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Unread 02-22-2018, 11:58 AM
Daleolgren Daleolgren is offline
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Brownouts , PDP and roborio

Our robot had been operating a week before final build day. Then three days before final day or robot experienced brownouts and max current draw .when on blocks it works fine.... when put on floor you canít turn without it dropping into a brownout condition. It only happens with the drive and no other aspects of our robot... We program I Labview. We checked out all connections and gearboxes and changed out all the drive controllers and also the batteries. The condition remains the same. Wondering if the roborio itself could cause this problem or the PDP possibility. Any help would be greatly appreciated.

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Dale Olgren
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Unread 02-22-2018, 12:12 PM
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Re: Brownouts , PDP and roborio

Sounds like it could be your drivetrain drawing too much current when loaded.

How many (& which) motors are you using? What gear ratio? What wheel size? How much does your robot weigh?
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Unread 02-22-2018, 12:15 PM
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Re: Brownouts , PDP and roborio

Check all your connections between the battery and Power Distribution Panel. A loose connection along that path can cause brownouts. Make sure all connections are tight
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Unread 02-22-2018, 12:15 PM
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Re: Brownouts , PDP and roborio

It would be helpful if you provide complete information regarding the type and number of motors used in your drivetrain, the gearboxes and gear ratios used and the size and type of wheels used.

What specific checks did your team do when you said your team "checked out all connections"? Did you check every single bolted/screwed connection? Did you check every single crimped connection? No exceptions.

Is it your radio or your RoboRio that is browning out? Is your robot wired correctly according to this diagram?
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Unread 02-22-2018, 12:16 PM
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Re: Brownouts , PDP and roborio

Can you easily turn the robot with one finger in this configuration?

* power off
* robot on carpet
* finger pushing on corner of robot frame
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Unread 02-22-2018, 12:25 PM
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Re: Brownouts , PDP and roborio

Something mechanical may have shifted. We experienced brownouts when a part in our drivetrain became misaligned and started rubbing against moving parts.

If you know which motors are plugged into which PDP slots, you should be able to go into the driver station log and see when exactly the brownouts happen and if any motors are pulling lots of current which should let you focus your debugging efforts more.
https://wpilib.screenstepslive.com/s...og-file-viewer

More info on high current draws and brownouts: https://wpilib.screenstepslive.com/s...24166/l/289498
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Last edited by Carly Buchanan : 02-22-2018 at 12:26 PM. Reason: add current draw link
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Unread 02-22-2018, 12:28 PM
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Re: Brownouts , PDP and roborio

Have you checked all the screw terminals between the battery and PDP? When we first ran our competition robot, we experienced brownouts when running our arm which we hadn't seen at all after weeks of running our practice robot. It turns out the PDP screw terminals were both loose, which significantly increased internal resistance and voltage drop.
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Unread 02-22-2018, 12:31 PM
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Re: Brownouts , PDP and roborio

Quote:
Originally Posted by Daleolgren View Post
.... when put on floor you can’t turn without it dropping into a brownout condition.
Another possibility is that your aspect ratio (wheelbase to track) is too long. A long, narrow skid steer robot cannot turn well because the scrub friction that is, friction opposing rotation) is greater than the drive traction when you attempt to turn. This is why long robots typically have six or more wheels, with the center wheels placed lower than the plane between the corner wheels, so that only two pair of wheels close together carry weight at a time.

How many wheels do you have, and what are the track width (distance from left wheel to corresponding right wheel) and wheelbase (front axle rear axle on same side) spacing?
If you have more than four wheels, how much "drop center" do you have for the wheels between the corners, and what type(s) of wheels are you using?
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Last edited by GeeTwo : 02-22-2018 at 02:24 PM.
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Unread 02-22-2018, 01:00 PM
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Re: Brownouts , PDP and roborio

We use 4 cims with planetary gear boxes 8-1 ratio..... we used 6 inch wheels and then tried 4 inch all the same results.... checked all connections . We started with victor sps and then sparks..same result... checked all alignments... everything is free with no binding.....our robot weighs 88 lbs
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Unread 02-22-2018, 01:02 PM
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Re: Brownouts , PDP and roborio

Checked all connections every thing is tight no loose wires
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Unread 02-22-2018, 01:09 PM
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Re: Brownouts , PDP and roborio

We checked all crimps and wire connections ( continuity and load ) ..... the roborio is brownout ..... we have been having issues with our radio having to be reconfigured... but we switched out with several different ones and eventually they all required reconfigure... the power issue happens whether wifi or tethered
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Unread 02-22-2018, 01:13 PM
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Re: Brownouts , PDP and roborio

Yes
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Unread 02-22-2018, 01:18 PM
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Re: Brownouts , PDP and roborio

Quote:
Originally Posted by Daleolgren View Post
We use 4 cims with planetary gear boxes 8-1 ratio..... we used 6 inch wheels and then tried 4 inch all the same results.... checked all connections . We started with victor sps and then sparks..same result... checked all alignments... everything is free with no binding.....our robot weighs 88 lbs
With an 8:1 ratio and 6" wheels you should be going about 17FPS, which is a little on the edge for spinning in place with skid steer.

How did you check for alignment?
How did you check for binding?

Put the robot on blocks and run it forward as fast as it will go. Then look at the logs on the DS. You should see the motors pulling less than 2 amps. Any motor drawing significantly more current will be an issue under load.

Also, have you checked your batteries. A battery beak or local automotive / battery place should be able to tell you if the battery is good. A fully charged battery should read around 13.2 V on the DS with a small load (robot powered) on it.
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Unread 02-22-2018, 01:24 PM
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Re: Brownouts , PDP and roborio

Quote:
Originally Posted by Daleolgren View Post
Checked all connections every thing is tight no loose wires
Make sure your PDP main power inputs have the right lock washers. They my look tight, but may vibrate and disconnect in the mS time range and cause the Rio to brown out as power droops.

Do you have any in line power connections (Anderson PowerPoles, etc)?

As someone else said, use the current measuring for the PDP smart dashboard.

Or - disconnect everything else and get down to just your drive train or just a motor and slowly start adding items back until you find what's causing it.

Also - did you load test your battery? Could be a bad battery or battery lead connection.
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Unread 02-22-2018, 01:55 PM
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Re: Brownouts , PDP and roborio

Quote:
Originally Posted by Daleolgren View Post
We use 4 cims with planetary gear boxes 8-1 ratio..... we used 6 inch wheels and then tried 4 inch all the same results.... checked all connections . We started with victor sps and then sparks..same result... checked all alignments... everything is free with no binding.....our robot weighs 88 lbs
1 Check your chain tension

2 Are you using a drop center?

3 What kind of wheels are you using?

4 Check to make sure your wheels and sprockets/belts are square

This summer we had most all of those problems and fixing them would have solved our problems. Drop center may not be as important seeing as you are only 88lbs. Hope you can figure this out!
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