pic: Bearing block idea

[cxcad]

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[Dan_Karol]

cxcad,

This tensioning method relies on the clamping force (essentially friction) to hold the bearing block in place. Under load there is a high likelyhood of the bearing block slipping and relieving the tension on the chain. I would highly recommend looking into some sort of locking CAM mechanism to hold the block in place after it is tensioned.

There are many methods of tensioning drive systems in FRC that are very similar to this that you might be able to use for inspiration (look at some of the West Coast Drive white papers)

Looks like a good start,
-Dan

I like the idea, but like Dan said this isn't too reliable of a method. What makes this any better than the standard WCD?

[geomapguy]

We used something similar for our shooter to eliminate the use of half links and such...not sure if it'd hold up for a drivetrain

[JesseK]

Originally Posted by Andrew Lawrence

I like the idea, but like Dan said this isn't too reliable of a method. What makes this any better than the standard WCD?

WCD is far from "standardized". There are 100's of variants.

Originally Posted by JesseK

WCD is far from "standardized". There are 100's of variants.

A true WCD does have standards it generally follows. There are variants inspired by the West Coast Drive, but they don't follow the same categorization.

[JesseK]

Originally Posted by Andrew Lawrence

A true WCD does have standards it generally follows. There are variants inspired by the West Coast Drive, but they don't follow the same categorization.

Standards imply widely-used best practices are usually published in some coherent form or another. Maybe there are traditions or recommendations for manufacturing capability, yet I haven't read anything about a standard WCD.

(You poked a badger with a spoon... )

1885 used friction to tension our live-axle wheel blocks through a 2x1 rail in 2013. It worked very well through 3 official 2 offseason events.

[cxcad]

Originally Posted by JesseK

1885 used friction to tension our live-axle wheel blocks through a 2x1 rail in 2013. It worked very well through 3 official 2 offseason events.

I don't quite understand the use of friction to tension. Can you provide an image?

[Bill_B]

Do something on the upper and lower surfaces of the block to increase friction. Likewise for the inside surface of the channel so that squeezing with your locking screw will have more effect. groove patterns of some sort like the "teeth" on a zip-tie.

[Chad987]

Originally Posted by Andrew Lawrence

I like the idea, but like Dan said this isn't too reliable of a method.

We've been doing this for six years now and have had no issues with it. It's simple to machine and light weight.
http://i.imgur.com/i7UTytH.png

[cxcad]

Originally Posted by Chad987

We've been doing this for six years now and have had no issues with it. It's simple to machine and light weight.
http://i.imgur.com/i7UTytH.png

Do you have bolts going on both on the top and bottom?
I designed this for it to be easy to machine and honestly I really don't understand how 254's system works. Can anyone shed light on that?

[Chad987]

Originally Posted by cxcad

Do you have bolts going on both on the top and bottom?
I designed this for it to be easy to machine and honestly I really don't understand how 254's system works. Can anyone shed light on that?

There are no screws on the bottom to tension it. We are using 1x1.5 tubing though, if you are planning on using sheet metal I would mount it with screws on both sides. http://i.imgur.com/kGi1xuv.png

Unfortunately I can't comment on how 254 tensions their belts. (Do they use belts?)

Originally Posted by Chad987

There are no screws on the bottom to tension it. We are using 1x1.5 tubing though, if you are planning on using sheet metal I would mount it with screws on both sides. http://i.imgur.com/kGi1xuv.png

Unfortunately I can't comment on how 254 tensions their belts. (Do they use belts?)

254 doesn't use belts on their drive. 25 chain is what they've run since 2004.

[Chad987]

Originally Posted by Andrew Lawrence

254 doesn't use belts on their drive. 25 chain is what they've run since 2004.

That's what I had thought but I haven't seen their robot in person this year so I was unsure. thanks

[nathannfm]

Originally Posted by cxcad

...honestly I really don't understand how 254's system works. Can anyone shed light on that?

This picture should help. The way I understand it, the bearing block is being pulled to the left by the left by the chain (not installed) until it contacts the side of the cam, as the cam it turned counter clockwise it pushes the bearing block to the right, tensioning the chain.

Originally Posted by Chad987

We've been doing this for six years now and have had no issues with it. It's simple to machine and light weight.
http://i.imgur.com/i7UTytH.png

Very interesting that in practice the friction of 4 bolt heads on the drive rail is enough to keep tension where theory says thats probably a bad idea. I will keep this in mind, thank you.

I guess now is a good a time as any to post what MOE uses. This is the first year we ventured into the realm of cantilevered drives after the unmitigated disaster that was mecanum in 2013 (If I called this a WCD someone might shoot me ).
We wanted a belt tensioner that did not rely on friction and we came up with a few ideas. (My favorite was a roller spool that we could change the diameter of to increase tension.) Ultimately we used what is shown in these pictures. There is a curved slot in the drive rail that the shoulder bolt can move through. As you tighten the bolt sticking out of the top of the section of U channel it raises the shoulder bolt and the roller on it pushing the belt up and tightening it. The countersunk 1/4-20 is the pivot point.