# Bag motor current draw

We are using two bag motors with an 81:1 versaplanatery on our lift this year. We want to use two talon sr’s with two of our PDP’s 30amp ports. We were wondering if the bag motors would trip these breakers if we run them at 100%. Let me know what you think.

``````  Thank you,
~Walker Ward
FRC Team 2906~``````

Not enough information. You also need the pulley diameter and robot weight to solve for stall current.

Look into the JVN calculator.

BAG motors stall at 54A. That is 180% of the 30A breaker rating.

The breaker curves indicate they “must hold” at 175% for somewhere between 2.2 and 9.2 seconds. So if your mechanism jams, you’ll pop the breaker somewhere in there.

However, the stall torque (~3.5 in-lbf) multiplied by 81 , times two motors, gives 587 in-lbf. What is your winch diameter? If it is small (say 2 inch or less) then the robot’s weight will not get close to stalling two BAG motors with your gear ratio – so, if your mechanism does not jam, your breakers are safe.

I would opt for 40A breakers.

Drum diameter: 2.5"
Robot weight: 90lbs

We also have a 2.5 : 1 attached to it with a chain and sprocket

Using the JVN calculator, I got this:
https://gyazo.com/f085223434ef931f599551445b4a6d14

I inputted the parameters: Bag motor, conservative 100lb load, conservative 3" drum diameter in case of rope wrap, 81:1 versaplanetary, and 2.5:1 chain ratio for a total of about 200:1.

Then magic things happen and we get the output. The calculator is predicting 3 seconds to move 24 inches and a loaded current draw of 11A. That’s very light and easy, and definitely beneath the 30A breaker. With this in mind, you can change the parameters on the spreadsheet again and try to gear more aggressively to push the current draw close to 30A.

I only used one motor too.

Alright, sounds great. Thank you! We will look into it further to try to get the exact measurements.