Go to Post I would much rather educate the audience than dumb-down the game. - dlavery [more]
Home
Go Back   Chief Delphi > Technical > Electrical
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
Thread Tools Rate Thread Display Modes
  #16   Spotlight this post!  
Unread 28-10-2013, 21:41
MichaelBick MichaelBick is offline
Registered User
FRC #1836 (MilkenKnights)
Team Role: Alumni
 
Join Date: Oct 2011
Rookie Year: 2010
Location: Los Angeles
Posts: 734
MichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant futureMichaelBick has a brilliant future
Re: Optical sensors getting tricked

Quote:
Originally Posted by yash101 View Post
Programming a consistent robot closed loop can be hard because you need to calculate the motor speed using the hundreds of variables
Not only is PID not required, you do not need hundreds of variables. A bang-bang shooter algorithm is incredibly easy to program(it's an if statement, if your programmers can program the robot to shoot they can program bang bang). Furthermore it only needs an encoder/ir sensor(we used banner sensors) to feed it RPM. As long as you know the speed of the wheel you don't need to account for any other variables.

For position PID is great. Though we haven't used it before, I have heard that limiting the controller to PD or just P is still a pretty darn effective motion controller.

To sum up, sensors don't have to be complicated. Even with complex code(like vision code) teams like 341 have made it much simpler and easier for the rest of us.
__________________
Team 1836 - The Milken Knights
2013 LA Regional Champions with 1717 and 973
2012 LA Regional Finalists with 294 and 973
To follow Team 1836 on Facebook, go to http://www.facebook.com/MilkenKnights
To go to our website, go to http://milkenknights.com/index.html

Last edited by MichaelBick : 28-10-2013 at 21:47.
  #17   Spotlight this post!  
Unread 28-10-2013, 21:46
Ether's Avatar
Ether Ether is offline
systems engineer (retired)
no team
 
Join Date: Nov 2009
Rookie Year: 1969
Location: US
Posts: 8,125
Ether has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond repute
Re: Optical sensors getting tricked

Quote:
Originally Posted by yash101 View Post
Programming a consistent robot closed loop can be hard because you need to calculate the motor speed using the hundreds of variables, mostly:
-battery voltage
-motor life
-controller life
-load on motors
-bearing stress
-multitudes of other variables
The above makes no sense. I think perhaps you are misunderstanding what "closed loop" means.


  #18   Spotlight this post!  
Unread 28-10-2013, 22:04
EricH's Avatar
EricH EricH is online now
New year, new team
FRC #1197 (Torbots)
Team Role: Engineer
 
Join Date: Jan 2005
Rookie Year: 2003
Location: SoCal
Posts: 19,824
EricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond reputeEricH has a reputation beyond repute
Re: Optical sensors getting tricked

Quote:
Originally Posted by Ether View Post
The above makes no sense. I think perhaps you are misunderstanding what "closed loop" means.
Perhaps I should take a stab at explaining exactly what it means as we're referring to it...

...And reducing the variables (very few of the ones mentioned actually apply in closed-loop control).

Actually, I'll start out with: The only variables listed that would have ANY effect at ALL on, say, a shooter, would be the battery voltage (which really only affects open-loop controls--unless it's totally dead) and the load on the motors (they do have to take a bit of load when the disc goes through--but that's why you have closed-loop control). All of the others have no effect on the control system, or should have been dealt with in the design of the robot (like bearing stress--just get a bearing rated for the load, don't worry about the bearing stress).

Closed-loop control goes something like this: The cRIO sends a command to the speed controller to have the motor go speed X. The controller boosts the motor to speed X (as the controller sees it) by boosting power. A sensor on the shooter wheel indicates speed and sends a signal to the cRIO indicating the actual speed. The cRIO then compares the actual speed to the set speed and then tells the controller to increase power, decrease power, or keep the same power.

cRIO->Controller->Motor->Sensor->cRIO->Controller...

