hello guys,
i need to know if there is anyway to create a speed detector for an rc car or anything that moves ?
if yes i need to know please how or where to look at a tutorial about this ?
For the 'anything that moves' part you would probably need a Doppler radar gun, but that's not an Arduino project. If you restrict yourself to RC cars then you could measure the speed by using two vehicle sensors a known distance apart and timing how long it took to cover the distance between them. The challenge would be what sort of vehicle sensor to use. One possibility is to use a light beam and detect when the beam is blocked by the vehicle.
It depends on the track and environment.
you can use an acceleration sensor and integrate the acceleration over time to get the speed. By doing that in 3 dimensions you can get the speed of the car.
i need to know if there is anyway to create a speed detector for an rc car or anything that moves ?
More than one way. You could use an encoder on a wheel, and determine how fast the wheel is turning. Assuming negligible slippage (not necessarily a valid assumption for an outdoor vehicle), you'd know the speed of the car (with a little math involving the wheel diameter).
Or you could use a ping sensor to measure the distance to something. As that something (it doesn't really matter what) changes distance, you'd know the car's speed.
Of course, if there is nothing around, then you have a bigger problem. Radar might work, but that's not cheap.
GPS shield and math
thanks guys for all the suggestion well 2 of them got my attention the most first one is the accelerometer and the second is the wheel speed
so about the wheel speed what king of encoder can i use ? is it expensive ?
can be a rotary encoder - Rotary Encoder - COM-09117 - SparkFun Electronics - you need to use interrupts to capture all pulses
robtillaart:
can be a rotary encoder - https://www.sparkfun.com/products/9117 - you need to use interrupts to capture all pulses
ah ok the rotary so i attach it to one of the 4 wheels inside the axis ?
PaulS:
Radar might work, but that's not cheap.
Radar guns (for sports use) are actually fairly cheap - around $100.00 USD. There's also the Hot Wheels version - which can be had for little money if you get lucky at a thrift store (that's how I found mine - got it for $5.00 a few years ago).
if you use a wheel encoder, put it on a non-driven wheel for better accuracy.
RC cars also use some sort of PWM for speed control of the motor, and typically there's little to no slippage between motor and wheels once you're going. And you might be able to measure the rotation of the driveshaft or a gear in the differential easier than a wheel. Google Hall effect sensors. Hooking one up to a Arduino should be fairly simple, I think.
There's even some code out there.
cptdondo:
RC cars also use some sort of PWM for speed control of the motor, and typically there's little to no slippage between motor and wheels once you're going. And you might be able to measure the rotation of the driveshaft or a gear in the differential easier than a wheel. Google Hall effect sensors. Hooking one up to a Arduino should be fairly simple, I think.There's even some code out there.
probably this one is the greatest and cheapest idea !! Thanks a lot i have to pit a sensor near the wheel plus a small magnetic peace which will give HIGH on the Input pin and then count one round, then i must measure how much distance the wheel go with one round and for how long and the last step i divide the distance by time and i get the speed amazing i started to love Solid Dynamics course finally !!
genius !!
thank you all of these can be useful for a perfect car 
You can build a rotary encoder yourself. Then you can customize it e. g. to the space available. In my blog I wrote a series of posts about rotary encoders. It begins with the basics of photointerrupter use and goes to a rotary encoder that not only gives you pulses but also gives you information about the turning direction. If interested look here:
about photointerrupters:
about rotary encoders:
The software side is due to come.
Hope this helps
Elektrix
Elektrix:
You can build a rotary encoder yourself. Then you can customize it e. g. to the space available. In my blog I wrote a series of posts about rotary encoders. It begins with the basics of photointerrupter use and goes to a rotary encoder that not only gives you pulses but also gives you information about the turning direction. If interested look here:about photointerrupters:
photointerrupter basics - heliosoph
photointerrupter schematic details - heliosophabout rotary encoders:
Make your own rotary encoder - heliosoph
Make your own quadrature rotary encoder - heliosophThe software side is due to come.
Hope this helps
Elektrix
great stuff of course it help and i understood it when i opened the page because i have taken a course about encoders and sensors
thank you i will look at the way to make it as soon as i finish my exams
hello guys,
i was building the hall effect sensor method, but actully this method doesnt work when the wheel gets up to speed, it works only for low wheel rotation speed 
and i guess same for the IR diode receiver because in the video it works when the wheel rotation speed become lower
so any idea how can solve this problem ?