SwarleyAUS
Posts: 2
Joined: Tue Sep 18, 2012 11:07 am

Emulating a RC receiver

Tue Sep 18, 2012 11:36 am

Hi guys,

First post, hopefully this is in the correct section... Admin feel free to move it - there's a few that this question could come under, I think. I did a search but "RC receiver" returns 34 pages of results, and more for "low voltage" =O if this has been asked just link me. =)

Anyway, Im looking to try to use my RPi as (ultimately) a wireless communication device for telemetry (GPS, etc) and controlling a quadcopter remotely or by use of pre-programmed waypoints (instead of a transmitter and receiver combo).

I would need 4 outputs that provide signal voltages to the quadcopter control board that range from 0.15 to 0.25V, 3 centred about 0.20V (+/-0.05) and one centred about 0.15V(+0.1) to mimic a RC receiver's output.

Firstly, I believe the latter will be easier to do =/ (for example) by using high-frequency switching with C to fluctuate the 3.3V GPIO from ~2.2 up to 3.3V, then passing though a step-down converter to get ~0.15-0.25V. Any ideas if this will cause any heat problems with the Pi?

Secondly - the hard part - does anyone have any ideas (Ive had a few) how to simply hold a steady 0.2V output with the GPIO (or other) and have it fluctuate between the aforementioned voltages without using an external regulator circuit or a massive resistor? haha!

Thanks a bunch guys! =)

Taylor

DuncanKennedy
Posts: 44
Joined: Sun Apr 22, 2012 3:35 am

Re: Emulating a RC receiver

Tue Sep 18, 2012 1:52 pm

Hi Taylor

If you do a search for 'control' and 'servo' you'll find a number of post regarding using the Raspberry to drive servos - one post talks about controllong a large number of servos (48) or more (IIRC). It's certainly doable, just have to see if any existing solutions match what you're trying to do.
Duncan
The mind is an infinite resource, provided you don't waste it!

SwarleyAUS
Posts: 2
Joined: Tue Sep 18, 2012 11:07 am

Re: Emulating a RC receiver

Tue Sep 18, 2012 3:18 pm

Ah ok great thanks! Have certainly found some interesting material.

I tested a mini receiver the other day so thats how I got the voltages that I was working from. Seems however that you can use any voltage given the receiver outputs a PWM signal (which I didnt think it did), and as I dont have a CRO (yet) my multimeter couldnt pick up on that!

Thanks again =)

catmaker
Posts: 50
Joined: Thu May 24, 2012 8:32 am

Re: Emulating a RC receiver

Wed Sep 19, 2012 4:00 am

Hi Taylor,
I would need 4 outputs that provide signal voltages to the quadcopter control board that range from 0.15 to 0.25V, 3 centred about 0.20V (+/-0.05) and one centred about 0.15V(+0.1) to mimic a RC receiver's output.
Y'know, an RC receiver output for RC servos is usually a digital signal called pulse-width modulation (PWM), and it's measured in milliseconds instead of voltages like you suggested above. For RC receivers and servos, the PWM signal per output is a digital pulse of usually 1.0ms to 2.0ms, centered at 1.5ms, and repeated more than 20 times per second. (I say 'usually' because we can now find servos that respond to PWM of 0.5ms to 2.5ms centred at 1.5ms). There are many googleable (new word? :) ) websites on RC servos that explain all these.

I think this thread would be better in Automation, sensing and robotics thread, but we need an admin to move this. In that section, there are many threads related to Pi-controlled RC servo interfacing, ranging from few servos to many. I too have a compact Pi-piggyback expansion board that does control 4 servos without much wiring jungle and also has a built-in UBEC for the Pi, servo and any other +3/5V circuitry you may want to hack. See Raspy Juice Rev.1 Beta in Add-ons...

Good luck in your project!

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