In which case if yours is only 27.5 it sounds like a 28xx. If the overlander spec sheet confirms that you may have an issue with your supplier. Yes the eflite motors are pricey. If you do go for a different motor consider the emax range from BRC I have been well pleased with the ones I bought together with the advice from BRC in Newcastle I assume they are still there

Tim Hickey14/05/2018 14:22:16
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Gangster,

4250/06 800kv as stated on the motor case and paperwork that came with it.

Its the diagram on the paperwork that shows a diameter of 27.8mm

The diagram on the website correctly shows 42mm diameter.

The physical size is correct. It is definitely 42mm dia (approx.)

I have emailed Overlander in hope of getting a better response than I got when I rang.

I agree. BRC are very good. I have had a few motors and other stuff from them.

They are still there although part of the Robotbirds group.

I can recommend their Hyperion aerobatic ARTFs. Cheap and very good quality.

Will have a look at their Emax motors before taking the plunge with the Turnigy.

Cheers.Tim

Tim Hickey14/05/2018 16:17:55
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Another update...

Have found another Overlander motor in the cupboard.

T4260/06 900W 500Kv 3-7s lipo prop from 15x8 (description as stated on the motor body and packing box)

Will give this one a go before buying a new one.

Tim

Biggles' Elder Brother - Moderator14/05/2018 17:37:47
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Does it say what the max current for this motor is Tim? On the face of it it sounds fine, but I find this way of specifying a motor by kV, Max Power and battery cell count very unhelpful!!

What kills motors is current - not power. To tell us the max power is 900W and it can take a 3-7s doesn't answer the key question - how much current can it take? You see a 7s at 900W is a current of approx 35A. But a 3s at 900W is a current of 81A!!! They are very different situations! So which is te max current - I wouldn't bet on the 80A!

BEB

Tim Hickey14/05/2018 18:07:20
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Hi BEB,
sorry, missed that bit of vital info. motor states that 60A ESC is recommended.
Tim.
Biggles' Elder Brother - Moderator14/05/2018 19:27:15
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Sounds good - go for it! smile

BEB

Tim Hickey14/05/2018 19:46:15
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Thanks BEB. A bit more confident with this one. Have removed the old motor but need to reduce the standoffs by 11mm. Job for tomorrow evening.
Tim
Geoff Sleath14/05/2018 20:53:59
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Certainly current is a vital piece of information for a motor as well as the kv. Unfortunately what's often provided is the peak current for a limited time (though often several 10s of seconds which is more than enough for most applications) when what would be good to know is the continuous current. Though it's true that both figures can vary with temperature.

I find it very frustrating when trying to choose a motor for a glow to electric conversion even when applying BEB's method of starting with the prop which seems counter-productive at firsat glance but works very well in practice.

Geoff

PatMc14/05/2018 21:19:26
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Tim, recommendation to use a 60A ESC doesn't mean that the motor will take 60A.

When a power & max cell count are quoted it really means power at that cell count. In effect they're giving the max current as aprox 35A.
This means that your 5s battery will be good for 5/7 x 900W = 643W - assuming that to be continuous running.
IMO you should be able to exceed that for short periods up to around 750W which should allow a scale like performance to the model.

BTW if you run the numbers given in Wiki for the Grob against those by Seagull - it's 17/100 scale. Scale power works out at 683W, scale weights 7.4lbs (empty) 10.7lbs (max loaded), power loading 92 - 64W/lb.

PatMc14/05/2018 22:12:48
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Posted by Andrew Ray on 14/05/2018 07:13:09:

What no one has said is that Kv is a figure that in all probability the motor will not achieve due to losses and more importantly it relates to the back EMF. As far as we modellers understand the use of the term it relates to the unloaded rpm. By checking the rpm with a prop on will not give you the answer.

To find the actual Kv you need to use the motor as a generator, spin it at a known rpm and measure the voltage output, but I have no idea how to achieve that with a brushless motor.

Edited By Andrew Ray on 14/05/2018 07:38:08

Andrew, the Kv unit used in model motor parlance is simply rpm/applied voltage for an unloaded motor. Which probably is not the true technical definition of the term but is all we really need to use.

It only takes a few minutes to measure the Kv for most new outrunner motors I get before they're put to use.

The motor is mounted on a piece of plywood, a couple of strips of adhesive tape of contrasting colour to the motor case stuck on aprox 180⁰ apart. The battery used must have sufficient capacity to run the motor a few minutes without it's voltage fluctuating, I normaly use a 2s lipo 2000AH battery. A DVM is attached to the battery terminals, ESC & Rx connected.
Tachometer readings are taken & voltage noted whilst the unloaded motor is running at full throttle. Divide the RPM reading by the voltage & we have the Kv. Tests must be done without artificial ac light sources that might interfere with the tachometer.

I've tested some motors with different ESCs & different battery voltages (using both lipo & Nimhs) but noted no significant variations in the Kv readings obtained.

I've found that the measured Kv is usually higher than the manufacturer's quoted figures with a few exceptions.

Edited By PatMc on 14/05/2018 22:15:52

Tim Hickey22/05/2018 12:29:54
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Hi Gents,

Just to close out this thread.

I have now changed the motor on the Grob to another Overlander I had in the drawer.

I used a Tornado thumper 4260/06 500KV. Used same 60A ESC and 5S 4500 lipo with a 13x8 prop.

Happy to report that all now seems fine.

A few days ago but from memory wattmeter showed no higher than 48-50A and in the high 600 low 700 watts.

Happy days. Thanks again for all your advice.

Tim

P.S. - After my pointless chat with a guy at Overlander on 14.5.18, I emailed for their advice and for them to check the prop/KV figures on their 4250/06 800KV that gave me the problems at the start.

Yep, guessed right...no reply.

Still rate their motors and will probably use again.

Nigel R22/05/2018 14:18:07
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"Still rate their motors and will probably use again."

At the risk of being vilified by Overlander fans, I wouldn't. They don't seem to add anything to the product (unlike e.g. providing advice and the customer service that 4-max do).

As I understand it, Tornado Thumper are rebadged XYH motors.

XYH motors are available from other sources (HK orange motors, DYS motors on AliExpress and banggood) at much lower cost.

I do not know if Overlander's flavour of motor has better bearings or tighter QC.

Overlander ESCs are rebadged Hobbywing - available as Turnigy Plush for much lower cost.

I do not know if Overlander's flavour of ESC has better spec'd componentry or tighter QC.

Overlander Lipos do seem to be a cut above the Zippy/Turnigy price range (slightly smaller/lighter for same spec), but you don't half pay for it, and provided you're not doing EDF or another very high current draw setup, the Zippy lipos are champion.

Your mileage may vary.

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