When you’re sending a space rover over 40 million miles to Mars to search for previous signs of life, you don’t look to make cost savings by procuring low cost motor technology. That’s why NASA’s engineers installed high performance, ultra reliable maxon DC motors in their Perseverance rover, currently exploring the red planet, as well as in the ground-breaking Ingenuity drone - the first drone ever to fly on another planet.
Not every organisation has NASA’s budget. But then again, the relative cost of a premium DC motor isn’t beyond the financial power of most OEMs or end users who rely on them. Instead, the decision usually comes down to short-term procurement cost compared to the value that can be achieved long term.
Reducing size and weight
Compact DC motors must typically fit within a particular space envelope, and this is an area where innovation in motor design has a distinct advantage. Leading technology, such as coreless rotors and optimised windings, as well as multi-pole configurations, assists in generating a high level of torque relative to motor size. As a result, a much smaller motor can be used, or alternatively, more torque can be generated for the same space envelope.
For applications such as aerospace, ROVs (remote operated vehicles), and AMRs (autonomous mobile robots), weight savings are also critical. Lower mass can increase application dynamics, while reduced weight could enable a higher payload, or installation of additional battery power.
maxon recently received an ROV application design that included four drive motors, based on large, 42mm diameter designs, reaching nearly 200mm in length. The motors we specified were just a third of the size – and still outperformed the original ones in terms of torque generation, and we also integrated maxon’s compact miniMACS6 programmable multi-axis controller. Combined, this gave the customer a huge space saving, enabling them to double the battery size and dramatically increase the range of their vehicle.
Technology such as a coreless design, optimised windings, and more powerful magnets, also contribute to higher efficiency, another advantage particularly important for designers of battery-powered devices.
The value of enhanced reliability
Enhancing efficiency also leads to improved thermal management, which is also crucial to ensure motor reliability. A recent project involving a humanoid robot head required specifying over 25 motors to control features such as the eyes, nose, and mouth. Within such a space-constrained footprint, and with so many motors operating together, it was imperative to rely on designs that would run at a relatively low temperature. This principle applies not just to thermal management but covers all aspects of motor design that impact reliability, whether that be the bearings, electrical integrity, or sealing from ingress.
For applications where motor operation is critical, like drone flight or implanted medical devices, the need to ensure reliability is clear: motors used in these applications require product compliance, such as SN EN ISO 13485 for medical devices, EN 9100 for aerospace, and DO-160-G for aviation.
However, if motors are not mission critical, should engineers use inexpensive commodity motors? Depending on the application, opting for a durable motor that lasts ten times longer than a low cost design could help balance the long-term replacement costs. The expense of downtime resulting from a failed motor could also be significantly higher than the price of the motor itself.
Optimising performance
Premium compact motors are also often characterised by the precision and dynamism they can achieve. For applications that rely on high performance, many engineers will already specify appropriate motor technology. While precision is critical for applications such as surgical robotics, and dynamism is vital for systems like high performance automotive brake control, designers from widespread sectors can enhance their applications by optimising the specification of the complete drive system.
To achieve precision, technology such as a coreless motor design that removes cogging torque is typically involved, along with the right gear head, encoder, and precise motor controls. Meanwhile, to optimise dynamism and enable rapid changes in torque, speed, and position, a low inertia approach combined with responsive control is crucial.
Expertise in specification and support
Whether the requirement of the drive system is to optimise performance, reliability, design integration - or elements of various criteria - engineering expertise in support can be key. The potential to discuss design needs with a drive system engineer helps ensure the right specification is achieved, and advice can enhance the design to improve the overall application.
Customisation of the motor or gear might also be advisable to achieve specific characteristics or meet certain environmental conditions. Even for urgent demands, customisation of production-based designs can be quickly achieved – in fact, around 80% of maxon’s projects usually involve some level of customisation.
An engineering partnership
An engineering partnership like this is increasingly called on thanks to globally changing needs, including sustainability. Many OEMs, and end users too, require components that will last a long time, and that can be recycled or safely managed at end of life. Responsible material sourcing, as well as ethical manufacture and partnerships, are aspects that we’re now commonly asked to prove. Ultimately, these demands are helping to enhance sustainable practices throughout the entire lifecycle of electric motors.
Engaging with a drive system specialist that has a holistic approach to quality, from product design through to service support, ultimately improves application reliability and performance. For many applications, this can also increase value, long term.
