Falcon 500 Regenerative voltage. Should I be conserned that it might damage other electronics on my robot

I plan to use the falcon for a non-FRC use and will have a Jetson Orin nano in the same circuit as the motors. So If I have to stop the motors using an E-switch, which will cut off the motors power contacts. So what will happen if there are any regenerative voltage produced from the two falcons in my case. I plan to use my motors on Coast mode. but brake mode would be beneficial as I’ve read that the regenerated voltage gets used by the motor during brake mode.

The regenerated voltage is sent back to the main power source, meaning that if your battery is normally 12V it may spike to 14V or so when braking. This is beneficial in cases where you need to send a motor additional voltage at some point.

In your case, the safety of the Jetson depends on its electrical specs. What’s its max input voltage? If it’s higher than 16V you’re probably safe. Otherwise, you’ll want to put it on a voltage regulator.

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Normally the battery sort of sinks the load. If you disconnect the battery while the motor are spinning and a high inertial load, you will have a pretty good voltage spike. Sort of depends on how big the inertial load is. Maybe keep the jetson on the battery side of the Estop contacts so it doesn’t see spike from an Estop?

Using 3 phase AC motors and a VFD which is a lot the same as a DC brushless motor, we always put the Estop contacts between the motors and the VFD.

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You have two questions here…

If you are talking about a Falcon that is powered and is in brake mode, then there is no regeneration going on. Brake mode turns on all three low side switches and shorts the three motor leads together.

If you are talking about a Falcon that is spinning while it is NOT powered, there’s a pretty good chance that it will produce a voltage on the power supply terminals due to the three phase bridge’s protection diodes rectifying the motor voltage onto the supply lines. How much you get will depend on a whole lot of things… If you are planning to spin the motors while the battery is disconnected you should consider adding overvoltage protection to the DC power line on the motor side of the disconnect. It could be as simple as a high power zener or a low voltage TVS device. A bit of work to add a power transistor would give you a lot more power handling than a simple zener. You can also get crowbar circuits that are designed to do exactly this protective function; keep in mind that they delivery a HARD short across the power supply terminals when they trip, so you -really- don’t want the battery to trip it…

My testing with a SparkMax and a NEO showed that an un-powered SparkMax does NOT produce enough energy to turn itself on. IE, it doesn’t matter whether you put a SparkMax in brake or coast mode when the POWER IS OFF. It always spins freely.

Yes, I spent waaay too much time exploring brake modes and all four motor operating quadrants :wink:

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max input voltage for jetson is 19V

Yeah, that a way to save the jetson

That’s on the devkit board. Those boards do contain a regulator but it’s not good enough for keeping one powered on a robot. You need a regulator. My suggestion is a 19v boost regulator.

Yes. I’ve also planned to use a boost regulator for constant 12v supply to the devkit.

If you’re using a boost regulator for 12v… what is your power source?

Boost means to increase the voltage from the source. Buck means to decrease it. Regulators come in one flavor or the other or sometimes both at once. The most interesting values that you’ll need to know about are the maximum current, max power, and minimum input voltage.

Boost only regulators tend to have higher efficiency but you can’t run them with a voltage source with a higher output than the output of the regulator… so in the case of an FRC battery or even an 18v or 24v power tool battery, you need to make sure you are using a boost regulator to boost higher than 12v (~13 isn’t uncommon for fully charged FRC batteries).

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Fresh off the charger I’ve seen 14.5V so there’s definitely a margin

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I ran across this nice article on regenerative braking for brushless motors. It includes some discussion on Voltages too. Keep in mind that ALL FRC motor drivers us a simple “turn on all three bottom switches” braking mode. No intentional regeneration.

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Fresh of what charger😳

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The typical one Battery Charger 3 Bank 6 Amp Dual Pro RS3 with SB-50A Connectors - AndyMark, Inc

It is definitely possible to power a SparkMax by spinning the attached Neo. Multiple energetic freshmen from our team (myself included, when I was one) have learned this when pushing a robot too fast and it suddenly stops moving as the drive motors brake.

It is sort of a surface charge. Once you put a load on the battery it will quickly drop to below roughly 12.6-12.9 Volts which is considered full charge for AGMs at no load.


Not a boost regulator. It’s a power supply board that takes in 8V to 32V and outputs constant 12V at 7A rating. So this way the components past the power supply shouldn’t get affected by the voltage spike right?

Edit - My main power source is 12V 119Ah Lead acid battery

Probably but your bigger issue is going to be what happens when your voltage sags below 8v…

From experience, we try to pick regulators with a lower input of about 5v but prefer those that can get down into the 3-4v range.

So the power supply is programmed that if the input goes below ~10.5V for a said period it will initiate a timer that’ll eventually cut off the output. A typical DC power supply used in cars to power the computers in it.