DC motors : Voltage Vs. Output speed Vs. Torque – AB-032 Released

N/L speed and Stall Torque on Motor Performance Graphs

N/L speed and Stall Torque on Motor Performance Graphs

Our latest Application Bulletin covers a topic that our sales engineers are frequently covering with customers. In AB-032 we cover the inter-dependent relationship between drive voltage, output speed and motor torque. You can read the full bulletin for an explanation of the fundamentals, but in the spirit of offering practical advice on our blog and monthly newsletter, here is a section regarding what we can do to alter the motor performance to meet your needs.

There are several methods in which the performance of a motor can be customised, whether this is a highly customised solution tailored to a customer’s needs or a simple adjustment to how the motor is operated. Some common modifications are listed below:

  • Windings: By modifying the number of turns in the motor coils and/or the cross-sectional area of the wire used, the terminal resistance, operating voltage/current and terminal inductance can be manipulated. This means that both the electrical and mechanical performance of a motor can be tailored to a particular specification quite easily.
  • Gearbox ratios: Gearboxes are an effective method of accurately altering DC motor performance using one or more gear stages. Whilst we do supply stock reduction gear motors, many of our customers like to develop their own set of gears. If you would like to experiment with your own gear chains, simple gear equations can be found here. However, we can offer custom gearboxes and stock part modifications so please feel free to contact an engineer if you would like to discuss your requirements and the options that we can offer.
  • Driving voltage: This can be a simple and cost-effective way to control the performance of our motors. There are several ways in which you can adjust the driving voltage to your motor, including PWM and even dedicated driver IC’s. We have previously discussed these topics in more detail at the following links – and 2.
  • Material selection: The materials used can significantly affect the overall performance of your gearmotor. Some of the potential options here are listed below.
  • Gear material: A common point of failure with micro gearmotors occurs at the final gear stage. This is the point at which the largest force is exerted when a load is applied to the motor. In this instance, the gear can fail long before the motor stall torque is achieved and the potential capabilities are not fully utilised. If this is the case, stronger gears can be added to the final stage(s) so that a higher torque and wider performance range can be achieved. In practice, this has been used with the 206-108 which stalls at roughly 17mNm due to gear failure. This is characterised on the characteristics chart by an abrupt halt in the torque-speed line long before stall (0 RPM) is approached. By inserting a metal gear at the final stage a torque of roughly 34mNm is achieved, doubling the torque capabilities of the motor and opening up a wider range of possibilities. This was given the part number 206-10C.
  • Lubricants: Ambient and operational temperature largely affects the efficiency of a gearmotor and the overall performance achieved at the output shaft. Whilst the electrical efficiency of the motor can often increase at low temperatures, the gearbox efficiency and effectiveness of the lubricant can reduce such that the overall performance is lessened. A common method of reducing this effect is to use a specified cold temperature lubricant. This can increase the efficiency of the gearbox and therefore the performance of the motor and the output. This means that the temperature range listed on the datasheet is not an absolute limit and there are several ways that it can be extended. If there are any queries, Precision Microdrives engineers will be happy to help out.
  • Encoders: If you require greater control of your gearmotor or use it within a positioning actuator, you may require an encoder. This is a typical modification that we can offer ranging from simple tachometers for speed measurement, incremental encoders for single reference positioning, all the way to absolute encoders for exact positioning of the output shaft. These encoders can also be used in closed loop control to maintain speed for a varying torque, vary the speed for a steady torque, or any combination of the two (examples discussed earlier in this article). Please do get in touch with a Precision Microdrives engineer if you would like further information on what we can supply.

Any combination of the above can be used together to achieve a wide variety of outputs from our gear motors. So, even if you cannot find a gear motor performance chart that meets your specification, please feel free to contact our engineers as there are a variety of ways that we can look to meet your requirements.