Shortened propeller. Please advise.

[YvesDL]

Calling to experienced pilots or technicians.

As a result of a bad crash, my P4A now has a slightly bent arm. Resulting with one of the grey propeller touching slightly the "body" of the P4A. Since that particular blade broke at both ends, the drone would fly, still being responsive and precise. That's with one propeller shortened by approx. 1 cm (1/2 inch) at both ends!

I later had other hardware related problems: camera broken and had to replace both ESC boards (ESC error on all 4 motors). That has been taken care of. Still have one grey propeller slightly touching the craft though.

My inquest regards that issue.

I prefer not changing the P4A "body" (repairs already costed alot). Can I safely shorten 1 propeller half an inch at both ends (so it won't touch)? Should I shorten the other corresponding grey blade too? (for better balance)

Please advise.

Best Regards,

Yves DL

Video: Flying with 1 broken blade (shortened by half an Inch on both ends) -Will be posted later today..

 

[solentlife]

I would not recc'd flying with such ... and much as it pains ... replacing the body would be your wisest move along with a new set of props.

Why does it fly with shortened prop ?

OK - the AC basically is controlled by a Flight Controller that receives information from many detection parts :
ie >
Compass
Barometer
GPS
Gyro
Accelerometers

It is the last two that we need consider. The gyro helps to stabilise the AC in the orientation you command. The accelerometers detect 'acceleration' in each direction contrary to command.

This basically means that the Flight Controller will adjust each motor and in so doing the thrust applied to maintain position / orientation / movement commanded. As long as each propeller is capable of producing the lift required - the AC will fly as commanded. If a propeller is smaller - that means Flight Controller will compensate by extra RPM - based on data flow from accelerometers etc.

Is it a good idea to run smaller prop ? Not really as the Flight Controller will using some of the 'extra margin' to compensate and you may find a situation that needs that ...
Second its increasing the wear and tear on that motor.
Thirdly - balance of the prop is likely poor - creating vibration to the motor bearings and the motor mount, as well as to all the electronics ...

My considered opinion is that you ought to fix the whole model and fly it as designed.

 

[Capt KO]

I’ve never done it but you might try a heat gun to straighten that arm. If it doesn’t work, I believe you will have to change the shell or eventually lose the drone. Sorry, fly safe

 

[Kirby Johnson]

I would not recc'd flying with such ... and much as it pains ... replacing the body would be your wisest move along with a new set of props.

Why does it fly with shortened prop ?

OK - the AC basically is controlled by a Flight Controller that receives information from many detection parts :
ie >
Compass
Barometer
GPS
Gyro
Accelerometers

It is the last two that we need consider. The gyro helps to stabilise the AC in the orientation you command. The accelerometers detect 'acceleration' in each direction contrary to command.

This basically means that the Flight Controller will adjust each motor and in so doing the thrust applied to maintain position / orientation / movement commanded. As long as each propeller is capable of producing the lift required - the AC will fly as commanded. If a propeller is smaller - that means Flight Controller will compensate by extra RPM - based on data flow from accelerometers etc.

Is it a good idea to run smaller prop ? Not really as the Flight Controller will using some of the 'extra margin' to compensate and you may find a situation that needs that ...
Second its increasing the wear and tear on that motor.
Thirdly - balance of the prop is likely poor - creating vibration to the motor bearings and the motor mount, as well as to all the electronics ...

My considered opinion is that you ought to fix the whole model and fly it as designed.

Oh Boy................

 

[solentlife]

Oh Boy................

Just interested what that is meant to mean ...

 

[Kirby Johnson]

Just interested what that is meant to mean ...

Oh, just the idea of considering flying something with mismatched prop(s) and an out of alignment motor mount. And the advice you fellows gave is highly accurate, maybe even optimistic. Reminds me of the tire which is only flat on the bottom.

 

[joelet]

You are going to get a lot of vibration which will eventually crack the shell anyway. So you should replace the shell. Just a question for you would you fly or get in an airplane with the same condition?

 

[Andy9]

Propellers are the most essential part of the drone to fly. They are very cheap so don't understand why the discusion on that at all. Replace it and there you go.

 

[solentlife]

Oh, just the idea of considering flying something with mismatched prop(s) and an out of alignment motor mount. And the advice you fellows gave is highly accurate, maybe even optimistic. Reminds me of the tire which is only flat on the bottom.

My 'novel ' about the Flight Controller is factual ... that is how it works. I was confirming what he found and why - that you can fly with mismatched props.

