DIY 32 Channel Controller

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DIY 32 Channel Controller

Postby DanSwan » Tue Oct 18, 2011 12:54 am

I am building an RC Square Rigger and it requires 32 separate controls. I can't find information about the coding used in RC, but have taught microprocessors and can probably develop an acceptable code if I can find out what the limitations of the transmitters and recievers that are available today. Can anyone help with current coding systems?
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Re: DIY 32 Channel Controller

Postby RCModelReviews » Tue Oct 18, 2011 3:58 am

Are these simple on/off controls or do they need to be proportional?

The only "standard" in the industry is the PPM frame which consists of a series of pulses (one for each channel) that can vary from 800uS to 2200uS with no specified inter-pulse gap except for the sync pulse which is typically 3.5mS- 8mS.

The format therefore is:

SYNC - Ch1 - Ch2 - Ch3 - ... ChN

Normally, the maximum length of any frame is restricted to 20mS, which limits the number of channels to about 8 or 9 -- otherwise the sync pulse becomes too short.

If you were planning to interface with any of the commercially available 2.4GHz transmitter modules and receivers then you'll have to stick with this.
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Re: DIY 32 Channel Controller

Postby DanSwan » Tue Oct 18, 2011 4:50 pm

Where can I find these Tx & Rx modules? Can I use serial digital codes with microprocessors on both ends with these modules if I stay within the 2.2 ms and is that per channel or total?

What exectly does proportional mean? If it is relative control, then all 32 controls will need to be proportional. For example: I will need to furl (close) the sails and unfurl (open) on each of the three masts separately. This would mean 2 controls for each of the three masts, etc. But once in position they would remain in position like a throttle. Is that proportional? There will be no lights or anything like that so I believe that all 32 will be proportional.
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Re: DIY 32 Channel Controller

Postby Rixx » Tue Oct 18, 2011 5:46 pm

I think you can make system with that many channels if you can handle the delay - you can treat four 8-channel PPM frames in row as one superframe. There are FRSKY receivers that output PPM stream which you could decode to your 32 channel superframe. From "sail' & "mast" keywords I guess you're talking about a boat, so RC system 4 times slower than airplane or heli system, should be okay.
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Re: DIY 32 Channel Controller

Postby ergocentric » Tue Oct 18, 2011 7:17 pm

Rixx wrote:I think you can make system with that many channels if you can handle the delay - you can treat four 8-channel PPM frames in row as one superframe. There are FRSKY receivers that output PPM stream which you could decode to your 32 channel superframe. From "sail' & "mast" keywords I guess you're talking about a boat, so RC system 4 times slower than airplane or heli system, should be okay.


Or four encoders and four transmitters in one box.
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Re: DIY 32 Channel Controller

Postby ergocentric » Tue Oct 18, 2011 9:27 pm

DanSwan wrote:Where can I find these Tx & Rx modules? Can I use serial digital codes with microprocessors on both ends with these modules if I stay within the 2.2 ms and is that per channel or total?

What exectly does proportional mean? If it is relative control, then all 32 controls will need to be proportional. For example: I will need to furl (close) the sails and unfurl (open) on each of the three masts separately. This would mean 2 controls for each of the three masts, etc. But once in position they would remain in position like a throttle. Is that proportional? There will be no lights or anything like that so I believe that all 32 will be proportional.


Back in the good old days of AM radios, we used on/off/on controls (servo pushing microswitches) to operate sail winches

servos are much cheaper and stronger now
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Re: DIY 32 Channel Controller

Postby DanSwan » Wed Oct 19, 2011 1:24 am

So what would this super frame look like and what modifications would I need to perform to make it work?
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Re: DIY 32 Channel Controller

Postby Rixx » Wed Oct 19, 2011 6:34 am

Dan, you need to do some research how PPM works, to build transmitter working with available 2.4GHz modules. For a very quick explanation: you first build transmitter hardware with 32 controls and program TX microcontroller to scan position of controls:

- build 8channel PPM frame with positions of first 8 controls
- send PPM frame to transmitting module
- repeat for other 24 controls in groups of 8

then at RX side you just take those 4 PPM frames and translate them into positions of your 32 actuators.

That's all for my idea, for actual implementation you need research and experiments :)
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Re: DIY 32 Channel Controller

Postby RCModelReviews » Wed Oct 19, 2011 6:40 am

There is another way -- just use four 8-channel PPM-based 2.4GHz modules and four 8-channel 2.4GHz receivers. Given that you can get the DIY boards for about $14 a pop and the receivers from about $20 a pop, that's a pretty quick, easy and not so expensive way to do it.

Otherwise, FrSky is releasing a new module/DIY that will accept up to 16 channels of data in a special PCM format (which they're documenting). You could use two of those and four 8-channel receivers at the other end.
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