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The great i.c. / electric finger chopping debate

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David Ashby - Moderator18/06/2020 09:30:46
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We were putting the world to rights at the club recently when conversation got round to the great i.c. / electric motor comparison which traditionally says that electric props are more dangerous because they'll try and keep turning when coming into contact with something, where an i.c. engine will stall and stop.

Then someone threw a spanner in the works by saying that an electric motor would stop too because the ESC would lose synchronisation and start to re-arm itself.

That's not a theory I would like to test but I wondered if anyone has some thoughts they could share here perhaps based on actual experience, or some technical aspect to confirm or otherwise.

Bob Cotsford18/06/2020 09:44:55
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I've seen plenty of 'pecks' on take-off that didn't stop the prop, and I did motor-boat a Dogfighter most of the way back across the river, that certainly slowed the prop down but the ESC kept driving the motor until it cooked. I suspect that short of a stout bone there's little in the human body that will stop an electric motor of any size. Mind you, when I dangled my finger tips in the prop of an idling OS 120 Surpass that didn't stop either!

Nigel R18/06/2020 10:00:59
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Many moons ago I stuck the tip of my thumb into an 049, which took off a big chunk of skin and cut a long ways into the nail before halting. If the angle had been different I cannot imagine it would have stopped before hitting bone. Painful lesson and I would not like to repeat it with anything bigger. Bob's story is enough for me.

Any electric will try and restart the prop for a period of time before waving a white flag. Listen to what happens if you nose over and stall the prop, that whine continues for long enough. I can't imagine anything other than the prop coming around again to continue hitting anything that remains in its path, although the first hit will diminish the prop speed and hence severity of the subsequent impacts.

Dickw18/06/2020 10:06:19
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As the load on our electric motor increases it slows down and so both the current and torques will increase. If you stick your finger in the prop it will tend to slow the motor (!) so both current and torque increase as the motor tries to maintain speed. That is the difference to IC.

Eventually the ESC will detect an overcurrent and may well shut down to protect itself, but unlikely to do this in time to save the finger.

Dick

Martian18/06/2020 10:17:56
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I have been chipped by ic motors and electric and the one thing they have in common is they both hurt and both spill blood having said that a 250 size heli rotor keeps on hacking away until you call it of they even follow you like a rabid dog .

Ace18/06/2020 11:10:40
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Lets be honest either is seriously going to ruin your day. If a nick neither will stall so repeated slashes. On a major strike the fist blade will either have stalled embedded, removed your finger or broken a blade with the second one also impacting. Possibly more likely with the flimsier elec props. If the resistance is sufficient to stall either prop the IC will not restart. However electric motors deliver constant torque so will restart immediately resistance is lowered or until it or the esc burns out. I believe the potential for repeated strikes is greater for this reason with electric.

Another question may be when/why fingers or other parts of your Anatomy come into contact with props. Any prop when running is obvious and usually avoided although an IC will bring fingers closer to adjust needles or remove glow sticks which I suspect when most IC contact occurs.. An IC won't (in most instances) start unexpectedly. However for electric once armed and there are no signs it is other than a few esc beeps. It frightens the living daylights out of me when I see people reaching through props to install a battery and in particularly with it resting in their lap or returning/leaving a plane in the pits still armed and unrestrained. As a rule you don't see running IC engines left that way. Don't get me wrong I like and fly both.

Keith Miles 218/06/2020 11:37:31
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A somewhat academic issue, in my view, as has already been suggested!

And I tend to agree that electric power is potentially far more dangerous as, unlike IC, zero rpm can instantly become high rpm if you are not VERY careful!

You ALWAYS know when IC is likely to bite you unless you are totally deaf!

Most of us who have been flying models for a few years have been there, at least once, albeit not necessarily injured as a result, and the cure is to ALWAYS do everything SLOWLY and methodically whether IC or EP!

David Hazell 118/06/2020 11:51:26
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I'm just edging back into the hobby. I had decided to go electric for my initial return, but then did a prompt about-turn and bought a 2nd hand ATS Flair Kite with a Super-Tigre 45 to learn on. It's a beat up old rat of a plane but I won't be heartbroken if I break it. When I introduced myself I mentioned I'd be going electric, thinking it would be safer, but it was clearly pointed out to me that electric could be considered just as or even more dangerous. I take heed and will approach electric with caution and care.

In my teens, before school one day I went and started up my OS35FP on its test bench in the garage. I'd been used to a 1.49 peewee diesel (i think it was called that) before that... I went to adjust the needle valve but estimated the size of prop based on my experience with a much smaller engine. My finger got caught in the tip of the prop and stopped the engine which was fortunately running rough and low rpm, but ouch. To say it hurt is an understatement. I ran back into the house screaming and running around the open plan layout in circles with my Mum panicking trying to catch me! No long term damage was done, but I do have a very healthy respect for spinning props and will make sure I have the tips painted on every prop!!

Brian Cooper18/06/2020 12:00:22
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It is also very probably a "numbers game" where the power output comes into play.

Motors and engines with low power outputs might stop. But motors and engines with big power outputs will not be that worried about a minor interruption like clouting a finger. . Indeed, some of the bigger stuff with more torque (certainly engines) will cut off your entire hand with hardly any drop in revs.

