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[DPRG] R/C heli technology
Subject: [DPRG] R/C heli technology
From: Triffid Hunter
triffid_hunter at funkmunch.net
Date: Mon Jun 11 18:12:31 CDT 2007
On Mon, 11 Jun 2007, dpa wrote:
> Howdy,
>
> Did my first hover today with my new helicopter, (a TREX-450 with a
> Spektrum DX7 radio, for those in-the-know :)
>
> This is some seriously cool technology. The gyro itelf is about the
> size of a nickle, and includes an 8-led "level meter" with 5 green
> leds for programming modes and a push button for user input! The
> motor is brushless with a very nifty speed controller that uses sound
> output for programming feedback and the R/C link for programming input,
> all based on timing, for things like slew rates, gain controls,
> and gain limits. Extremely nice.
>
> The whole thing lights up like a Christmas tree and sings like R2-D2
> during powerup. I love it!
>
> The heli uses a 2200 mAh 11.7v LiPo battery pack about the size
> of a small Snickers candybar, that charges in just one hour.
>
> Once again I think we robot folks have a great ally in the R/C car/
> plane and now helicopter crowd. Seems like one of these "heading
> hold" gyros might be just the ticket for odometry+gyro robot
> navigation, indoors or ourdoors.
>
> Does anyone know of a brushless speed controller that can be reversed?
>
> The helicopter, of course, just runs the motor in one direction and
> reverses the pitch of the blades, but a robot needs to be able to
> reverse its motors in software. The speed controller has three
> leads and reversing any two of them reverse the direction of the
> motor. That suggests that it would not be difficult to build a
> controller that can reverse the motor. Anybody know if such a
> thing exists?
>
> best,
> dpa
As far as I know, brushless speed controllers are basically trinary 3 bit
shift registers with a 1, 0, -1 pattern walking around the ring
synchronised to the motor's hall sensors or just running free with an
acceleration profile. You can also do 3 phase PWM for finer control.
To reverse motor direction, all you need to do is reverse the shift
direction - swapping two leads is one way to do this, but it should be
easy in software too.
I'm currently playing with a maxon motor controller that supports
bi-directional brushless motor control.
http://www.rcgroups.com/forums/showthread.php?threadid=127606 should be a
good read too.
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