Go to Post Replay/video isnt a BAD idea, its just not a GOOD idea for FIRST. - Ashley Christine [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
  #1   Spotlight this post!  
Unread 19-01-2008, 20:02
Tim Skloss's Avatar
Tim Skloss Tim Skloss is offline
Dr. Skloss
FRC #0930
Team Role: Parent
 
Join Date: Jan 2002
Rookie Year: 2000
Location: Waukesha, WI, USA
Posts: 73
Tim Skloss is a jewel in the roughTim Skloss is a jewel in the roughTim Skloss is a jewel in the roughTim Skloss is a jewel in the rough
Using a different gear tooth sensor

There seems to be evidence that one of the two gear tooth sensors (GTS) sent in the FIRST KOP may be bad. We had one that worked and another that didn't. Autonomous accuracy is very important to our strategy this year so we HAD to have good tracking on both sides of our drive train.

As of this writing, I am not aware of any replacements available for the GTSs sent in the KOP. So we set out to adapt a low-cost COTS GTS to the Andy-Mark gearboxes. This thread explains how we did it.

I'm telling this story now because as of today we verified that the implementation was working well and we have the accuracy predicted in the mathematical analysis. We considered encoders, but to mount them requires more tricky mechanical linkages and parts.

The sensors are Honeywell model 1GT101DC. They are available from DigiKey for about $25. All you need is one PWM cable and a 5K-ohm resistor to connect it to the robot controller. The signal lead needs to be connected to the +5VDC lead via the resistor (pull-up for the sensor's open collector output). Software for reading the sensor's output can be found in this thread.

The sensor outputs a digital high level when it does not detect a ferrous object at its tip. When a ferrous metal is sensed at the tip it pulls the output low. (Therefore it can also be used as a limit switch!) Generally we mount the sensor 0.5 to 1.5 mm away from the gear or sprocket teeth. You can find the optimum distance by observing the output on an oscilloscope; tune for a 50% duty cycle when the gear/sprocket is rotating rapidly. An advantage of this setup is that you can quickly remove the GTS at the competition to clean off debris that tends to collect on the magnetic parts (gear tooth filings).

Of course mounting them into the AM gearboxes requires some effort, but it is manageable if you have a drill press. We drilled a hole in the "top" of the gearbox as show in pictures 1 and 3. The main hole was drilled directly above the gear so that the sensor will point directly at it. A smaller hole was drilled and tapped for a 1/4" bolt used to secure the sensor to the gearbox. Add a spacer and you have a secure mount as shown in pictures 4 and 5. Adjusting the length of the spacer allows you get the sensor-to-gear distance just right.

You will notice a few things:
-We machined a replacement aluminum plate for the gear box to allow us to more easily mount it to our chassis. Our chassis is made from ITEM brand extrusion which allows quick and easy construction, adjustment, and excellent maintainability.
-The GTS is sensing the high-speed 50 tooth gear that is driven by the CIM motors. This gives us more resolution in distance measurement. Currently we see 0.07 inch-per-tooth resolution using this setup and a 15/22 tooth sprocket ratio driving 6 inch wheels.
-Picture 6 shows our controls breadboard. We have been able to develop our autonomous code without the need for a rolling robot using this arrangement since kickoff. Today we moved the controls to the chassis for the first time and were able to show precise autonomous movement forward and in turns. The team was amazed at the accuracy, and frankly so was I!

So that's it. I hope to put this thread on the gearbox GTSs to rest. Hopefully FIRST (or someone else!) will make the KOP GTS boards available for purchase so teams can replace their faulty ones. Until then we are moving on to develop our autonomous and robocoach strategies.

Good luck teams!
Attached Thumbnails
Click image for larger version

Name:	gts1.jpg
Views:	236
Size:	80.4 KB
ID:	6067  Click image for larger version

Name:	gts3.jpg
Views:	234
Size:	63.0 KB
ID:	6069  Click image for larger version

Name:	gts4.jpg
Views:	265
Size:	64.5 KB
ID:	6070  Click image for larger version

Name:	gts5.jpg
Views:	300
Size:	61.8 KB
ID:	6071  Click image for larger version

Name:	gts6.jpg
Views:	295
Size:	79.9 KB
ID:	6072  

__________________
---------------
FIRST Mentor and Team Leader
C.O.R.E 2062 a NASA, GE Volunteers and Rockwell Automation FRC Team
  #2   Spotlight this post!  
Unread 19-01-2008, 22:01
KTorak's Avatar
KTorak KTorak is offline
Fire Rescue 47
AKA: Kyle Dersch
FRC #1023 (Bedford Express)
Team Role: Driver
 
