Drivetrain Calculator Help File: Brushed Motors

A full walk-thru of a drivetrain analysis using the drivetrain calculator is available here: Run Amok Drivetrain Analysis Example

Input Values: Brushed Motors

Operating Voltage Enter the voltage available to your robot drivetrain. If the motor file was loaded from the pull-down menu a suggested value is offered.
Stall Amperage Current consumed at full voltage with the motor shaft unable to rotate (stalled). Available from motor specifications.
Voltage Constant (Kv) RPM produced by this motor for each volt applied. See Converting Motor Specs
Torque Constant (Kt) Torque produced by this motor for each amp consumed. See Converting Motor Specs
Weight Class This is a pull-down list of common weight classes. Select the weight class in which the robot will compete and the next field will populate with the maximum weight allowed in that class.
Actual Robot Weight If the weight of your robot differs from the maximum weight for the class, enter the true weight here - in pounds. Do not include any magnet downforce here - that will be entered below.
Magnet Downforce Your robot may have magnets on the chassis or wheels to add traction on steel arena floors. This field is the additional tractive force (in pounds) created by these magnets. The default value '0' implies no magnets and/or no steel floor.

Magnet downforce will improve pushing power and acceleration, but will cause greater current consumption by the drive motors and require greater ESC and battery capacity. The calculator will show the effect of that downforce on current consumption, pushing force, battery requirement, and acceleration.

Motors-per-side The robot is assumed to have an equal number of drive motors on each side. For robot with 2 motors (1 per side) enter '1' here. Four motors (2 per side) enter '2' here, and so on.
Gear Ratio Gearing after the motor output shaft. For gearmotors with no additional reduction or increase enter '1'. See Optimum Gearing Tips for ratio selection help.
Wheel Diameter Enter the diameter of your drive wheels in inches.
Tire Coeff of Friction The friction coefficient of the tire, i.e. how 'grippy' it is. The default value '0.9' represents a typical best case. You may enter lower values for known 'slick' conditions.

The calculator assumes that 100% of the robot weight is supported by driven wheels. The coefficient of friction may be adjusted to compensate for robots where this is not true. Example: for a robot with 60% of the weight on the driven wheels, enter the product of '.60' and '0.9' which is '0.54'.

Average % of Peak Drain Estimate the average current drain as a percentage of the calculated peak load. Example: if you expect to spend 50% of combat time at full power and 50% at 25% of full power, enter (100+25)/2 = '62.5'. The default of 70% is based on average combat power usage.

Calculated Values

Torque Per Motor Torque required at the output shaft of a given motor to spin the wheel(s) driven by that motor (the "breakaway torque").
Amps Per Motor Amperage required to deliver the breakaway torque by a single motor
Theoretical Top Speed Top speed this drive train would reach at the operating voltage, given sufficient time and distance. Real-world speed will be lower due to friction and drag.
Total Peak Amps Total Amperage for all motors at breakaway torque.
AH Required - 3 Min Battery capacity required by the entire drive train to finish a 3 minute match at the % average drain specified.
AH Required - 5 Min Battery capacity required by the entire drive train to finish a 5 minute match at the % average drain specified.

About the Calculator

History The original Team Tentacle Torque/Amp Calculator was written by Steve Judd of Tentacle Combat Robotics, a highly respected combat robot builder and a selfless supporter of the sport. Steve died in 2010 after a long fight with respiratory disease; his loss is deeply felt in the community.
This Version Following Steve Judd's death, Team Run Amok began a series of updates to the calculator that include support for new motors, expanded help files, and revised formating. Most recently we have modified Steve's core program to create a separate version for brushless drive motors.
Other Versions has an unmodified copy of the original torque/amp calculator with an updated list of motors. You can find the SPARC version here: SPARC Torque/Amp-Hour Calculator