CAD: Making a cam mechanism

[JesseK]

I am trying to create a cam lock mechanism for the Stackerbox-Mecanum chassis I posted earlier this week, yet I can't seem to get the dimensions quite right. Below is the result of 3 hours of my best efforts to figure it out. Ideally, the curve would be smooth. In exactly 270 degrees, I need the radius of the cam to smoothly go from 1" to 2" and then back to 1" in the remaining 90 degrees.

Currently I am using the spline tool in a solidworks sketch, but that seems to be too innaccurate for real-world applications. Any suggestions?

[Jeff K.]

It would be easier if you could make it only one sided and just have it go straight or make small radii back to the original 1". If you are trying to get it to go back smoothly you may have to just have it be symmetric and have the far opposite side of the 2" be 1".

[Madison]

Attached is a CAM generated in Solidworks 2007. Your original post is unclear as to whether you're looking for a radius or diameter of 2"; this is built with a 2" final radius. It's trivial to make another with smaller or larger dimensions.

This was made with Solidworks' Toolbox Cam tool. It automagically generates the proper sketch geometry for the cam you need based on a series of parameters. This is the first time I've really used it, so I don't know much about its limitations, but making this first one work was pretty straightforward.

[Greg Needel]

I also tried making this cam in pro-e which my result was okay but not perfect maybe if I had spent more than 10 mins on it....



anyway the question I have for you is how critical is the cam to have a follow cam profile? You could just use a cylinder piece of stock and drill the rotation hole offset from the center and get a cam effect. If you use a 3in piece and drill it .5 in off center you will get the same extreme's that you are looking for.

I guess I am wondering if the quick transition is actually necessary.

[JesseK]

Originally Posted by Greg Needel

anyway the question I have for you is how critical is the cam to have a follow cam profile? You could just use a cylinder piece of stock and drill the rotation hole offset from the center and get a cam effect. If you use a 3in piece and drill it .5 in off center you will get the same extreme's that you are looking for.

I guess I am wondering if the quick transition is actually necessary.

A very slow transition is what I'm after actually. The application for the cam is to act as a lock against a sliding Stackerbox transmission that acts as a low-maintenance chain tensioning system. The cam itself will have very little force put on it since the 4 bolts from the transmission will be tightened into the sliding plate, but the cam is necessary to make the overall tensioning system more reliable.

A symmetric cam may work just as well as what I want, but if I can have my cheese and eat it too then for now I will. In all actuality, to create the actual lock from 1/4" aluminum plate (I'm also looking into hardwoods) on a CNC, it will take either two passes for setup, or the final 90 degrees of the cam will have to be manually cut.

[Greg Needel]

Originally Posted by JesseK

A very slow transition is what I'm after actually. The application for the cam is to act as a lock against a sliding Stackerbox transmission that acts as a low-maintenance chain tensioning system. The cam itself will have very little force put on it since the 4 bolts from the transmission will be tightened into the sliding plate, but the cam is necessary to make the overall tensioning system more reliable.

A symmetric cam may work just as well as what I want, but if I can have my cheese and eat it too then for now I will. In all actuality, to create the actual lock from 1/4" aluminum plate (I'm also looking into hardwoods) on a CNC, it will take either two passes for setup, or the final 90 degrees of the cam will have to be manually cut.

Gotcha, I didn't realize that you were looking to use the over center cam for a long actuation, I was looking at the short transition side of the cam. I still think for a tightening mechanism a symmetric cam would would, and you could always cut a flat at the extent to act as a lock. Either way they should both work. Have you thought of how you are going to lock the cam in position yet if the tension required is somewhere before the over center feature?

[JesseK]

Originally Posted by Greg Needel

Have you thought of how you are going to lock the cam in position yet if the tension required is somewhere before the over center feature?

Since the cam should have only a small amount of force that tries to "unlock" it, simply tightening the #10 bolt that mounts the cam to the side plate should do the trick. Combined with the four #10 transmission bolts, I believe the setup will be strong enough to keep the chains properly tensioned for at least several matches, though I could be wrong.

[JesseK]

Originally Posted by M. Krass

Attached is a CAM generated in Solidworks 2007. Your original post is unclear as to whether you're looking for a radius or diameter of 2"; this is built with a 2" final radius. It's trivial to make another with smaller or larger dimensions.

This was made with Solidworks' Toolbox Cam tool. It automagically generates the proper sketch geometry for the cam you need based on a series of parameters. This is the first time I've really used it, so I don't know much about its limitations, but making this first one work was pretty straightforward.

Measurements of your part give me radii from ~.79 to ~1.79" in 270 degrees. So I rigorously Googled for how to enable the cam toolbox. After about an hour and 43 revisions later I have almost recreated your exact cam. It's wierd because as I decrease the follower radii the cam radii doesn't adjust properly. Right now it's driving me nuts so I'll have to play with it more before we try to mill the final version. Rev #43 has a 1" radii difference in 270 degrees so I can make it work in the next drive train CAD revision.

Thanks a ton