Can anyone help with my RC problem?

I have these controls

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXLDP9**&P=ML

On the receiver end each channel has 2 negatives and one positive so you can switch polarity. My transmitter is not doing anything on any channel and I get constant current flow in one direction even when the transmitters off. I don’t know much about these types of controls and I looked through the manual and can’t find anything to help. Is there something wrong with the controls or is something else going on? Can anyone help?

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westfw8 years ago
I don't think you're understanding how RC receivers work. Usually each connector on the receiver has three pins - two are power (+V and GND) The third pin had a "PWM" signal - a periodic pulse whose width is dependent on the position of the joystick or switches on the transmitter. There is probably not much you can see with just a voltmeter - you need a device designed to connect to an RC receiver (like a servo or speed controller), or fancier equipment like an oscilloscope.
kendallickes (author)  westfw8 years ago
Yes I have the matching receiver on 72.23 mhz. I’m trying to make an rc robot from scratch. My thought was that they transmitter puts out a signal and the receiver energizes the ‘channel.’ Basically I thought I could cut a servo wire and connect it directly to what I want to control. i.e. a relay or motor. I have been testing the receivers connections at a cut servo wire by connecting it to a small electric motor. 2 of the 3 wires always make the circuit work, the other does nothing. You said there are 2 positives and one negative? I though it was 2 negatives and one positive? Like I said I never used them before just want to be clear. Do the servos somehow decode a pulse signal from the transmitter? If so can I take a servo apart and connect my wires where the servo motor is to run the relays on my circuit? Or is there some other/better way to make this work?
  • Do the servos somehow decode a pulse signal from the transmitter?
Yes. There are pretty complex electronics inside a servo. If you want just a "switch" that can be turned on or off by the transmitter via one of the receiver connections, you need more electronics, especially for a device that takes significant power like a motor. Places that cater to RC folk, especially the robotics crowd, will be happy to sell you such switches for not much more than an entire servo :-( Or you can build your own, but there's a pretty steep learning curve if you want that to be cheaper than buying one. (Most modern designs use a micrcontroller.) It's not uncommon for RC modelers to perform hacks like having a servo motor flip a mechanical switch.

I did a bit of web searching, but I didn't see what I'd consider a good tutorial on how RC works at the digital electronics level. Most of the "technical" tutorials seem to center on the issues associate with the radio section :-(

The receiver connections have two "power" connections (one pos, one neg), and a "signal" connection. The signal connection is low power; I hope you haven't burnt yours out by connecting it directly to motors. If you connect a small motor directly to the power connections, it should work (but it isn't remote controlled at all.)

For initial "playing", I suggest you get some actual servo motors. Modifying a servo motor for continuous rotation based on transmitted stick position is a more common modification that building the electronics necessary to connect a traditional motor to the receiver outputs...
kendallickes (author)  westfw8 years ago
Thanks for the response. So I hooked up a servo to my receiver and the servo ran fine. My transmitter made the servo turn let and right when I moved the stick like it should(yesterday I didn’t have a servo to test it with). So I took the servo apart and de-soldered the motor from the board. Now I have a place to hook my relays for my 12v motors. I’m trying to figure out how to connect my system so when the polarity switches on the 4.5v side it will change on the 12v side. Basically when I push the joystick left I get +,- and I push it right I get -,+ I’m sure there is an easy way to make this work but its late and my brain is not working. Thanks for the info, rc makes a bunch more sense to me thanks to you!
That's very good progress!

Hmm. The tough part is probably getting the motor to be off when the stick is in the center. You can probably use two SPDT (or DPDT) relays with the coils connected with diodes... (It'd be so easy with a microcontroller. I wonder if someone makes an easy-to-use microcontroller based THING aimed at remote control enthusiasts that can't otherwise program. I mean, some of the speed controllers and such have "programming" modes involving wiggling the sticks in a not-uncomplicated fashion. You'd think there would be a market for something similar with "general purpose" outputs...)

Here are a couple other ideas to look at.

https://www.instructables.com/id/How-To-Radio-Control-DC-Motors-Cheaply/
https://www.instructables.com/id/How-to-make-an-H-bridge/
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