Re: receiver question 1b: interference [TANKS]

["Amir Tahvildaran" <adt22-at-drexel.edu>]

Hmph, I think I installed the relay diode correctly with your description 
and this site's diagrams:
http://www.kpsec.freeuk.com/images/diopro.gif
http://www.kpsec.freeuk.com/components/diode.htm

here is the problem relay with the diode installed, white is + relay coil, 
black is - relay coil:
http://www.cs.drexel.edu/~adt22/tank/relay_diode.jpg
does that look right?  I didn't test it reversed because I was pretty sure 
that (a) it was right (b) it would blow something up if it was wrong.

Anyway, when I activate this trigger relay I still get activity on the 
rotate.  What is *really* bizarre is that when I touch the bare black wire 
(relay coil), it activates the rotate!  I know that the body has some 
electrical property, like high capacitance or something - but I still don't 
understand whats going on...

Here are two overall shots of this messy circuit:
http://www.cs.drexel.edu/~adt22/tank/overall_turret_circuit.jpg
http://www.cs.drexel.edu/~adt22/tank/overall_turret_circuit2.jpg

and a movie that *shows* when I tough the coil wire, the turret starts 
rotating:
http://www.cs.drexel.edu/~adt22/tank/crazy_circuit.mpg

By the way, the diode I am using is the same as the type I used for my first 
tri-pact motor controller (3amp 1000PIV).

Does this still sound like a RF interference problem?  I think I'm going to 
redo this circuit with smaller relays on a prototype board and hope that the 
problem goes away or becomes obvious (to me).

Thanks,
Amir

----- Original Message ----- 
From: "Amir Tahvildaran" <adt22-at-drexel.edu>
To: <tanks-at-rctankcombat.com>
Sent: Thursday, June 22, 2006 9:32 AM
Subject: Re: receiver question 1b: interference [TANKS]


> Uh-oh, educational content...
>
> Thanks, I'll try to squeeze in as many more questions as I can before you 
> go on vacation ;)
>
> ----- Original Message ----- 
> From: "Frank Pittelli" <frank-at-rctankcombat.com>
> To: <tanks-at-rctankcombat.com>
> Sent: Wednesday, June 21, 2006 10:41 PM
> Subject: Re: receiver question 1b: interference [TANKS]
>
>
>> Amir Tahvildaran wrote:
>>> I'm seeing some kind of interference from the trigger firing - I hooked 
>>> up the second channel (1/2 channel) of the MRC to a door lock actuator 
>>> (via a relay) and now when I fire and release it, the turret rotate 
>>> jolts a little - the scorpion mini is somehow activated (it coincides 
>>> with the relays clicking).  Right now I'm guessing I should have diodes 
>>> somewhere in the mix, but again would appreciate any pointers.
>>
>> WARNING ---- Educational Content Follows ----  WARNING
>>
>> Whenever a coil is de-energized, the collapsing magnetic field generates 
>> a voltage spike (sometimes quite high) that *travels in the opposite 
>> direction* of the normal current flow that energized the coil.  Since 
>> relays consist of a powerful coil, they generate a powerful spike.  The 
>> voltage spike traveling down the wires in turn generates an RF signal 
>> that can be picked up at quite a distance.
>>
>> In order to eliminate these effects, you need to hook a diode across the 
>> coil wires *in the reverse direction*.  That is, you should connect the 
>> diode so that it *does not* pass current when you want to activate the 
>> coil.  Then, when the coil deactivates and spikes, the diode will allow 
>> the reverse pulse to shunt to ground quickly, thereby limiting it's 
>> effect.
>>
>> Basically, whenever you use a relay, you should use a diode on the 
>> control lines.  Since the relay coil doesn't draw much current and the 
>> reverse spike doesn't generate much current (although the voltage can be 
>> quite high), a small capacity diode (e.g., 1 amp) should suffice.
>>
>> I use two LEDs on my trigger relay.  One that lights when the coil is 
>> activated and the other that lights when it is deactivated.  It provides 
>> a nice indication of what is happening.
>>
>> Frank P.
>>
>>
>>
>>
>
>
>