Keep in mind that if you are lifting a proportionally lighter load, the motor will be able to turn proportionally faster. You need to also account for the weight of the arm itself which acts as a point mass at around half its length (or center of gravity). With these results, we know with a gear ratio of 3:1 the CIM can easily supply the torque needed at over nine times the required minimum speed! We can use a higher ratio and still move plenty fast and raise the lifting capability as needed. For example, if you want to use a CIM motor to lift a 1kg mass at an extension of 0.5 meters: If you need the arm to move at a minimum speed of one rev/sec at that loading, the motor needs to be geared at 60 rpm or faster when generating this torque (‘or faster’ since torque increases as it slows down). For example, if you want to move a mass of 1kg at the end of a 0.5m arm, then you only need 0.5kg*m of torque or 4.9Nm minimum (gravity applying a force of 9.8N/kg). This means that you simply want to know if you are gearing your motor to a suitable torque for moving the load at your ideal speed. Then, take advantage of the fact that, with electric motors, speed and torque are inversely proportional. All you need is the motor torque and length of your lever arm to determine what force can be lifted. The force/acceleration calculation from the previous section can be reused by making friction = 1 for positive engagement. Robotic Actuator CalculationsĬalculations for lifting masses on an extended arm are much more straightforward to do by hand. However, its battery capacity calculator assumes that you have a coefficient of friction of one and that the motor is basically operating at full load 100% of the time so it vastly overestimates capacity. If you need your robot to work on slopes and not just flat ground, this Drive Motor Sizing Tool will help you out as well. There, you can find a great article about optimizing the gearing for a robot drivetrain and a combat robot drivetrain calculator that makes it easy to determine what wheel diameter and gearing is required. One great resource can be found at Ask Aaron. So (in real life) with a load, you run close to the peak efficiency point. You will also likely know your wheel size from your design, meaning you can know what geared rpm you’re looking for.įor use in a robot drivetrain, you determine your gear ratio by choosing a target speed and gearing it to be slightly faster at the no-load RPM. When designing your bot, you need to know the ballpark for how much it will weigh and what top speed you want, and if it needs to carry any extra weight lump that in as the robot weight. You can also take some shortcuts by assuming you want to operate a bit below max rpm for a given motor and ensure it has enough torque to accelerate your robot at a semi-reasonable pace at startup. While knowing these calculations is a good way to get a sense of the size of the motor needed and a ballpark for what stall torque is needed, using a ready-made calculator is far easier than working out these numbers for every motor you look at.
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