Apr 22, 2022
As we continue with the mower project new issues have arisen that made themselves apparent through testing. During a low speed test of the mower with the new transmission, some warping occurred in the transmission mount due to the torque from the motor. Other factors contributed to this as well, such as trying to shift into a higher gear while the engine was still running. Although this might be perfectly fine in a conventional clutch and transmission setup where there is a physical clutch that separates the engine inertia to the transmission, our case was much different.
First of all, we don't have a physical clutch. Our “clutch” is a belt tensioner that relieves belt tension on the drive pulley, but does not prevent a full separation of movement from the engine. This is perfectly fine for stopping most of the engine torque to the rear wheels in order to apply the brakes, but not good for shifting while moving. Because we tried to shift while this tensioner was applied, it caused more stress on the transmission mount and warped it out of alignment. Even if we tried to put it in gear and release the belt tensioner the mower would not move forward. James and I had to push the mower back to the shop, diagnose the issue, and design a new stiffer transmission mount.
After discussing designs and placement of the transmission and if we were going to continue to utilize the jackshaft or not, we settled on a design that was simple but stiffer than the old mount. In order to make it stiff and resist deflection, I ran a framework for the underside out of square steel tubing with cross members for added rigidity.
The red triangles are where supports will be put in
This will be the foundation for the thick steel plate we will put on top. The steel plate will help a lot in terms of reducing flex and overall deflection, while also providing a mounting spot for the transmission. After the plate was on the top, James welded around the edges to secure it in place. We also welded along the bottom where the tubing meets the plate.
The next blog post will be dedicated to the testing of this new transmission mount design. Stay tuned for updates!