Propeller choice for quadcopter

[dirty_d]

I'm planning on building a pretty large quadcopter. The motors I've been looking at have been the 4240 - 5055 size turnigy motors. I'd like to have a lot lot more power than I really need so that it will have lots left over to stabilize itself in wind etc. I figure the whole thing will probably weigh 8-10 pounds rtf. I'd like it to be able to easily lift another 15 pounds(maybe even more if its reasonable) which I don't think should be too much trouble with four motors of that size.

What I'm not too sure about is what size prop to use. What I need really, is a lot of static thrust. And from what I understand the most efficient way to create that is by moving a large volume of air at a low velocity, so I need a large diameter propeller. I'm not too sure about the pitch though. More pitch would seem to give you more thrust and a higher possible airspeed, but how does efficiency fit in there? will a lower pitch prop give you more static thrust more efficiently?

I've been thinking 16X10 APC mainly because its one of the only large pusher APC props i can find. Another possibility is the 15x4. I think id have to spin the 15x4 a lot faster than the 16x10 to make the same static thrust, but which would be the more efficient?

Thanks for any help anyone can provide.

[slipstick]

Adding pitch increases the load on the motor and so the current it takes but without providing appreciably more static thrust. So if static thrust is what you want go for as much diameter as you can manage with low pitch. Maximum thrust efficiency comes from large diameter props turned relatively slowly.

Of course the battery voltage plays into the whole equation too and you haven't said what battery you're intending to use.

BTW why do you need pusher props.....is that something to do with "quadcopters", about which I know approximately nothing ?

Steve

[dirty_d]

I'm just going to use whatever battery voltage I need to get the rpms I need to get the trust I want with whatever prop I choose. I'd rather use the higher kv versions of the 5055 size motors so I can get away with 3 or 4s.

I need two pusher props and two normal ones so the torque cancels out. The yaw is controlled by speeding up one matching set of props, and slowing the other.

so 16x10 isn't really a good idea then? 15x4 is pretty low pitch, but I'd rather go bigger if it means better efficiency and lifting power. There is an 18x6 APC prop that comes in regular and pusher, but ouch $33 in pusher, $22 regular.

[CNY_Dave]

Pusher props just have the 'other' surface precision-machined, correct? Other than that, they're all the same...

He's probably going to have the props below the motors.

Dave

[dirty_d]

They're all going on top, the difference is that one is made to rotate clockwise, and the other counter-clockwise.

[JZSlenker]

For multi rotors you want a minimum 2:1 thrust-weight ratio. Take this and any payload weights into account when calculating your motor/prop combination. What Flight Controller will you be using?

[dirty_d]

im making my own based on an atmega324 and an mpu-6050 6axis gyro/accelerometer.

[Glacier Girl]

Well the other way to look at it. Low kv motors on a higher cell count. Less amp draw with same props so you can use not only a smaller esc, but also a lower C rated pack(s)

Also if you are looking at thrust vs speed, look at a 3 or 4 blade prop.

[dirty_d]

Yea I may go that route. My main concern right now are the propellers. The18x6 APCs sound about perfect if the damn things wouldn't cost me $110 for the four of them. Doesn't more blades mean less efficiency?