Join Date: Jan 2005
Rookie Year: 2005
Location: Montgomery Village, MD
Posts: 899
KTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond reputeKTorak has a reputation beyond repute
Send a message via AIM to KTorak
Re: Using a different gear tooth sensor

We actually just got in some Honeywell ones from DigiKey. I'm not sure what model, as i'm not up with what the programmers are up to, but from when I played with them today, they seemed pretty cool.
__________________
Kyle D- Myspace - Facebook
2008 Bedford Express Driver & Build & Design (Team) Co-Leader
2007 Bedford Express Driver & Build & Design (Team) Leader
2006 Bedford Express Driver, Build Team Member, & Board of Directors
2005 Bedford Express Rookie, Build Team Member & Robot Operator
-
2008 - GLR Quarter Finalist
2007 - GLR Finalist & Boilermaker Finalist & MARC Off Season Event Winner
2006 - GLR Johnson & Johnson Sportsmanship Award & Archimedes 7th Seed Quarter Finalist
2005 - GLR Finalist & Judges Award.
2004 - GLR Semi Finalist.
2003 - GLR/DTR Quarter Finalist & GLR/NAT'L Rookie All Star.
  #3   Spotlight this post!  
Unread 22-01-2008, 17:55
galesc galesc is offline
Registered User
FRC #0171
 
Join Date: Sep 2006
Location: Platteville, WI
Posts: 3
galesc has a little shameless behaviour in the past
Re: Using a different gear tooth sensor

Good job with the research it is very much appreciated. Did you do any research or do you have any speculation about why one is good and one is bad? Is there any known part of the circuit that is bad on one and not the other?

Just try to get to the root of the problem.

Thanks.
  #4   Spotlight this post!  
Unread 22-01-2008, 20:25
efoote868 efoote868 is offline
foote stepped in
AKA: E. Foote
FRC #0868
Team Role: Mentor
 
Join Date: Mar 2006
Rookie Year: 2005
Location: Noblesville, IN
Posts: 1,424
efoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond repute
Re: Using a different gear tooth sensor

we skipped the gear tooth sensor and went straight for shaft encoders. The programming team just got a mock up drive train, so we're going to be playing around with them.

I'm not sure the model, but I will post that if it works.
__________________

Be Healthy. Never Stop Learning. Say It Like It Is. Own It. Like our values? Flexware Innovation is hiring!. We're looking for Senior Automation, Software, and System Engineers. Check us out!
  #5   Spotlight this post!  
Unread 22-01-2008, 22:19
Tim Skloss's Avatar
Tim Skloss Tim Skloss is offline
Dr. Skloss
FRC #0930
Team Role: Parent
 
Join Date: Jan 2002
Rookie Year: 2000
Location: Waukesha, WI, USA
Posts: 73
Tim Skloss is a jewel in the roughTim Skloss is a jewel in the roughTim Skloss is a jewel in the roughTim Skloss is a jewel in the rough
Re: Using a different gear tooth sensor

Quote:
Originally Posted by galesc View Post
Good job with the research it is very much appreciated. Did you do any research or do you have any speculation about why one is good and one is bad? Is there any known part of the circuit that is bad on one and not the other?
Thanks.
I would have to assume that it is not component failure if one of the two boards is failing routinely. More likely there is a defect in the circuit board or the wrong part was placed during automated assembly. This happens quite commonly in electronics manufacturing, however it should have been picked up during acceptance tests.
__________________
---------------
FIRST Mentor and Team Leader
C.O.R.E 2062 a NASA, GE Volunteers and Rockwell Automation FRC Team
  #6   Spotlight this post!  
Unread 24-01-2008, 19:41
SuperBK's Avatar
SuperBK SuperBK is offline
Registered User
AKA: BrianK
FRC #1225 (Amperage Robotics)
Team Role: Mentor
 
Join Date: Jan 2007
Rookie Year: 2006
Location: Henersonville, NC
Posts: 358
SuperBK is just really niceSuperBK is just really niceSuperBK is just really niceSuperBK is just really nice
Re: Using a different gear tooth sensor

Do you guys think these Honeywell sensors would work looking at the SIDE of a gear instead of at the teeth directly?

