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zurczurc posted an update 4 months ago
Bonjour Gael, il y a 2 ans, j’ai construit mon Inmoov et je me suis arrêté avant d’assembler mes jambes, car j’espère qu’un jour les jambes motorisées d’Inmoov seront disponibles. Gael comptez-vous poursuivre le projet Inmoov et terminer les jambes motorisées? Comme je suis chez moi à cause du COVID-19, j’ai l’intention de reprendre le projet et de terminer. Je vous remercie.
The legs are a very difficult part to make.
They need to be strong, lightweight and fast.
There is also the issue of balance which is also very difficult.
Gael has released the static legs and they do hold the robot up.
Just a note, in order to achieve the strength required to support the rest of the robot, some of the components exceed the 120mm x 120mm x 120 build volume he has managed for the rest of the robot.
There are a number of makers working on this problem of motorized legs, and you can be sure that when they have been successful, they will share how it works with Gael. The real trick is in creating something where the parts are easy to get all over the world. That task is harder than you might think.
What has made the rest of the robot popular, is its easy to print and the bulk of the parts are not expensive, unless you choose to get more expensive parts 🙂
The platform also lends it self to modifications, some of which have been worked back into the official list of parts.
If you find yourself with a lot of spare time, maybe have a look at the problem and see what kind of solution you can come up with?
If you have questions about different aspects of the challenge, by all means ask.
Also have a look through the google forum, as the subject has been looked at before.
If you do choose to tackle the problem, I wish you all the best of luck and look forward to seeing the results.
In the list of modified parts there are my contributions. At the moment the money is tight, but I will see more calmly, I am very good in hardware but not in mechanics.
I understand the mechanics, but are not very good in the cad design.
Within the static legs that Gael has created, he has re-used parts from his early prototypes of a motorized version.
I would love to see the rest of the parts around the knee for the motorized version as what I have seen so far and the video on YouTube of the testing of the knee look very promising.
Not so convince on the ankle or the foot, but this is an early prototype.
Due to the weight the leg components will need to carry, I think all the joints will need to have bearings in them, but for early testing, we may be able to get away without them.
During construction of the hand, it was recommended that 200lb fishing line be used like tendons in the fingers. I do not see why we cant use the same left over line doubled up for the ankles, with the motors located in the tibia.
There are three axis we need to allow for in the ankle.
If we establish a naming convention such as Pitch, Roll and Yaw, where:
Pitch is the movement that the toes move up and down.
Roll is the movement where the foot rotates along the length of the foot.
Yaw is the rotation where the toes move left or right.
The pitch and Roll are not difficult to do, a universal joint at the ankle, will do this nicely especially when the motors are in the tibia and tendons are used, But Yaw makes this more difficult.
But this I was thinking, why does the Yaw have to occur at the foot?
Why can we not rotate just below the knee and rotate the hole of the tibia, ankle and foot?
This is just my thoughts on this problem.
I was thinking more about walking robots the last week or so after seeing a robot elbow design using cables to drive it.
I was also looking at how other bipedal animals (Birds, Chickens and Ducks) walk and the distribution of the muscles.
It occurs to me, the further up the robot the mass is, the easier it is going to be to make it balance.
To that end, the info gained from the video gives me an idea or two.
We could create a universal joint at the ankle attaching to the sides of the feet and the shin and back of the tibia.
Before I go too far, I think a couple of definitions need to be established, that is the rotations of each of the joints in the ankle.
We need three degrees of freedom here.
The first would be the front of the foot moving up and down, that I would define as Pitch.
The second is the rotation of the foot down its length, that i would call Roll.
Finally, the rotation of the ankle so as the toes move side to side would be termed Yaw.
The pull cable system here would allow for 4 cables (Tendons) to be used connected to two motors to control the joint. If we use the basis of a cable connected to the tibia as a fixed point, then running down the back left of the ankle around a pulley on the left side to an intermediate pulley or two at the front of the foot and then to the right side, running around the right side pulley emerging at the back right of the ankle, then that cable running up to the motor, that would be the first of a pair to a motor to drive the foot up and down, Pitch.
These motors may be in the upper section of the tibia, but are not required to be located there, they could be located in the thigh if we use a semi ridged tendon sheath such as a 4 mm PTFE tube, as used in a lot of 3D Printers.
The same type of setup can also be used for the Roll action of the foot.
A similar arrangement could also be used for a toe operation.
The tendon, could in theory with the 2:1 advantage we gain, be the same 200 Pound fishing line we used for the fingers. that would net us a tension of around 180 Kg or 400 Pounds.
If we work off a 50 mm diameter set of pulleys in the ankle and assume the motors can pull 90Kg or more on our tendon, and from the pivot of the ankle to the ball of the foot, then we could apply 30 newtons of force into the ground. either lifting or tilting the robot.
Of course, if we could work out how to fit in more pulleys, then we can increase that a lot 🙂
We don’t need to have huge ranges of movements with each of these joints, unlike the knee and I haven’t looked hard at the Yaw movement of the ankle, but that two could be done with a set of pull cables.
This is just food for thought.
Comments, Ideas ect are welcome.
I’m sort of hoping someone comes up with a simpler idea that is cheaper to create 🙂