Template:DCBLDCMotor Controls
Without any configuration, you can directly control your motor using the properties in this area of the program.
Target Velocity
This property allows you to control the power being supplied to your motor. At a constant load, increasing the Target Velocity will increase the speed of your motor.
Units of duty cycle are used because the controller uses a pulse-width modulated (PWM) signal to modify the average voltage across your motor.
The table below shows the result of different Target Velocity values when using a 24-volt power supply.
| Velocity | Result |
|---|---|
| 0.0 | The motor is not being powered. The average voltage across your motor is 0V. |
| 1.0 | The motor is fully powered. The average voltage across your motor is 24V. |
| -1.0 | The motor is fully powered (in reverse). The average voltage across your motor is -24V. |
| 0.5 | The average voltage across your motor is 12V. |
| -0.5 | The average volage across your motor is -12V. |
As shown above, Target Velocity does not guarantee a particular velocity in RPM, m/s, etc. (for this, view the Velocity Controller guide). Instead, it allows you to increase motor power, decrease motor power, or reverse the direction of your motor.
Related Parameters
It is important to understand the different parameters that may impact the Target Velocity property, these are listed here:
- When setting a new Target Velocity, the controller will intelligently accelerate (or decelerate) to the new target based on the Acceleration property. This allows for smooth and repeatable movements that improve power consumption.
- The controller can reduce the Velocity if the current through your motor exceeds the Current Limit or Surge Current Limit. This will help keep your system safe in a variety of situations.
- Other conditions such as Over Temperature, Energy Dump, E-Stop, and Failsafe may also impact your Velocity.
Other Considerations
There are two advanced methods of configuring your Phidget that relate to Target Velocity:
Please view the documentation on these topics for more information.
Current Limit
Current limiting is an advanced, yet easy-to-use feature that intelligently monitors and controls the current through your motor. This will help to keep your system safe in a variety of situations.
The datasheet of your motor will specify the following parameters:
- Rated Current
- Stall Current
We recommend setting your Current Limit to 1.1x the rated current of your motor. For increased performance from your motor, review Surge Current Limit.
You may choose to increase the Current Limit significantly above the rated current of your motor. In these situations, it is important to understand how heat will impact your motor.
The heating of your motor increases with the square of the current through your motor. Below is a table showing the approximate time to failure of a 24VDC motor with a 20A rated current and 100A stall current.
| Operating Voltage (VDC) | Operating Current (A) | Heating Rate | Approximate Time to Failure |
|---|---|---|---|
| 24 | 20 | Normal | N/A |
| 24 | 40 | 4x faster than normal | minutes |
| 24 | 100 | 25x faster than normal | seconds |
Many applications rely on a motor operating at higher-than-rated power levels. This is typically done at a low frequency which allows for adequate heat dissipation. Implementing a Surge Current Limit is one way to easily achieve this.
If your Phidget does not have the Surge Current Limit feature, you may consider dynamically adjusting the Current Limit yourself by monitoring the CurrentInput channel.
Small motors may have a stall current that is less than the minimum Current Limit of your controller. In these situations, your controller will not be able to provide current limiting protection. Consider using a more suitable motor controller or monitor the current yourself via the Current Sensor channel.
Current is directly proportional to torque. If you have an oversized motor that may cause damage to your system downstream, a purposefully reduced Current Limit can provide an extra layer of protection.
Over Temperature conditions may reduce your Current Limit.
