RC control of jrk 21v3

I’m trying to use RC to control a motor with the jrk 21v3. The RC signal parameters from the receiver are 2kHz pulse rate, which apparently is outside the range of the 21v3, is that correct?

However the 18v15 simple motor controller could handle this pulse frequency, according to my reading of the datasheet?

Could you shed some light on why such a discrepancy in the RC input specifications?

As a followup to my questions, in reading the “Suimple Motor Controller” manual there is an error in the RC pulse frequency specification:

“Works with RC pulse frequencies from 10 to 333 Hz” (p. 5)

“…RC pulse frequencies from 10 Hz to 333 kHz are permitted…” (p. 37)

Which is correct?

Hello, wygonski.

Thank you for reading our user’s guides carefully and uncovering the error in the Simple Motor Controller user’s guide. The correct upper limit is in fact 333 Hz, not 333 kHz. I have corrected the online version of the user’s guide.

Are you sure your RC receiver’s signal has a 2 kHz pulse rate? That is unusual because the typical servo pulse signal is much slower, around 50 Hz. Does your RC receiver work with normal RC servos or do you have to buy special ones for it? Could you provide the name of the receiver or a link to some technical information about it?

A 2 kHz signal would be too fast for the jrk or Simple Motor Controllers, but maybe you could make a filter to turn it into an analog voltage. Then it would work with either the jrk or Simple Motor Controllers.

–David

Thanks very much for your reply.

I am attempting to repurpose the RC Tx / Rx pair from a EF Stinger Helicopter to control another motor (a home-built ferris wheel). I probed on the receiver with my scope while operating the controls, and the 2 kHz signal I referred to drives a MOSFET on the receiver which drives the rotor’s motor. So I understand now that the 2 kHZ signal is the heli motor’s PWM signal, and is not the RC control signal. This is a 2.4GHz RC control system and the receiver consists of a Nordic nRF24L01 2.4GHz transceiver chip and an ATMEL microcontroller. The Nordic nRF24L01 has an SPI interface to the microcontroller, so I don’t think a typical RC PWM signal is available. I can’t think of a way to use this RC controller for my purpose, unfortunately. Any thoughts?

So on to plan B. I’d like to have a joystick communicate wirelessly with a receiver connected to a simple motor controller. I’m thinking of connecting one Wixel to a joystick and a second Wixel to a simple motor controller. Is there some existing firmware that would support this configuration? I’d rather not develop any software.

I just re-read the last paragraph of your reply—converting the PWM to analog is a great suggestion, thanks!

A simple RC lowpass filter (perhaps with an op-amp buffer) to the jrk 21v3 will be my first attempt. Will there be any problems if the analog input to the controller has a bit of ripple at 2 kHz? Also, what is the input characteristic of the analog input? Will I need to buffer the RC filter?

Maybe, but the Simple Motor Controller takes several analog readings and averages them together so that should help.

The inputs are high impedance, and in addition they have a 1 kilo-ohm resistor in series, so I don’t think you will need a buffer.

–David