That's actually not true electric helicopter models are becomming more frequent every day, especially since the introduction of brushless engines. look at
Also the trend for slow flyer and foamies (Not VTOLs though) is interesting. Look at the MovieStar from
carries 400gr of payload for 7/8 mn at the speed of 10m/s with
8 cells of 2,4Ah NiCad. You'll find some helicopters.
About NiMH batteries they have the inconvenient that they do not support quick charge as well has NiCad. They are for now mostly used by competitors who can afford enough battery packs so that they only need to be charged once twice a day.
>Firstly - is this realistic for a payload of a power supply and the
>>associated electronics? What type of battery would you reccommend, if
>>each motor draws ~2.5 amps at 12v?
> You could try some NiMH batteries, but the weight of the batteries alone
> will likely be 1 kilo. Even fairly large 3-5 Ah batteries would drain
> very quickly deliverying 2.5*8 amps.
> Let me ask you: have you seen many self-contained electrically powered
> VTOL craft? Do you think there might be a reason they aren't common? >
> -- Gordon
> Robots for Less at Budget Robotics:
_____________________________________________ The problem is, gas motors are awfully:
Finicky messy loud expensive
My engine of choice is OS. If you aren't going to have a lot of air running over it, as in a geared down slow, big blade arrangement, consider R/C car or heli engines, as they have a bigger heat sink.
On the subject of helis, consider how they achieve variable thrust on the tailboom, or on the main rotors of the more expensive helis. They vary the pitch of the blades, on the fly. This allows them to adjust their thrust quickly and accurately.
If it were my project, I would do it a couple of ways. Either electric, via umbillical for power, because when I finally finish it, the miracle battery will have been invented, or gas engine(s), with reduction, and variable pitch blades, (or vectored thrust.)
My first stab at it, would be to mount an engine on a stick, with a bearing or hinge, and try to get the engine to keep the stick level. This way, I could experiment with propulsion, sensing and control notions, without buying 3 engines etc. ( be sure to limit it, so it cannot hurt someting, or you)
It would also do you well to pay attention to what Tramm Hudson is doing. He is doing auto-pilot for R/C helis. No matter what you do, his work is applicable.
While I am at it, have a look at the IsoPod or the 803-mini from New Micros Inc. (
) I have interfaced the 'pod to the standard R/C servos quite easily in their high level,multi-tasking language, without having to deal with servo co-processors. It wil also easily handle the digital servos people are using on R/C heli gyro/tail rotor controlls. Since it handles the servo control in hardware, there is NO software overhead.
Just to mention, think about the time constant of your system, keeping masses low, and closer to the C/G. This will keep you responsive.
Depends on speed etc - blade design is a big subject not really relevant to crm. Try an aerodynamics group.
However you should definitely look at cowling on the input to the fan tube. The peripheral airflow is absolutely crucial - adding a cowling to an intake tube can more than double the airflow because otherwise the inrushing air flows fastest at the middle, where the blade speed is minimal.