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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Carbon_Rod wrote ...
RC prop calculators are common, and are usually badly written too:
Such a small maze.... yawn... gridSLAM + MDP for the win... =)
yes ill agree with your program comments, but as for your last comments, ill be sure to point them out to the 8 other international University teams!!!
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
@Patrick 99% of students make similar mistakes, and tend to repeat prior design mistakes the year after seniors graduate. You may find experiencing the transition process rather sobering... as it highlights a fundamental problem with human behavior and science.
You can be certain at least 1/3 of the teams will have power system failures of one type or another.
The best part in judging these types of events, is having someone forget to cite a colleague or your own work in presentations. LOL
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
Carbon_Rod wrote ...
You may find experiencing the transition process rather sobering... as it highlights a fundamental problem with human behavior and science.
I think it shows a lack or rigour and public mindedness in educational engineering. Even within single schools there seems to be a lack of impetus to ensure know-how gets passed on, outside of them the information shared is sadly pathetic.
In my opinion most publications in the engineering studies are mostly useless without reproduceable research.
PS. why are ducts rarely used on quads BTW? Do they mess up control too much in non-hover? Or is it simply too hard to build light ones?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
AS for Pinkys comments, first the ducts are quick to break, second they wheigh alot, especially for the lighter (sub 400g) machines....Third, since your increasing the mass towrad the far right and left, that means your decreasing the P values in the PID and Kalman filters, reducing dynamic response.
yet heres mine: S-2 fiberglass and balsa, 84 grams. Meant for a 10x4.7 Slow-flyer prop.
the Michigan crash from the above video clip. Note the broken prop wing. This machine wheighed in at just a few grams less than the 1.500 kg allowed by rule.
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
There are a number of reasons why propellers are twisted in that way. The big ones in this case, however, are probably that the parrot folks didn't optimize their props to any great degree and came up with a shape that a) looked like other propellers and b) worked well.
The #1 reason for the twist on a conventional aircraft is so that the angle of attack is the same at all points on the blade; AOA determines the lift-to-drag ratio, which for a prop is essentially the ratio of thrust to engine torque. When the aircraft speed is zero the AOA is equal to the blade's pitch at that point. However for nonzero airspeeds the AOA is not equal to the pitch and is given by the combination of the airspeed and the linear velocity of the prop at that point on its radius.
Think about that and you'll see why Parrot probably didn't spend too much time thinking about their props. You've probably noticed that while every airplane on the planet has a twisted prop, every helicopter on the planet has straight/untwisted rotor blades... the reason being that the airspeed through the rotor is only significant when a helicopter climbs straight up or down, so there is no twist necessary to maintain a constant AOA. Most helicopters don't spend too much time flying straight up or down, and when they do they do so slowly... ergo not much bonus.
With that in mind the prop design for the parrot probably had more to do with a desire to have a prop of a given size and then increasing the pitch at the root to squeeze every ounce of thrust possible out of that diameter, efficiency be damned. If parrot optimized their prop for battery life they'd have HUGE, thin, flat props as mentioned, not unlike what you see on human powered helicopter attempts.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
AndrewM wrote ...
There are a number of reasons why propellers are twisted in that way. The big ones in this case, however, are probably that the parrot folks didn't optimize their props to any great degree and came up with a shape that a) looked like other propellers and b) worked well.
The #1 reason for the twist on a conventional aircraft is so that the angle of attack is the same at all points on the blade; AOA determines the lift-to-drag ratio, which for a prop is essentially the ratio of thrust to engine torque. When the aircraft speed is zero the AOA is equal to the blade's pitch at that point. However for nonzero airspeeds the AOA is not equal to the pitch and is given by the combination of the airspeed and the linear velocity of the prop at that point on its radius.
Think about that and you'll see why Parrot probably didn't spend too much time thinking about their props. You've probably noticed that while every airplane on the planet has a twisted prop, every helicopter on the planet has straight/untwisted rotor blades... the reason being that the airspeed through the rotor is only significant when a helicopter climbs straight up or down, so there is no twist necessary to maintain a constant AOA. Most helicopters don't spend too much time flying straight up or down, and when they do they do so slowly... ergo not much bonus.
With that in mind the prop design for the parrot probably had more to do with a desire to have a prop of a given size and then increasing the pitch at the root to squeeze every ounce of thrust possible out of that diameter, efficiency be damned. If parrot optimized their prop for battery life they'd have HUGE, thin, flat props as mentioned, not unlike what you see on human powered helicopter attempts.
Masterful, Masterful points you make Andrew!!! This is why i post here, for the enlightenment i otherwise wouldnt benefit from ! I never thought of the absence of the heli rotor twist!
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Thrust bending and centrifugal twisting forces aside, In general there will usually be a small fan cut into the motor housing itself to keep the copper insulation from burning off.
Usually people cook motors by choosing the wrong blade pitch, diameter, or drive motor performance class.
@Andrew... this needs more cow bell.... much more...
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The Physics Of Propellers (And Electrical Motors).
