Interesting week last week and growing interestingier as we start this one.
Last Monday, we were doing some range testing at 60 mph in the eCobra when the Netgain Warp 11HV let out all its smoke and ceased operation somewhat noisily.
This led to a crusade to swap the motor that I’m more than a bit pleased with as it was pretty much completed in three days. Netgain had a new motor to us in less than 48 hours and our penchant for installing and reinstalling things several times had of course led us to a pretty straight forward replacement from beneath without having to move too many other parts – transmission and drive shaft of course. But no batteries or major rewiring.
Unfortunately, we had no video camera operating at the time. So no cool video of the tower of smoke next to the Interstate. Oh well….
The other interesting thing to happen early THIS week is that we put the hood on the car. This is normally a not particularly exciting evolution and always toward the end of the build, when we are doing more driving that building.
In this case, it had a very strong effect. Recall I had been grousing about the rolling resistance, the brakes, and so forth on this car because it was taking between 1.65 and 2.25 Ah of energy at 215 volts to make a mile of distance. This is just horrendous. At the upper end this is like 475 wH per mile or more. And it had shot all my range calculations completely out of the saddle.
Actually, things get better with the hood on. This should be obvious to all, but I didn’t think it would account for this much difference. It makes THIS much difference. As soon as the hood was on, we dropped to 1.409 Ah per mile – right in the 300 wH per mile range where this 2961 lb car should be.
I may have mentioned some efforts to develop something more consistent than our soap box derby for a coast down test.
We took the car up to 75 mph on a flat road section and put it into neutral. Time mark 0 was called at 70mph and the time noted at each 10 mph until stopped. We ran this three times in each direction, east and west, and then averaged the results.
The coast down test is conventionally used to determine aerodynamic drag and rolling resistance. But it is difficult to do that with accuracy and requires humidity, temperature, and other factors to be truly accurate. But we think we can do a quick average procedure and have the curve and times as a baseline. This should let us compare to this baseline after changes for example. We’ll put on the original tires and rerun it for example to see what the effect is.
This is a bit more trouble than rolling it down the street in front of the shop. But accounts for aerodynamics in addition to rolling resistance and drive train efficiencies.