Possible to Adjust Speed

[Daniel_LaFleur]

Originally Posted by aziobro

Is it legal to use more than one valve? This would allow twice the flow rate into the cylinder.
Would you have to make sure that the Cv was smaller?

Is it legal? Yes.
Do you need to lower the Cv? No.

Will it produce twice the flow? no. This is due to a number of factors including turbidity (sp?) when recombining the flows, etc. Experiment with this, as it is a good learning point in fluid dynamics.

Hint: use 'Y' connectors

[cbpetrovic]

Originally Posted by ligerbots

Hey,
I was wondering if anybody knew of a relatively simple method of adjusting the speed or volume of air flow into the piston? Basically allowing the piston to shoot out real fast or to slowly shoot out.
Thanks for your help!

Yes, there is. Use a "Y" to connect your piston to the air source, one leg has a restrictor in it, the other does not. Use a check valve to prevent bleeding air from the "unactivated" side and there you go.

Feed air from the unrestricted side and you get a rapid deployment of the piston, and from the other side a restricted air flow reduces the speed.

[kmcclary]

Originally Posted by ligerbots

Hey,
I was wondering if anybody knew of a relatively simple method of adjusting the speed or volume of air flow into the piston? Basically allowing the piston to shoot out real fast or to slowly shoot out.
Thanks for your help!

This is quite easy to do.

1) Y-tie your exhaust ports together on your piston control valve and run it into the pressure input port (P) of a second valve (call it valve2).
2) On one output of valve2 (A or B), attach a flow control to meter the exhaust. Leave the other output port (B or A), and the exhaust ports open.

Now, when valve2 is set to the open position, the cylinder runs at full tilt (or at whatever rate the flow controls are set to on the cylinder itself, if included). When valve2 has the flow control switched in, your cylinder will "exhaust slowly", based on the flow control's setting.

Couple this with additional flow controls on either or both ends of the cylinder to adjust individual full speed 'default' flow rates in each direction (and considering the limited amount of total air we have anyway), and this should give you plenty of rate options. I've found it covers over 90% of typical FIRST multi-rate applications.

Note that many valves are "piloted", which means that they need a bit of air pressure on the input (P) port to accomplish switching so YMMV with them. IOW, depending on what valve you use for "exhaust plugging", if it is spring return or not, AND which way you default it, it may take a fraction of a second for the exhaust air to build up in front of it enough to switch the valve.

Therefore, with spring return valves I normally suggest the "unenergized" state to be the metered/restricted flow state, JUST to make sure it WILL build up enough air pressure to switch to the other state. Those valves will automatically return to the unenergized state (regardless of coil signal !) once the pressure drops enough. In this app, that is OK.

BTW, you COULD try to meter the source with a second valve, but if you try it and set the restricted flow rate too low, you will find under some pneumatics plumbing circumstances (and valve choices) the directional valve will fail to respond due to insufficient pilot pressure (or on spring return valves, it can go the WRONG WAY!). Switching a flow control in/out of the EXHAUST plumbing instead overcomes this problem.

Does this make sense?

- Keith

[Wayne Doenges]

What if you used a servo that will turn CW or CCW without stops? You could use a piece of tubing to match the servo output and the flow control knob.

[kmcclary]

Originally Posted by Wayne Doenges

What if you used a servo that will turn CW or CCW without stops? You could use a piece of tubing to match the servo output and the flow control knob.

Not sure of this year's rules regarding servos. (CAN you use stronger ones THIS season, or continuous rotation servos? You couldn't in previous years.)

Bear in mind that the kit regulators take a LOT torque to turn. Probably way too much for the basic kit servo.

Now you CAN easily make a servo in software with a pressure regulator, a window motor, a 10-turn potentiometer, and TWO pressure transducers (1 for output, 1 for SYSTEM pressure, to make sure you CAN reach it before trying).

In addition to a simple closed loop servo routine in software, you also need to do a few other things:
(a) put both software limits to the pot AND a mechanical friction/slip clutch between the motor and the pot/regulator set, to keep from breaking either one should the motor or software go crazy and attempt to turn it too far in either direction.
(b) monitor the full system pressure as well, to disable the servo routine when the system has insufficient pressure. Otherwise, you will "polarize" the servo wide open, trying to get it to a setting you simply can't reach.

But there are simpler methods.

Example - Create a Buffered Supply Tank, at any programmable pressure.

Use a center-blocked valve (or a pair of kit valves), two flow regulators, a pressure transducer, one Clippard tank, and software. Software is similar to the compressor routine. In this case though, whenever it is out of range EITHER way, pulse one or the other valve coil to either fill or drain the tank until it reaches the desired pressure.

One flow regulator controls the tank FILL rate (NEARLY wide open), while the other controls the BLEED-OFF (probably a fairly low setting, to prevent TOO much air waste from a user's "setting indecisions" ). A software variable now determines the tank's desired "set" pressure, and it "automagically tracks it".

Simpler: Monitor the cylinder's pressure with a transducer. When the cylinder reaches the desired force, just cut off its supply! (Again, use a center-plugged [center-off] valve.)

FYI, a center plugged valve is one of the order options for valve parts in the familiar KoP SMC SY3000 series. See the SMC datasheets for more info.

Does this make sense?

- Keith

[Mark McLeod]

Originally Posted by kmcclary

Not sure of this year's rules regarding servos. (CAN you use stronger ones THIS season, or continuous rotation servos? You couldn't in previous years.)

We are still limited in power (except we are allowed to gang up an unlimited number of them), but as long as they are COTS and unmodified, you can use continuous rotation servos.

<R52> Motors specifically permitted on 2010 FRC ROBOTS include:

A. All motors, actuators, and servos listed in the 2010 KOP,

B. An unlimited number of COTS servos with a maximum output torque of 55 oz-in and maximum rotational speed of 100 rpm at 6 Vdc (e.g. HITEC model HS-322HD or HS-325HB servos, as provided in the KOP),