Chain Tensioning

[Oblarg]

Originally Posted by asid61

Personally, regardless of belt or chain, I would use tensioners.

Tensioners on a belt are decidedly unnecessary, in my experience, and will do nothing but add additional friction.

[asid61]

Originally Posted by Oblarg

Tensioners on a belt are decidedly unnecessary, in my experience, and will do nothing but add additional friction.

Friction, but only if you use on-belt tensioners. Plus, that would be pretty low anyway depending on the setup.
I'm thinking more of cams or screw tesneioners. Even better would be to use 192 method that they used on the gearbox: screw holes that were slightly farther or closer to the other side of the belt, from -50 to +50 thousandths. It's a really clever system.

[mrnoble]

Has anyone used the nautilus cams from WCP? We are planning on incorporating them into one of our off-season drive bases this fall as the chain tensioner. I guess I don't understand what the big deal is about using tensioners anyway; why would that be less of a problem in a design than doing c2c calculations? I've worked with teams that have done both, with both chain and belt, and it seems to me that the advantage would tilt toward adjustability.

[cxcad]

Originally Posted by mrnoble

Has anyone used the nautilus cams from WCP? We are planning on incorporating them into one of our off-season drive bases this fall as the chain tensioner. I guess I don't understand what the big deal is about using tensioners anyway; why would that be less of a problem in a design than doing c2c calculations? I've worked with teams that have done both, with both chain and belt, and it seems to me that the advantage would tilt toward adjustability.

You need the bearing blocks for that to work. The cams are there to adjust the blocks. The advantage of chain tensioners is to keep the chain in proper tension at all times. Over time chain stretches especially under aggressive driving.

[BBray_T1296]

If you have a significant length of chain, and need to take some play out of it, a simple method of easily taking out slack is to wedge a loose plate sprocket between the chains as such. I suppose this could work for belts too.
The green sprocket is not fixed or touching anything but the chain, and remains in place with no need for support. Since it is not transferring any load either, it can be made of extremely pocketed aluminum and can be super light weight.

[asid61]

Originally Posted by BBray_T1296

If you have a significant length of chain, and need to take some play out of it, a simple method of easily taking out slack is to wedge a loose plate sprocket between the chains as such. I suppose this could work for belts too.
The green sprocket is not fixed or touching anything but the chain, and remains in place with no need for support. Since it is not transferring any load either, it can be made of extremely pocketed aluminum and can be super light weight.

keep in mind that you have to stop it from falling over, especially under load.
It will auto-align, but having a small bearing block setup would be good.

[Chris is me]

Originally Posted by asid61

keep in mind that you have to stop it from falling over, especially under load.
It will auto-align, but having a small bearing block setup would be good.

Why would it fall over? The tension of the chain and the two existing fixed sprockets should keep the chain level.

[R.C.]

Originally Posted by asid61

keep in mind that you have to stop it from falling over, especially under load.
It will auto-align, but having a small bearing block setup would be good.

Is this "broscience" or have you ever had an actual issue with floating sprockets.

[DampRobot]

Originally Posted by mrnoble

Has anyone used the nautilus cams from WCP? We are planning on incorporating them into one of our off-season drive bases this fall as the chain tensioner. I guess I don't understand what the big deal is about using tensioners anyway; why would that be less of a problem in a design than doing c2c calculations? I've worked with teams that have done both, with both chain and belt, and it seems to me that the advantage would tilt toward adjustability.

Yeah, 100 did last season, and I just loved them. Basically, take anything that slides (on slots, as a bearing block, a VersaBlock, etc) that needs to be tensioned and put a cam next to it. Your bearing block/whatever will never slip, and the cams are real easy to design in and use.

I think of the tensioner vs c-c debate like this. If you want to put a chain/belt between two points in something that is getting milled (like a plate or piece of tubing) and you don't care a ton about slack in the system, go with exact c-c spacing, as it'll make your life a ton easier. If you're going between two points where it's difficult to get good tolerances (like from the bottom of the robot to the top of a big welded superstructure to drive an arm) or where it's critical you dial in the tension so it can handle lots of torque, go with sliding tensioners. It'll be much easier to dial in the exact tension you want, and you can soak up the tolerance stack up through the sliding tensioner system.

[Oblarg]

Originally Posted by DampRobot

I think of the tensioner vs c-c debate like this. If you want to put a chain/belt between two points in something that is getting milled (like a plate or piece of tubing) and you don't care a ton about slack in the system, go with exact c-c spacing, as it'll make your life a ton easier. If you're going between two points where it's difficult to get good tolerances (like from the bottom of the robot to the top of a big welded superstructure to drive an arm) or where it's critical you dial in the tension so it can handle lots of torque, go with sliding tensioners. It'll be much easier to dial in the exact tension you want, and you can soak up the tolerance stack up through the sliding tensioner system.

This is very, very sound advice.

It occurs to me that I should try using one of those cams on a piece of 80/20, to capitalize on its natural sliding capability.

[notmattlythgoe]

Originally Posted by DampRobot

Yeah, 100 did last season, and I just loved them. Basically, take anything that slides (on slots, as a bearing block, a VersaBlock, etc) that needs to be tensioned and put a cam next to it. Your bearing block/whatever will never slip, and the cams are real easy to design in and use.

I think of the tensioner vs c-c debate like this. If you want to put a chain/belt between two points in something that is getting milled (like a plate or piece of tubing) and you don't care a ton about slack in the system, go with exact c-c spacing, as it'll make your life a ton easier. If you're going between two points where it's difficult to get good tolerances (like from the bottom of the robot to the top of a big welded superstructure to drive an arm) or where it's critical you dial in the tension so it can handle lots of torque, go with sliding tensioners. It'll be much easier to dial in the exact tension you want, and you can soak up the tolerance stack up through the slidithis thread to figure tensioner system.

You don't need to go exact c-c and have a bunch of slack though. Use the information provided in this thread to figure out the correct distances for a tensioned chain.

[marshall]

For tensioning chain, we had great luck with these this past year:

http://www.zoro.com/i/G0347697/?category=6001

Slipped off twice that I can remember and it was about a minute to get it back on and we added a little extra tension (they are adjustable) after to take care of it.

We were happy with them. They are also completely off the shelf so we'll be able to use them again.

[DampRobot]

Originally Posted by notmattlythgoe

You don't need to go exact c-c and have a bunch of slack though. Use the information provided in this thread to figure out the correct distances for a tensioned chain.

True, but if you had a design that was intolerant to any slack, I feel most comfortable with a sliding tensioner in the system.

[asid61]

Originally Posted by R.C.

Is this "broscience" or have you ever had an actual issue with floating sprockets.

I've tried it a couple times just as a concept for chain tensioning during the season. The sprockets had a tendency to fall out. Just my experience.

[BBray_T1296]

Originally Posted by asid61

I've tried it a couple times just as a concept for chain tensioning during the season. The sprockets had a tendency to fall out. Just my experience.

We had a couple sprockets in our <shudders> crab drive, and those were in <again shudders> long runs of horizontal chain, none of which fell out*


* That drive had 99 billion problems, chain slack being one, but sprockets falling out was not