Cable through Flexible Housing?

[james.lynch]

Hi,


I was wondering if anybody could help me? what I'm trying to do is simulate through Mechanism something similar to a flexible brake cable on a bicycle.


Say for example, I have a lever attached to one end of a moving mechanism, and a cable attached to this lever to operate it..


Essentially, what I want to do is "attach" the outer casing of the cable to the mechanism, so when the mechaism moves, the cable moves too. And when I pull the other end of the cable, the lever movesin the same way no matter what position or motion the mechanism is in.


I have been playing around with 2 slot follower connections to a flexible 3d curve with a constant distance between the two points but havent go it to work.


Thanks for your help,


James

 

[Luis Aguirre]

James,


This could be done using measures in combination with force motor. You will assign a measure that will track linear distance that the cable travels. In order to obtained the linear distance you may have to use a "user defined" measure. For example create a measure to track the rotation of the lever andcall it "rot_disp". Now create ameasure of the totalcable that will wrap around asthe lever is pressed using a "user defined" measure and called "cable_dist". Since cable_dist"is a function of the "rot_disp" the following equation will have to be included in the "user defined" measure:


cable_dist= rot_disp*R where "R" is the radius of the pulleythat the cable wraps





Now use the cable_dist measure to create a "user define" force motor. In other words the force that the motor will create is a function of the distance travel by the cable or in our case the output of the cable_dist measure. if it is linear then the force motor function may look like:





Force motor= cable_dist*3


Therefore as the distance increase the motor generates a force that is 3 times that distance. You may be able to create more complex force distance relation but the basic procedure that I try to show here will be the same.





Luis


P.S. User defined measures and force motors are only available in WildFire
Edited by: Luis Aguirre

 

[james.lynch]

Luis,


Thanks for the great reply!

to be honest, I'm a bit of a nivoce with Mechanism at the momment, I don't know ecactly how to do what your saying, but I do understand it so I'll have a go at it later today.


I do have one question though, my cable may not actually travel around a pulley of single radius, or even be planar, the idea is for it to use the outer cable housing as a cable guide and that could be 3d spline curve, or at the very least a series of straight lines and defines curves..


I suppose if I can somehow simplifythe path down to straight lines and arcsI could use the method you described above, but I was hopeing to use a spline.Anybody know how to set up a measure to calculate the linear distance of a spline?


Thanks for your help,


James
Edited by: james.lynch

 

[Luis Aguirre]

James,


Read the online help regarding "user defined" measures and "force motors". The idea behind the technique I proposed is not to have the spline interact with your mechanism (although you can create itfor visual effects) but have force motor simulate the interaction of the cable with the mechanism. Let me know if you have any questions once you read the online help.


To answer your second question. If you have BMX you can use it in conjunction with MECHANISMto measure the distance (length) of the spline.


Luis
Edited by: Luis Aguirre

 

[james.lynch]

Thanks for clearing that up,


Appriciate it.