Quote:
Originally Posted by Monochron
Do you have a good way to estimate load for a system? For instance, if you were building a flywheel for the Fuel, what is appropriate load? And would that load chance as you increase throughput?
And just to clarify, using the flywheel example, if you reduce voltage to a motor at this gear ratio to allow headroom to keep your flywheel speed steady, would this change the required gear ratio? Or are you still able to hit peak power with this given ratio at each voltage? My question is really, is the ratio needed for peak power at 12V the same ratio needed for peak power at 6V?
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For a system like an arm or a conveyor belt, you can usually find the load using a simple free body diagram. For a flywheel, however, the load depends on a lot of factors (including ball weight, wheel MoI, compression, ball compressability, wheel compressability, time in contact with ball, etc). You can guess the load for a given set up by gearing the flywheel 1:1 and measuring how much the wheel slows down when a ball is launched, but AFAIK there is no good way to calculate the load on a flywheel. I usually set up a prototype with an easily-changeable ratio (e.g. easily accessible belt/chain/gear reduction or VersaPlanetary) and change the gear ratio until I'm satisfied with the top speed and spin-up time.
In an ideal DC motor, doubling the voltage doubles the free speed, stall torque, free current, and stall current, and quadruples the max power. This also doubles the torque where max power occurs, so your gear ratio should be halved to remain at the max power point on the motor curve. Halving your gear ratio, combined with a doubling of the free speed, will result in a 4x increase in speed at that point. Conversely, if you only provide your motor with 6V instead of 12V, you should double your gear ratio to remain at max power, and your speed at that point will be quartered. JVN's first calculator allowed users to specify input voltage, but he took away this ability in the later versions. I think this is an important feature to have, so I will add it into the next version of my spreadsheet.