Our team is looking at doing an offseason robot that runs using 2 FRC batteries in series.
We are planning on using some brushless motors (not NEOs) and some 775s.
I know that Talons are rated for up to 28 volts, but the RoboRIO, PCM, and PDP are only rated to 16 volts
Can we run the RoboRIO on a 12v regulator and connect it to a Talon running on 24v with CAN?
What other issues might we run into when running 24 volts?
I think the first question has to be why are you running your offseason robot on 24V? There are a good number of downsides, and you haven’t given any benefits. Is there a reason you have to use 24V?
Edit to add: there’s no reason I can think of why you can’t use a buck-boost converter to lower the 24V main power to 12V input for the roboRIO. Why you’d want to…I don’t know.
I also question the motivation to go series rather than parallel, but assuming you did, you could still branch off a 12V supply from one battery, to power the things that need it.
Most off that stuff is commoned to the 0V. So you probably be good running the 12 volt stuff off the first battery. Or use a third battery commoned to the 0V for the electronics. It could probably be smaller or even Li-ion. You obviously want to provide over current protection to the stuff running at 24 V by something other than the PDB. Lots of solutions for that. You can start at powerwerks web site. Not sure if you are planning to run the 775s at 24V. I would talk to Vex before doing that. They have pretty good customer service and will give good advice.
I can’t speak for the OP reasons for wanting to use 24V, but you get better power densities and efficiencies at the higher voltage.
Just to riff off of what @FrankJ posted, you can tap off, but there are issues depending on what your 24v load is vs your 12v load. Battery packs in series are very dependent on how well they are charge matched.
It’s extra weight, but you might want to consider a 12v power source and a 24 volt power source. That also helps you with not accidentally dumping 24 volts into something that isn’t going to like it.
I realize I didn’t explain why I want 24 volts.
I want to run a Torque Boards electric motor off of it. This is not for the 2019 robot, this is for a project that has more powerful motors on the drivetrain, as well as 24v solenoids (which I know the PCM takes care of, but anyways)
We want to make a Tank robot, but also use the FRC control system. The motors we want to run work better at 24v. They’re actually rated for 44v, but we decided that 2 half the power of the motors is good enough for our application.
It looks like running two seperate systems might be the way to go. The 775 motor doesn’t need to run 24 volts like we want the drivetrain to.
If your 12 V loads are fairly small (RoboRIO, radio, etc., no motors), you could also use a DC-DC buck converter to regulate your 24 V bus down to 12 V.
So as other people have said, there are ways to make it work. But you should really think about whether doing this is the best use of your off-season time. “Practice how you play” isn’t just true for driver training; it goes for mechanical and electrical design as well. Using items that you won’t be able to use during the season won’t help when you need to do the same thing for next year’s competition robot. Off-season projects should be practice for the real thing; the more you deviate, the less prepared you’ll be when the time comes to build your robot for real.
Can runs at 5V max (differental voltage) so if you run a talon at 12V or 24 V or any other controller at whatever voltage does not matter the circuitry inside the controller takes care of that. Now PWM if you need it is 5V too and the same holds true for that. Just make sure everything is properly grounded cause the higher the voltage the more a “floating” ground can cause damage. The advantage of running at 24 V is that if you want for example put out 120 Watts of power at 24V you need 5A at 12 V you need 10A now that has implication on wiring and electrical components. Most transistors and MOSFETS are rated at a higher voltage anyway (usually >50) so the critical thing becomes the Amps. So a Talon for example can put out 2x the watts (or HP if you want) at 24 than at 12 with the same heat dissipation and current as the output stage is a H bridge and PWM and so the drop over the MOSFET is in relation to the current and not power
Generally I agree, however there are certainly reasons and scenarios for building something with some non-FRC legal parts involved. For example, if building a T-shirt cannon robot, you may want to utilize pneumatics with a working pressure over 60PSI. In this case, they feel they need a more powerful drivetrain… without knowing why they chose that route or what problem they are trying to solve, I don’t think we can really give advise on whether or not this is the correct path - better to ask questions with a goal of helping to determine if it is the correct path or if they are overcomplicating it.
And plumbing and valves significantly larger than FRC-legal!
Someone mentioned to me they’d had issues with SRX motor controllers on a 24V robot. Apparently they fail sometimes but I don’t know the exact scenario.
SRX’s should be fine at 24v.
They will turn off an led above a certain voltage, though. That’s oftentimes mistaken for a failure, but it’s by design.
I’ve run Talons at 24V before, they’re fine for it.
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