Conference Research

How to Control Those Extra Robotic Limbs You’ve Always Wanted

Recently, at an IEEE Conference, MIT researchers proposed a new control method which provides easier and more stable feedback that does not necessarily require existing limbs to control the artificial limbs.


Artificial limbs aim to help people by either replacing or assisting their original limbs to execute daily tasks. Usually, the installation of robotic limbs is set up and operated by other fingers or toes to control their functions, such as lifting and jumping for example. Recently, at an IEEE Conference, MIT researchers proposed a new control method which provides easier and more stable feedback that does not necessarily require existing limbs to control the artificial limbs, and Evan Ackerman updated his blog to follow this thread.

f1.PNGFigure 1

Figure 1 shows users demonstrating a prototype of MIT’s extra robotic limbs, providing additional support to the body (left and middle). To control the robotic limbs, a user wears a sensor vest that measures EMG activity of four pectoral and abdominal muscles (right). By learning to voluntarily contract those muscles, the user can position the limbs to help with physical tasks.

Evan is excited about the extra robotic limbs, thanks to their potential in enhancing his ski-boxing, as well as other practical applications. The main difficulty he encountered while using those extra limbs is control, because a person is coming out ahead if they are using one of their real limbs to control the fake one.

At the IEEE International Conference on Robotics and Automation in June 2017, a paper titled “Independent, Voluntary Control of Extra Robotic Limbs”, presented by researchers from MIT, proposed developing a control system for an extra pair of robotic waist-appendages that’s easy and comfortable to use, and doesn’t interfere with control of your real arms and legs.

The abstract of their presentation is the following:

Abstract: Current wearable robots assist their users by acting in parallel or in series to their natural limbs. We propose a different approach to wearable robotics, consisting of devices that provide users with additional, independent robotic limbs. We present a wearable robot prototype that can achieve these goals with an extremely light weight apparatus. In order to control additional robotic limbs as if they were a part of the user’s body, we need voluntary signals that are independent of natural limb motions and comfortable to measure. One suitable solution – explored in this study – is the use of muscle activation signals generated by the torso. We hypothesize that a human is competent to move the extra limbs voluntarily and independently without interfering with the natural arms and legs. We developed a wearable suit to measure these signals, and we tested three possible real-time control strategies linking torso muscle contraction to the motions of two simulated extra limbs. The experimental data show that the velocity control strategy yields highest motion accuracy, minimum muscular effort, maximum independence from the natural limbs and fastest learning rate. This control strategy has then been applied to the control of the physical robot prototype, worn by human subjects. All of the subjects achieved accurate (normalized tracking error < 0.5), independent (normalized natural arm motions measured by joysticks < 0.15) control of the robotic limbs.

This abstract provides twofold information. Firstly, it answers Evan’s problem, which is whether or not the old-fashioned operation of controlling extra robotic limbs or hands limits the function of his real appendages for other purposes. In the new method, the controlling operation involves using a small bit of exiting limbs, such as controlling an extra arm with your toes. Secondly, it solves the question of whether the human brain is capable of handling six individual limbs, instead of the usual four. Their solution involves hijacking a couple muscle groups in one’s torso and using them to control the robotic limbs.


MIT PhD candidate Federico Parietti and engineering professor Harry Asada explained their ideas, which Evan summarized as: “The robotic limb control comes from four EMG (electromyography) sensors: two stuck to your pecs, and two to your abs. Flexing your left pec rotates the left robotic limb forwards, while flexing your left abs rotates the limb backwards. It sounds a little bit awkward, but the question here is whether your brain can adapt to use new muscle groups to drive six limbs in arbitrary directions all at the same time.


The future aim for the researchers is to see what other muscle groups they can hack into. They suggest that the trapezius and latissimus dorsi, which are muscles in your shoulders and the middle of your back, might work. These muscles could be used to control extra degrees of freedom, or perhaps even more sets of extra limbs.

Technical Comment:

The idea of this paper is great, and may be extended to other fields to help humans accomplish tasks too dangerous or difficult with only four limbs. In addition, if you are a fan of Call of Duty, you may find out what is presented here is a realization of the multi-functional limbs in the game. At the first stage, people can apply those limbs as normal human limbs, which will learn the routine functions of our hands and feet. However, engineers can also give those artificial limbs extra abilities, such as super grip/leaping strengths that far outperform normal human limbs. This can be highly useful for people who work in special circumstances, such search and rescue personnel.

Another possibility for this new method to control artificial limbs, is to combine it with brain-machine interface (BMI) technology, so people can activate their extra limbs through brain signal directly, rather than the indirect muscle signal. This way, people can control their extra limbs just like their natural limbs in the future. The development of BMI still needs time, however, before being ready and accessible for industrial application. But it looks exciting to bring visual masterpiece into the real world.


Author: Bin Liu | Editor: Zhen Gao | Localized by Synced Global Team: Xiang Chen

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