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 can’t 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.

Thank You,

Dale Olgren
Mentor / Co-coach Team 4375

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?

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

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?

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

  • power off
  • robot on carpet
  • finger pushing on corner of robot frame

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.

More info on high current draws and brownouts:

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.

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?

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

Checked all connections every thing is tight no loose wires

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


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.

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.

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!

We are using 8 inch inch wheels with 4 to 1 direct drive planetary gear boxes on each of of our 4 cims … so we have no chain or sprockets… previously I miss stated the ratio and wheel size… we do plan to order add on reduction to actually make it 8 to 1 ratio… the wheels are softer rubber ( grey ) smooth

Yeah, it makes sense that you are browning out. That’s 46.5 ft/sec free speed. Waaaaaayyyy too high for the CIMs, they don’t have enough torque to handle that. Even 8:1 on 8inch wheels is pushing it if that’s your only speed. You probably want to go for 12:1 or so.

4:1 with 8’’ wheels will not move at all, with 6’’ wheels is still almost guaranteed to cause constant brownouts, and with 4’’ wheels it will likely do so while turning or accelerating at low speeds unless the drivetrain is exceptionally efficient or other precautions are taken.

I would not recommend gearing for above ~14 ft/sec (theoretical no-loss speed at 12v) unless you absolutely know what you are doing.

Direct drive to each wheel with 4 CIMs sounds like you’re either running 4 wheel drive with sticky wheels or mecanum. Once you get the gear ratio down to something sane like 12:1, mecanums should turn fine no matter where the wheels are, unless you have them installed backwards. 4 sticky wheels will need a wide wheelbase to turn well, though.

Can you post a picture of the bottom side of your robot for us to look at? Don’t open the bag, though. Even a picture through a bag will probably work since we just need the approximate wheelbase aspect ratio.

So we use 6"omni in each corner we have the versa clamping style gear boxes and we do 5.14:1 reduction so far we haven’t browned out at all. But will we be seeing brownouts later in the season