# How much torque is needed to mix melted marshmallow with rice krispie?

I am designing a robot to make rice krispie treats!

More specifically, I want to use a fork to mix the melted marshmallow with rice krispie. I am currently specing out the motor, and since marshmallow+rice krispie is not a typical engineering material, I am struggling to find out theoretical viscous force for my mixture, which I think is the main force that my motor needs to overcome. Alternatively, I want to create this scenario in lab and find out experimentally how much torque I need to apply and for how long in order to thoroughly mix the two. One idea I have is to set up a jig that mounts a high torque stepper motor to the fork, spin it about its tall axis, and gradually increase current to observe mixing results. But this method will take some time to set up.

Do you know a quicker and more accurate way I can figure out how much torque I need to apply in order to mix these two experimentally? Or do you know a way to figure this out theoretically without needing to build anything? Welcoming creative solutions!

• You can probably just eyeball it in your mind's eye. Imagine you stirring it at your desired speed with a crank on your end and the same type of mixing end you are going to use on the other end. Make a mental note of how long the crank is and the feeling of force on your hand. THen imagine how much force you need to hold in your hand to feel the same. Torque = Radius x Force. If you double the speed, the torque should be increased by four times: a squared relationship. – DKNguyen Aug 12 '20 at 16:43
• is melted marshmallow a rheopectic, newtonian or thixotropic fluid? – Solar Mike Aug 12 '20 at 17:52
• You 100% need to do this experimentally. But, before you start trying to measure torque etc - you need to just experiment with the best mixing action. it almost certainly won't be 'around in circles'. Look at how existing industrial mixing machines or even domestic stand mixers move... – Jonathan R Swift Aug 12 '20 at 18:20