The program could look something like:
speed = 100
if (sensor < 95)
//speed increase
else if (sensor > 105)
//speed decrease


An open-loop control, by contrast, goes:
cRIO->Controller->Motor

and looks like:
speed = 100

in code.
__________________
Past teams:
2003-2007: FRC0330 BeachBots
2008: FRC1135 Shmoebotics
2012: FRC4046 Schroedinger's Dragons

"Rockets are tricky..."--Elon Musk

  #19   Spotlight this post!  
Unread 28-10-2013, 23:55
MrForbes's Avatar
MrForbes MrForbes is offline
Registered User
AKA: Jim
FRC #1726 (N.E.R.D.S.)
Team Role: Mentor
 
Join Date: Feb 2006
Rookie Year: 2006
Location: Sierra Vista AZ
Posts: 6,033
MrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond repute
Re: Optical sensors getting tricked

Quote:
Originally Posted by yash101 View Post
Would you rather shoot 100 frisbees into the goal at a 60% accuracy, or would you shoot 60 frisbees and make all 60 into the goal?
I don't remember how many goals we made...but we did get high seed and won the Arizona regional
  #20   Spotlight this post!  
Unread 29-10-2013, 07:09
Gdeaver Gdeaver is offline
Registered User
FRC #1640
Team Role: Mentor
 
Join Date: Mar 2004
Rookie Year: 2001
Location: West Chester, Pa.
Posts: 1,370
Gdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond repute
Re: Optical sensors getting tricked

This thread is starting to smell of a simplicity VS. complexity argument.
  #21   Spotlight this post!  
Unread 29-10-2013, 08:03
mechanical_robot's Avatar
mechanical_robot mechanical_robot is offline
Registered User
no team
Team Role: Driver
 
Join Date: Jul 2013
Rookie Year: 2013
Location: United States
Posts: 92
mechanical_robot will become famous soon enough
Re: Optical sensors getting tricked

Quote:
Originally Posted by MrForbes View Post
we got around it by designing our robot so it doesn't need any sensors other than the compressor pressure switch. It's amazing what you can do with mechanical design, to eliminate the need for software
Only problem with this is that mechanical problems are harder to fix at competition. At competition it is much quicker to fix a sensor or fix a peice of code than it is a mechanical part. Though if I may ask what sensor have the mechanical parts replaced?
  #22   Spotlight this post!  
Unread 29-10-2013, 09:11
tr6scott's Avatar
tr6scott tr6scott is offline
Um, I smell Motor!
AKA: Scott McBride
FRC #2137 (TORC)
Team Role: Mentor
 
Join Date: Dec 2007
Rookie Year: 2005
Location: Oxford, MI
Posts: 535
tr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond reputetr6scott has a reputation beyond repute
Re: Optical sensors getting tricked

http://www.chiefdelphi.com/forums/sh...8&postcount=25

These with the polarizing filter are very tough to fool.
__________________
The sooner we get behind schedule, the more time we have to catch up.

  #23   Spotlight this post!  
Unread 04-11-2013, 22:24
Sparks333's Avatar
Sparks333 Sparks333 is offline
Robotics Engineer
AKA: Dane B.
FRC #1425 (Wilsonville Robotics)
Team Role: Alumni
 
Join Date: Feb 2004
Rookie Year: 2003
Location: Wilsonville, Oregon
Posts: 184
Sparks333 is a glorious beacon of lightSparks333 is a glorious beacon of lightSparks333 is a glorious beacon of lightSparks333 is a glorious beacon of lightSparks333 is a glorious beacon of lightSparks333 is a glorious beacon of light
Send a message via AIM to Sparks333
Re: Optical sensors getting tricked

Quote:
Originally Posted by EricH View Post
Perhaps I should take a stab at explaining exactly what it means as we're referring to it...

...And reducing the variables (very few of the ones mentioned actually apply in closed-loop control).

