Active Suspension

heshoy

Hi guys, im a student at the electromechanical department in alexandria university, Egypt.
so this is my graduation year and we decided that our graduation project would be "Active Suspension", it detects road profiles and u know "holes and bumbs" and moves the suspension vertically in order to keep a high ride quality, so im in charge of the sensors and how to process the sensor's output, so im gonna need some help with what kind of sensors should i use for detecting the depth of the road? its gonna be mounted at the bottom of the vehicle and actively measures the distance between the vehicle and the road
after all the googling ive done i found that the best option is the ultrasound distance sensor but i have no experience at all with it, so pls guys help me with any recommendations and suggestions, sorry for making it long

Gadgetman

The best sensors for this is some kind of laser, but then you'd be talking quite expensive stuff.
(There are commercial equipment out there for measuring roads, mostly for wear management on asphalt, but it's a small market, so really pricy)

I fear that Ultrasonic isn't going to work very well on a moving vehicle. At least not if it moves quickly.
(You will at least have to take the speed into consideration regarding doppler and so on, and it must be pointed forwards. It's too late to detect a bump if it's already at your wheels)
but as this is the type of equipment that you're more likely to be able to source cheaply, it's the way to go for the moment.
I would use at least two sensors, pointing forward in a 45degree or flatter angle, one in front of each front wheel. (pot hole detectors)
A third one, also facing forward, in the centre can be used as a 'general quality' and reference.

What kind of suspension are you going to use?

Personally I prefer the Citro

Mark_T

Hmm, sounds quite a hostile environment for ultrasound, given tyre noise, air turbulence... High Q transducers would help filter out stray signals including doppler-shifted reflections and tyre noise. Pointing slightly forwards of straight down seems a good starting point, you want strong signal from square-on reflections, but you want to compensate for the moving air dragging the signal backwards at speeds of interest. You might want transmitter fairly forwards of receiver to allow for this drag.

shimniok

Sounds like a fascinating project!! Is this going on a real vehicle or is it a proof of concept? A Sharp IR sensor should work ok for a proof of concept. Otherwise, you might look at using a simple laser pointer mounted near a camera (e.g., CMUcam) to detect the "dot" and calculate the position of the road directly in front of the tire using parallax. What about sensing the movement of the shock/tire relative to the suspension and actively changing damping based on that?

Erlend

There should be lots of space below the vehicle motor. You could mount a 1x2' metal plate there - on insulators - and treat the plate-ground as a capacitor. Add an oscillator circuit and you would have an ultrafast distance detector, where distance is a function of frequency. Of course to make this work you need also to have some connection to ground, but it could be really high impedance so should not be hard to fix.

Erlend

Edit:
You should go for the 'Derivative' part of PID control algorithm, meaning it is only the change rate of the distance that matters. That way you do not need to worry about calibrating distance, changes due to humidity, etc.

heshoy

Thanks a lot for all your responses guys u really inspired me with a lot of thoughts, but i had many questions and i wish u guys can answer it, since im a complete beginner here..
i wanna measure the height of the bump as i get closer to it and the sampling rate has to be high, my model is gonna go for 1 meter/sec only though, so putting that in mind which is better laser or ultrasonic or IR sensors?
another thing is, im not gonna measure depth of a flat surface, its gonna be "curvy" so im not sure if the laser sensor is a good idea here since the reflected beam might go somewhere else far away from the receiving end, so im looking forward to see ur suggestions, again thanks in advance
Regards.

edit: guys i was watching a video and seems like there is other suggestions, they are similar in the components needed. they both require a horizontal laser beam and a camera, as the surface gets closer the laser beam becomes "horizontally shorter" and somehow the camera detects the length of the beam
the second method is by detecting the whole beam intensity as light intensity decreases as distance increase, what do u guys think?

heshoy

shimniok wrote: »

Sounds like a fascinating project!! Is this going on a real vehicle or is it a proof of concept? A Sharp IR sensor should work ok for a proof of concept. Otherwise, you might look at using a simple laser pointer mounted near a camera (e.g., CMUcam) to detect the "dot" and calculate the position of the road directly in front of the tire using parallax. What about sensing the movement of the shock/tire relative to the suspension and actively changing damping based on that?

thanks a lot firstly, secondly to answer your question about sensing the shock , we thought about that but we arent sure that the response of the motor would be fast enough to do some lifting action while driving through the bump, predicting it first with a sensor would make it faster i guess.
what about the laser and the cam thing? can u tell me where can i find more information about that and how to interface that with a servo motor?

RickInTexas

I saw this EE Project a while back, looks pretty cool, and more ambitious than what I sense your after.

[h=3]Robotic Surveyor[/h]

shimniok

heshoy wrote: »

thanks a lot firstly, secondly to answer your question about sensing the shock , we thought about that but we arent sure that the response of the motor would be fast enough to do some lifting action while driving through the bump, predicting it first with a sensor would make it faster i guess.

Don't guess. Calculate. You're an engineer. You can't just toss out ideas -- you have to actually analyze and evaluate them

Doesn't the motor have to move the suspension just as quickly as the terrain fluctuates relative to the wheel? If the motor is too slow how does starting early help? Extreme case, let's say you're traveling fast enough that the bump comes and goes under the wheel in 0.1sec but your motor takes 10 seconds to lift. You can start 10 seconds early but what will happen?

what about the laser and the cam thing? can u tell me where can i find more information about that and how to interface that with a servo motor?

Say you have a laser and camera mounted facing the same direction but a few inches apart, and angled towards each other. You have a box 6" away and you angle the laser towards the camera until the laser dot shining on the box shows up in the center of the camera's image. What happens to the laser dot in the camera image if you move the box farther away? Or closer?

You might look at using a Wiimote camera. It operates at 120 fps and works great with a low power infrared laser. also, one camera can sense multiple lasers.

Michael

heshoy

RickInTexas wrote: »

I saw this EE Project a while back, looks pretty cool, and more ambitious than what I sense your after.

Robotic Surveyor

Thanks a lot rockintexas that raised my hopes too, i read the whole page u sent me but they didnt mention the type of ultrasonic sensor or linear motor they used, do u know exactly the components they used?

rwgast_logicdesign

i second the above push for the wiicam. i have a few wiimotes i specificaly bought for lidar type stuff. anyways since the wiimote is pretty quick and is able to see 4 lasers, it may be able eliminate the problems with the suspension rsising or lowering to laste. using a wii cam i could detect bumps waayyy before the bot is there, and if u set 4 lasers in a line a few feet apart hitting the ground in front of you, you can sample 4x the data. the wiimote cam is also 200hz i belive meaning you can get two hundred samples of four lasers a second. im putting two cams on my bot, just found a killer deal on geniune wiimotes