Solenoids

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Posted by Alan Partington at 1/28/2001 1:44 PM EST


Student from Crescent School.



Has anyone been able to control the double solenoids so that you can control how far the pistons go out.

Thanks alot,

Alan

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Posted by Patrick Dingle at 1/28/2001 2:47 PM EST


Other on team #639, Red B^2, from Ithaca High School and Cornell University.


In Reply to: Solenoids
Posted by Alan Partington on 1/28/2001 1:44 PM EST:



Is that what they're supposed to do? I couldn't figure out how to work it.

Patrick

: Has anyone been able to control the double solenoids so that you can control how far the pistons go out.

: Thanks alot,

: Alan

[archiver]

Posted by Anton Abaya at 1/28/2001 11:46 PM EST


Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.


In Reply to: Re: Solenoids
Posted by Patrick Dingle on 1/28/2001 2:47 PM EST:



: Is that what they're supposed to do? I couldn't figure out how to work it.

: Patrick

: : Has anyone been able to control the double solenoids so that you can control how far the pistons go out.

: : Thanks alot,

: : Alan

umm, Josh on 419 should know this, but I do know that the double solenoids allow a piston to move up and to move down...

err soemthing like that...

wanna answer this one joshie?

-anton

[archiver]

Posted by Josh at 1/29/2001 12:47 AM EST


Engineer on team #419, Rambots, from Wentworth Institute of Technology.


In Reply to: double solenoids...
Posted by Anton Abaya on 1/28/2001 11:46 PM EST:



: : Is that what they're supposed to do? I couldn't figure out how to work it.

: : Patrick

: : : Has anyone been able to control the double solenoids so that you can control how far the pistons go out.

: : : Thanks alot,

: : : Alan

: umm, Josh on 419 should know this, but I do know that the double solenoids allow a piston to move up and to move down...

: err soemthing like that...

: wanna answer this one joshie?

: -anton

From what i can get out of the instructions: the double solenoid is used as almost a lock for the piston. In a single solenoid, the electicity opens the gate so that air flows out of the piston and the piston can drop. When the electricty is released, the gate is closed so the air leave. But the piston can still be moved because of the low preasure in the chamber

The double solenoid then provides a continual preasure to one side. so that even when the electicity is off, the preasure in one side is still high. When you give it another shock, instead of just opening the gate, it allows the air out of one side, and allows the compressor to pump air into the other side, locking the piston in the other direction imobilizing it. it will lock in either the up or down direction dependign on what valve in teh double solenoid is open.

I know it's a little confusing, i have to run some tests on it yet to make sure of it myself. i'm pretty sure the double solenoid doesn't actually control how far a piston reaches, just where it's locked in place. If i find anything different, i'll pots it here.

Oh, and if your trying to wire them up, they REQUIRE the two diodes that are shown in the wiring diagram in the manual. If you don't hook it up right, you won't get them to work. and make sure you have the diodes in the right direction, they ARE polarized, the little band on them shows which side is positive (it's indicated by the line on the triangle in the diagram.)

HTH

Josh
Team 419
Yes, i can be serious sometimes.

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Posted by Andy Baker at 1/29/2001 1:12 AM EST


Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.


In Reply to: Re: double solenoids...
Posted by Josh on 1/29/2001 12:47 AM EST:



Double solenoids don't really lock the cylinders any better than the single solenoids do. They both will hold the cylinders in position. The only time that a cylinder will lose it's position is when pressurized air is dumped from the system.

A doulbe solenoid shifts the valve from one side or the other by means of a quick pulse of the solenoid. Once the valve is shifted by solenoid A, it travels over to the B side. The valve will stay there until it is shifted by solenoid B, back to the other side.

A double solenoid should be used on a cylinder that is held in either the extended or retracted position. This type of valve will keep a cylinder in position even after electricity is shut off to the valve. (maybe this is what Josh meant by "locking").

A single solenoid valve will hold a cylinder in the actuated position as long as the solenoid is getting a signal to actuate. But, when the solenoid is not moved, the valve will keep the cylinder in it's unactuated state, if you plumb the tubing right. If you set up the tubing so that the cylinder is vented during the unactuated state, then it will move freely... but it won't be forced into the unactuated position once the solenoid is de-activated.

For more technical help, get your local SMC, Festo, Clippard, Bimba, or Parker salesperson to help you out... they may even want to give you free tools, along with some technical advice.

Andy B.

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Posted by Joe Johnson at 1/29/2001 2:31 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Single and double solenoids... here's the difference:
Posted by Andy Baker on 1/29/2001 1:12 AM EST:



Is anybody else worried that the "STOP" button may actually make some robots move violently?

I know I am.

Think about it, teams that use the single acting valves will have to have the "disabled" state be the state that puts the robots "in the box."

This is by no means is the "safe" position.

Consider the following:

Robot is enabled running about doing its thing. Someone foolishly puts a part of their body near the robot. A careful drive, seeing this condition hits the "STOP" button trying to prevent anything bad from happening to the person (fingers in gears for example).

What happens? Well... what might happen is the robot will revert to its "in the box" state and happily provide 100+ of force to the arm or what ever. If the person's body part is in the way, well, too bad for that body part.

