Why do we have to use a transmitter all the time?

[DadHav]

Has anyone ever tried to run a GB motor by making something the input of the speed control might be tricked into believing the receiver telling it what to do? What I'm asking I guess is: Can you run a motor without a receiver and transmitter?
John

[Felix]

Has anyone ever tried to run a GB motor by making something the input of the speed control might be tricked into believing the receiver telling it what to do? What I'm asking I guess is: Can you run a motor without a receiver and transmitter?
John

John, you can buy or build a servo tester like the one at http://www.astroflight.com/e/env/0001fmmROfVJJyEgWU667J5/store/store-Chargers.html?link=/store/store-type-tem.html&item=products:af-105.

If you do a web search you'll find some pretty simple designs based on 555 timers.

Felix

[Felix]

Here is a link to one design for a 555 based servo tester http://www.uoguelph.ca/~antoon/gadgets/servo3.htm.

I have not built this one but have built similar designs.

Felix

[LBMiller5]

Yes you can!!!! You simply need a circuit that sends a signal to the speed controller that is the same as what it gets from the receiver. I built one last week and it works great. In fact, I use the BEC circuit in the speed controller to power it as well, so I don't even need to run a seperate power pack.

The output that gets sent out of our receivers to the servos or speed controller is a variable pulse width signal that is repeated 50 times per second. The pulse width is 1.5 milliseconds wide at neutral, and decreases to 1 millisecond at one extreme, and increases to 2 milliseconds at the other extreme.

It is very easy (If you are handy with electronics at all) to make one of these pulse width modulator circuits. All you need is a 556 dual timer IC, a few resistors, a few capacitors, a 10K potentiometer, a female servo lead extension, and a little box to put it all in. I built mine for about $10-12 worth of parts and an hour of my time.

I found a schematic on the web for one of these that works perfect. Here is a link to the site:

http://www.seattlerobotics.org/encoder/200210/servoex/ServoExcerciser.htm

Here is a copy of the schematic that is on the site:

http://innov8tivedesigns.com/rcgroups/ServoDriver.jpg

The part on the left side of the schematic is a free-running oscillator that generates a trigger pulse every 20 milliseconds. Adjustable resistor R2 lets you adjust the timing. It is not critical for our application, anything between 15 and 25 milliseconds will work fine.

The part on the right side controls the width of the output pulse. R4 is the 10K Potentiometer (Variable resistor) that controls the width of the pulse. With the Pot set to 0 Ohms, you will get about a 1 millisecond pulse out, and with the Pot set to 10K Ohms, you will get about a 2 millisecond pulse out. Anywhere in between gives varying angles on the servo or throttle setting.

Since the BEC on the speed controller brings +5 volts in on the red wire, the BEC can power the entire circuit.

The website where I got this goes through all the theory about how it works, and also has full size templates for etching your own circuit board. I built mine in a Radio Shack box similar to the one shown in the article.

Hopefully that answers your questions. With one of these you can try out your motors any time you want. You can even use one in the pits at the flying field to run up your motor to test it without having to turn on your radio.

Lucien

[DadHav]

Thank you Lucien, Felix. Ive seen advertisements for servo testers, but never really though about them for running a motor. It's a good idea. I have everything needed to make one and even have some dry etch circuit boards in my work shop, but they don't look to expensive to buy either.
Thanks again
Happy motoring
John

[LBMiller5]

You need to be careful if you use a "Store bought" servo controller. These have their own power to drive the servo, and if you plug in a speed controller with BEC (Battery Elimination Circuitry), the two power sources will fight each other.

To prevent this, you would need to take a servo extention lead and modify it by cutting the red wire at one end. Then you would take this modified servo extension and plug it in between the servo tester and the speed controller. This way you would only send the pulse signal and ground to the speed controller, and the power leads would not fight each other.

If you have a speed controller that has a switchable BEC, or a jumper you can remove to disable the BEC feature, you can turn off the BEC and hook it up directly to the speed controller. With this type of controller, the modified servo extension is not needed.

Have fun building and testing your motors!

Lucien