Quote:
Originally Posted by garyk
A simple contributing factor may be crud on your battery terminals & leads (pigtail). This afternoon one of my students at 668 was adding pigtails to a new battery and scrounged some sandpaper from the school's wood shop with which to clean them to bright shiny metal. At 100 amps each hundredth of an ohm is going to cost you a volt.
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I would echo this with ensuring all connections are good, but especially your high current connections. Loose leads can lead to small, but important resistance elements. At the 100 AMP quoted above, the a 0.01 Ohm connection would have 1 Volt drop. During initial acceleration, you can pull as much as 500 amps (momentarily) from a 4 CIM drive. this same 0.01 Ohm would be 5V or thus get you a brownout.
As and LRI, I got to diagnose a few of these last year:
A few were loose PD connections (hard but not impossible with new PD board).
Loose main break connections (every year, even good teams will have loose connections here because it is easy to over-torque and break these as well).
Loose Battery cables at the battery terminals.
Poor battery/robot connection. Often this is either the springs being bent/loose in the connector, or damage on the terminals. Damage often comes from using alligator clamps to charge batteries, of shorting leads on batteries to test systems (this practice can lead to pitting/crud on the connection which shows up as resistance under high loads.
Besides these, the other times I saw brownouts were due to poor gearing. Often with mecanums. These robots were geared to go too fast, and spent the majority of their time in the stall half of the motors power curve. This would lead to hot motors as a symptom beyond the brown out. Often the brownouts would occur after the teams drove into an un-moveable object. This year typically it was trying to get totes from the landfill. The team would drive into the totes repeatedly trying to get a grip on a tote. Every time the drive stalled, they were pulling several hundred amps which would drop the voltage, then brown-out occurs which cancels motor which increases voltage which give control back which leads to stall which leads to high current which leads to voltage drop......
I did see the bad gearing with a couple of the kit-bot chassis too.
I saw a couple times were there were issues of binding in the transmissions themselves. Once corrected, the issue went away. for two of them they had miss-assembled the toughboxes which was causing the gears to rub.
I also saw brownouts due to batteries not being charged enough. Teams with only 2 batteries tended to wear down the batteries
As others have said, mostly mechanical or electrical connection issues causing high currents.