Solenoid feedback or Sensor?

[VEN]

I don't know much about pneumatics so my question is, does the solenoid have a feedback function that tells us in what position the linear actuator is? do we get any sensors with the kit? Im asking because say you have the pneumatics hooked up to lift your arm, you don't want it to slam to it's full position and then slam back onto the robot.

Thanks

Vova

[Thorcat]

There is no sensor in the KOP, but a magnetic sensor option is avaliable from Bimba. this sensor is only useful for finding when the actuator has reatched it's limits. If you only want to ensure that your actuator does not travel at breakneck speeds, you will want to use a restrictor valve.

[kmcclary]

Yes you can order magnetic versions of the cylinder, but if using the mag sensors provided, you still only get two positions indicated, via switch closures.

Better ways:

1) If the pneumatic is operating an arm pivot, contrive a way to attach a 100K linear taper potentiometer to the hinge of the operated joint. They're available in both single turn and multi-turn, so I've always been able to gear one up appropriately with hobby store plastic gears, to monitor the joint somewhere near the pivot linkage.

The "pot" is wired into an Analog Input and read. Interfacing and reading a potentiometer is described in the RC manual. (CW travel end = +5VDC [red], CCW travel end = Ground [blk], and center wiper = signal [wht]).

2) If you are monitoring a linear axis, you may be able to:

A) Attach a rack and pinion system somewhere to operate a feedback potentiometer. The rack goes onto the linear axis, and an appropriate sized pinion gear for your desired throw goes onto the shaft of a multi-turn 100K linear taper potentiometer.

B) Use a 100K linear taper "string pot" to "follow the cylinder's action". BUT, there are two problems: (1) With most cylinder apps, if the cylinder is not aligned with the axis of motion, you may now have set a trig problem for yourself. After all, the cylinder's motion is not of interest, the AXIS motion is! It is MUCH smarter to simply follow the axis or joint itself, as described above. (2) I've yet to find a cheap string pot! So although I've used them before in industry, to date I've never done it on a FIRST robot. (I guess you COULD "make one", but I've yet to find an app where that's really worth the trouble. Again, I've always been able to somehow monitor the joint angle or axis directly with a standard potentiometer.)

Does this answer your question?

- Keith