The Odrive uses 12 fets per motor, 4 fets per phase I assume arranged in an hour bridge configuration. Comparing it to other brushless drives like the VESC, they manage to make do with only 6 fets in a half bridge configuration. I assume there must be an advantage to using full h bridges vs half bridges, can anyone explain what it achieves? Does it outweigh the costs of doubling up on the fets, especially if we move to higher voltage rated components?
The Odrive uses a regular half bridge configuration but have 2 fets connected in parallel to get the resistance down to half.
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Yes exactly: It turns out that using 2x cheap mosfets was better value than using 1 good one.
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Silly me. I guess I should have looked at the schematics a little more closely instead of making assumptions.
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Makes sense for the 24V design. Do you think if you move to 48V you might move to a non-parallel layout? A quick perusal of the internet suggests like there are good options in that range. I don’t know all the relevant parameters but would something like this work? It would make for a more compact board as well.
Hm, I would probably go with 2x this part. The price to RDs on ratio (aka current handling) is about the same, but spread over 2 devices gives better surface area for thermal conduction.
Now that ODrive v3 is in production I think we should stick with ON-Semi and that footprint for now, but I think there are better solutions if we have the freedom to chose a part with any footprint: but I think it’s too risky to do that right now. There are quite a few “large” modifications I want to do some day, so ODrive v4 will happen at some point, and then we can optimise even harder, and also change the layout.
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