Actually, I'll start out with: The only variables listed that would have ANY effect at ALL on, say, a shooter, would be the battery voltage (which really only affects open-loop controls--unless it's totally dead) and the load on the motors (they do have to take a bit of load when the disc goes through--but that's why you have closed-loop control). All of the others have no effect on the control system, or should have been dealt with in the design of the robot (like bearing stress--just get a bearing rated for the load, don't worry about the bearing stress).

Closed-loop control goes something like this: The cRIO sends a command to the speed controller to have the motor go speed X. The controller boosts the motor to speed X (as the controller sees it) by boosting power. A sensor on the shooter wheel indicates speed and sends a signal to the cRIO indicating the actual speed. The cRIO then compares the actual speed to the set speed and then tells the controller to increase power, decrease power, or keep the same power.

cRIO->Controller->Motor->Sensor->cRIO->Controller...

The program could look something like:
speed = 100
if (sensor < 95)
//speed increase
else if (sensor > 105)
//speed decrease


An open-loop control, by contrast, goes:
cRIO->Controller->Motor

and looks like:
speed = 100

in code.
This is a textbook bang-bang velocity controller with deadzone - definitely a closed loop system. What I came here to say is that while any control system has to control a setup that does indeed have hundreds, nay, thousands of variables, the magic of a closed-loop controller is that it will compensate for either not knowing them or knowing them badly - your classic open-loop controller assumes it has perfect information about its system, and that the system itself is perfectly modeled by your controller; it has to, since it has no feedback from the system it is controlling. The trick is, in order to actually get a perfectly modeled system, you DO have to consider all those pesky variables, or just tune it for a particular circumstance and pray it never leaves that island of stability. A closed loop controller can have a much rougher model of the system its controlling, and will magically find parameters that optimize its model (some of the really neat ones can even change their models to better adjust for different control regimes). Of course, you do have to worry about things like lag and complexity in your controllers, as well as having to sense things about the system you're controlling to provide feedback, but thanks to the better modeling abilities of a closed-loop controller, it can be operated much closer to instability, which increases the rate at which it converges to the desired output. In short - if you need speed and precision, go closed-loop.
__________________
ICs do weird things when voltage is run out of spec.

I love to take things apart. The fact that they work better when I put them back together it just a bonus.

http://www.ravenblack.net/random/surreal.html

Last edited by Sparks333 : 04-11-2013 at 22:30.
  #24   Spotlight this post!  
Unread 04-11-2013, 23:07
Gdeaver Gdeaver is offline
Registered User
FRC #1640
Team Role: Mentor
 
Join Date: Mar 2004
Rookie Year: 2001
Location: West Chester, Pa.
Posts: 1,370
Gdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond reputeGdeaver has a reputation beyond repute
Re: Optical sensors getting tricked

Our team has used many different sensors and controllers over the years. My favorite still is the organic analog computer coupled with a organic analog visions processor. Each year we put 2 of them behind the driver station physical connected to the driver station computer. Being an analog system the programming is very difficult. Training a neural net is very time consuming. This year we have devoted allot of resource to train our analog system. We went to ever off season competition we could. Got to train those nets.
  #25   Spotlight this post!  
Unread 04-11-2013, 23:12
ekapalka's Avatar
ekapalka ekapalka is offline
Registered User
FRC #3216
 
Join Date: Dec 2012
Location: Bermuda
Posts: 277
ekapalka has a spectacular aura aboutekapalka has a spectacular aura about
Re: Optical sensors getting tricked

I have no idea what you're talking about, but the words 'neural net' have piqued my interests... You mean that you have a neural net managing your vision tracking, and that you have to endlessly test to train it?
  #26   Spotlight this post!  
Unread 04-11-2013, 23:14
MrForbes's Avatar
MrForbes MrForbes is offline
Registered User
AKA: Jim
FRC #1726 (N.E.R.D.S.)
Team Role: Mentor
 
