General > General Technical Chat
Electric car for £9500?
tggzzz:
--- Quote from: Siwastaja on October 12, 2023, 05:34:37 am ---
--- Quote from: tggzzz on October 07, 2023, 08:30:53 pm ---What's the peak and mean LIDAR output power? How does that compare to eye-safe limits/
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I don't know exactly in numbers, but what I do know is that industrial LIDARs that have been approved to use in the middle of people (e.g. workers in factory) and where direct eye contact just centimeters apart does no harm, have been demonstrated in use in automotive conditions (e.g., rain) and work fine, too, to distances of at least 100 meters. The problem is mostly in price (and all those nasty engineering details like keeping the sensor glass clean, but apparently they somehow manage to do that with cameras, too.
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I presume the required power is the same as for RADAR, i.e P=range4 See p16 of https://www.ll.mit.edu/sites/default/files/outreach/doc/2018-07/lecture%202.pdf Thus if, say, 1mW is sufficient for 1m then 10W is required for 10m and 100kW for 100m. Ouch.
But that's peak power. In slowly changing environments the environment won't need to be "sampled" often, so the mean power could be much lower. But streets are fast-changing, so the mean power would be higher.
Overall, "numbers, not adjectives" are necessary :)
Siwastaja:
--- Quote from: tggzzz on October 12, 2023, 09:49:25 am ---Overall, "numbers, not adjectives" are necessary :)
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On the other hand, you can observe the fact that an apple falls from a tree towards the planet, and an airplane takes off and flies, without knowing the value for g, or how the wing aerodynamics are calculated. I have made a similar observation about LIDARs. They exist in full-autonomous car prototypes I have personally seen demonstrated, using the exact same LIDARs sold for industrial environments approved working close to humans, and I have personally seen these LIDARs map obstacles in automotive environment. Thus, I don't need to know what the exact power is, and how eye safety is exactly proven; this would require deep dive into the relevant legislation and look at the LIDAR manufacturer's (e.g. SICK).
In the end, devil is in details and I don't exactly know how well modern state-of-the-art LIDARs perform in presence of thick rain/snow, but my educated guess is, they do work, unlike cameras. One distinctive feature of a modern LIDAR is, for given direction, it can represent multiple echoes (distances).
tggzzz:
--- Quote from: Siwastaja on October 12, 2023, 10:31:56 am ---
--- Quote from: tggzzz on October 12, 2023, 09:49:25 am ---Overall, "numbers, not adjectives" are necessary :)
--- End quote ---
On the other hand, you can observe the fact that an apple falls from a tree towards the planet, and an airplane takes off and flies, without knowing the value for g, or how the wing aerodynamics are calculated. I have made a similar observation about LIDARs. They exist in full-autonomous car prototypes I have personally seen demonstrated, using the exact same LIDARs sold for industrial environments approved working close to humans, and I have personally seen these LIDARs map obstacles in automotive environment. Thus, I don't need to know what the exact power is, and how eye safety is exactly proven; this would require deep dive into the relevant legislation and look at the LIDAR manufacturer's (e.g. SICK).
In the end, devil is in details and I don't exactly know how well modern state-of-the-art LIDARs perform in presence of thick rain/snow, but my educated guess is, they do work, unlike cameras. One distinctive feature of a modern LIDAR is, for given direction, it can represent multiple echoes (distances).
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Points taken, but how wings work is an exceptionally bad example: most explanations - especially in school textbooks - are simply wrong!
I think you'll find there are cases where LIDAR is better than cameras, and vice versa. "Sensor fusion" has long been an interesting and important topic.
W.r.t. multiple echoes/distances, that introduces ambiguities as well as resolves (ho ho) them.
tom66:
What I don't fully appreciate with LIDAR is, when a substantial number of cars are running LIDAR, will there not be an issue with interference between similar LIDARs using similar wavelengths? I presume there is some kind of CDMA or similar on the light pattern, but still could imagine eventually the additional light will reduce the sensitivity too much as it becomes difficult to separate 'your' code from 'their' code. But maybe this limit isn't reached in practice.
coppice:
--- Quote from: tom66 on October 12, 2023, 12:05:32 pm ---What I don't fully appreciate with LIDAR is, when a substantial number of cars are running LIDAR, will there not be an issue with interference between similar LIDARs using similar wavelengths? I presume there is some kind of CDMA or similar on the light pattern, but still could imagine eventually the additional light will reduce the sensitivity too much as it becomes difficult to separate 'your' code from 'their' code. But maybe this limit isn't reached in practice.
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LIDAR is highly directional, so the conflicts are probably not that big an issue. What happens as more and more cars have ultrasonic and radar sensors, with quite broad beams? The ultrasonic stuff is only going to mess things up at low speed for other cars close in, but radar cruise control illuminates quite a lot of cars on a busy highway.
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