High Speed Encoder Problem

[Hugh Meyer]

The periodic rate can be controlled either by a fixed value or follow the driver station. If it is set to follow the driver station, which is the default, then the period time will vary because of being a windows app. If you set the period to a specific value the cRIO will maintain a very precise periodic rate. This could also be a source of your problem.

-Hugh

[Ether]

Originally Posted by Hugh Meyer

The periodic rate can be controlled either by a fixed value or follow the driver station. If it is set to follow the driver station, which is the default, then the period time will vary because of being a windows app. If you set the period to a specific value the cRIO will maintain a very precise periodic rate. This could also be a source of your problem.

-Hugh

... or you could read the actual elapsed time since the last sample, rather than assuming it is 20ms.

[Ether]

Originally Posted by Hugh Meyer

The periodic rate can be controlled either by a fixed value or follow the driver station. If it is set to follow the driver station, which is the default, then the period time will vary because of being a windows app.

Is this situation different at competition than at home?

Does the FMS follow the user's DS, or is it designed to send TeleOp packets at 20ms ?

And even if it is designed to send at 20ms (rather than following the user's DS), I guess the problem would still exist, albeit perhaps in a slightly different form, yes? no? still thinking about it.

[Mark McLeod]

At competition the DS packets are still sent by the DS.
FMS only orders the DS to change modes, but the DS has to send that command to the robot.
Any slow down in the DS PC will delay packets.

One of the checks for slow or lost packets is the CPU utilization on the DS.
(If in the Classmate Driver acct. use: CTRL-Shift-Esc -> Performance)
A saturated netbook can be a cause of lost and delayed packets. I see that pretty often.

[Ether]

Originally Posted by Mark McLeod

At competition the DS packets are still sent by the DS.
FMS only orders the DS to change modes, but the DS has to send that command to the robot.

Thanks Mark. That makes sense. I think I knew that at one time but forgot (face palm).

So Hugh's comment about DS packet timing variations caused by Windows scheduling of the DS applies equally at home and at competition.

[Hugh Meyer]

Originally Posted by Ether

Is this situation different at competition than at home?

Does the FMS follow the user's DS, or is it designed to send TeleOp packets at 20ms ?

And even if it is designed to send at 20ms (rather than following the user's DS), I guess the problem would still exist, albeit perhaps in a slightly different form, yes? no? still thinking about it.

Ether,

We use C++. There is a configuration variable that sets the periodic rate. If it is zero then the rate will follow the driver station. If it is not zero then the value entered will be the periodic rate. I tell our programmers to ALWAYS set the rate. We have not settled on a value for this year yet. We use a scope to be sure all of our traffic on the CAN bus is complete. This is detailed in other threads as you know.

As best I know FMS does not fiddle with this. Last year we used 100 msec and would show up on FMS as a long ping time. A few times the FTA would tell us about it, but it didn't seem to be a problem. I have some photos of the FMS screen showing this. I will try to find them and post here, but this season has been very busy, so don't hold your breath. :-)

Maybe we should start a new thread about this?

-Hugh

[Brian Selle]

Originally Posted by Hugh Meyer

Ether,

We use C++. There is a configuration variable that sets the periodic rate.

What is the class.method that you call to set this? Is it available in Java?

[Ether]

Originally Posted by btslaser

What is the class.method that you call to set this? Is it available in Java?

I'm going to start a new thread, as Hugh suggested, to discuss this. When it's up I'll post a link here.

EDIT: Here's the link:
http://www.chiefdelphi.com/forums/sh...d.php?t=103676