The Spinout of Sparrow Number 96
About 11 am on Wednesday July 12, 2000 in clear, sunny weather, I turned Sparrow #96 from Santa Cruz Avenue in Menlo Park onto southbound Fremont Street. Fremont Street is a straight side street with little or no traffic. At the time, the street was clear on both sides except for a pickup parked on ahead at about 765 Fremont.
Traveling in cautious slow acceleration at about 20 mph and at about 821 Fremont, (as indicated by the beginning of a single skid mark, there was a loud click of a relay and the d.c. motor kicked into full acceleration, immediately beginning to lay rubber. Acceleration may have brought the speed to about 35-40 mph in the next 45 feet, as I realized what was happening and applied hard brakes to try to slow down as I headed toward the pickup truck. (At that point there was a single skid mark transitioning to two parallel skid marks.)
During the next 90 feet, the vehicle veered slightly to the left (as parallel skid marks indicated). I reached for the panic switch, which forced me to let up on the brakes a little and turn the steering wheel. I couldn't quite reach it as the vehicle swerved slightly to the right while I was still applying brakes and as the vehicle started to accelerate again.
As I approached the back of the pickup truck, but before reaching it, the vehicle flipped right, tipping left as it spun end for end and went into a tumble over the windshield and then falling onto the right side. It did not hit any object. The vehicle, having lost power during the tumble due to the inertia switch, came to rest on its right door after rolling across its nose and sliding some distance backwards on its right side. The cab lay on the curb of the sidewalk, 45 feet from the evident point of the spinout on the opposite (left) side of the road, facing the backwards from the direction of travel. The address is 750 Fremont Street. I release my seat belt and climbed out of the open left window. Power was dead. I wasn't.
I am slightly bruised from hitting my left chest on the steering wheel and have a slightly pulled neck and a bump on my left forehead from bouncing off the left side of the door frame. There have been no other signs of physical injury.
There was no broken glass,
although the windshield cracked, the door hinges of the rear access panel
snapped, and the content of the storage compartment were dumped undamaged out
of the broken door after the vehicle came to rest. The force of the tumble
flipped my eyeglasses from the car through the left open window, probably
during the nose roll. The eyeglasses were found on the left sidewalk about 10
feet past the dead hulk. With the help of a neighbor who heard the skidding
from a block away (and fully expected to find two
crushed vehicles), I righted the car and left it to be towed away.
As an engineer and a driver with 35 years experience (I have owned three Porsches and completely rebuilt and set up the suspension of one of them), I can offer the following observations about the causes and dynamics of this mishap. The power train and motor controller are obviously the initial cause of the mishap. The placement of the dead switch makes it hard to access without diversion from the task of trying to brake and steer a vehicle out of control. (I would suggest putting it in the center of the steering wheel!) The tumbling is the result of unexpected change in wheel loading, possibly uneven braking and loss of traction causing an unbalance in the relatively high center of gravity. The vector of the forward motion from the high center of gravity keeps the car from going into a (preferred) flat three-point spin, which it should do on a skid pad. The road conditions were typical and only slightly irregular, and they probably played little role if any in the loss of stability.
Due to the weight distribution and rear drive setup of the vehicle, this sort of mishap is likely to be repeated. This is not a stable vehicle. Fortunately in this case, speed was not high and the road was clear, or there could have been more serious consequences. As a lawyer, I caution the manufacturer to be warned.
Observations about the street and the damage to the vehicle indicate how the vehicle tumbled and why it is unstable. A very slight depression (less than about ½ inch deep and about 12 inches wide in the road from a utility cut is evident just after the end of the dual skid. The down-path face of the depression shows a fat asphalt patch about 4 inches square that looks like a tire burn, although it could be a preexisting mark. The depression may have caused the rear wheel to lift and lose traction while brakes were being applied, causing loss of tracking and an end-to-end flip. The depression may have played no role in the mishap, as the rear wheel simply spun out. Steering quickness also seemed to play no role, although it is possible that a sharp turn could force the same sort of spinout and tumble.
In this instance a single skid mark of about 15 feet length trails to the left beginning about 10 feet after the end of dual skid mark as the motion carried the vehicle in a slight curve to the left as it tumbled. Body marks on the pavement adjacent the downstream side of the skid mark plus scrapes on the road indicate the vehicle had already flipped end to end before it tipped over first to the left going backwards, leaving rubber from the left wheel.
The vehicle hit the ground in at least four orientations: Left side moving backwards after it tipped over downstream, a nose roll counter-clockwise around a vertical axis rotating clockwise, and right side twice, coming to rest, right side facing backwards. This is confirmed by marks on the street and marks on the vehicle. This kind of rollover can be described as a “break dancer's spin.”
Ken Allen, July 12, 2000