Bowden Cables

[greywanderer012345]

I think I have some really good ideas for using bowden cables in robotics, but I'm still very new to mechanical engineering concepts, and I'm wondering if I'm missing something about their use. I don't see them used or posted about at all on robotics forums even though they could be used for many things. Why don't I see them being used? I'm sure I'm not the first person to consider it. Especially for robot arms with appendage control, they could be used to keep the weight and size of the motors at the base. It would work similar to those robot arm toys, only with servos pulling the cords that curl the fingers... Does anyone know why they are not used more often?

[Graynomad]

They can build up a lot of resistance and get hard to pull/push, maybe that's why.

______
Rob

[Soeren]

Hi,

Why don't I see them being used? I'm sure I'm not the first person to consider it.

You are not, but perhaps not as much as Bowden cable (i.e. a more or less specified combination of inner and outer cable), but rather other variants over the theme.

Apart from friction, there's the added weight of Bowden (especially the standard type sold cheaply for bicycle brakes/gears), so usually a plain wire (i.e. no outer cable/sheat) is used, with pulleys where it corners.
Thinner Bowden type cable can be found industrially and would be more suitable, but it is hard to come by for hobbyists.

[waltr]

There are several varieties of these cables used in model airplanes. Check any good RC airplane hobby shop.

[want2learn]

Perhaps try snakes from R/C planes, a bit more compact than Bowden cables and only require one linkage per appendage rather than the two for Bowden cables.

Also, you won't be able to keep the servos for fingers etc in the main body of the robot without affecting their movement when moving other areas of the arms (unless the arms have very limited degrees of freedom).

Another reason they aren't used commonly is the required maintenance and difficulty in setting up correctly, especially if you exceed the normal working capacity of the cables.

Jim

[greywanderer012345]

you won't be able to keep the servos for fingers etc in the main body of the robot without affecting their movement when moving other areas of the arms (unless the arms have very limited degrees of freedom).

Wouldn't the movement of the appendages be virtually unaffected by the position of leading joints if the cables were guided through the joints like fishing line through a rod rather than fixed in place at the joints. I can bend my brake cables on my bicycle without affecting the state of the brakes. I thought cables like this would allow more freedom than wire and pulleys.

[want2learn]

Wouldn't the movement of the appendages be virtually unaffected by the position of leading joints if the cables were guided through the joints like fishing line through a rod rather than fixed in place at the joints. I can bend my brake cables on my bicycle without affecting the state of the brakes. I thought cables like this would allow more freedom than wire and pulleys.

You can bend your bike cables without affecting the state of the brakes because any flexible part of the system is sheathed (added friction) and generally has only 1 degree of freedom.
In your robotic arm you'd need a push-pull setup which means 2 wires per linkage, bicycle cables aren't efficient enough for your use unless your project is pretty big. Having several cables running in a confined space means at some point at least one of them will be affected by the movement of the joint. Bowden cables are just like rods, when run in a straight line the setup is quite straight forward and simple. Bring movement or flex in their supporting structure (ie. bending joints) and they get complicated.

[greywanderer012345]

Thanks for all of the responses. I'm  still not completely convinced that it would be inefficient for me. I'll have to build something myself and of it's a mistake then I'll learn from it.