Edit: I meant looking at the side of the teeth. Right at the edge of the gear. Drilling a 3/4 hold in the side of the gearbox looks like it could weaken it. For those that did drill it, did you have any problems? How big does the hole need to be. Our sensors should be arriving today.

Brian
__________________
Brian K
Team 1225 Robotics Mentor

Last edited by SuperBK : 25-01-2008 at 08:52.
  #7   Spotlight this post!  
Unread 24-01-2008, 22:52
TubaMorg TubaMorg is offline
Programmermechanicalelect ricalcoach
AKA: Dan
FRC #1480 (Robatos Locos)
Team Role: Mentor
 
Join Date: Jan 2006
Rookie Year: 2005
Location: Houston
Posts: 450
TubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond reputeTubaMorg has a reputation beyond repute
Re: Using a different gear tooth sensor

Quote:
Originally Posted by SuperBK View Post
Do you guys think these Honeywell sensors would work looking at the SIDE of a gear instead of at the teeth directly?
Brian
Keep in mind that Hall effect sensors work by detecting a change of position of a ferrous material in close proximity to the sensor. If the sensor is is positioned to "look" at the side of the gear, then it won't know if anything has changed.

We wanted to thank Tim for this post, we are utilizing his research. We opted to change the mounting location so that we detect the output gear and changed the mount location to the side of the gear box. The greater distance from the wall of the gear box to the gear eliminated the need for a spacer. The distance was just right. Thanks Tim!
  #8   Spotlight this post!  
Unread 24-01-2008, 23:24
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: Using a different gear tooth sensor

Quote:
Originally Posted by Tim Skloss View Post
More likely there is a defect in the circuit board or the wrong part was placed during automated assembly. This happens quite commonly in electronics manufacturing, however it should have been picked up during acceptance tests.
apparently it wasn't picked up, resistors R3 and R4 are switched on one of our boards
  #9   Spotlight this post!  
Unread 07-02-2008, 00:37
billbo911's Avatar
billbo911 billbo911 is offline
I prefer you give a perfect effort.
AKA: That's "Mr. Bill"
FRC #2073 (EagleForce)
Team Role: Mentor
 
Join Date: Mar 2005
Rookie Year: 2005
Location: Elk Grove, Ca.
Posts: 2,384
billbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond repute
Re: Using a different gear tooth sensor

Similar to what Tim did, we installed Honeywell encoders and both of our transmissions. Here is a picture of what ours looks like. We installed our gear tooth sensors on the output gear.
__________________
CalGames 2009 Autonomous Champion Award winner
Sacramento 2010 Creativity in Design winner, Sacramento 2010 Quarter finalist
2011 Sacramento Finalist, 2011 Madtown Engineering Inspiration Award.
2012 Sacramento Semi-Finals, 2012 Sacramento Innovation in Control Award, 2012 SVR Judges Award.
2012 CalGames Autonomous Challenge Award winner ($$$).
2014 2X Rockwell Automation: Innovation in Control Award (CVR and SAC). Curie Division Gracious Professionalism Award.
2014 Capital City Classic Winner AND Runner Up. Madtown Throwdown: Runner up.
2015 Innovation in Control Award, Sacramento.
2016 Chezy Champs Finalist, 2016 MTTD Finalist
  #10   Spotlight this post!  
Unread 07-02-2008, 14:48
Code Monkey Code Monkey is offline
Registered User
FRC #1622
 
Join Date: Dec 2007
Location: San Diego
Posts: 10
Code Monkey is an unknown quantity at this point
Re: Andy Mark encoders

We are using the encoders built into the Andy Mark Transmissions. I took one off for testing (works with new C18 encoder code perfectly) but I am worried about the coupling to the shaft. Has anyone taken one of these apart? I would like to put some sticky glue onto the coupling to keep it from slipping.
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
Gear Tooth Sensor marco_alchemy Electrical 7 06-02-2008 09:54
A different kind of gear tooth question Semicolon Electrical 3 12-01-2008 16:24
Gear Tooth Sensor? Raikon Kit & Additional Hardware 3 09-02-2007 16:40
Gear Tooth Sensor nukem Programming 9 04-02-2006 20:21
Gear Tooth Sensor Talha Electrical 1 23-01-2006 21:29


All times are GMT -5. The time now is 15:25.

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