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EDF for about 4kg thrust using low cost motors

Old 02-08-2020, 04:34 PM
  #1  
Shantz
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Post EDF for about 4kg thrust using low cost motors

I need to design an EDF for a project which requires around 4kg thrust for a VTOL Hopper/Lander vehicle which utilises thrust vectoring.

Buying a EDF unit for this much thrust would cost way too much for my budget.

Instead I can build the props and the frame on my own and buy the brushless motor separately. Can you provide some suggestions for purchasing a motor (or motors) for under $35?

Last edited by Shantz; 02-08-2020 at 05:10 PM.
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Old 02-09-2020, 12:03 PM
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solentlife
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Suggest looking at eCalc .... and try combos of motors and EDF / ducted props.

4kg is a lot of thrust and would require a serious EDF .... most likely a ducted prop would be better ...

To get that sort of thrust - I have 48 to 50 size brushless motor and anything from 14" prop upwards !
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Old 02-09-2020, 04:13 PM
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quorneng
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Shantz
It would help if you describe what the 4 kg of thrust is for and how it is to be used in VTOL For instance one motor or many?
All VTOL requires specific control and stability features that are likely to make the required thrust not the most difficult element to achieve.
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Old 02-09-2020, 07:19 PM
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ron_van_sommeren
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The better the questions, the more info, the better the answers can be.
E.g. you would not be the first one to mistakenly assume that prop thrust must be higher than plane mass in order for a plane to be able to fly at all.

As Nigel suggested in post #2 e-calculators such as www.ecalc.ch (18 languages) can get you in the ball park (software: garbage in, garbage out).
A watt-meter is a must, it will let you check/refine/debug your new/changed power system, and watt-meter will pay for itself several times over.

Forum usage: entering country and/or region and/or location in your profile makes it possible for us to refer your to help, shops, events, people, clubs, ...
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Old 04-02-2020, 06:52 AM
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Shantz
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Originally Posted by quorneng View Post
Shantz
It would help if you describe what the 4 kg of thrust is for and how it is to be used in VTOL For instance one motor or many?
All VTOL requires specific control and stability features that are likely to make the required thrust not the most difficult element to achieve.
I am trying to design a rocket style body with 4 thrust vectoring vanes/fins in 'plus' configuration. Because the motor and prop will be seated inside the rocket body tube, I did not opt for a ready-made EDF. I think it will be more beneficial if I use a stand-alone motor and prop.
I will probably have a inner diameter of 8 inches with the body made of PVC. I can use one or two motors in opposite directions to counter torque. most of the weight would be of the 4 batteries (3S 3300mAh) and a payload of 500gm near the top. I can reduce the body weight to 2.5 kgs
It will have a rocket style launch and therefore requires high acceleration. I also want to hover. This is my current design.
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Old 04-02-2020, 11:28 AM
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quorneng
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I fear that to produce 4 kg, or even 2.5 kg, of thrust within an 8 inch diameter body you would have to use a multi bladed fan. A prop will not create such thrust. Using two 4" (100 mm) diameter side by side I doubt even EDFs would achieve it.
Then there is the problem of getting the air into the fans efficiently and keeping the duct lengths as short as possible.
If it has electronic stability sufficient for it to hover then the launch acceleration is not really critical as long as it is up wards!

What you are attempting is quite a challenge so I strongly advise that you take it in gradual stages.
Your first task surely is to try to find what sort of thrust could be achieved from the biggest prop(s) your design can accommodate. 75% of this figure would give you a 'target' all up weight for your complete rocket.
Unless this looks a feasible then I am afraid it is "back to drawing board" to work out another way of doing it.

This was exactly how I approached my own EDF 'rocket'.
Having selected an EDF (I had already used similar in EDF planes) I built just the inlet and exhaust section and fitted it onto a test stand to see how much thrust was available.
From the result I judged it would be just feasible but only by using extremely light weigh construction. lightweight components and a very highly stressed battery with a full power duration of less than 1 minute.
Click image for larger version

Name:	06May18.JPG
Views:	14
Size:	180.6 KB
ID:	187923
It worked and took off vertically but the gyro controlled vanes in the exhaust were never sensitive enough to allow a hover. However once air born it flew very nicely as a normal RC plane at much reduced throttle.
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Old 04-02-2020, 12:11 PM
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Shantz
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Originally Posted by quorneng View Post
I fear that to produce 4 kg, or even 2.5 kg, of thrust within an 8 inch diameter body you would have to use a multi bladed fan. A prop will not create such thrust. Using two 4" (100 mm) diameter side by side I doubt even EDFs would achieve it.
Then there is the problem of getting the air into the fans efficiently and keeping the duct lengths as short as possible.
If it has electronic stability sufficient for it to hover then the launch acceleration is not really critical as long as it is up wards!

What you are attempting is quite a challenge so I strongly advise that you take it in gradual stages.
Your first task surely is to try to find what sort of thrust could be achieved from the biggest prop(s) your design can accommodate. 75% of this figure would give you a 'target' all up weight for your complete rocket.
Unless this looks a feasible then I am afraid it is "back to drawing board" to work out another way of doing it.

This was exactly how I approached my own EDF 'rocket'.
Having selected an EDF (I had already used similar in EDF planes) I built just the inlet and exhaust section and fitted it onto a test stand to see how much thrust was available.
From the result I judged it would be just feasible but only by using extremely light weigh construction. lightweight components and a very highly stressed battery with a full power duration of less than 1 minute.
Attachment 187923
It worked and took off vertically but the gyro controlled vanes in the exhaust were never sensitive enough to allow a hover. However once air born it flew very nicely as a normal RC plane at much reduced throttle.
If I reduce the amount of batteries to 2, it'll make the weight of electronics and batteries just under 1 kg. Foam frame would be the better option to reduce weight but I am not sure how I will mount everything on such a fragile frame. What frame did you use for your project?
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Old 04-02-2020, 02:56 PM
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quorneng
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For a "vertical riser" saving weight is key but you are still quite a bit above my rocket which weighed just 695 g ready to go. It had about 850g static thrust available.
The development and build is described here and was, to put it mildly, rather long and complex. The initial concept proved to be unworkable so had to be revised and then a new bigger version built. In all it took 7 months work before the first vertical take off took place.
Yes it worked but most definitely not a simple build. The fact that it was a true scale model did not make much if any difference to the way it performed and having proper wings did at least get over the problem of landing.
Do you have any sketches/drawings of what you are proposing.
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