Question
Asked September 15 2018

Community Question

I'm pretty new to EZ-Robot, so I apologize if this is a basic question... I've got a couple of Turnigy servos and a linear actuator working with EZ-B, but I'd like to add a continuous rotation servo with position feedback. I'm working on an R2-D2 project and this servo would be used to rotate the periscope that comes out of the droid's dome. As it's kind of pie shaped, ensuring it's back in the proper position prior to retraction is important.

I came across this Parallax Feedback 360 High-Speed servo which seems to fit the bill. In addition to the normal three wires, there's a fourth with position information from the built-in Hall effect sensor. Where would I plug that fourth wire into and what bit of the EZ-B software will let me read it?

Thank you.
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Synthiam
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September 19 2018

Quote:


assumed it worked like the GetServo command that does not actually check the port just returns the last value it was set to.
So I assumed the GetPWM would just compute the PWM for the current position.


GetPWM is analogous to GetServo: does not compute the PWM instead returns the last/current PWM value.
September 19 2018
To obtain Parallax servo 360's feedback you will need an extra controller:
1) measure the duty cycle and translate to servo position

2) track the servo's position in real time (not in EZ-Builder) and implement a closed loop code (PID) to control the current position and the desired position, basically is what a servo PCB does.

Last year i started to develop a plugin to use with EZ-Builder and to interface EZB with the external controller (Parallax Propeller).

The initial idea was to use with Cube Machine, allowing the Gripper to rotate 360 degrees and multiple times.

I detected some issues with the Parallax library code, so i started my firmware version in C and i found some other issues too. Propeller has 8 cores but no interrupts, timers etc, so everything needs to run with your code, so the next step was to use some spin/assembler code and redo the firmware.

I was running out of time (Cube plugin Project), busy at work too so Bob convinced me to use EZR HD servos (Strong/Silent).

I end up using the Parallax servos in another project (not an EZ-Builder) and the plugin is on hold waiting for better days:)

Plugin create date:
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wow! almost a year ago
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I can't promise when, but, I'll come back to finish the plugin.
September 20 2018
Thank you PTP for the update.
I was sort of close with my assumption, as it does not read the port.
September 20 2018
Thank you PTP for the detailed reply.
September 20 2018
Thank you all for your feedback. Does anyone have experience with any other continuous rotation servos with position feedback?