Here is my nightmare scenario:

Step #1:
Same as above but someone does not hit the button until the said body part is actually caught in the gears of the machine.

Step #2:
The foolish person screams, "HIT THE STOP BUTTON!"
Step #3:
The drives hit the "STOP" button

Step #4:
The foolish person yell, "TURN IT BACK ON! TURN IT BACK ON!" because an air cylinder is putting the hurt on him.

Step #5:
Return to Step #2 -- repeat until foolish person passes out or until the batteries are drained.

Do I just have an overactive imagination or is this a realistic possibility?

Thoughts, comments?

Joe J.

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Posted by ChrisH at 1/29/2001 5:09 PM EST


Engineer on team #330, Beach 'Bots, from Hope Chapel Academy and NASA JPL, J & F Machine, Raytheon, et al.


In Reply to: single acting valves -- FIRST, you're scaring me...
Posted by Joe Johnson on 1/29/2001 2:31 PM EST:



: Is anybody else worried that the "STOP" button may actually make some robots move violently?


Joe,

You are right to be concerned. However there is a solution right in the box with the other pnuematic stuff. It's called a pilot operated check valve. Used properly it will cause a single solenoid valve to act like a double. As I recall there are two of them. I learned about this at a seminar held by Team 22 HOMER last weekend, but it's also in the manual (which somebody had borrowed or I would have read it before)

The setup we got this year is powerful enough to hurt people badly if not used with care, but the same could be said of the battery we use, or the motors, or surgical tubing for that matter.

I highly recommend that any pnuematic setup be "breadboarded" and tested before installation on the robot. This will help find unexpected operating modes (ie. "bugs" or "features" to you software guys and gals). In aircraft-land we actually mock up the entire hydraulic set-up of a new aircraft on a big steel frame called the "iron bird". The Iron Bird "flies" many hundreds of hours before the "real" airplane gets air under the tires once. The whole purpose is to find out if the system does anything unexpected. If the big boys that do it for money spend time on it maybe you should too!

With pnuematics as with any other power source, use it responsibly! AND READ THE MANUAL FIRST!!!!

Chris Husmann, PE
team 330 the Beach'Bots

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Posted by Gary Bonner at 1/30/2001 12:10 PM EST


Other on team #433, MINT, from Mount Saint Joseph Academy and Pew Foundation.


In Reply to: Re: single acting valves -- FIRST, you're scaring me...
Posted by ChrisH on 1/29/2001 5:09 PM EST:



: You are right to be concerned. However there is a solution right in the box with the other pnuematic stuff. It's called a pilot operated check valve. Used properly it will cause a single solenoid valve to act like a double.

With what do you operate the pilot? The other single valve? The list of valves is pretty short to start with. And there’s only one pilot operated check valve in the kit.

The assortment of components in the pneumatics kit is tempting, but the limited number of valves severely constrains what you can do. To justify adding the weight of the compressor, tanks, etc. to your robot, it would be nice if you could do more than one or two things with it.

[archiver]

Posted by Lloyd Burns at 1/29/2001 12:30 AM EST


Other on team #188, Woburn Robotics, from Woburn Collegiate and Canada 3000, ScotiaBank, Royal Bank Financial.


In Reply to: Solenoids
Posted by Alan Partington on 1/28/2001 1:44 PM EST:



: Has anyone been able to control the double solenoids so that you can control how far the pistons go out.

: Thanks alot,

: Alan

. In the pneumatics booklet, there is a clue in the paragraphs on the double-coil valve. It is important to remember these coils control pilot valves, not the main valve, so pressure must be present or you will neither see nor hear any action at all.

. The action of turning on the valve (apply voltage to coil A) allows the pressure from port P to push the valve to allow air to go from P to A (and B goes to its exhaust port), while turning off the current to coil A stops the flow from P to A, but it does not connect A to the exhaust port either. Both B and A are isolated, neither at pressure nor at atmosphere. The result is that the piston stops where it is. To further extend, pulse A again. To retract, pulse coil B which pushes the main valve all the way back, connecting port A to the exhaust, while P is now cleared for port B, retracting the cylinder.

. By placing a flow control (the gray, right-angled little spigots) in the line to P, (not a good idea - low pressure = erratic operation) or in the air lines from valve to cylinder, or yet again, in the exhaust ports, you can slow down the piston to a controllable speed, and you can stop it at any extension you need. Have you tried putting 60 PSI on the 3/4" bore cylinder (uncontrolled speed = recoil !!!) ? :-)

[archiver]

Posted by Joe Ross at 1/29/2001 4:58 AM EST


Engineer on team #330, Beach Bot, from Hope Chapel Academy and NASA/JPL , J&F Machine, and Raytheon.


In Reply to: Solenoids
Posted by Alan Partington on 1/28/2001 1:44 PM EST:



I don't have the nice little booklet that came with the pneumatics right now, but I remember it STRONGLY suggesting that you only use the full stroke of each cylinder. It said that the cylinders were only designed to hold the load when the were fully extended or retracted.

There may be a way to only extend a piston only a certain distance, but I wouldn't try it in light of what that booklet said.

Joe Ross
Beach Bot, Team 330