Be careful out there. . Let's keep the blood on the inside. laugh

brokenenglish18/06/2020 12:01:56
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Posted by David Hazell 1 on 18/06/2020 11:51:26:

I'd been used to a 1.49 peewee diesel (i think it was called that)

Sounds like a PAW to me!

Engine Doctor18/06/2020 12:07:54
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Respect and fear in equal measures as both I/C and electric power can present a clear and present danger if basic safety measures are not taken . If you have been bitten by either type of power you will undoubtedly have respect and fear embedded in you mind.

Quote from O/P "Then someone threw a spanner in the works by saying that an electric motor would stop because the ESC would loose synchronisation and start to re-arm itself " David , I hope he was sent to the naughty corner for a couple of hours .smiley

Utter rubbish ! That's a dangerous theory that I wont be putting to the test any time . In my experience they Load up more and only quit when the ESC or some part of the circuit fails due to the high current draw .

A friend of mine , after repeated warnings about setting up his electric model with the propeller found out the hard way. His model started unexpectedly while on his living room table even with the So Called "Power cut" on the TX switched on. He instinctively reached out to stop it and received serious lacerations to his fingers wrists and forearms . On top of that he had the added embarrassment of his blood being spattered all over the freshly decorated walls ceiling and furniture . He takes notice now.

ken anderson.18/06/2020 12:28:32
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get a pork sausage ...put a bit of dowel through the middle and introduce it to the prop...ic and electric...wear eye protection etc....bit primitive but that will tell you and show you the result? yes/no...

ken anderson...ne...1...tech dept.

Nigel R18/06/2020 13:00:31
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Cooked or raw?

Petrol power tools are 20cc and up of fairly lazy petrol engine. The average mains powered angle grinder is 750W, a circular saw 1kw, chainsaw 1kw - 2kw. All of which, IC or electric, are thoroughly lethal in the wrong hands.

A 40 class electric (and IC) is around 800W. A 60 glow is roughly a 1200W of electric, a 20cc petrol maybe 1500W. Similar power levels all driving rotating sharp things.

Draw your own conclusions. Mine were, both are deadly, little to choose between the two, and most of all, stay out the way of the spinning thing.

Some flyers handling of electric kit leaves me cold.

Apologies for any deviation from thread intent.

Edited By Nigel R on 18/06/2020 13:01:20

John Stainforth18/06/2020 13:04:39
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...a.k.a. bangers and mash!

Andy Stephenson18/06/2020 13:18:53
180 forum posts
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Starting off as a schoolboy in the 60s with small diesels using floppy plastic props (there weren't any GF re-enforced ones back then) if you got your finger in the prop it hurt like hell but did no permanent damage. This was an object lesson for the future to respect the propeller which has stood me in good stead in avoiding injuries.

When I am training student pilots these days I make a point of talking about prop safety as I don't think there is enough in the manuals on this subject.

A.

john stones 118/06/2020 13:41:59
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Seen a fair few I.C related ones, the props all kept munching, not seen one stop yet, digits tend to get removed before that happens.

MattyB18/06/2020 13:59:10
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Posted by Keith Miles 2 on 18/06/2020 11:37:31:

A somewhat academic issue, in my view, as has already been suggested!

And I tend to agree that electric power is potentially far more dangerous as, unlike IC, zero rpm can instantly become high rpm if you are not VERY careful!

You ALWAYS know when IC is likely to bite you unless you are totally deaf!

I only fly electric, but I completely agree with this. You can argue the toss about which power source will injure you more if you feed it a digit (not an argument I particularly want to prove either way!), but the statistical chance of an accident occurring is definitely higher on electric. IC engines don't generally jump into life without any warning!

Having seen a few accidents in the pits from models leaping into life unexpectedly every electric model I own now features a multi layered "sticky" throttle cut (the largest ones also has some physical isolation of the motor via an arming plug). However many TXs aren't capable of such functionality, and I've seen first hand that a "dumb" throttle cut that doesn't take into account the stick position can be almost as dangerous as no throttle cut at all. If I didn't have a TX capable (thanks goodness for OpenTX yeswink 2) I'd use arming plugs on every model.

Edited By MattyB on 18/06/2020 14:00:49

Richard Clark 218/06/2020 14:08:37
398 forum posts
Posted by MattyB on 18/06/2020 13:59:10:
.........if I didn't have a TX capable (thanks goodness for OpenTX)

YAWN

Bob Cotsford18/06/2020 14:18:26
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What worries me are club sites where starting point and release points are a fair distance apart. One local club in particular has a 30 or 40 yard path from the pitts to the strip and people are carrying running models and a transmitter along this grass path. Bad enough when it's dry and the path trimmed but an accident waiting to happen on untrimmed wet grass! At least with electric you can use shorting plugs, throttle locks or just disconnect the battery for the trip(!surprise). I have to admit to leaving a starter in the flight box and annoying people by restarting the motor there.

Steve J18/06/2020 14:30:07
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Posted by MattyB on 18/06/2020 13:59:10:

IC engines don't generally jump into life without any warning!

I have never seen an electric motor start spontaneously. They only seem to start spinning when a control is moved on a transmitter. In fact, if you are using a system were the receiver is bound to a particular transmitter, there is a pretty good argument that the safest thing is to have your transmitter turned off until just before takeoff.

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