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Motor longevity

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Geoff Sleath08/09/2016 00:42:52
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3448 forum posts
307 photos

I'm going to regret this post, I think

I've had a Max Thrust Riot for several years since just after they were introduced. It's been my warm up model for ages and the one I fly before test flying something more precious in either gold or time. With the lump of steel removed from the front and increased control surface movements it's very aerobatic and sturdy enough to fly in any flyable wind. I do at least a couple of touch and goes every flight and the undercarriage may bend a bit but comes back for more.

My original very tatty airframe met its Waterloo earlier this year when for reasons unknown (though I had been doing some repair work when the fuselage started coming unglued at the back) I took off with reversed ailerons. I must have flown it about 300 times so I quickly convinced myself to buy a bare airframe and fit the original components including the motor and esc.

This year I bet I've done another 100 flights so 400 x 8 = 3200 minutes (53 hours) estimated motor/esc time. That's pretty good for what is probably a very cheap motor that will cost very little to replace. It turns a 12x6 prop on 3S for a max of 30 amps IIRC (it's long time since I checked).

Is it really worth buying expensive motors?

Geoff

MattyB08/09/2016 07:47:01
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1960 forum posts
30 photos

It depends on the application and the eleven of performance needed. For relatively low stressed (I.e low current and well cooled) powertrain as in most sport models such as the Riot I would say not; you might lose out very slightly on efficiency and therefore duration, but longevity of my cheap motors has been fine for the amount I fly, and the slight reduction in duration per pack is more than offset by the large savings that allow you to buy more batteries.

It's at the high end (EDFs, needle nose competition electric gliders with rocket like launches etc.) where the jibes quality kit matters. The higher quality motors will operate at well over the 3W per gram rule of thumb for cheaper ones, meaning higher currents can be used in less well cooled installations and the motor will still perform.

robert chamberlain30/08/2017 04:12:20
125 forum posts

Hello, I have an AXI 2814/20 mounted on a Gentle Lady rated at 25 amps max. I have propped it not to pull this limit. This outrunner gets extremely hot even on short runs to launch it and is mounted to the front of the fire wall with no cowling. Just how hot is too hot? Either the outer case or the coils inside.? Am I correct in understanding that magnets loose their power ( are ruined) if this limit is exceeded? Bob Chamberlain

Denis Watkins30/08/2017 04:41:32
3914 forum posts
61 photos

Hi Bob, you are right to have concern, and your instinct with hot metal is spot on. 3 things are going on and I can comment on two of them.

I cannot say why your motor is getting very hot and lads with similar problems will come forward and tell you why.

As you say, magnets degrade with heat quite rapidly and as they degrade the motor will get hotter !! so it is a vicious circle. Heat permanetly damages magnets

As you suspect, heat and metal go hand in hand. When we want to change the properties of metal, we heat it up.

The copper in the motor will soften considerably with heat. The solder can remelt, but oddly as solder get very warm and cools, it actually gets more brittle as some of the constituents evaporate, namely zinc, and your supple 60/40 solder becomes another mixture, and being brittle, it breaks.

Ben B30/08/2017 08:34:38
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1403 forum posts
4 photos

Bob- have you tried changing the timing on the ESC? Too fast on the timing and you'll get lots of heat because the pulses will trigger too late to create rotation.

Stevo30/08/2017 10:04:21
2699 forum posts
419 photos

I too have a Riot, and it seems to go on. and on. and on. Direct competition with SWMBO.

I did stuff it in heavy, and bent the shaft, new motor was £28. Again, it's gone on and on... always on 4 cells and original ESC too

Edited By Stevo on 30/08/2017 10:04:43

Trevor Crook30/08/2017 15:01:02
869 forum posts
65 photos

Geoff, the vast majority of my motors are cheapies from Hobbyking etc. The only models with more expensive brands are a couple I have bought secondhand, with Hackers fitted. I've had a magnet come loose some years ago, but that aside, have never had a motor fail on me. I've bent the odd shaft in crashes, which possibly wouldn't happen with more expensive brands, but replacing the odd motor for this reason I find acceptable. (I know you can often get replacement shafts, but I've never bothered.) Some of my fleet must have completed hundreds of flights.

I've had a similar experience with ESCs. It helps to run everything well within its limits, eg if your setup pulls 40A, use a motor and ESC that can handle at least 50A continuously.

Josip Vrandecic -Mes30/08/2017 18:46:50
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2993 forum posts
260 photos

Dear Geoff , the price of any engines/ motors are proportional to the value of each model. So, if the model is expensive or you like it (sentimental value), pay a high price and... vice versa......There is also a medium-sized solution, models and motors/engines of mediocre value, but I like extremes ...lol...wink

All the best

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