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There are two ways that stall currents are usually handled: Most commonly you just over rate the controller enough to deal with peak currents. This works fine unless things are heavily overvolted or you're using particularly large motors. The other alternative is to use current limiting as you say, where you read off the current and ramp down the input until it comes back down below the limit. Charles Guan has many pages on the development of the Rage Bridge which is definitely worth a read; this uses current limiting so you can get an idea of how it works. For featherweight motors though I'd advise just over rating the controllers enough to handle what you need. A good page to read for that is Chuck McManis' MOSFET rating page , which gives you an idea of what FETs you need. For an 18v 775 you'll probably want a continuous rating of about 60A or near enough.
As for components, I'd advise using HIP4028 driver chips to drive the MOSFETs; I tried using other things but this is by far the easiest. Few things to watch out for though with the HIP4082; need to run them on at least 10v (I use ~15v), have a PWM frequency of >1kHz, and don't let the high side signals go above about 98% duty cycle else the charge pump will run out of juice. Probably won't make much sense atm but hopefully after doing some research you'll see what I mean :L
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Some really great information both in your post and in the links, thanks a bunch! I'll take a look at the driver chip you recommended, although we were planning to use an ATMega and write our own firmware, mainly due to wanting to incorporate a few quality of life features, like a gyro to help steering. Might be a good idea to make a barebones version first though and worry about fancy features later.
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The driver chip needs to be driven by a microcontroller; all it does is interface between the microcontroller and the MOSFETS. The stuff in my previous post is mostly stuff I wish I knew when I started; hopefully should save you from a lot of the mistakes I made during my ESC's development
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Ahh right. Sorry I jumped to conclusions that it was a replacement for a microcontroller! Lots of reading to do for me this weekend I think :)
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Rapidrory, where did you buy your HIP4028's from? Having a hard time tracking them down online.
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Awesome thanks. They seem like they are pretty straight forward to use. One thing that is confusing me though is that their BHS (pin 15) is getting connected to the main circuit power, surely this would fry the controller with such high currents. I'm sure I'll figure it out though. Thanks again!
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That's a high impedance sense line, so no current is going to it (It's the reference voltage for the charge pump). It's isolated up to 80v (Hence the 80v rating) so the controller won't care what sort of currents are flowing through the H bridge as long as the voltage doesn't exceed 80v (which it won't in your application).
One thing the data sheet doesn't make very clear is that you'll need some ~10 ohm resistors between the driver chip and the MOSFET gates (gate resistors). Keeps the peak drive currents to below what the chip is rated for (1.25A). Also stops resonance in the drive lines and the like but you don't really need to worry about that; just fit some 10 ohm gate resistors and you'll be fine :L
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Ah perfect, all makes sense now! Let the breadboarding begin :)
