Caito wrote:Hi Guys!
I was thinking if there was a way to make a fairly "cheap" slip angle sensor. Or put in other ways, a device that could measure longitudinal and lateral speed with respect to ground. Based on other commercial sensor I've seen, I believe ca. 25Hz is enough.
Of course, one alternative is to use optical mouse sensors. Although they have a limited speed capability, you could put another sensor to have a broader speed range. Still, it doesn't sound easy enough, you need optics, sounds unreliable (at least for me).
Nowadays having so much data throughput and processing capability I thought why don't just point a camera to the ground. Then you just find a reference in the image and see where it moved on the next image. It needs quite some processing, but that's offline and is "easily" done. Basically you can move images to find the point of max correlation, or actually search for on piece image on the other, etc. There are many ways to do this.
My question is how blurry would that image be?
As some ball park number. Imagine capturing a spot of 20x20cm and a frame of 500x500 pixel, this means 40mm per pixel. If you want a "still" frame, you would want less than a 40mm movement. Suppose we want this until 50 m/s (180 kph), this would be a 1/1250 shutter speed. With 20cm movement being the maximum allowed between frames, we need a 250Hz frame rate. As you increase spot size you reduce the frame rate, but would increase error I guess.
But I don't know much about photography so that might as well be pure bs.
Do you think something like this could work? Is it worth a try? What problems can you see?
Yes it is, but if you look at the sensors, they're usually tiny and very specific. Quoting one of Agilent's datasheet, max speed is 12ipm (roughly 110kph) and would require specific lenses to make it work at the distances and speeds required. It's not simple enough.langwadt wrote:
an optical mouse is a camera
That's not enough to calculate slip angle. GPS is horribly noisy and imprecise. You need accelerometer AND gyroscope measurements to correct it and even then its not a particularly robust or precise measurement.NL_Fer wrote:The cars have g-sensors and gps right?
What if you use the non-zero exposure time of a single frame and calculate the angle directly out of the streaks of the asphalt pattern of one single picture?Greg Locock wrote:If you imagine two consecutive frames of a speckled pattern, how quickly can you decide on the 3 possible transformations between the two? (rotation and x and y).
mrluke wrote:Do you really want a super sharp image?
Using a known shutter speed wouldnt the extent and direction of the blur tell you the movement / slip? Actually if you could measure it very precisely wouldn't it actually give the slip angle?
This idea (from both of you) seems to be the most straightforward. As long as the asphalt is not too smooth. I guess you would want to aim the camera somewhere between the wheels, away from the tire tracks that are rubbered in.Shooty81 wrote:What if you use the non-zero exposure time of a single frame and calculate the angle directly out of the streaks of the asphalt pattern of one single picture?