Problem with RC circuit *images*

[jman571]

Okay, so before I continue, I'm going to say that what I've done I here I know I SHOULDN'T HAVE DONE but I did it anyways, because I wanted to test out all the components before I even did any soldering, so yes, instead of doing soldering, I just kind of connected some cheap wires I found in my house to the motor and battery leads by sort of wrapping it around them  Well...now that we've got that over with, here's my problem.

The above picture shows the simple RC control circuit that I wanted to make, it essentially the same as what Dimension Engineering did here: http://www.dimensionengineering.com/appnotes/simple_robot/simple_robot.htm

And if you read this thread: http://www.societyofrobots.com/robotforum/index.php?topic=3173.0 you'll get some background on what I'm trying to do here.

So everything seems to be connected properly to my motor controller, and yet I am unable to control the motors when my transmitter is on. I think the problem resides with the receiver as everything else seems to be working fine. Below are two pictures, one is a picture of the transmitter crystal, and one of the receiver crystal. As far as I know they are both Channel 88 (75.95MHz) and so should be able to communicate.


EDIT: The weird thing about the reciever crystal is that on the other side it does say CH88 75.950, but on the side I took the picture of, it says 75CH88 75.495 GWS

Here's what I DO know:

• 1.)I turn on my transmitter first, then turn on my receiver like you're supposed to. I am not able to control the motors whatsoever, however the motor controller's status LED shines bright blue, indicating it is connected to a receiver source. No attempts to straighten the receiver antenna or improve the proximity to the transmitter have worked.
• 2.)When I turn off the transmitter, and the RC circuit is still powered, the motors jerk around a little, turning back and forth, seemingly randomly, this seems to continue for a while. When I turn the transmitter back on they cease to move. I think they're moving because the receiver is just getting interference from somewhere. This leads me to believe two things, 1: my motors are working, and 2: there is something wrong with the receiver/transmitter/motor controller.
• 3.)When the RC circuit and the transmitter are both powered, and I remove the transmitter crystal, the motors jerk around again.

So there's my problem in a nutshell. When the transmitter is turned on, nothing at all happens. When it's off, stuff happens, but I can't control it.

To add insult to injury I think I may have overcharged my NiMH battery, because when I picked it up from charging last time, it was very hot (hot enough that I couldn't hold it for more than a few seconds right after charging) It's kinda my fault because this little piece that I removed from the charger, was the reason the battery wasn't charging, and so I assumed it would take a full charge after putting the piece back in (a little over 3 hours set to 0.9A mode), but the thing finished charging in less than an hour for some reason  Must've came pre-charged, I'm sure...

Anyways, any assistance would be appreciated on this matter. If you need some more detailed pictures, or more information, feel free to ask. All the pictures I have can be found here: http://www.flickr.com/photos/12017635@N07/sets/72157604699684442/

One more thing, I unfortunately do not have a multimeter, but I think my uncle might, as he is an electrician, so I may be able to obtain one.

[AndrewM]

Do you have anything else you could connect to the receiver to see if it is working correctly, like a servo?  Barring that, you will need to check the pins on the receiver for ground, power and signal with a multimeter.  I imagine you don't have another crystal pair to try?

[jman571]

Do you have anything else you could connect to the receiver to see if it is working correctly, like a servo?  Barring that, you will need to check the pins on the receiver for ground, power and signal with a multimeter.  I imagine you don't have another crystal pair to try?

I don't have another crystal pair right now, but I realize they're cheap, so I wouldn't be too upset if I had to go out and buy new ones (the only problem I can see is finding the particular brand I have, unless they're pretty much universal).

I will be going over to my uncle's tomorrow and will test the pins on the receiver with a multimeter, thanks for the suggestion.

Just to be clear, did it matter which way I inserted either crystal? Because there is no polarity distinction, and I would have no idea how you would figure that out anyways.

[AndrewM]

I believe RC Crystals are nonpolarized, so it doesn't matter which way you plug it in.

[Steel_monkey]

Are the the crystals taken from same RC bundle ( transmitter+receiver) ? As I can see, they are, so receiver-transmitter pair should work. If this receiver-transmiter are PPM ( see documentation) you can see reaction on you transmitter input visually. If you don't have o-scope like me, you can use your soundcard to check the receiver output reaction on transmitter. Make simple resistor divider 1/50  ( only 1 part of 51 from input signal will reach the soundcard input, it is made for its safety), solder wires to it from input and microphone jack to the output ( GND is the closest to cord terminal as I remember).
Check everything twice!!
Power receiver from battery pack or PC which you are using for -scope role, don't power from wall adapter
Then, plug jack into PC microphone port, connect groinds of receiver and your new cable ( it should have two wires- signal, which goes to the divider input, and grund, which goes to divider ground). Now, you have two options- hear for input from you speakers/headphones ( sound will change as you move transmitter joysticks), or download one of numerous free soundcard-oscilloscope programs, or just sound record program. On the record you should see pulses on the output change their length. If you are interested, I can explain clearer.

[jman571]

Thanks for that method to test my receiver/transmitter Steel_monkey, but I think I will first ask a friend to borrow his transmitter and crystals, to determine where the problem is originating from. He's also making an RC robot like myself. I've now soldered what I needed to in my circuit, so wiring being a problem is out of the question. I've now narrowed down to what could possibly be the problem.

• 1.)The transmitter/receiver crystals are not functioning, and thus, no signal is being recieved/sent.
• 2.)The transmitter/receiver crystals are not on the same frequency, or the transmitter can't handle that frequency. This theory came about because the transmitter is listed as supporting frequencies of 35 , 36 , 40 , 41 , 72 , and 75MHz. But since I'm using frequency 75.95MHz, perhaps this is too close to 76 MHz, and the transmitter cannot use this frequency.
• 3.)The transmitter is broken.
• 4.)The receiver is broken
• 5.)The motor controller is not sending enough voltage/amperage to the receiver to allow it to function. I was unfortunately not able to check out this theory today as I did not have a multimeter.

I didn't want to include this in my theories, because if it holds true I'm downright screwed. That is: my motor controller is broken/doesn't do as adverstised, and simply the signal is going from my transmitter to my receiver, and to my motor controller, where then it gets lost forever, and the motors don't move.

[Admin]

The weird thing about the reciever crystal is that on the other side it does say CH88 75.950, but on the side I took the picture of, it says 75CH88 75.495 GWS

odd . . . it sounds like you have mismatching of crystal frequencies. If the transmitter crystal and receiver crystal aren't the same frequency, it won't work:
http://www.societyofrobots.com/remote_control_robot.shtml#RFrefchart

Other than that, use a multimeter on your entire circuit to trace the problem.