Chief Delphi - Helicopter Project

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- - Helicopter Project (http://www.chiefdelphi.com/forums/showthread.php?t=48599)

Re: Helicopter Project

Quote:

Originally Posted by Matt Krass

Atmel AVRs are ....

I agree with the AVR option. I've started using them for the same reason(s). Free C compiler, lots of application notes, software examples (assembly and C) and development hardware is cheep!

You may want to look into the mega AVRs since they have hardware multipliers which may be handy for processing multiple PID loops quickly (not necessary, but nice).

Re: Helicopter Project

Hey guys, once again, thank you for all your comments.

Before I get into target operation and manuevering (sp), I would first like to get the Copter to atleast hover on its own under the programmed codes.

Running it through my head, I figure what I would need for this, simply to get the Copter hovering on its own, would be the Copter, ADXL213 Dual-axis Accelerometer or Memsic 2125 Dual-axis Accelerometer, whichever I decide to use to balance the Copter out, and the Microcontroller along with all the programming sofrware. If there is anything I am missing, please let me know. Again, thank you all

Take care
- Miguel

Re: Helicopter Project

hovering is actually the most challenging aspect of this auto pilot project.

When the HC starts to hover the downdraft of the blades will push the air straight down. After a few seconds the air will start to swirl in a donut pattern, the air that was being pushed down goes outward, then back up, and is then sucked through the blades again.

the result is, the air at the center of the HC developes a downward velocity. In order for the HC to maintain its height you must apply more and more pitch/power.

So you are going to need a way to measure altitude in order to hold a fixed altitude while hovering.

Re: Helicopter Project

[quote=
So you are going to need a way to measure altitude in order to hold a fixed altitude while hovering.[/QUOTE]

IR or Ultrasonic range sensors...

Quote:

I agree with the AVR option. I've started using them for the same reason(s). Free C compiler, lots of application notes, software examples (assembly and C) and development hardware is cheep!

Thats the problem I had with 16 series pics when I started working with pics: no free C compilers. So I started using 18F series pics and used the RC code as a guide to make mine work. After a while I finally got a 18f458 to run a servo!

Re: Helicopter Project

Quote:

Originally Posted by MDelgado1989

At minimum you will need three gyros and three accellerometers. It took me about 3 hours of flying time to hover a battery pack without crashing. That's flying time, not counting time spent waiting for spare parts. Micro helis are so cheap becase they make money on the spare parts. As Ken was saying, any change in roll or pitch requires an increase in throttle. The best analogy I've seen is balancing a marble on a piece of glass. I'm not going to say it can't be done, but it will be very difficult. As I said in a previous post, it's not just controlling the heli, its being able to carry your sensor and processor payload too. A micro heli can only handle a couple of extra onces of weight.

Go to http://rcgroups.com and visit the micro heli forum. There is a sticky with a PDF called the "Electric Helicopter Beginner's Guide". Essential reading.

Re: Helicopter Project

Quote:

Originally Posted by KenWittlief

When the HC starts to hover the downdraft of the blades will push the air straight down. After a few seconds the air will start to swirl in a donut pattern, the air that was being pushed down goes outward, then back up, and is then sucked through the blades again.

Actually there are two phases of hover - HIGE and HOGE
Hover IN Ground Effect and Hover OUT of Ground Effect.

What Ken describes is IN ground effect - the ground is causing the air to recirculate and can cause turbulence, but it can also require less power to hover in this condition.

Hover OUT of ground effect means the helicopter is high enough that the air dissipates and the ground has no effect on the rotor system.

Re: Helicopter Project

I dont think it is limited to the ground effect altitude.

I found this on a website - it appears to be a run-away sort of thing, once it starts to happen you cannot lift out of it, unless you move forward out of the ring of airflow:

Quote:

According to the Federal Aviation Administration (FAA) Rotorcraft Flying Handbook, pages 11-5 to 11-7, Vortex Ring State (Settling with Power), "Vortex ring state describes an areodynamic condition where a helicopter may be in a vertical descent with up to maximum power applied, and little, or no cyclic authority. The term 'settling with power' comes from the fact that the helicopter keeps settling even though full engine power is applied. In a normal out-of-ground effect-hover, the helicopter is able to remain stationary by propelling a large mass of air down through the main rotor. Some of the air is recirculated near the tips of the blades, curling up from the bottom of the rotor system and rejoining the air entering the rotor from the top.

However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in accelerating the air in a doughnut pattern around the rotor. In addition, the helicopter may descend at a rate that exceeds the normal downward induced-flow rate of the inner blade sections. As a result, the airflow of the inner blade sections is upward relative to the disc. This produces a secondary vortex ring in addition to the normal tip-vortices. The secondary vortex ring is generated about the point on the blade where the airfoil changes from up to down. The result is an unsteady turbulent flow over a large area of the disc. Rotor efficiency is lost even though power is still being supplied from the engine."

Re: Helicopter Project

Quote:

Originally Posted by KenWittlief

I haven't seen it with the model helis, but with a fixed-pitch model you have little or no control when dropping altitude because the blades aren't spinning fast enough to maintain cyclic authority. If you hover at about 20' then try to land the tail will drop and the cyclic turns to mush. You'd have to be pretty good to drop straight down.