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A fall from almost 20 feet height - the Spot robot of Boston Dynamics looks like a dead creature now. But, it will recover like an intelligent animal with the help of its smart motor arrangement and intelligent mechanism. The angle of the Spot robot leg is quite interesting. It’s a backward bend design. Ohh, now there is one more robot to compete with the original Spot robot! The maximum speed both the robots can achieve is almost the same, but what about this stair climbing challenge?
This forward bend robot collides with the stairs, but the backward bend leg gives it a clear advantage, allowing it to climb over stairs.
A funny reason why Spot’s engineer chose a backward bend design is because this type of robot can give you a handshake quite easily.
Let’s achieve this amazing Spot robot design starting from the simplest design possible. In this simple Spot design, each leg obviously needs two motors for its operation. These visuals clearly show the details of the motor connection at the hip joint. A planetary gear set is used in between the motor and upper arm. This is for torque multiplication. You can see how it operates the upper limb when you power the motor. Now, let’s see how the knee motor is connected. The stator of the knee motor is fitted with the lower end of the upper limb. The lower limb is now connected with the rotor of the knee motor. It’s an interesting arrangement. The upper limb is supported by a motor and this limb is supporting another motor.
Using these 8 motors, you can achieve any angle for the 8 limbs. We can now attach a controller to the robot and vary these angles randomly. Clearly, the robot won’t be able to make any meaningful movements if we simply feed it random angles. The Spot robot may even get stuck.
We can imitate nature and resolve this issue. Here, we are recording the angles of the limbs of a dog at different instances while it walks. Now, let’s feed the robot with these angles. Hurray! The robot moves forwards smoothly.
However, with this design the Spot’s battery charge quickly depletes. Let’s analyse why this is happening. When the hip motor rotates, it has to lift the weight of the upper limb, lower limb and knee motor also. During the leg lifting operation the various forces which are acting on the motor are shown here. You can reduce power required for this lifting just by moving the knee motor closer to the hip motor.
Since the knee motor weight is closer to the hip motor, the torque required drastically reduces. However, how to control the lower arm? It is far away from the knee motor. The answer is obviously a mechanism between the knee motor and lower limb. Before understanding this mechanism, let’s make a small design change so that the torque requirement will slightly be reduced. Replace all these bulky legs with thin - carbon fibre legs. Now, let’s get into the mechanism that the Boston dynamics engineers came up with to operate the knee joint.
To achieve this mechanism they first extended the lower limb behind the knee joint. Now, if the motor can give a linear motion to the tip of the lower limb, it will obviously rotate. The best way to produce linear motion from a motor is a ball-screw mechanism. For clear understanding let’s consider this bolt which is directly connected with the motor. When the motor rotates the nut and bolt rotates together as a single piece. There is no linear motion here. However, when you arrest the nut you get a linear output motion from the nut. In the robot ball-screw arrangement also there won’t be any linear motion if the ball nut is not arrested. This is why a carrier is used. The carrier arrests the rotation of the ball nut and the ball nut moves linearly. Perfect, now the lower limb is controlled quite accurately using a motor far away.
This forward bend robot collides with the stairs, but the backward bend leg gives it a clear advantage, allowing it to climb over stairs.
A funny reason why Spot’s engineer chose a backward bend design is because this type of robot can give you a handshake quite easily.
Let’s achieve this amazing Spot robot design starting from the simplest design possible. In this simple Spot design, each leg obviously needs two motors for its operation. These visuals clearly show the details of the motor connection at the hip joint. A planetary gear set is used in between the motor and upper arm. This is for torque multiplication. You can see how it operates the upper limb when you power the motor. Now, let’s see how the knee motor is connected. The stator of the knee motor is fitted with the lower end of the upper limb. The lower limb is now connected with the rotor of the knee motor. It’s an interesting arrangement. The upper limb is supported by a motor and this limb is supporting another motor.
Using these 8 motors, you can achieve any angle for the 8 limbs. We can now attach a controller to the robot and vary these angles randomly. Clearly, the robot won’t be able to make any meaningful movements if we simply feed it random angles. The Spot robot may even get stuck.
We can imitate nature and resolve this issue. Here, we are recording the angles of the limbs of a dog at different instances while it walks. Now, let’s feed the robot with these angles. Hurray! The robot moves forwards smoothly.
However, with this design the Spot’s battery charge quickly depletes. Let’s analyse why this is happening. When the hip motor rotates, it has to lift the weight of the upper limb, lower limb and knee motor also. During the leg lifting operation the various forces which are acting on the motor are shown here. You can reduce power required for this lifting just by moving the knee motor closer to the hip motor.
Since the knee motor weight is closer to the hip motor, the torque required drastically reduces. However, how to control the lower arm? It is far away from the knee motor. The answer is obviously a mechanism between the knee motor and lower limb. Before understanding this mechanism, let’s make a small design change so that the torque requirement will slightly be reduced. Replace all these bulky legs with thin - carbon fibre legs. Now, let’s get into the mechanism that the Boston dynamics engineers came up with to operate the knee joint.
