OCCRA
Go to Post We're not behind, the rest of the world is ahead! Yeah. Thats it. - Curtis Williams [more]
Home
Go Back   Chief Delphi > Technical > Control System > Sensors
CD-Events   CD-Media   CD-Spy   FRC-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Reply
Thread Tools Rate Thread Display Modes
  #1   Spotlight this post!  
Unread 10-14-2011, 09:11 AM
siggy2xc siggy2xc is offline
Registered User
AKA: Tyler Siegrist
FRC #1756 (Argos)
Team Role: Programmer
 
Join Date: Mar 2010
Rookie Year: 2009
Location: peoria
Posts: 70
siggy2xc is an unknown quantity at this point
Anything better than a gyro?

Is there something else we could use to accurately measure the rotation of the robot? The gyro we have slowly drifts off and within 2 minutes of driving around, its a good 30 degrees off. Or if we spin quickly then it gets thrown off by a large amount. We just need to know the direction we are facing relative to the driver. Maybe there is a better gyro or some sort of compass?
Reply With Quote
  #2   Spotlight this post!  
Unread 10-14-2011, 11:47 AM
Chris Hibner's Avatar Unsung FIRST Hero
Chris Hibner Chris Hibner is offline
Eschewing Obfuscation Since 1990
AKA: Lars Kamen's Roadie
FRC #0051 (Wings of Fire)
Team Role: Engineer
 
Join Date: May 2001
Rookie Year: 1997
Location: Canton, MI
Posts: 1,404
Chris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond repute
Re: Anything better than a gyro?

Quote:
Originally Posted by siggy2xc View Post
Is there something else we could use to accurately measure the rotation of the robot? The gyro we have slowly drifts off and within 2 minutes of driving around, its a good 30 degrees off. Or if we spin quickly then it gets thrown off by a large amount. We just need to know the direction we are facing relative to the driver. Maybe there is a better gyro or some sort of compass?
We've been using encoders attached to two dummy wheels for the last few years. It works very well. You can calculate the heading from the difference in the distance the two wheels have travelled.
__________________
-
An ounce of perception is worth a pound of obscure.
Reply With Quote
  #3   Spotlight this post!  
Unread 10-14-2011, 02:49 PM
ajlapp ajlapp is offline
Registered User
AKA: Anthony Lapp
None #0118 (Team RUSH and Robonauts)
 
Join Date: Sep 2001
Rookie Year: 1996
Location: Ortonville, MI
Posts: 570
ajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond reputeajlapp has a reputation beyond repute
Re: Anything better than a gyro?

Chris,

Do you recommend blending this two encoder technique with a gyro for increased redundancy/accuracy?

In our experience, the kit gyro provided last season had very little drift, though we use it in short burst only before resetting it.
__________________
Anthony Lapp
FIRST Engineering Mentor
Owner/Operator 221 Robotic Systems
221 Robotics Systems - Quality Hardware, Made in the USA
RobotOpen
anthony@221robotics.com
Twitter us: @221RobotSystems
Team 1 --> 94 --> 68 --> 221 --> 857 --> 27 --> 118
Design Engineer/Fabricator and 17 year vet
Team Rush (FRC27) and Robonauts (FRC118)
Reply With Quote
  #4   Spotlight this post!  
Unread 10-14-2011, 08:53 PM
Joe Ross's Avatar Unsung FIRST Hero
Joe Ross Joe Ross is offline
Registered User
FRC #0330 (Beachbots)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1997
Location: Los Angeles, CA
Posts: 7,901
Joe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond reputeJoe Ross has a reputation beyond repute
Re: Anything better than a gyro?

Different gyros have different maximum turn rates. Some that have been in the KOP in the past have been as low as 75 degrees/sec, which is easy to max out. If you used one of those, I would recommend getting a gyro better suited to your operation. We typically use gyros designed for 300 degrees/sec.

How much does your gyro drift when the robot doesn't move for 2 minutes?

If your gyro isn't mounted stably, you'd have problems.

Last edited by Joe Ross : 10-14-2011 at 09:06 PM.
Reply With Quote
  #5   Spotlight this post!  
Unread 10-14-2011, 09:20 PM
Chris Hibner's Avatar Unsung FIRST Hero
Chris Hibner Chris Hibner is offline
Eschewing Obfuscation Since 1990
AKA: Lars Kamen's Roadie
FRC #0051 (Wings of Fire)
Team Role: Engineer
 
Join Date: May 2001
Rookie Year: 1997
Location: Canton, MI
Posts: 1,404
Chris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond reputeChris Hibner has a reputation beyond repute
Re: Anything better than a gyro?

Quote:
Originally Posted by ajlapp View Post
Chris,

Do you recommend blending this two encoder technique with a gyro for increased redundancy/accuracy?

In our experience, the kit gyro provided last season had very little drift, though we use it in short burst only before resetting it.
You can combine the two, and there are various techniques.

For Breakaway we had a problem with one of our encoder wheels losing contact with the floor when we drove over the lip near the tower. That caused our heading to get all out of whack. We wound up adding a gyro so we used the encoders up until we were within a few inches of the lip, then we'd switch to the gyro. Whenever we were using encoder-based heading we would constantly reset the gyro heading to the encoder heading. Once we switched to the gyro heading, we would keep track of a correction constant for the encoder heading once we switched back to the encoder based heading. It worked pretty well.

A project that I've been involved with at work combines inertial sensors (like the gyro) with wheel-based sensors. We have a novel way to combine them that I would love to share, but I'm sure my company wouldn't be happy if I did that.

In general, if you can solve the problem with fewer sensors, you're better off due to simplicity. Only add more sensors to solve a problem you can't solve otherwise.
__________________
-
An ounce of perception is worth a pound of obscure.
Reply With Quote
  #6   Spotlight this post!  
Unread 01-13-2012, 12:28 AM
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: 180
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: Anything better than a gyro?

Try a complimentary filter - it biases measurements depending on the frequency of the input. The gyro would be useful for high-frequency measurements, but will quickly drift in a low-frequency environment. An encoder, likewise, will probably be susceptible to wheel slippage at high speeds, but will work well when speed is slow. A very, very simple two-tap complimentary filter is simply to do:

total_rotation = 0.5*gyro_new - 0.5*gyro_old + 0.5*enc_new + 0.5*enc_old;
gyro_old = gyro_new;
enc_old = enc_old;

This is essentially a high-pass filter on the gyro with a low-pass filter on the encoder. This has the inherent flaw that it allows high-frequency noise from the gyro to enter the system, so a low-pass with a higher cutoff than the highpass filter might be required for the gyro first.

Hope this is useful.

Sparks
__________________
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
Reply With Quote
Reply


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 06:33 PM.

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