Get the SoR Robotics Android App on Android Market for FREE. See this forum post for details.
0 Members and 1 Guest are viewing this topic.
[...] I am looking to acquire a sensor that will: 1. Run on 5v power. 2. Measure tilt from 0 to ~90 degrees. 3. Output 0.5v at 0 degrees. 4. Linearly increase output to ~4.5v as the unit reaches a ~90 degree angle.
Hi,Quote from: DigglerD on April 05, 2010, 03:45:40 PM[...] I am looking to acquire a sensor that will: 1. Run on 5v power. 2. Measure tilt from 0 to ~90 degrees. 3. Output 0.5v at 0 degrees. 4. Linearly increase output to ~4.5v as the unit reaches a ~90 degree angle.It's pitch (as related to your rear axle) that you wanna measure, so you should be looking for a gyro.Don't mine your specs too much. I guess you have 12V (or 24V) allready and the rest is just creating the interfacing to suit your ECM.Actually, it doesn't even have to be particularly linear, as it will be a closed loop (motor, chassis, gyro and all). And it should never get anywhere near 90° as long as the electronics work A couple of other possible ways to detect front end lift:- IR distance detector (but it may be too slow?).- Strain gauge on the front suspension.(just off the top of my head - there's allways several ways to shave a goat).Btw. How long time from start to a lift of say 5°, 10°, 15° etc. (just trying to get a comprehension of what timing restraint there will be).
I wonder if an ultrasonic range finding is fast enough? The idea of measuring how high the front wheels are off the ground sounds to be the most reliable to do.
I like the idea of setting 0 with the clutch (or in my case, transbrake) as that would be very simple. However, my understanding of gyros is that they measure the speed of change in tilt but not the actual angle of tilt... I need the latter.
I will check out the boat idea... do you have any idea what the assist may have been called?
correct. you would need to integrate the output.not really a problem though. if your rate of change becomes anything other than zero then you need to ease up on the throttle.have you any electronics or programming experience? you will probably need a simple microcontroller to read the rate gyro and convert the output into something your engine management understands.
if you want a ready made circuit along with a (non C) programing and development environment, Arduino.cc has a big following.personally, i don't see the point of the Arduinos as it is just an AVR chip with a clumsy programing environment but they have a huge user base so there must be some advantage. bear in mind, i tend to like doing things the hard way... i think the Arduinos are fairly easy to get started on.dunk.
my timing computer has a 5v output for sensors.
Why not linear? I figure as tilt increases, my correction should also increase. But yes... 90 degrees and we're beyond sensors and correction
How would you go about this method?
The infrared sensor was my first approach. I purchased one of these [---] and it actually ...kinda works but the measurements don't seem reliable and, I was worried about terrain irregularities as the car moved down the track.
A strain gauge (or distance sensor) on the front suspension will only tell me when the front suspension is fully unloaded. At that point, the wheelie can be 1" high or 4' high with the same reading from the sensor. In my application I would prefer to have the front wheels around 1" off the ground (full strain or travel) as this will apply maximum weight (traction) to the rear wheels.
I'm not precisely sure on my start time but luckily my ECU has a graph where I can plot my start based on the voltage output of the sensor. In this sense, the sensor can be really dumb as I have upstream devices that can handle the extra computing.
It's not to avoid linear, but it just doesn't matter very much, as you just want to have X amount of tilt. If X rises a little, you counter it a little, if X goes high, you counter a lot - main thing is that you end up where you wanna be.Since 90° is bad, you want full correction to come on before that point anyway (unless you're related to Evil Knievel of course ).
You obviously can regulate down with a signal of 0.5V to 4.5V, or is that the total voltage controlling it that you want to modify?
That is probably due to missing decoupling and shielding - I imagine a drag racer being even more (electrically) noisy than a street car.You probably would be better off with a sensor covering a shorter distance, as you will then get more resolution over the range you will be using. Take a look at this page at the bottom of which is a comparison table to the different sensors (and each page has got a datasheet link for that sensor).Mounted in a suitable height, I can't imagine it should have any problems with irregularities on a track (or the cars would as well). Besides, do you plan on doing the entire track with your front wheels in the air? (Oh well, just watched the video link that didn't work yesterday... Seems that's the way to go - saves on front tires as well ).More than 1 IR sensor could be used (just like the auto-focus on a camera) and the result averaged.
Would the traction change much from barely touching (i.e. a few kg max. on the front axle) to 1" above ground?
If 1" above ground is the sweet spot, why don't your ECU take that into account - I imagine that a race ECU is a bit optimized compared to a street car (just look at Mega Squirt and it's still for street cars) and I would think that it would be easy to measure when the least power is wasted (something like: power applied/[mass x acceleration])?
I have never been to a drag race (or tilted a drag queen for that matter ), so I have no idea of how fast a car goes into the air. Are we talking 10ms, 100ms, 1s or something different (just a ballpark guess based on your experience).
You can reliably measure the tilt angle using a 2 axis accelerometer with a single axis gyroscope. The sensor readings are fusing using a Kalman filter.Your requirements for measuring the tilt angle were:1. Run on 5v power.There are many accelerometers and gyroscopes that run on 5V.2. Measure tilt from 0 to ~90 degrees.The accelerometer can read angles from -180 to +180 degrees. The gyroscope just reads angular velocity, the rate of change of the angle.3. Output 0.5v at 0 degrees.Using a 5V power supply, the accelerometer will read 2.5V at 0 degrees, lower than 2.5V for negative angles, and higher than 2.5V for positive angles. The gyroscope will read 2.5V at 0 degrees angular velocity, lower than 2.5V for counter clockwise rotation, and higher than 2.5V for clockwise rotation.4. Linearly increase output to ~4.5v as the unit reaches a ~90 degree angle.The accelerometer will give you a linear output voltage from -180 to +180 degrees. The gyroscope will give you a linear output voltage between its maximum rated angular velocities.Remain unaffected by lateral acceleration and deceleration.The Kalman filter removes high frequency noise from the accelerometer readings, the type you get when you violently shake the accelerometer, and uses the resulting signal to correct the gyroscope drift.I have used this exact combination in my balancing robot, and it works great.Good luck!