# AMD Spreadsheet question, What is definition of "stall voltage"?

Is the stall voltage under the “ratio” heading in the AMD spreadsheet the voltage at stall (meaning about to backdrive) or the voltage needed to hold the specified weight in position (for example holding 40 lbs weight when the stall load is 100lb)? Or is there not a difference? The legend on the sheet says it is the latter.

The Stall Voltage input/output shows what voltage you need to provide the motor(s) with the given gear ratio to hold the given load in position. So that’s the second option. It’s useful for mechanisms with air-cooled motors that you want to hold at stall without burning the motors.

The At Stall input shows what ratio you need so that the motor will exactly stall with the load given. It’s only useful in a few cases and you can usually ignore it. You rarely want to design a mechanism so that it stalls with the given load because if you give the motor full voltage then it will just be able to resist the load, not move it.

Edit: also make sure you’re using the most recent version v3.4. There was an error fixed with the stall voltage calculation when using more than one motor in the mechanism.

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Sorry about the typo. I really like your spreadsheet and apologize for my ignorance, but which “stall voltage” is the one needed to hold up the proposed load and which is the one needed to hold up the maximum load the motors can lift?

No need to apologize, I’m glad people are making good use of it. “Stall Load” is the maximum weight this mechanism can lift at the voltage that you specified. “Stall Voltage” is the voltage needed to hold the specified load in place (ignoring the voltage that you specified).

For example, let’s say you’re designing an elevator with air cooled motors. You’ll want the Stall Voltage to be below ~4V and you want the Stall Load to be well above the highest weight you forsee the elevator needing to lift.

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You probably won’t believe this, but this is the first time I have ever understood this concept. I have read dozens of articles posts and they always go over my head, leaving me more confused than I started. Thank you for doing this.