Hi forum.
I am going to control some servos and a Maxon motor controller called DEC 24/1 (can’t submit link to datasheet due to forum rules) and I hope to do both with the SSC-32.
The motor controller has an input that accepts 0 … 5 V in 1024 steps to control the speed.
Can anyone imagine a way to generate these values with the SSC-32?
Thanks, Grusgaard.
Hi Grusgaard,
The SSC32 provides 32 PWM signals; appropriate for controlling model R/C servos. They require a .5 to 2.5 mS pulse every 20 mS. This is position information only. And positions can be changed at varying rates.
I don’t know about the URL prohibition.
Why do you need an SSC32 in the “circuit”? Why not just use 10 bit D/A converters (I2C or SPI, even parallel) off of your main 'Bot processor, and go from there?
These D/A converters could also be routinely updated from a separate uP, and managed by a simple command interface in similar fashion to that done in the SSC32; but that would require software as well as hardware development.
HTH
Alan KM6VV
Alan newly registered users can’t post links until they have posted 1 text message and 24 hours, or something like that, to keep the spam-bots at bay.
grusgaard you can rectify and filter the PWM signal from the SSC-32 output and then use an op-amp circuit to zero offset and then scale the resulting voltage up. The problem is you only get 50 updates a second and this tends to make some ripple in the output unless you have a really long time constant filter… which in turn means it doesn’t respond quickly to step changes in input.
there are other ways you can do this electronically (i.e. analog) but not knowing your skill level I hesitate to sit and write stuff for an hour.
the digital option is to put a small PIC micro with a capture input to read the r/c servo PWM and translate that to its own high frequency PWM output, which is easily rectified and filtered in to an nice analog voltage. the practicality of this is whether you have the tools to program a PIC and some time to write a simple program.
one really simple idea that did occur to me (and will probably make most people shake their heads at the foolishness of) is to plug a cheap servo into the ssc-32, then open it up and take the wiper voltage from its position pot as your analog output. you are not going to get 10-bit accuracy, you might still need to offset and scale it with an op-amp, but it exploits the pwm-to-voltage circuit of the servo contoller to get a nice stable output and would not require much more than basic electronic soldering skills and an expendable servo.
First, I need the SSC in the product to have an easy way of giving some mechanisms position control. It’s actually not a robot, but a mechatronic design. Therefore if the SSC could control the Maxon, I’d have only one unit to focus on.
I think I’ll try to consider the rectification. Not being a electronic engineer - but instead mechanical with an interest for the electronics - I would be grateful for a hint on how to realize the op-amp circuit. It doesn’t matter if the response of the circuit is quite slow - as long as it’s (few) seconds.
And for the simple idea… I actually thought of having a cheap servo turning a potmeter! (that’s my skill-level concerning circuit-creativity)
Thanks again, Grusgaard.
I am trying to do this, but the feedback? circuit from the servo, seems to have a pot with three leads coming off. The voltage is not stable or predictable based on the pot position. I need to disable or bypass this feedback pot…or ? Any ideas?
Mark
Have you considered the Open Servo project? This replaces the standard servo eletronics board with a custom electronics board. Some of the features you get from this is position feedback, current sensing, and PWM or I2C control. There is a LOT more an Open Servo can do.
8-Dale
Below is how I got analog position feedback from a standard servo.
Hi Grusgaard,
If you clock a 10-bit counter at the appropriate rate to match the PWM signals, those 10 bits of data can be fed to a D/A with a 5v reference, and you should have your control signal.
Alan KM6VV
