Chain Tensioning Methods

[Daves]

What are some advantages and disadvantages of various types of chain tensioning?

The methods I am familiar with are the following:

1. Idler sprocket
2. Rotation of differential eccentric with axle rotation
3. Translation of differential along horizontal plane

The reason I am asking is that we currently are using the eccentric rotation method with rod ends for adjustment. However, with our large pillowblocks, the rod ends only allow for about 1/4" (10 mm) of chain adjustment. Also, if more rotation was allowed, the rear sprocket and differential would move vertically slightly, which would affect sprocket ground clearance, c.g. height, and the c.v. joint slant angle.

http://www.geocities.com/fif4183/images/diff.txt

The possibly better design is what is shown in the picture (linear translation). Unrelatedly, that is a Taylor-Race differential, torque-sensing but not a Torsen.

Is the linear translation method really any better? Should I be concerned about the vertical changes with the rotation method? How much force can set screws (not shown) hold on their own?

[Daves]

What are some advantages and disadvantages of various types of chain tensioning?

The methods I am familiar with are the following:

1. Idler sprocket
2. Rotation of differential eccentric with axle rotation
3. Translation of differential along horizontal plane

The reason I am asking is that we currently are using the eccentric rotation method with rod ends for adjustment. However, with our large pillowblocks, the rod ends only allow for about 1/4" (10 mm) of chain adjustment. Also, if more rotation was allowed, the rear sprocket and differential would move vertically slightly, which would affect sprocket ground clearance, c.g. height, and the c.v. joint slant angle.

http://www.geocities.com/fif4183/images/diff.txt

The possibly better design is what is shown in the picture (linear translation). Unrelatedly, that is a Taylor-Race differential, torque-sensing but not a Torsen.

Is the linear translation method really any better? Should I be concerned about the vertical changes with the rotation method? How much force can set screws (not shown) hold on their own?

[Colin]

We've used both linear translation and idler sprocket. The linear translation was the simplest but we had problems with the diff pulling forward, however this was more a design flaw than anything else. Last year due to space constraints we used an idler pulley. This allowed the diff to be mounted rigidly and added to the stiffness of the rear chassis. Originally I was against the pulley as I thought we would have wear issues, as we were using a nylon wheel rather than a sprocket, but this was not the case and we're still got the original wheel on the car. This year we're sticking with the idler pulley. If your going this way have a careful look at the loads as our pulley mount to the chassis was slightly "under designed"� last year.

[fsae_alum]

In 02, we used a system where we mounted the diff and shimmed it horizontally with metal shims. The mounting bearings for the diff were attached vertically to a bulkhead between the diff and the engine and we would just loosen the 2 mounting bolts per mounting bearing (think huge pillow block) and slide more shim stock in until the chain had the tension we wanted. It was a bit bulky but it worked flawlessly. The bolts were only there to locate mostly and were really under fairly low loads. The way it was designed, for the chain loosen up, the shims would have to compress.

For the 04 car, the new guys used turnbuckles in tension to hold the diff from the rear. That worked pretty good except when somebody dumped the clutch at 6k thinking it was in Neutral and subsquently bent the frame and diff mounts from the resulting system jerk. Grrrr....

Two different ways...one over-designed and one under-designed. The perfect area is in the middle. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Chris Clarke]

Colin,

Were you the team with the gold chassis who had the idler pulley at Detroit this year? I have some pictures of it, but could not remember which university the car was from.

[Colin]

no we didn't make it to detroit this year unfortunatly

[Beast]

How many other teams used a idler pulley/wheel?

We (FL Tech) used a linear type (bolt through frame rail and clamping bolts, like a bicycle wheel) which had no problems other than being a pain to reach adj.

[drivetrainUW-Platt]

I know talkin to one team that they had the threads strip out of there aluminum turnbuckle from forces on it, on our next car i will probably be making a steel turnbuckle so we wont have to worry about this problem. just thought i would mention it for teams considering the aluminum ones

[Daygo Nighthawk]

We used some internal chain tensioner from a Harley.

Wasn't my first choice for chain tensioning, but all my other solutions would have taken too long and held back the building/completion of the car.

The positives of this design are that the differential is in a stationary position. Therefore, theres no chances of chain/diff misalignment, or additional CV/tripod misalignment/interference.. look at the tripod housing clearance here:
http://sae.ucsd.edu/media/carbuildapr-may2004/021.jpg

You can see a little edge of the "shoe" to the right of the shifter shaft, obscuring some chain links here:
http://sae.ucsd.edu/media/carbuildapr-may2004/020.jpg

Sorry I don't have better pictures of it; it's pretty obscured and tightly packaged back there, and we didn't take pictures of it.