How to lower voltage drop?

What is the best way the lower the overall voltage drop?

Lower the voltage drop across what?

Well, right now we are just running 4 neos and 4 775 pros for our swerve and were having large voltage drops when we move them.

You can do a couple of things such as adding ramp rates and making the assembly more efficient to turn.

Current limiting on the SRXes for turning, adaptive current limiting on the Spark Maxes for propulsion are probably your best bet.

You will get a large drop when you turn motors on quickly. This video has some good info: https://www.youtube.com/watch?v=yO9xIVv8ryc

Really, the moral of the story is try to start the motors more gently (speed ramping for accel and deccel)

is there any example code of how to do ramp rates on the Spark MAXes

what programming language do you use?

using talons would require us to use CIMs instead of NEOs

1 Like

Yeah I didn’t think that through my bad.

1 Like

Anyways I will give an example in each language.

Java:
motorController1.setRampRate(0.2);
C++:
motorController1::setRampRate(0.2)
Labview:
Should be a command to setRampRate() like the ones above.

If you look at the CANSparkMax object in the REV docs, you can see it has a setRampRate function which takes in volts/s iirc, and you can set the adaptive current limit to reduce the drop with setSmartCurrentLimit(). Hope this helps!

You should also check your whole electronics system, especially the wires between the battery and PDP. All of the connections should be completely tight. If you can wiggle them, your connection is adding a lot of resistance to your system which increases the voltage drop.

2 Likes

Additionally, you might want to consider making a jump to 10 gauge wire (from the required 12) for all 40 amp connections, and from 6 to 4 or even 2 (for longer runs) on your battery wires. We’ve also been moving away from crimped connections where possible, but it requires a bit of soldering expertise. Edit: while this is technically “worse” than crimping, I feel that there’s generally less margin for error. We’ve had some bad experience with crimped connectors, even with the pull test.

Great suggestions from everybody so far. One more:

Check your battery voltage and age. Batteries fresh off the charger should be reading close to or even above 13V. In my experience, a battery reading 12.5V or lower when sitting idle is due for a charge.

Batteries that are a few years old, or those who’ve been heavily used during a previous season may look OK coming off the charger, but will not perform as well and will dip lower quicker.

Overall it would be useful to see current logs from all of the motors in your drive. Mechanical binding or friction can cause excessive current draw.

This.

Also: ensure all of your power wire crimps were made with the proper tools. You can also increase wire gauge sizes across the board (we used #2awg for main power) to further reduce voltage drop.

Proper crimping will provide a lower-resistance connection that soldering. A proper crimp cold-welds all of the (mostly copper) wire and terminal material together into a solid section. Proper soldering also forms a solid mass, but solder is less conductive than copper, and so results in a less-conductive joint.

More importantly - use a battery beak or similar to inspect the internal resistance of the battery. We frisbee anything over 0.017mΩ. A higher internal resistance means more voltage loss for a fixed current draw.