I am using the JRK 12V12 for a project where we are closing the loop on an actuated brake system. There is a linear actuator which actuates a master cylinder to generate brake pressure and an inline pressure transducer providing feedback.
What I am interested in is changing the feedback configuration through a serial command so that we can fully retract the linear actuator after it has reached zero pressure target in order to open the brake fluid resevoir to the line.
Is there any serial commands for setting feedback from analogue to none, or can this only be set via usb with the configuration utility?
There are no serial commands for changing any of the configuration parameters, including the feedback mode. One reason for this is that we wanted people to be able to configure their jrk and then not worry that the configuration might get corrupted when they send the wrong serial bytes.
You might be able to configure the jrk to do roughly what you want though. Configure your feedback so that zero pressure corresponds to some positive Scaled Feedback value, say 500, and higher pressures correspond to higher values. Then when you set the Target to 0, the Jrk should keep expanding the cylinder in an attempt to reach 0 (which of course it never will because the lowest possible Scaled Feedback is 500).
Be careful to make sure that the linear actuator can not destroy itself in this mode! You can set a duty cycle limit for some extra protection while you are experimenting.
This sounds like a pretty cool project and we’d appreciate seeing some pictures or videos when you are done! What’s the brake being used for?
Thanks for the response. We actually ended up doing exactly what you suggested. We have a firgelli linear actuator that is rigidly coupled to a hydraulic master cylinder and an inline pressure transducer. We use the pololu for running the closed loop control on the brake actuator and a higher level controller which interfaces over the TTL serial line.
The pololu is part of a larger safety/parking brake system for a medium sized fully autonomous UGV. We were looking for a quick solution for a proof of concept braking system and your product was perfect. I have to say I am very impressed with the product, and so were some of my co-workers.
We ended up picking a sensor with a 0.5-4.5V (0-1500psi) output, when we are setting an active target the controller is allowed to close the loop and the master sets the motor off command after some persistence around the target. When we retract we command zero and let the actuator go to the limit switch (as you said because it will never be able to reach zero target). Sending the motor off command is necessary to reset the integrator on the controller to prevent it from winding up.
We used quite a bit of the fault detection on the controller which was great to have for a proof of concept safety critical system. For our application a redundant motor controller would have been perfect.
Thanks for the help, keep up the great work. Pololu has some great products! I just ordered an orangutan X2 for a cool UAV project I am doing at home. Time to dust off my EKF notebook