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skelstar
4th April 2006, 14:41
Im an electronics eng. and I have been having a bit of a play with an IC (chip) that has a 2 axis accelerometer built into it. What this means is that it measures the amount of acceleration/force in two seperate directions (outputs an analogue voltage).

My question is: Can anyone see a use for this on a bike...ie. on the track?

My initial idea was to use it on a bike to measure acceleration/decceleration and maybe work out cornering speeds and forces. This thing would be able to tell you how hard you are cornering. I thought it could be used to record lean angles but due to the construction of the device its effected by gravity. What I mean by that is that if you hold the device flat, then tip it over 90 degs the output voltage will change. The bike tips when it corners and therefore the devices output changes with both gravitational force and centrifugal acceleration.

So....any thoughts?

I figured with a bike that has a digital speedo/tacho you could collect some interesting data. Would be difficult to collect realtime, but maybe good for practicing on a particular track. Have the same type of unit on two different bikes and it would show what each bike is doing?

skelstar
4th April 2006, 14:43
Datasheet for said device is here:
http://www.ortodoxism.ro/datasheets/analogdevices/573918736ADXL150_250_0.pdf

Motu
4th April 2006, 14:49
I use one for brake testing every day...I guess I could turn it backwards?

skelstar
4th April 2006, 14:50
You could. You could put four of them on your bike ;).

bugjuice
4th April 2006, 14:54
you could really use a 3rd sensor, to measure outer g's too. There's the forward and backward motion, tilt/lean motion, then the 3rd being the lateral forces pushing down the bike as you're cornering

skelstar
4th April 2006, 14:59
Well imagine the chip has two sensors that measure in the same plane as the chip. X being forward and backward, Y being side to side. The X part is easy, the chip doesnt change its' attitude' in that plane (unless monos), but the side to side stuff is harder. Unless you can stop the chip/package from tipping with bike, the Y axis is never going to be in the same plane as the lateral forces due to cornering. There will be a component of gravity too. The only way I can think of getting around this is by putting it on your helmet as you head doesnt/shouldnt really tip with the bike.

RantyDave
4th April 2006, 15:03
I have been having a bit of a play with an IC (chip) that has a 2 axis accelerometer built into it. [snip] I thought it could be used to record lean angles but due to the construction of the device its effected by gravity.
Ummm, skel, gravity is an acceleration. As for actual practical uses I dunno but will leave it in the back of my head and see what we come up with.

You could stick one at either end of a shock absorber and use the difference to derive some description of behaviour curve. A nice graph showing what it is that an Ohlins does that a generic doesn't? Repeatable shock settings?

Should be pretty trivial to use an accelerometer to do halfway scientific testing of brake pad material...

Any plans on what you're going to use to collect the data?

Dave

skelstar
4th April 2006, 15:19
Yeah, know about Grav and acc. I have it set up so that if I start the device, and tip it up 90deg it measures 5VDC, tip it back and then back another 90degs (ie 180deg in total) it reads 0VDC. Its all gravity. A guy at work is wanting to use it as a yacht heeling/lean indicator. Hence my thought about bike lean angles.

Collection via a micro. A PIC18F252 to be precise. Probably just logging the data and spitting it out via rs232 back at the pits.

Like your 'shock' suggestion though.

Motu
4th April 2006, 15:21
You could. You could put four of them on your bike ;).

My brake tester also checks for lateral forces too,it picks up brakes pulling to one side.Not really useful as it only measures max and average results.

RantyDave
4th April 2006, 15:39
A guy at work is wanting to use it as a yacht heeling/lean indicator. Hence my thought about bike lean angles.
Ah, right. Difference is that a heeled yacht is going in a mostly straight line whereas a bike going round a corner is experiencing centripetal acceleration. In fact if you measure the heel on a bike using an accelerometer it'll measure zero since the forces (torques) have to all equal out to prevent angular acceleration round the roll axis ... otherwise known as falling over.

You could measure tip-in accelerations though. You'd get cool numbers from high siding too.

PIC is a good choice.

Will think some more about characterising shock absorbers.

Dave

skelstar
4th April 2006, 15:50
The way this thing is constructed, it will measure gravity at rest. If I sit it on the desk, I can tell you which way up it is based on the voltage its spitting out. If I stick this on the deck of a yacht, it will tell you what the heeling angle is. Static. The construction inside the chip amounts to something that behaves like a strain guage (like a modern electronic scale). Does this mean I have to allow for different gravitation constants? ;)

An idea for use of the data from riding around on a motorbike. Just demostrating the lateral forces:

cowpoos
4th April 2006, 16:03
if mounted on a wheel it could measure the gyroscopic forces... lmfao....lol.....bwaaaaaaahhhhhhh....he he he he.....lol

2much
4th April 2006, 16:04
I'm guessing these are used in G-tech meters. I've used a G-tech meter on my car a number of times, and it would work the same on a bike. It can give you 1/4 mile times, 0-100 times, cornering G's, braking G's, etc...

Here's the info on it: http://www.gtechpro.com/

skelstar
4th April 2006, 16:04
Oh dear, I kinda expected that poos. Do I get an assist? ;)

sAsLEX
4th April 2006, 16:05
I am nearly an Engineer, and am building a Inertial Navigation system using Micro-Electromechanical Systems accelleromaters and Gyros with GPS updating using Kalman filters.

Will give pitch roll heading basically the full navigation solution, but the MEMS thingys have quite bad drift in the gyros etc which is why I am using the GPS to update its initial position estimates regulary to limit the effect of the drift.

