PWM to analog output: R/C radio to control analog joystick functions - any ideas?

[wingnut]

Same Problem

Hello All,

I am about to start a similar project and I have been thinking about this same issue. I have attached the spec. sheet on the controller I have, a P&G VSI 70 controller on a Merits wheelchair. I also would like to control via R/C and have looked into ESC's, specifically the Sabertooth 2X25, but it seems like I would be spending $$ needlessly as the existing controller would be thrown away. If anyone could take a look at the attached schematic and let me know if the circuit discussed in this thread would apply I would really appreciate it. I like the idea of building with IC's or programming a PIC/Stamp. Any help would be greatly appreciated. Great site!!

 

[dave h]

Forrestking,
been researching R.C.lawnmowers.This site may be of help.Has two different setups;the first is simply using a potentiometer on the end of the servo! The second is more complicated( and outside my knowledge) but uses a picaxe microcontroller. Hope have been of help. Dave

**broken link removed**

 

[ammazzadraghi]

Hello all,
i'm italian are practically the same conditions of wingnut, I would like to know if you've found the solution ... I think it is necessary seeeduino interface, the problem that I can't programming.
Ciao Maurizio, sorry for my English.

 

[Shapowpow]

Hi,

Just found myself a Pride Quantum 1650 and build a dspic controller for it with a couple opamps. There are a bunch of safety technologies embedded in the joystick circuits dsp, but I cracked all of them with diodes and resistors etc. The backend of my board is based on ccsc written on a ds30f4011 and a bunch of op amps, transistors (similiar design to the four opamp guy, except im a little lazier on the filtering , and it is working.
on the dspic side i put up a command line GUI over rs232 with control for overriding pwm values, calibration of center position etc. if anybody wants the code or an idea roughly on how to build it (the interrupts to measure pulsewidth were a little tricky, please let me know.

Still fine tuning now, but RC-joystick control works on my end (the joystick was a PG Drives series one, inductive 12V 5-6 wire with 6V center, the board has ripple detection and will not start if there are oscillations on the axis inputs (serious filtering on my end).

 

[Shapowpow]

Hi,

One more thing, Penny and Giles (PG Drives..... the pgdt site) are forced to submit their joystick patents which are available on the web. (just an FYI for those of you trying to figure out how on earth your PG Drives joystick works).
hall effect sensors inside a massive metal ball basically.

Also a few more interesting things happened to me:

1) I accidentally put 12V on ground and ground on 12V on my p.s. which blew some circuitry inside the joystick module. I recovered (and actually I think this was secretly a blessing), but putting the output of the 12V regulator im using to drive the op amps directly on the power wire (red wire) on the joystick input to the circuit). Very useful. I recommend frying your joystick circuit and doing the same (im totally not joking! if its the same board I have)

2) The controller I have is the PG 50543.3 (massive sticker on it). 24V batteries, and extreme motors (wheelchair I have was made for 1000lb weight).

 

[Roff]

Post deleted.

 

[Roff]

If the Joystick is fed with 12V, it puts out 6V centered, and swings from 4.8V to 7.2V. Here is a four opamp solution that produces the same amplitude, centered at 6V. It relies on a clean, accurate 12V supply.

It uses 12V rail-to-rail CMOS op-amps. First stage U3 just squares and amplifies the PWM signal so that it swings from 0 to 12V. The RC network produces a voltage whose average value is derived directly from the PWM ratios. It has a lot of ripple, so I pass it through a three-pole Butterworth filter with a cutoff of 1Hz (U2 & U1). The final stage U4 offsets the signal to 6V, and provides gain so that the signal matches the same swing as the Joystick. Varying R1 (65.5K, make it a fixed value in series with a trimpot) will center the swing at 6V.

I think that the delay of a 1Hz lowpass filter will make controlling the cart difficult. The human controller does not get near-instantaneous feedback from his commands, which makes the loop (with the human in it) prone to overshoot, maybe even oscillations.
If the OP has microcontroller skills, that sounds like the way to go to me.
This guy has a similar problem. I sketched an analog solution that I did not post, but I mentioned it in post #5 of that thread.
My proposed solution does not have the delay of the 1Hz PWM filter, and in fact will respond to each RC pulse before the next one arrives. It does this by pulse width to voltage conversion (ramp, sample, and hold), not by pulse stretching. No filtering is required, but could be added if desired.
I don't think this method can compete with the microcontroller solution, but it is an "analog" (no programming required) option. I'll work on a simulation only if the OP is interested.

 

[magvi]

its kinda funny but micro controllers like attiny 2313 costs lesser than opamps here in springfield

 

[alec_t]

The link in post #1 is broken