Join Date: Feb 2006
Rookie Year: 2006
Location: Sierra Vista AZ
Posts: 6,033
MrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond repute
Re: Optical sensors getting tricked

I think he's referring two a couple of students.
  #27   Spotlight this post!  
Unread 04-11-2013, 23:18
ekapalka's Avatar
ekapalka ekapalka is offline
Registered User
FRC #3216
 
Join Date: Dec 2012
Location: Bermuda
Posts: 277
ekapalka has a spectacular aura aboutekapalka has a spectacular aura about
Re: Optical sensors getting tricked

whoosh

You have no idea how relieved I am :P I thought that FIRST programming had just sailed over my head and continued to evolve while I wasn't looking. My team was considering using an ANN last year, but we figured that the costs outweighed the benefits.
  #28   Spotlight this post!  
Unread 05-11-2013, 10:11
otherguy's Avatar
otherguy otherguy is offline
sparkE
AKA: James
FRC #2168 (The Aluminum Falcons)
Team Role: Mentor
 
Join Date: Feb 2010
Rookie Year: 2009
Location: CT
Posts: 443
otherguy is a splendid one to beholdotherguy is a splendid one to beholdotherguy is a splendid one to beholdotherguy is a splendid one to beholdotherguy is a splendid one to beholdotherguy is a splendid one to beholdotherguy is a splendid one to behold
Re: Optical sensors getting tricked

Quote:
Originally Posted by Gdeaver View Post
We had a similar problem in 2012 with sharp IR sensors from Pololu electronics.
http://www.pololu.com/catalog/product/1134
The SHARP IR sensors can be GREAT if used in the right application, but here are my lessons learned.
  • The version linked above is affected by long wire runs and supply voltage fluctuations. You can remedy this by putting a capacitor 'backpack' on the sensor, across the supply voltage pins (VIN, GND). I think we used soemthing around 300uF electrolytic cap. This significantly reduced our intermittent detections due to supply voltage fluctuation.
  • There are quite a few different models of these sensors available, they are each tuned to work at different distances. Make sure you get the right sensor for the job. You need to know the minimum and maximum distances the object you are trying to detect will be from the sensor. This page has a good break down of ranges supported by different models.
  • The larger versions that are mounted within their own plastic housing MUST be mounted so that the plastic is isolated from the chassis. I know it sounds crazy, but the plastic shroud on these is conductive.
__________________
http://team2168.org
  #29   Spotlight this post!  
Unread 05-11-2013, 10:25
MrForbes's Avatar
MrForbes MrForbes is offline
Registered User
AKA: Jim
FRC #1726 (N.E.R.D.S.)
Team Role: Mentor
 
Join Date: Feb 2006
Rookie Year: 2006
Location: Sierra Vista AZ
Posts: 6,033
MrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond repute
Re: Optical sensors getting tricked

Quote:
Originally Posted by antimatter_john View Post
Only problem with this is that mechanical problems are harder to fix at competition. At competition it is much quicker to fix a sensor or fix a peice of code than it is a mechanical part. Though if I may ask what sensor have the mechanical parts replaced?
Huh, we have spent a lot of time at competitions trying to get electronic stuff working, and failed. Mechanicals are easy to fix....maybe because I'm a mechanical engineer, with 30+ yrs experience fixing stuff. I guess it's not what it's made of, it's what you know?

Our Ultimate Ascent robot was designed to not require sensors, it just does it's thing based on it's design. Autonomous just requires the robot to be placed where it belongs, and it shoots into the goal. Shooting during a match works by driving the robot into position and shooting...position being determined by parking the robot against the pyramid. Angles and positions are fixed by design, and the actuation is pneumatic, it's either up or down, no "in between" positions that would require sensor feedback to control.

We've spend days, make that weeks, trying to get sensors to deliver useful information to control robots over the years, and generally failed miserably at it.
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


All times are GMT -5. The time now is 19:19.

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


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi