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Cogging torque in permanent magnet motors

Introduction Cogging is an undesirable characteristic of some permanent magnet motor designs. It's also known in stepper motors as 'detent' or 'no current' torque. Cogging torque is generated when the sides of the rotor teeth line up with the sides of the stator teeth within the motor. We can think of permanent motors as having a magnetic circuit as well as an electrical circuit, and when the rotor and stator teeth are aligned the 'resistance' in the magnetic circuit is at its lowest. Cogging Effects Therefore when you ro…

MTTF published results for vibration motors 307-103 and 307-104

Introduction At PMD we not only manufacture high-quality miniature motors and mechanisms, but we also design and make our own testing equipment. This means that we have a wide range of proprietary dynamometers, environmental and longevity testing equipment so that we can have confidence in the reliability of our parts. One of the instruments is a dedicated MTTF (Mean Time to Failure) testing machine, designed for vibration motors.  307-104 in the MTTF test machine Our vibration motor longevity testing machine can test …

When LRA's don't behave as expected (Part 2 of 2)

This blog post is part two of a 2-part series. Part one was a quick re-cap of how LRA’s work and how they are driven by dedicated driver ICs . This part is about what happens when the LRA’s don’t work entirely as expected with selected driver IC’s, how to diagnose this, and what to do about it. Introduction In part one of this blog post we explained that to get the most performance from an LRA, we need to drive it at its resonant frequency. The individual resonant frequency of an LRA will vary within a high-volume manufactur…

When LRA's don't behave as expected (Part 1 of 2)

This blog post is part one of a 2-part series. Part one is a quick re-cap of how LRA’s work and how they are driven by dedicated driver ICs. Part 2 is about what happens when the LRA’s don’t work entirely as expected with selected driver IC’s, how to diagnose this, and what to do about it. Introduction Linear Resonant Actuators (LRAs)   are becoming evermore popular in haptic applications. As an alternative to Eccentric Rotating Mass (ERM) vibration motors, they have several distinct advantages: they provide a faster r…

Vibrating Christmas Tree Instructable from our London Engineering Team

Introduction Christmas time in Northern European countries is a time of rest, feasting for the cold months ahead, and spending time with family. For our readers with Children, you’ll know all too well that keeping them busy and engaged is important. Also being engineers, Christmas is a great break to hack together some fun projects. This is a simple project that some of us have done with our own Children and can be assembled in the few hours after Christmas lunch, when all the adults in the family mysteriously fall asleep! …

Choosing an NTC for a current limited battery powered motor applications

Introduction On our last blog post, we talked about motor surge protection in battery powered systems . One of the suggested methods was adding a Negative Temperature Coefficient (NTC) thermistor, but we didn't explain how to choose an NTC for a project that includes miniature motors.  The first two main problems that we should take into account when designing a battery powered application are the short circuit and the over-discharge.  Fortunately, many batteries have an internal electronic protection circuit which prevents…

Motor Surge protection in battery powered systems

Introduction When considering a project including a miniature motor, the selection of the appropriate battery is crucial. Many variables may come into consideration, and a balance in regards of requirements, is often necessary. Li-Po rechargeable batteries are the preferred option for many of our customers when designing portable devices. A proper understanding of the battery risks, and how to overcome them, should be considered right from the start of a design brief. Li-Po batteries have a good charge-discharge characteristic and …

Connecting external actuator (vibration motor) to the M20-200 Haptics Kit

Introduction Our haptic feedback evaluation kit is an inexpensive tool for everyone interested in implementing a vibration alerting or haptic feature into a project. It allows application engineers and designers to understand the performance of the various actuators that we produce. It can also be used by inexperienced users, who have just started working in the fascinating world of haptic feedback. The M20-200 haptics evaluation kit is pre-fitted with 6 actuators of 4 different types . However the range of motors we produce is …

Decay Modes for Motor H-Bridge Drivers

Recently we had a few customers asking about driving our DC gear motors with H-bridges, and specifically, whether they would need additional fly-back diodes for each transistor in the bridge. As it happens - you don't, and there are a few options that can be arranged 'for free' my some small modifications to the timing of the drive signals to the transistors in the bridge. What is Decay? Decay is the re-circulation of current within a motor driver that uses pulse-width modulation (PMW). The inductive nature of DC motors means that …

New Haptic Feedback Evaluation Kit tutorial: Driving multiple LRAs

Our latest tutorial covers driving multiple LRAs from a single source We recently added a new tutorial for the M20-200 Haptic Feedback Evaluation Kit , which looks at driving multiple LRAs from a single source. Unfortunately, driving multiple LRAs at the same time is extremely problematic for a single haptic driver as many of the excellent features (such as auto-resonance) don't work when there are several LRAs connected in parallel or series. We cover this topic in full (including how to drive multiple ERMs) in this b…