Wireless Relay Launch System from 2.4ghz R/c Components

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FlyBack

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The attached photos show how the new digital spread spectrum 2.4ghz R/c components can be used to make a wireless launch controller. The essential elements include:

12 Volt - Solenoid controlled launch box

Transmitter : Spektrum Dx-7
Receiver: Spektrum AR6100
R/C Relays: Dimension Engineering Pico Switch and Battle Switch

Special Transmitter Mods:
Mechanical lock-out on firing channel (gear)

Visual Back-up:
Strobe light on aux2-channel

Notes:

The mechanical lock-out ensures the firing circuit cannot be completed by merely "bumping" a switch on the transmitter.

The strobe light allows the user to visually verify a solid radio link to the launch box, from a distance, without firing anything.

Regards

FlyBack

2.4ghz_remote.JPG


2.4ghz_remote_key.JPG


2.4ghz_remote_key_assembly.JPG


2.4ghz_remote_plug.JPG


2.4ghz_remote_gear_switch_mod.JPG
 
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WillMarchant

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Looks like you're using the relays to masquerade as the switches on the control head of your https://pratthobbies.com/ ULS-M1? Good idea.

How are you meeting the safety code requirement for a firing switch that returns to the off position? Does one of the transmitter switches already do that? Or does the switch you added serve that function?
 

FlyBack

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Looks like you're using the relays to masquerade as the switches on the control head of your https://pratthobbies.com/ ULS-M1? Good idea.
Thanks Will, that is exactly what I've done. The relay ignition launch box is actually more like this one: Pratt Hobbies Base Module. The R/c gear replaces the hand controller (and its associated wiring).

How are you meeting the safety code requirement for a firing switch that returns to the off position? Does one of the transmitter switches already do that? Or does the switch you added serve that function?
The gear switch on the DX-7 transmitter is not spring loaded. To be in full safety compliance it is apparent I will have to add a momentary on pushbutton switch in series with the key switch I added already. Thanks for pointing that out. It will be an easy fix. (See photo below.) This momentary switch will then become the "firing" switch and the gear switch a secondary arming/safeing switch. The removed-on key switch will still be the primary arming switch. It may not be clear in the photos that it is wired in series with the gear toggle switch.

Regards

FlyBack

momentary_pushbutton_switch.jpg
 
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WillMarchant

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Nice project, FlyBack!

I've been thinking about replacing the cable of a Pratt system with a pair of "wireless serial cable" boards. I'd clock a parallel to serial converter into a UART on one end to tap the output of each of the outputs on Doug's hand controller and feed the serial data to one of the transmitter boxes. At the other end the serial output would go into a UART and get clocked into a serial to parallel register.
 

FlyBack

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Will,

Interesting idea. Certainly a lot cheaper than buying a $350.00 R/c 2.4ghz transmitter and receiver. However, I have no idea if the relays I used would recognize the output from your parallel register (or whether you would even need them). One call to Dimension Engineering would answer that tho... really helpful folks there.

I use the Dx-7 transmitter to fly my RBG's. My goal was to use the same device to light the motors I use to fly them... no more fumbling with hand controllers or yelling back and forth at the RSO.

The Spektrum gear has two other features I needed... Model Match and Global Unique Identifier (GUID) Binding. I can bind both the receiver in the launch controller and the receiver in the model I intend to fly to the same transmitter. Or put another way, I can fly two receivers with one transmitter. Out of the whole 2.4ghz range (and everything that operates in it) they will only "hear" and respond to that exact, unique transmitter.

One additional note...for George Gassaway (I know he's gonna ask :D). If the receivers loose signal they hold the last position data sent in memory. Since channel 4 (gear) is on a toggle it is either "high" or "low". I found in testing I could turn the transmitter OFF, wait a while, turn it back on and the relays would not flinch at all.

Regards,

FlyBack
 

H_Rocket

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I would be concerned about one thing. That would be a spurious signal. AT RC events there is a board that allocated frequencies to prevent one radio from controlling another aircraft. What are you planning to prevent a transmitter other than your own from initiating a launch? The few wireless systems I have seen have a rolling code system to reject any signal source except the desired one.
 

JoeG

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Your question has already been answered.

The new "spread spectrum" radios match the receiver to a specific transmitter as explained below.

The Spektrum gear has two other features I needed... Model Match and Global Unique Identifier (GUID) Binding. I can bind both the receiver in the launch controller and the receiver in the model I intend to fly to the same transmitter. Or put another way, I can fly two receivers with one transmitter. Out of the whole 2.4ghz range (and everything that operates in it) they will only "hear" and respond to that exact, unique transmitter.
Unlike the long used 27,53, and 72 mhz channels this is on 2.4ghz. Way up on the spectrum. The receiver will not respond to any signal of any transmitter other than the one it is linked to.

As far as radio control goes, "It's a whole new ball game."
 

JoeG

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I was wondering if the relay could be wired through the trainer switch on the Tx. It's momentary. Just not sure which way is on or off.

That would satisfy the safety requirement if it would work. I'm not an electronics guy though.
 

FlyBack

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I was wondering if the relay could be wired through the trainer switch on the Tx. It's momentary.
Hmmmm, that thought crossed my mind too! When I looked at it I saw two problems right off the bat: (a.) the trainer switch also doubles as trim for aux2, (b.) it is really hard to get to the terminals on it.

It also appears that the trainer switch is only active in that mode when the buddy plug is installed. Just from looking at the wiring I couldn't figure out a way to use it. I would need a complete circuit diagram for the Dx-7 to figure out a workaround. Unfortunately the circuit diagram is not available to the public.

I came to the conclusion it would be simpler to mount the momentary switch in the same external box the key switch is in. The advantages doing it that way are: When the safeing/arming box is unplugged and removed, the transmitter works (and looks) just like it did out of the box. The trainer plug can be restored easily by removing the 3.5mm jack and the gear switch operates normally.

Finally, I kind'a like the ergonomics of having the firing switch on the back of the transmitter. It is a comfortable reach for fingers of my left hand (while still holding the transmitter with my left hand).

DJ
 
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FlyBack

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Finished and tested the momentary switch mod. This gives me three layers of redundancy in the firing circuit. The arming key, the gear switch and the momentary firing switch. I have also included a better shot of the strobe (which gets mounted to the very end of the launch rail). Photos below.

2.4ghz_remote_key_assembly_mod0.JPG


2.4ghz_remote_key_mod0.JPG


2.4ghz_remote_strobe.JPG
 
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