Personally as another says - WHY do it though ... a Phantom is not a cheap toy and care / attention to using good condition items is advised.

I have a couple of damaged DJI props - the blades make excellent paint stirrers / filler paste applicators etc.

 

[cheddarman]

You will completely change the aerodynamics of that propeller, greatly reducing its lift at a given speed. If its mount is bent it will also be out of alignment with the body. The AC computer will try to compensate for this loss of lift by increasing its speed and if it can't get the lift back up to where it should be the drone will behave very erratically bearing in mind how a drone actually flies.
For the sake of saving a small amount of cash, not worth the risk.

 

[solentlife]

You will completely change the aerodynamics of that propeller, greatly reducing its lift at a given speed. If its mount is bent it will also be out of alignment with the body. The AC computer will try to compensate for this loss of lift by increasing its speed and if it can't get the lift back up to where it should be the drone will behave very erratically bearing in mind how a drone actually flies.
For the sake of saving a small amount of cash, not worth the risk.

Think this has already been explained ?

 

[cheddarman]

No harm in emphasising it over and over again as anybody who would even contemplate doing such a thing need to know that everybody thinks it a bad idea.
Wasn't meaning to steal your thunder.

 

[RedDog7]

One other matter to consider, the crash could have damaged the the hub of the prop. It could be a hairline crack which is invisible to a cursory glance. Flying the quad with such a crack could result in the prop breaking during flight and you'll end up with far more damage. You may be able to get your hands on a Phantom which had been given swimming lessons. It wouldn't cost much as only the shell would be salvageable.

Good luck and happy flying,

 

[grego122]

What's cheap now will be more expensive in the end but it's up to you! Good luck.

 

[cheddarman]

Looks like YvesDL just posted for something to do, not really after advice! Oh well,!

 

[RedDog7]

Don't you hate that? Someone asks a question and doesn't even bother to acknowledge the guys helping him, let alone a thank you. My usual thought is that it's a youngster, but in this case it isn't.
It's almost impossible to get a please or thank you out of them these days. In fact it's often hard to get more than a couple of words at times. I just tried to buy some spare parts for a P2 on Gumtree (part of Ebay) I made an offer and told the seller I'd pay via Paypal the reply was "OK send money" So I explained I needed a Paypal Username and all I got was "????" I elaborated and explained how Paypal works and the reply "????" I withdrew my offer.

It seems the younger generation is losing the ability to communicate. Please note: I'm not saying it's every youngster, but from experience it does appear to be a large percentage of them.

 

[cheddarman]

EH?

 

[bsartist]

Propellers are the most essential part of the drone to fly. They are very cheap so don't understand why the discusion on that at all. Replace it and there you go.

Because it wasn’t just about a bad prop. He is trying to get around a bent arm.

 

[solentlife]

It seems the younger generation is losing the ability to communicate. Please note: I'm not saying it's every youngster, but from experience it does appear to be a large percentage of them.

I am reluctant to agree with you 100% .... I tend to think of personal communication skills as having suffered due to TV ... then Computers ... then Internet ... and todays scourge ! Mobile Phones ....

Spend time anywhere people congregate ... sit ... wait .... and its Texting time ! Even heaven forbid that anyone expects to TALK on the phone !!

 

[YvesDL]

Thanks everybody for all your input,

Some answers to above interrogations:
- The no.1 gray propeller Is shorter because it slightly touches the p4a frame (arm) which is bent following a crash. I straitened it as much as I could, using heat but it still touches very slightly when mounted by a full length propeller. My idea was to remove 1/8 of an inch at both ends of that particular propeller, so it doesn’t touch. My concern is about avionics and the instability that fix could induce.
- I did test the drone with such a modified prop and it did fly straight, with no evident or detectable abnormal behaviour. And the blade doesn’t touch the frame even at full speed in sport mode, with heavy breaking and direction change.
- Of course the best would be to change the frame (if not the whole drone). Just wanna try to extend this one’s life without putting any more money on it (crash repairs already cost me a cam/gimbal, and 2 ESC boards (p4a got 4 chips separated on 2 boards) so roughly 500$.
- That drone is used for deep wood flying. Mostly for hunting preparation purposes. It never flies special operations involving flying near houses or people or even animals. It is kinda expandable. That is the context here. I’m no engineer, was just wondering if anybody ever tried a fix like that.

Best regards to all. It’s been like candy reading you all!