To achieve this mechanism they first extended the lower limb behind the knee joint. Now, if the motor can give a linear motion to the tip of the lower limb, it will obviously rotate. The best way to produce linear motion from a motor is a ball-screw mechanism. For clear understanding let’s consider this bolt which is directly connected with the motor. When the motor rotates the nut and bolt rotates together as a single piece. There is no linear motion here. However, when you arrest the nut you get a linear output motion from the nut. In the robot ball-screw arrangement also there won’t be any linear motion if the ball nut is not arrested. This is why a carrier is used. The carrier arrests the rotation of the ball nut and the ball nut moves linearly. Perfect, now the lower limb is controlled quite accurately using a motor far away.
All there is left to do is add some absolute encoder and torque sensors, and this spot robot is ready to strut flawlessly and confidently into its next challenge.
At the beginning of this video, we saw a Spot robot have an accident. The solution to recover from this position is an interesting design change. Bring one more motor in and connect its rotor with the body of the hip motor. Looks like a crazy arrangement, right? This is what happens to the hip motor when the tilt motor operates.
When you operate all four new motors together, the legs widen, and the robot appears to be much more graceful. This smart robot is toppled now. Let’s see how it recovers from this position. The importance of the third motor we introduced - the tilt motor is pretty clear from this visual. To know more about this interesting motion, please check out our detailed video. Our robot is back on its four feet.
The walking pattern we saw so far is known as trot motion. Our beloved furry friends, dogs and cats, walk this way. Our Spot robot can do one more interesting walking pattern: crawling. Obviously, the robot will select this kind of pattern when stability is of utmost importance.
The Spot can also be fitted with an arm on its mounting rails. This arm includes six motors for 6 DOF and a gripper to grasp objects. To detect objects, a camera is placed inside the gripper like this. With this arm, it can easily pull the levers in industries or open doors in a people-filled environment.
The Spot robot we have developed is really smart. However, it is interesting to know that such a smart robot will fail during a simple stair climb down case due to the similar reason we explored in the intro. We have already explored that the Spot robot’s backward bend legs help it to climb up without any collision. This means the backward backward leg will collide with the stairs while climbing down.
Here’s a trick to solve this issue. Just program the robot to walk backwards during the climb down operation. This is why the Spot robot has a set of visual cameras on its back!
Now the genius part of the video - the main reason behind the selection of the backward bend design. Look at these wild animals, their leg angles are exactly opposite when we consider their longest limbs. Mr. Jackowski went ahead with a backward bend design for the Spot robot. We are able to walk because our legs drive a reaction force from the ground. The same is the case with the robot too. In a good robot design both the motors should resist this reaction force or participate actively in robot motion. Which design has this quality? To find out the answer, let’s do an experiment, but here instead of the electric motors we are using torsion springs. What do you think, in which design will both these springs get compressed?
I hope most of you have given the answer B. In the design A when I apply the force the spring 2 is not at all getting either compressed or stretched. But, in the design B, both these springs are going for a compression.
This shows that in the backward bend design both the motors will play an equal role. This is exactly why the Boston Dynamics engineers selected backward bend design for the Spot robot. You can easily find the reason behind it with this torque analysis.
At the beginning of this video, we saw a Spot robot have an accident. The solution to recover from this position is an interesting design change. Bring one more motor in and connect its rotor with the body of the hip motor. Looks like a crazy arrangement, right? This is what happens to the hip motor when the tilt motor operates.
When you operate all four new motors together, the legs widen, and the robot appears to be much more graceful. This smart robot is toppled now. Let’s see how it recovers from this position. The importance of the third motor we introduced - the tilt motor is pretty clear from this visual. To know more about this interesting motion, please check out our detailed video. Our robot is back on its four feet.
The walking pattern we saw so far is known as trot motion. Our beloved furry friends, dogs and cats, walk this way. Our Spot robot can do one more interesting walking pattern: crawling. Obviously, the robot will select this kind of pattern when stability is of utmost importance.
The Spot can also be fitted with an arm on its mounting rails. This arm includes six motors for 6 DOF and a gripper to grasp objects. To detect objects, a camera is placed inside the gripper like this. With this arm, it can easily pull the levers in industries or open doors in a people-filled environment.
The Spot robot we have developed is really smart. However, it is interesting to know that such a smart robot will fail during a simple stair climb down case due to the similar reason we explored in the intro. We have already explored that the Spot robot’s backward bend legs help it to climb up without any collision. This means the backward backward leg will collide with the stairs while climbing down.
Here’s a trick to solve this issue. Just program the robot to walk backwards during the climb down operation. This is why the Spot robot has a set of visual cameras on its back!
Now the genius part of the video - the main reason behind the selection of the backward bend design. Look at these wild animals, their leg angles are exactly opposite when we consider their longest limbs. Mr. Jackowski went ahead with a backward bend design for the Spot robot. We are able to walk because our legs drive a reaction force from the ground. The same is the case with the robot too. In a good robot design both the motors should resist this reaction force or participate actively in robot motion. Which design has this quality? To find out the answer, let’s do an experiment, but here instead of the electric motors we are using torsion springs. What do you think, in which design will both these springs get compressed?
I hope most of you have given the answer B. In the design A when I apply the force the spring 2 is not at all getting either compressed or stretched. But, in the design B, both these springs are going for a compression.
This shows that in the backward bend design both the motors will play an equal role. This is exactly why the Boston Dynamics engineers selected backward bend design for the Spot robot. You can easily find the reason behind it with this torque analysis.