Inexpensive Radio Control

[AndyID]

I saw this TX/RX pair online and thought it might be possible to use it for for 00 gauge radio-control. The price was under 23 USD so I thought I'd give it a go.

 

 

It's intended to be used to control skid-steer models with two motors or model boats with two props. The transmitter controls are very simple - four button. Both motors can be forward or reverse and one of them is turned off when a direction button is pressed.

 

I thought it might be possible to add a simple pulse-width modulator circuit at the transmitter to control locomotive motor speed by rapidly switching the motor on and off. Based on my very limited testing I think that will work.

 

The operating range seems to be pretty good and the receiver is just about small enough to fit inside most 00 locomotives. As there is only one motor to control it should be possible to parallel the motor drive circuits to increase the current capacity. For large locos and larger scales that need a lot of current it should not be too difficult to boost the drive by adding an external drive circuit. The transmitter and the receiver come already paired but it's supposed to be possible to pair any transmitter with any receiver of this type. I bought two of these so I should be able to test for interference.

 

I'll post more if I make any progress.

 

 

[H2O]

Looks interesting.  The receiver looks like a mix of through hole and surface mount, is the through hole chip an H bridge driver (L293?). If you can find the part number the data sheet should tell you the current rating. I'd guess the surface mount chip is the rf receiver.

Not sure what the over air protocol is, presumably it includes addressing if you can pair devices. You may be limited on the rate of pulse width modulation depending on the length of the messages. I'd try starting with a low pwm rate and increase the frequency until it becomes unreliable.

Could you use the 'second' motor for controlling lights or a remote uncoupler?

Best of luck with tinkering.

Edited May 11, 2022 by H2O
Edit chip part number

[otherplanet]

What are the dimensions of the receiver? It could also potentially be used for other applications, for example, controlling the gates of a distant level crossing without having to route wires through to it. Or maybe have side doors on a milk van that open whilst at the platform?

[AndyID]

4 hours ago, otherplanet said:

What are the dimensions of the receiver? It could also potentially be used for other applications, for example, controlling the gates of a distant level crossing without having to route wires through to it. Or maybe have side doors on a milk van that open whilst at the platform?

 

It is sitting on a one inch grid in the photo and it does lie flat on the floor of a 00 open wagon. I think they could be very useful for remote operation of features on very large layouts. Are they available in the UK?

[AndyID]

On 10/05/2022 at 23:47, H2O said:

Looks interesting.  The receiver looks like a mix of through hole and surface mount, is the through hole chip an H bridge driver (L293?). If you can find the part number the data sheet should tell you the current rating. I'd guess the surface mount chip is the rf receiver.

Not sure what the over air protocol is, presumably it includes addressing if you can pair devices. You may be limited on the rate of pulse width modulation depending on the length of the messages. I'd try starting with a low pwm rate and increase the frequency until it becomes unreliable.

Could you use the 'second' motor for controlling lights or a remote uncoupler?

Best of luck with tinkering.

 

The second channel could be used for some other feature.

 

The response time is a bit too slow for conventional PWM to control motor speed. It takes tens of milliseconds for the receiver to turn on its output but I have some ideas 🙂

[DCB]

Sounds ideal to operate an H0 diesel's on board controller's knob, vi a servo.   Trouble is I have spent 20 years searching for a suitable servo and a compatible speed control.  Like most people with garden railways I need fail safe where the loco carries on going when it loses signal. not stops dead half way down my 6ft plus drainpipe tunnel.

[AndyID]

8 hours ago, DCB said:

Sounds ideal to operate an H0 diesel's on board controller's knob, vi a servo.   Trouble is I have spent 20 years searching for a suitable servo and a compatible speed control.  Like most people with garden railways I need fail safe where the loco carries on going when it loses signal. not stops dead half way down my 6ft plus drainpipe tunnel.

 

You could just use super-capacitors as an electronic flywheel. They can keep locos going for quite a long way without any power on the track.

[AndyID]

Looks like the minimum input pulse has to be at least 30mS. I've been messing around with supercaps to smooth the supply to the motor and that seems to work with the 3 volt motors I have.

 

In fact, if the intended application is only for shunting (which is what I had in mind) the supercaps combined with the right amount of resistance introduce so much inertia that you don't even need PWM. You just push one button to accelerate and the other button to brake 😀

[AndyID]

I though about using 555 timers for the PWM controller but, as it turns out, they are no so easy to find these days so opted for an Attiny44a micro instead. I've used them as pulse generators before (quite a while ago!) and I had to use some features that I'd never used before but I've finally managed to get it to do what I want it to do, approximately. It's a simple single-knob forward/reverse controller that only needs a basic linear potentiometer. If the RC thing does not work out I can use the microcode in other controllers.

[AndyID]

Well it does work, sort of. The ATTiny44a code lets me control speed and direction from a single potentiometer. The problem is the RF pulses are long and I don't think there is any way to make them shorter. So you end up with low frequency pulse-width modulation and stop-go action at low speeds 😀

 

I can fix that by putting some super caps across the motor but that makes it quite difficult to control the locomotives. I suppose I could include a brake at the controller to dissipate the charge in the caps but I don't think that will be too satisfactory in a lot of situations. Oddly enough it seems to work best with a seriously modified ex-three-rail Hornby-Dublo 4MT tank but it has a lovely Sagami motor, a flywheel and a low friction two-stage gearbox. It also works quite well with a Bachmann diesel shunter and I'll probably limit the radio control use to shunting operations.