OCCRA
Go to Post TL, DR: You may be skilled at karate on your own, but imagine how much better you'll be with Mr. Miyagi mentoring you. - artdutra04 [more]
Home
Go Back   Chief Delphi > Technical > Pneumatics
CD-Events   CD-Media   CD-Spy   FRC-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
Thread Tools Rate Thread Display Modes
  #1   Spotlight this post!  
Unread 01-13-2010, 07:47 PM
WorkingFromHome's Avatar
WorkingFromHome WorkingFromHome is offline
Full of Awesomeness
AKA: That One Guy Who Does Stuff
FRC #2587 (Discobots)
 
Join Date: Jan 2010
Rookie Year: 2008
Location: Earth. Where else?
Posts: 1
WorkingFromHome is an unknown quantity at this point
Pneumatic Actuator Speed?

Does anyone know a good formula for figuring out the speed of a pneumatic actuator? I've looked all over the place, but all I can find are ways to get the force.

Thanks for the help,
WorkingFromHome
  #2   Spotlight this post!  
Unread 01-13-2010, 10:01 PM
kirtar kirtar is offline
Alumnus
FRC #0461 (Westside Boiler Invasion)
Team Role: Alumni
 
Join Date: Jan 2008
Rookie Year: 2007
Location: West Lafayette, IN
Posts: 169
kirtar will become famous soon enough
Re: Pneumatic Actuator Speed?

One thing you can do is take a scale (that is to say a reference such as a meter stick) and use a video camera. This may require a high speed camera that you don't have though depending on how fast this is. What you can do is tape it with the scale and go frame by frame (remember, frames have a constant rate).

If you're using a piston and not a rotary pneumatic, you can actually just focus on the piston and put the scale there so you won't reallly need a high speed camera. Basically, start at the first frame in which it starts to move (record measurement), go to the frame in which it is fully extended and then divide the distance traveled by (Numer of frames/Frame rate), and then carry through the calculation through any linkage you have it hooked up to.

Hope that made sense and was helpful.
__________________
  #3   Spotlight this post!  
Unread 01-15-2010, 02:41 PM
StevenB StevenB is offline
is having FRC withdrawal symptoms.
AKA: Steven Bell
no team
Team Role: College Student
 
Join Date: May 2005
Rookie Year: 2005
Location: Stanford, CA
Posts: 398
StevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond reputeStevenB has a reputation beyond repute
Re: Pneumatic Actuator Speed?

Quote:
Originally Posted by WorkingFromHome View Post
Does anyone know a good formula for figuring out the speed of a pneumatic actuator? I've looked all over the place, but all I can find are ways to get the force.
I'm looking for the same thing. All I know is that it has to do with the rate of airflow through the tubes.
This paper has some useful information, but I don't really understand the equations they present.
__________________
Need a physics refresher? Want to know if that motor is big enough for your arm? A FIRST Encounter with Physics

2005-2007: Student | Team #1519, Mechanical Mayhem | Milford, NH
2008-2011: Mentor | Team #2359, RoboLobos | Edmond, OK
2014-??: Mentor | Looking for a team...
  #4   Spotlight this post!  
Unread 01-20-2010, 12:09 AM
vamfun vamfun is offline
Mentor :Contol System Engineer
AKA: Chris
FRC #0599 (Robodox)
Team Role: Engineer
 
Join Date: Jan 2009
Rookie Year: 2003
Location: Van Nuys, California
Posts: 178
vamfun is a glorious beacon of lightvamfun is a glorious beacon of lightvamfun is a glorious beacon of lightvamfun is a glorious beacon of lightvamfun is a glorious beacon of lightvamfun is a glorious beacon of light
Send a message via AIM to vamfun
Re: Pneumatic Actuator Speed?

I couldn't find any either so I wrote an excel program that integrates the forces to get the piston step response. The response is dictated by the valve coefficent of flow Cv or effective area. The effective area of the SMC valve is 4.86mm^2. A valve is either operating in subsonic or sonic conditions. When it is in sonic conditions, the flow rate is limited by the speed of sound. Otherwise , it varies as the square root of the pressure drop across it. It gets a little more complicated because every component in the pneumatic flow chain has its own Cv (area) and the squared Cv's add like resisters in parallel.

You can take a wag at the maximum possible piston speed assuming it is restricted by the speed of sound.

speed_ips = 13500*factor*A_valve/A_piston

where A_valve = 4.86mm^2, A_piston is the area of the bore and factor is a degradation due to the system fittings and piping. factor reduces the effective A_valve. I would use factor of .3 to .5.

So rewriting this in terms of cylinder bore_in we get

speed_ips = 84.76*factor/bore_in^2

Assuming a factor of .5 and a bore of 1 in then the max speed would be about 42 ips. A 2 in bore would be 1/4 that.

The above assumes standard day sea level conditions.

My model shows that the SMC valve is sized well to keep the .75 in bore cylinder in sub sonic flow conditions most of the time. The 1 and 2 inch bores are flow limited unless driving very large loads. So if you want speed, use the smallest bore. If you want kinetic energy, load the piston as much as you can with a weight. This slows the piston down and allows the piston to be work limited (piston force*stroke) rather than speed limited. When work limited, you can typically get an efficiency of about 35% of what the piston could deliver if moving really slow against a heavy weight than when it is pushing a lighter load.

For example, when pushing a 10 lb load at 60psi with a .75 in bore , a 12 in stroke can deliver about 8.6 ft lbs of kinetic energy. The max would be =Bore*Force = 1ft*24lbs=24 ft lbs, so 35% efficiency. A 10 lb load would be typical of a piston pushing a 2lb weight with a 5 to 1 lever arm.

These results are yet to be verified with FRC testing... I have however done some verification with the vex pneumatics while working with a vex catapult. Here are some forum posts if you are interested:
http://www.vexforum.com/showthread.php?t=18391
http://www.vexforum.com/showthread.php?t=19042
http://www.vexforum.com/showthread.php?t=19003
Also a little more in my vex blog: http://vamfun.wordpress.com/

Last edited by vamfun : 01-20-2010 at 01:39 AM.
Closed Thread


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
pic: Pneumatic Gate Valve Actuator MrForbes Extra Discussion 17 09-09-2014 06:56 PM
pic: Four-Speed Ball-Lock Single-Pneumatic Transmission Design Bootsie Extra Discussion 14 08-25-2009 02:55 PM
Pneumatic Actuator Calvin_1631 Pneumatics 1 02-22-2007 11:12 AM
pneumatic actuator for storage tank aksimhal Pneumatics 3 01-13-2007 11:19 PM
Pneumatic Actuator limit? Moshingkow Rules/Strategy 4 01-08-2003 02:16 AM


All times are GMT -5. The time now is 06:46 AM.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi