P10221: Baja 1 (Baja Driveline Test Development)

Drive System

Image:big.jpgImage:small.jpg Image:drivesystem1.jpg Image:enginedrivesprocket.jpg Image:entiredrive.jpg Image:broken bolts.jpg Image:broken hub.jpg Image:steelhub.jpg


The drive system served its primary function of transferring the torque the engine produced to the dyno so it could be quantified. The drive has allowed for a multitude of successful dyno runs. Over many dyno runs, much was learned through several driveline issues that came up. The necessity for all sprocket bolts to require thread locker, as well as, lock washers became obvious after the first run when loosening was noticed. With proper precautions and due diligence this is not a significant problem.

After the first few runs we thought we had issues with tension not holding in the chain, but we later dismissed this as chain stretch and sprocket wear. Our tensioning system has been proven to work, however a quicker adjustable solution is suggested as a future improvements to the system. Currently, the slackening of the chain requires all of the stands mounting bolts to be loosened and re-tightened, a laborious process. View windows were also put into the chain guard to more easily inspect chain tension and condition without removal.

Baja and Formula agreed that a stouter dyno hub, made out of steel, would be a good upgrade. The original aluminum hub had high potential for tear-out and aluminum silting had been noticed around the hub bolts after several dyno runs. The new steel hub is much larger but retains the same mounting geometry.

Experience on the dyno has proven our original thoughts about the safety hub were not completely correct. The system works, but the designed failure occurs too often. The designed shear bolts fail in what we believe to be fatigue instead of the anticipated shear. If the bolts are replaced every three runs, they don't fail unnecessarily, supporting this theory. This is obviously not ideal and thus should be addressed. A recent attempt using stronger screws relocated the failure to the engine hub itself as seen in the above gallery. Torque spikes had not been seen in the data and thus this was deemed a safe test. Fracture occurred at the stress concentration created by the keyway and clamping slots used for mounting of the hub. Further inspection showed what appeared to be casting flaws in these areas as well. The solution was implemented of machining a new hub out of a solid piece of steel, which is also pictured in the gallery above. This hub does not feature the slotted clamping technique and has a thicker face to provide more stability and thread engagement to the shear bolts.

This hub has proved to be an improvement, however occasional loosening of the shear bolts from vibration still occurs. A solution using bolts with nylon inserts and shear pins along with said bolts has been proposed. The pins may perform better under the alternate loading of the engine, and the nylon inserts in the bolts may prove to be more effective than thread locker.

Return to Home