>Ok, I've finally gotten around to working on my Saturn EV. Tuesday I >installed a new clutch master cylinder so now I can drive the car just by >myself, it was fun having someone sit in the car and hook up a battery then >try to not smash your fingers in the hood while the car started to drive >away. Anyhow, I took some pictures. First you can see the car with it's few >month collection of dust at: >members.aol.com/evracr/saturn.jpg >As for the motor I need some opinions of whether or not the mount I made will >hold up. A picture of this is located at: >members.aol.com/evracr/motor.jpg >I made a 1/4" thick alluminum brace that hangs the rear end of the motor off >of the origional engine mounts. The wrap around mount hooks to the passenger >side drive shaft half way support. The transmission has a rubber boot it sits >on and is held in place with a dog bone bar across the top. All the >transmission mounts are stock. Alright EV guru's, will this setup hold up? > >Tonight it looks like I will be making card board boxes the size of the >Trojan T-875's I decided to go with so I can figure out where I'm going to >put them all. And on the subject I have decided to simmer down a little and >go with 120 volts of 8 volters. My origional plan was 192 volts, but after >speaking with Jesse James at Sunbelt battery he recommended the 8's highly so >I think for a first time conversion I'm going to slow down a bit. Thanks in >advance to anyonw who comments on my motor mount. > >Later, >Ricky Suiter It is not clear from the photo what you have done for a front or rear motor mount. There are two, separate, goals you are trying to achieve with the motor mounts. The minor goal is to support the weight of the motor. The major goal is to react the torque impressed on the transmission by the drive line. Folks tend to get focused on the minor goal and seem to forget all about the major goal. When we were using wimpy, low amperage controllers, bad motor mount design was not much of an issue as long as the motor didn't fall out of the car under it's own weight. Now that we are building some pepper cars, bad mount design becomes a safety issue. The forces impressed on the transmission housing by the axle shafts is enormous. 1,000 foot-pounds of torque is not unusual. Peak (spike) torque can be many times that number when the car goes over railroad tracks or hits a pot hole. You have to design the mount system to hold the transmission in position as it reacts these output torques. The motor end bells are designed to withstand about 400 ft-pounds of torque. They work great for reacting all the torque that the motor can produce. They are not designed to react 1,000 ft-pounds of torque that the reduction gears of the transmission can produce. They are definitely not designed to react the 3,000 to 5,000 ft-pounds of peak torque that you will get when hitting a pot hole. There are only four 1/4 inch bolts holding on the end bells. These will instantly shear right off if you go much above 3,000 ft-pounds. Under cyclic loading, they won't take more than about 400 ft-pounds. Thus, you really don't want to use the motor to react the transmission torque. What often makes matters worse is that grabbing the outboard end-bell puts a major bending moment on the motor. As the transmission tries to rotate upward, you are holding it from doing so by the end of the motor. The forces on the end of the motor are about 1/2 ton (and much, much more when hitting a pot hole.) The force is about the same as putting a jack under the end of the unsupported motor and lifting the front of the car off the ground (but in the opposite direction.) Again, the tensile forces on the 1/4 inch bolts on the shaft end of the motor are about 1,500 pounds. This is enough to break them. Don't forget that you are also twisting them. The bolts holding the shaft-end bell in position are loaded to about twice their yield strength. They will fail in short order if the transmission is not well-supported elsewhere. In race cars, they don't worry much about supporting the engine. They typically make a super-duper transmission mount to react the driveline torque. This keeps the engine from flipping over in the engine compartment. The torque of the engine is not what makes it twist, it's the torque of the driveline reacted by the transmission. Since electric motors are much lighter and produce much, much more torque than the ICE that they replace , you need to focus on keeping the transmission in place, rather than supporting the weight of the motor.