Was going to trail it on my bike depending on how small I get it.

2much
4th April 2006, 16:09
I am nearly an Engineer, and am building a Inertial Navigation system using Micro-Electromechanical Systems accelleromaters and Gyros with GPS updating using Kalman filters.

Will give pitch roll heading basically the full navigation solution, but the MEMS thingys have quite bad drift in the gyros etc which is why I am using the GPS to update its initial position estimates regulary to limit the effect of the drift.

Was going to trail it on my bike depending on how small I get it.

Oh please can I have a play? What a great way to measure the height/angle of your wheelies and stoppies!

RantyDave
4th April 2006, 16:10
An idea for use of the data from riding around on a motorbike. Just demostrating the lateral forces:
Eh?

That's just my point, from the perspective of something rigidly mounted on the centre of gravity of the bike+rider there are no lateral forces. All the forces act directly "down" through the wheels. Even when cornering. If it wasn't for riders hanging off (which buggers up our sums by changing the CoG) then you'd be able to calculate the centripetal acceleration acting on a bike purely by looking at it's lean angle.

I'd suggest reversing the operation and calculating lean angle by measuring force acting downwards from the bike's perspective, but that wouldn't work because you'd get false numbers when the bike accelerates in the vertical plane for some other reason - going up a hill, hitting a bump, running over a toddler ... that sort of thing.

We're easily getting into the "needing a piece of paper" territory here. Which means only one thing, needing a pub. Should we reconveine the KB bike telemetry and shit talking project after TCWNR at some point?

Dave

skelstar
4th April 2006, 16:46
Could do re: pub. Weds is 'visiting my non-mb mates' night at the moment.

Maybe Newbies ride this month.

Theory: you are right Dave. Peice of paper and workmates and we have worked it out (with your guiding :)).

All of the force is directed straight down through the tyres/seat. ie in the vertical plane of the bike (g in pic). We know what the force is due to gravity. So if we drew a vector triangle (see pic), we know two sides v and g, so we can measure the angle. Going up and down hills/slopes will be an issue though. Not too bad on the track though.

stanko
4th April 2006, 17:45
You could make a Dynomometer. You can measure rpm, the mass of the bike and the acceleration So you should be able to calculate the horsepower of the engine. its just like a rolling road dyno except instead of accelerating the known mass of the drum you use the mass of the bike. Needs maths that I cant comprehend - but talks cheap!

skelstar
5th April 2006, 08:40
Woo, another idea: put a sensor above the back wheel (measuring in the vertical axis) and a sensor on the swing arm (again measuring in the vertical axis). Take the difference between the two signals....shows how the suspension is travelling for suss settings...

RantyDave
5th April 2006, 08:47
You could make a Dynomometer.
Absolutely! The maths is easy, the hard part is opening the throttle and leaving it absolutely _pinned_ until you get to max RPM.

"But we were doing a dyno run, officer"

Dave

sAsLEX
5th April 2006, 08:51
Woo, another idea: put a sensor above the back wheel (measuring in the vertical axis) and a sensor on the swing arm (again measuring in the vertical axis). Take the difference between the two signals....shows how the suspension is travelling for suss settings...

Linear potientiometer would be a million times easier

skelstar
5th April 2006, 09:09
But a potentiometer isnt going to tell you what the whole bike is doing force-wise, only the seat. All bumps/corners are not created equal.

sAsLEX
5th April 2006, 09:15
But a potentiometer isnt going to tell you what the whole bike is doing force-wise, only the seat. All bumps/corners are not created equal.


Keep the strapdown INU on the bike and have the potientiometer as well, should be easy to log another signal that needs little maniupulation compared to another accelerometer etc

skelstar
5th April 2006, 09:29
True, but if you have two devices (very cheap I think) that are reading with the same magnitude and can be setup exactly the same, then they are easy to compare against each other. Besides, you are going to be using an ADC for the pot or accelerometer anyway. I like avoiding using mechanical devices anyway. These units can be potted in resin and would be near bullet-proof.

sAsLEX
5th April 2006, 12:46
Datasheet for said device is here:
http://www.ortodoxism.ro/datasheets/analogdevices/573918736ADXL150_250_0.pdf

heres my beastie http://www.cloudcaptech.com/crista_imu.htm

skelstar
5th April 2006, 12:52
Looks pretty cool. Cost?
Found another chip by freescale that is 3D and is pin configurable for 1.5G,2G,4G, 6G...US$10. Measures 6mm x 6mm.

sAsLEX
5th April 2006, 13:11
Looks pretty cool. Cost?
Found another chip by freescale that is 3D and is pin configurable for 1.5G,2G,4G, 6G...US$10. Measures 6mm x 6mm.

No Idea, I aint paying.

R6_kid
5th April 2006, 18:53
i've seen a fully done setup for sale on trademe for around $750, had a digital output on it so you could see what was going on at any given time, and also a computer output.

I think some skylines came out with one inbuilt into the dash, so there is a use there. If it works i'll take one. I find stuff like that really interesting, even if i cant really work out what it means :doobey:

FlyingDutchMan
6th April 2006, 09:36
I've been working with an accelerometer at work. Goes +-3G in two axis. Quite a cool little thing, but as discussed ealrier on, its not much good for accurately measuring lean angles. If its static, it can measure them pretty good - but to make sure you've got a good reading, you have to take the ambient temperature into account.

skelstar
6th April 2006, 09:41
Got a 3 axis one today. Will have a bit of a play.