Hi all, for my uni design project i need to determine the rate at which front suspension moves through its travel on a mtb when riding off road, to get an average result on how much the suspension moves in a certain amount of time. I've thought about using a linear potentiometer or a linear variable differential transformer but they are super complicated and the uni won't be keen on letting me ride around with them connected to my bike. Can anyone think of a simple method i may be over looking.
Thanks in advance

iPhone accelerometer?

http://www.apptism.com/apps/acceleron

(There are probably other apps, that's just the one that turned up first with a bit of searching)

thanks Jim, don't think the app would work as i need to measure the relative movement between the fork crown and the suspension lowers, i think the app would measure the whole movement of the bike.

Not if you strapped your phone to the stanchions?

Hmmm, I suppose you're right. Two iPhones then, one on the brace and one on the crown 🙂

Ha don't even have one iPhone!

borrow the data logger and pot,, you can ride inside make yourself a minitest track,,
i have used a ladder laid flat on the floor and ride over the rungs,,try this first as you have a known input as in the real world you have no idea what the input is

you can look for jack down ( front end getting lower as you ride along the ladder normal cause too much rebound)

i have done tests with accelormeters on on the wheel rim one on the hub and one on the bars,, this was a static test on a vibration rig ,,

interestingly we could see virtualy no difference between the rim and hub

I have run dataloggers on DH bikes ,, and they survived important thing to note is the logging rates must be at least 10 x your fastest movement i have recently been doing some work with Brookes uni on this sort of stuff

Video camera mounted on downtube with reference marks on lowers and uppers. Am sure some analysis tools for the resulting (preferably high speed) video already exist… somewhere.

a video camera on the down tube filming the lowers looks quite cool (dunno if it would be any use though)

1000fps video camera? Either off bike if a sample of a few seconds is enough, or bodge a mount and ride with it.

strap it to the sliders, you'll get slider accelerations, strap it to the stanchions and you'll get frame accelerations. Use 2 and you'll be able to do the maths to determine the difference I suppose. You can use linear pots fairly easily with the right portable datalogging kit.

In fact there's an easy way of doing this (for someone with electronics knowledge) – use the linear pot as part of the tuning circuit for an oscillator (ie. get a change in frequency from the change in resistance) and use a cheap MP3 voice recorder to record your "sounds". Then take those sounds and compare to known frequencies for different extensions – bingo, cheap, easy, portable datalogging. (you'd need to check up on the sample rates of the recorder and ensure your tones were within its visible spectrum of frequencies, and as mentioned above make sure the sample rate stays well above the suspension motion rate (3-4x is usually plenty to reconstruct a decent signal).

cheers for the help guys, I have some linear potetiometers, which I think Coffeeking means, as the resistance changes as the pot moves, this would give me good indication of travel to resistance.

Ade ward, think this way would work but my uni aren't sure what gear they haver that I could use :/

I thought of using the infra red dots they use for mapping the movement of humans, for modelling, thought they'res issues with that method as well!

Yup, the linear potentiometer (pot) will do it if you can mount it well enough. The reason I suggest converting resistance to frequency is that logging DC signals takes more specialist equipment (though it's far from hard) and I was hoping to find you a solution you could do with some bits from maplin and some software, rather than dragging about IR dot-making kit or pro dataloggers. The latter would obviously be the best solution if possible!

I think the ir dots thing has potential,, we use dartfish software for biomechanics,, and it is good but it may have a problem tracking as you ride past,, or the camera would need some sort of outrigger off the side of the bike ,,to get both the spots in frame
i have only seen it measure realtive angles and not velocities,,

I'm loving the over-complication factor here. Seriously, how complex and how many errors do you want to introduce? Outrigger vibrations, scaling etc etc.

£5 of maplin electronics, £20 mp3 recorder and a bit of simple framework to mount the linear pot and you have a fully portable device with up to 44khz sample rate and the files are directly accessible using dozens of bits of software like matlab? 🙂

I like the pot method best, and think it could work with some jiggery pokery, thanks again for the help, i may be intouch in the future if thats ok?