AB : DC motors - Voltage Vs. Output speed Vs. Torque - Precision Microdrives
This relation can be used to compute the steady state (constant speed - no acceleration) The graph above shows a torque/speed curve of a typical D.C. motor. Precision Microdrive explain how an increased voltage will increase the speed and an increased load will decrease the speed of a motor. The relationship between voltage, torque and output speed is a common topic of In relation to DC motors and gear motors, we will typically refer to the 'Rated.
In DC series motors, field winding is connected in series with the armature, i. Therefore, the Ta-Ia curve is parabola for smaller values of Ia. Therefore, after magnetic saturation, Ta-Ia curve becomes a straight line. The shaft torque Tsh is less than armature torque Ta due to stray losses.
- Understanding D.C. Motor Characteristics
Hence, the curve Tsh vs Ia lies slightly lower. In DC series motors, prior to magnetic saturation torque increases as the square of armature current, these motors are used where high starting torque is required.
As we know, flux is directly proportional to Ia, speed is inversely proportional to Ia. Therefore, when armature current is very small the speed becomes dangerously high. That is why a series motor should never be started without some mechanical load. But, at heavy loads, armature current Ia is large. And hence, speed is low which results in decreased back emf Eb.
Due to decreased Eb, more armature current is allowed. From the above two characteristics of DC series motor, it can be found that when speed is high, torque is low and vice versa.
Torque relationship to speed in a DC motor - Electrical Engineering Stack Exchange
Characteristics of DC shunt motors Torque vs. Hence, the Ta-Ia characteristic for a dc shunt motor will be a straight line through the origin. Without the ability to adjust the motor speed with the voltage whilst maintaining this constant torque, it would be very difficult to read and play this information at a steady rate.
This same principle can be applied to a wide variety of applications and is often critical to their successful operation.
Many of our DC motors and gear motors can operate across a wide variety of speeds and loads, this allows our customers to explore the possibilities of their project and usually reach a suitable solution with a single motor. How to read the Typical Performance Characteristics Chart The Typical Performance Characteristics chart appears on the front page of each of our data sheets.
This graph is an extremely useful tool that illustrates the typical behaviour of an individual motor.
Characteristics of DC motors
As we have previously discussed, many of our customers are looking for a motor or gear motor that will operate at a given speed and load.
One of the best places to find a solution is our online catalogue and we can always help to recommend suitable motors and discuss customisation options. This means that the data sheet values for speed are taken under controlled and specific conditions and do not represent the full capabilities of any single motor.
This is where the typical performance chart is a useful tool to view a wider range of the motor capabilities. The blue line on the Typical performance Chart above shows the speeds at which the motor will operate between a point of no-load all the way up to its stall torque approx.
For example; if a customer requires a steady speed and torque of RPM and 0. Rated load — 0. The image above illustrates this and demonstrates that the is, in fact, suitable for the customer based on their fixed speed and torque requirements. In this section, we will outline the relationship between speed and torque and explain the limits of each before considering the further effect of voltage on these parameters.
Please note that the motor must not be operated to stall as this will almost certainly lead to premature failure The no-load speed is the maximum output speed the motor will achieve at a given voltage.
At this point, the motor is running freely and under no external load Our DC motors and gear motors can operate anywhere between these limits before reaching stall. Whilst the performance chart illustrates how speed is affected when applying various loads, it does not indicate that the speed of our DC motors is also directly proportional to the voltage applied.
Characteristics of DC motors | raznomir.info
The theory behind this principle can be found here. In short, this means that we can control the speed of a motor independently of the torque and it allows us to maintain a steady speed for a variable load and also maintain a steady torque with a varying motor speed. This principle is employed to ensure that our CD player and cassette tape are played correctly and would probably include a closed loop feedback system that will measure the motor speed and adjust the driving voltage to either maintain a steady speed for a variable load or provide a variable speed for a fixed load.
Some common modifications are listed below: 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 motorsmany 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.
This can be a simple and cost-effective way to control the performance of our motors.
We have previously discussed these topics in more detail at the following links — 1 and 2 Material selection: The materials used can significantly affect the overall performance of your gear motor. Some of the potential options here are listed below Gear material: A common point of failure with micro gear motors 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 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 C Lubricants: Ambient and operational temperature largely affects the efficiency of a gear motor 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.