Re: Flexible Floating Idler Tensioner
 

Not that I've seen. You don't really need the flexibility. You can use any #25 sprocket so long as it's bigger than both of your other sprockets. You can slide it towards one of the ends for more tension.

We have a kind of weird but still cheap way of making chain tensioners. We buy small sprockets, bore out the hub and put a bushing in. We then buy a mini-bike motor for each tensioner needed and remove the tensioner that is included on the motor. We put the sprocket on where the pulley is. We then mount the tensioner on a piece of angle aluminum which can be mounted inside our drive rail, arm upright, etc...

Total cost is still cheaper than purchasing a chain tensioner. Plus, we have a bunch of 3.5" CIM motors sitting around.

Re: Flexible Floating Idler Tensioner
 

Any pics???

Re: Flexible Floating Idler Tensioner
 

Our tensioners can be seen here:

http://www.wintechpc.com/matt/galler...serialNumber=2

Re: Flexible Floating Idler Tensioner
 

Andy, the problem with that type of spring loaded tensioner is that it only works well in one travel direction. In the case of the pictured robot, if you occasionally shimmed up the gearboxes by putting washers under the base plate mounting bolts, you'd have the chain properly tensioned and wouldn't really need tensioners.

Re: Flexible Floating Idler Tensioner
 

I don't think I understand what you are saying. Our gearboxes are side mounted. Are you talking direction of travel? Because if you angle the tensioners right, it shouldn't matter.

Re: Flexible Floating Idler Tensioner
 

I think I get what he's saying. Think of a bike chain tensioner - it works because you pedal forward so the tension goes from the front sprocket to the back one, and the spring loaded thing picks up the slack.. However, if you try to pedal backwards (imagine that there is no one way ratchet thing for a bike), the tension would pull the spring before it would turn the wheel. I guess it would work if the springs were very strong though.

I hope that made sense.

Re: Flexible Floating Idler Tensioner
 

Didn't notice that you have them attached from the rear. If you were to lift the gearbox straight up, the chains would tighten. That would require a slight slot in the inner frame mounting holes - not much.

A bi-directional chain drive either needs two tensioners, or a provision to snug up the chains such that no tensioner is needed.

Re: Flexible Floating Idler Tensioner
 

Hmm, I wonder how much weight we really save in using #25 chain. This year, to save weight on the tensioners we wound up building the tensioners into already-existing mounts on the chassis, but in return we wound up sacrificing effieciency of the drive train. The power loss from it was enough to merit using an extra pound or two for them next year.

There's an interesting calculation that can be done here to figure out if it's worth it to use #25 chain instead of #35 chain in order to save weight. First, some assumptions (correct me if I'm wrong):

- Ignore mechanical advantage of lighter chain
- Ignore strength advantage of heavier chain
- Ignore the fact that improperly tensioned #25 chain is more susceptible to failure and/or slip during sudden direction reversal or high stress moments than #35 chain
- The rolling chain tensioner will never be available for #25 chain
- Average team with good building skills and capability
- #35 Tensioner listed above (estimated): 2oz. (.125lbs)
- #35 Chain, Weight/Ft*: .23lbs
- #25 Avg Chain tensioner weight: 4-6oz. (.25-.375lbs) -- Assumes usually a bolt, small piece of aluminum, and some plastic composite for the lightest forms
- #25 Chain, Weight/Ft*: .15lbs

Drive Train (4WD omni/mecanum to 6WD all powered wheels)
==================
Avg Length of chain used: 8-14ft
Usual # of chain tensioners used: 4-6, depending on if it's direct drive or not

Therefore
#35
Chain Weight: 1.84-3.22lbs
Tensioner Weight: 0.5-.75lbs
Total: 2.34-3.97lbs

2.34lbs for a mecanum drive and 3.97 for a kitbot modified for 6WD

#25
Chain Weight: 1.2-2.1lbs
Tensioner Weight: 1.0 - 2.25 lbs
Total: 2.2lbs - 4.35lbs

2.2lbs for a mecanum drive, 3.1lbs for highly skilled direct drive teams, and 4.35 lbs for a kitbot modified for 6WD with avg build skill

Manipulators (Arms, widgets, w/e)
==================
Avg Length of chain used: 2-5ft
Usual # of chain tensioners used: 1

#35
Chain Weight: .46-.1.15lbs
Tensioner Weight: .125lbs
Total: .585-.1.275lbs

#25
Chain Weight: .30-.75lbs
Tensioner Weight: .25-.375lbs
Total: .55 - 1.145lbs

Conclusion
==================
We can see that higher skilled teams who have time-tested chain tensioning techniques can really benefit from the weight loss found in #25 chain, but for mecanum drive or rookie/average teams the weight differences are negligible, IMO.

*Reference: http://www.laceyharmer.com/products/rollerchain.htm

Re: Flexible Floating Idler Tensioner
 

Whatever you do, get the best quality chain you can. Maybe something like this: http://tsubakimoto.com/product/drive...class3/10/3/2/