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Originally Posted by chitu
1. If I go for Magnetic Sensors , they do not give the Vehicle Slip So how to accomadate.
2.Radar Sensors Do give the True Ground Speed but they are pretty Costly .
(Any suggestion on RADAR Sensors that are costeffective )
3. If I have to choose among Magnetic Sensors , which would be better .
1. MagnetoResistive
2. Halls / Differential Halls
3. Inductive
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Hi.
In practice, the amount of slippage between the automotive tire and the road surface is negligible and can be ignored. On a robot (I am guessing that's your application?) slippage can be more significant. But, it very much depends on what exactly your goals are.
If you are trying to actually navigate based on pure dead reckoning, your errors will eventually creep up and get you. It's like driving a car with your eyes closed, steering by stopwatch.
The actual type of sensor you use is less important than how you interact with the surface to be measured. All of those technologies will accurately measure the rotation of a wheel, from which you can measure speed and calculate distance (but not direction). You may find that Hall sensors with conditioned outputs are easier to interface than inductive or magnetic sensors, which may require separate conditioning circuitry.
Inductive sensors need a higher wheel speed to give a useful output than magnetic sensors, but they are very similar otherwise. Hall can detect zero speed, as can optical.
Instead of radar, look at optical. Think of your optical mouse - it's pretty accurate, right?
For the rotational sensors, instead of using a vehicle wheel, use a dedicated measurement wheel which will not slip and can sense direction. Think of, say, a baby carriage front wheel - it rotates to allow steering. There's a type of wheel with an offset axle that rotates around the point of ground contact. Now, instead of a smooth wheel, think something with teeth, like a gear, but bigger teeth, that won't slip at all ever.
As the robot moves, the gear senses motion. If the robot turns, a second sensor senses the turning of the measurement wheel.
I hope this helps. If you can get into more details as to the goal, we all can get more exact in our advice.
Good Luck,
Don