GPS for Speed - Page 1
Forum section: electronics / projects

author: guimtl
author_rank: Contributor
timestamp: June 09, 2018, 02:01:15 am
content: Hi,I've been asked to think about tracking max speed of a drag race car.if possible get also average speed and other spec ( like witch car has passed the finish line first and in how many seconds) of a race. on cars and motor bikes... speed and specs can be quite high... 300km in less than 20secs.do you think GPS can be so fast ? I could send data over lorawan and keep tracking gps values....should I focus on a 'police' speed radar instead of getting a GPS in the vehicule.I see tag heuer has 'gates' with '''ir sensors''I don't even know how police radar works yet... just came home and starting thinking about possibilities...what do you guys think ?

author: metrologist
author_rank: Super Contributor
timestamp: June 09, 2018, 02:09:31 am
content: no. think time over distance and fast position sensors

author: guimtl
author_rank: Contributor
timestamp: June 09, 2018, 02:12:52 am
content: what would you call a 'fast position sensor' ?

author: hamster_nz
author_rank: Super Contributor
timestamp: June 09, 2018, 02:18:08 am
content: The internal models used within most GPS have tracking and noise dampening in them.So if you are not moving the models predict you will be still, and that any rapid change in speed is most likely be due to positioning errors.Sudden accelerations can also upset the tracking loops that provide the timing information used to calculate the receiver's position, so you are likely to see a temporary drop in accuracy during sudden accelleration.If you did want to sense speed without external inputs what might work is a sensor that also uses accelerometer and maybe gyro data to augment the GPS info. The buswords to look for are 'sensor fusion' and 'kalman filter'.... or sense the non-driven wheel speed?

author: metrologist
author_rank: Super Contributor
timestamp: June 09, 2018, 02:50:33 am
content: I think you mean 300kmh. 300km in 20 sec is darn fast.sensor speed depends on what resolution you want. if you want 1m resolution, then sensors need to respond in the amount of time it takes a 300kmh to travel 1m.

author: guimtl
author_rank: Contributor
timestamp: June 09, 2018, 03:09:49 am
content: I left my notes at the office, but I think it was a track of 1km and the vehicule was able to get up to 300km...tag heuer should know their business... maybe I should stick to gates...

author: Rerouter
author_rank: Super Contributor
timestamp: June 09, 2018, 03:12:14 am
content: For top speed, I think the 2 line break timing method is going to be your most reliable, most drag race vehicles will cross the finishing line at maximum speed,So you have 2 line break sensors (similar to those they use for store door sensors)When the first 1 breaks, you trigger your camera to take a photo of the winner,When the second breaks, you use a micro or bit of electronics of your choosing to record the delta and calculate the speed,

author: texaspyro
author_rank: Super Contributor
timestamp: June 09, 2018, 05:04:52 am
content: Navspark makes some affordable GPS receivers with a 50 Hz update rate. Here's a paper talking about noise effects:http://navspark.mybigcommerce.com/content/WhyIs50HzGPSSpeedNoisy.pdfBasically with 50 Hz at low speeds noise effects are more prominent than at high speeds.

author: Aeternam
author_rank: Unknown
timestamp: June 09, 2018, 07:26:28 am
content: Formula One uses Correvit optical sensors to measure longitudinal and lateral speed and acceleration:https://youtu.be/4pFxA3h1SSg

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 09, 2018, 03:44:29 pm
content: I haven't formally investigated it, but have found GPS to be reliable and credible (which is different than proven accurate) for acceleration and speed for "fast" production vehicles. With some major caveats. First, there are signs of lag in the faster vehicles I have observed. The second, which may be quite important to you in Canada, is that this reliable performance occurs in the more southerly areas of the US. The worse satellite geometry in northern Oregon and Washington, combined with buildings, trees and other obstacles to GPS reception very noticeably degrades the performance. Even to the point of occasionally changing the sign of the velocity. And finally, when I have operated a GPS on a commercial airliner (I know, against the rules), some models cut off operation at speeds considered not possible for ground vehicles. Somewhere in the neighborhood of 200 km/h.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 09, 2018, 06:16:09 pm
content: If it's a straight track, put a CW transmitter in the car and use Doppler shift relative to a receiver on the ground inline with the track to measure the speed. Easier than trying to detect backscatter off a car that likely has a lot of carbon fiber, although making that work isn't that difficult.