Go to Post The point of FIRST is not to create pretty robots. It's to teach kids about science, technology, and engineering. - Cory [more]
Home
Go Back   Chief Delphi > Technical > Electrical > CAN
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
 
 
Thread Tools Rating: Thread Rating: 2 votes, 5.00 average. Display Modes
Prev Previous Post   Next Post Next
  #27   Spotlight this post!  
Unread 24-04-2012, 11:35
techhelpbb's Avatar
techhelpbb techhelpbb is offline
Registered User
FRC #0011 (MORT - Team 11)
Team Role: Mentor
 
Join Date: Nov 2010
Rookie Year: 1997
Location: New Jersey
Posts: 1,624
techhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond reputetechhelpbb has a reputation beyond repute
Re: TI and future Jaguars

Quote:
Originally Posted by Tom Bottiglieri View Post
As far as control signals go, CAN is a "nice to have". The first rev of CAN in FRC had some major bugs and for me the first impression there was enough to write it off. On top of that, these interfaces are very highly abstracted out at the software level. I don't see how a student benefits any more from writing (-1,1) into an abstracted CAN interface than they do with an abstracted PWM interface.
As to everything else you ask for it's all quite reasonable and I feel quite doable. Perhaps not in the first prototype PCB but I'd like to think we test till we are sure that reliability is the prime concern.

One thing that does concern me personally is the issue of size. I've used the horizontal surface footprint of the Victors as sort of my idea of a guide. So I want to keep that surface foot print as much as possible. My idea of stacking modules would risk increasing the height from the top surface of the fan to the surface the unit sits on. To me, increasing that height in some cases by 0.5" doesn't seem a lot to ask. I may be wrong and others have a different opinion.

You are correct that when one merely uses the CAN bus like a glorified PWM that the amount of information basically communicated is similar. The real advantage of CAN for communications would come when you can really use the sensors, the fault detections and possibly a motion control environment on the electronic motor control. Then PWM and CAN are quite different. PWM doesn't give you a lot of choices to even upgrade the electronic motor control firmware through it.

Also there's a potential difference in performance. PWM needs to transit several cycles for a PWM interfaced electronic motor control to operate. It's possible that a single byte at high speed communicated down a CAN bus could start a series of events that's intricate on the electronic motor control.

Obviously any general purpose communications bus has an advantage of flexibility over strait binary I/O on a single wire. Whether that binary I/O happens to look like PWM or whether it's a classic digital I/O port ON/OFF state from the FIRST digital sidecar.

I seriously take your concerns about reliability to heart. I hope that the community will police itself about quality and not merely rely on FIRST approval as the cardinal level of achievement. Many of us are professional engineers here and I'm sure we know how to address this responsibility and can fix issues that effect it.

To help insure this I've been working on a website idea where anyone with a quality issue can report it without necessarily having to return the item. Obviously some errors will get induced with reporting like that, but I think we can statistically pull the information about any quality issues out of the noise. With all the flexibility it's important to me that if we have a bad module we know where they are, we see any reports of it quickly and hopefully can offer quick response to deal with it. I don't want to hide from any issues I want to deal with them straight on till the thing is very hard to break.

Also as I'm putting my personal money into this, if my choice were to ship something marginally unreliable for next year or wait till the year after. Even if it cost me more time and money I put reliability first when it comes to something like this. I won't let this be a rush. There's no need. There's still plenty of existing Jaguar stock at DigiKey and floating between teams that if we wait till next year for approval it shouldn't be a crushing problem.

Last edited by techhelpbb : 24-04-2012 at 11:46.
Reply With Quote
 


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 00:28.

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