In the chat room: Drew Camp (foggydog214@gmail.com)


4:16 PM Drew: You've been invited to this chat room!
 hpidriver@gmail.com has joined
  Kevin has joined
 hpidriver: like this one:
  http://www.sparkfun.com/commerce/product_info.php?products_id=692
4:17 PM Drew: that one only seems to go to +- 3g
4:18 PM hpidriver: http://www.sparkfun.com/commerce/product_info.php?products_id=8685
  if we use it along with something like this
  we should be able to get accurate analysis of impact
4:19 PM Kevin: can you explain how your comming to that conclusion?
  because 3g accel. + 100lb sensor doesnt make sense
 hpidriver: well it was first suggested by the guy who originally worked on this a couple years ago
4:20 PM Kevin: did he offer any reasoning?
 hpidriver: well we want to measure the force
  that the player is taking
4:21 PM not just how fast the helmet is moving
  know i dont really know about the physics and how to calculate stuff
  but thats something our M.E. guy has to come up with
4:22 PM Kevin: well, F=MA
 hpidriver: well yea
 Kevin: that is a start lol
 hpidriver: lol
 me: haha
 hpidriver: but i mean coming up with a set equation our processor can use
4:23 PM that can closely show had "hard" the hit is
 Kevin: you cant properly measure the acceleration with +/- 3 g though
 me: the most you can accurately measure with a 3g acceleromet is about 5g.. 3 squared * 3 .. root of it
 Kevin: its like havceing a scale, that tells you, i weight more than 5 lb, or i dont
 me: trying to measure a... yeha, what kevin said
4:24 PM yeah*
 hpidriver: well 18g is the highest value we found
4:25 PM so we dont have much choice unfortunately
 Drew: we have found single axis ones that go up to 250g
  we are just having trouble finding ones that are 3axis
4:26 PM hpidriver: im not sure what the 18g rating is in the title
  but in the data sheets it says the max is 10000g
  http://www.sparkfun.com/datasheets/Accelerometers/ADXL320_0.pdf
 me: that 10,000g is for overload protection
 hpidriver: although thats the max the device can withstand
4:27 PM me: so it takes 10,001 g to break it
4:28 PM hpidriver: i mean it says its designed for what we are trying to do
  so i dont think getting caught up so much on these numbers is doing much
4:29 PM i mean, we cant really buy one of those several hundred $ ones
 me: There have to be other ones out there, we just gotta look
4:30 PM Kevin: we might have a missunderstanding about what the project is supposed to do, what are you hoping ot have the final design accomplishing?
 me: I mean, the 1-axis ones are 8$.. so 3-axis ones shouldn't be much more than 30$.. the ones we found are overkill
4:31 PM the one from Measurement Specalties was designed for high performance airplanes/jets
4:32 PM hpidriver: helmet ultimately is designed to determine if a certain impact/hit was hard enough to cause concussion injury etc
4:33 PM me: Yeah, thats the ultimate goal... which means you gotta be able to measure ~70-90g
 Drew: or more
4:34 PM me: we CAN make it work with the 1 axis accel, its just going to take a lot more wiring and work.
 hpidriver: but were trying to look at more than just how fast the head accelerates separately from the body/neck
  we want to get data from inside the helmet
  like impact on the players head
4:35 PM ie. able to test safer helmets
  maybe thats where we are differing views on
4:36 PM Kevin: ok, but that only takes care of the compression impacts
  what abut all the others, inertial impacts and ones that dont compress rather "throw"
4:37 PM hpidriver: well lol thats the accelerometers
  or gyro sensors
  but those arent cheap either
4:38 PM measuring tilt over time we could calculate acceleration
 Kevin: lets get both teams together so it isnt like us arguing with you
  i feel kinda bad
 hpidriver: nah its cool
  let me get louis
 Kevin: cool
4:39 PM me: you guys seen the riddell iq hits helmet?
4:40 PM hpidriver: the HITS system?
  yea
  like a grand
 Kevin: its outrageous isnt it
 me: yeah, $$$.. but it works with 6 accelerometers and measures up to 160g
4:41 PM we were planning on using 3 (minium needed to form a plane)
  but if they can build and sell it for under 1000$, there has to be a cheaper option for accelerometers.. we just gotta find em.
4:42 PM hpidriver: well another idea as a cheaper alternative
  would be using just pressure sensors along the inside
4:43 PM and we would have a dummy head and we would hit the helmet from various directions and log the sensor data
  thats if we cant straight measure g's
4:44 PM me: have you looked at presure sensors yet, I have not... How sensitive are they?
 Kevin: I like the idea of beating a dummy with a bat
 hpidriver: yea they are pretty accurate
4:45 PM and they are paperthin
4:46 PM up to 1000lbs it can measure
 me: gonna crunch some numbers real quick...
4:49 PM hpidriver: 1000lbs of force is about a ko punch from a heavyweight i believe lol
  should be enough for a concussion
4:50 PM oh and louis cant join us
 me: ok...
 hpidriver: he's sitting too close to our professor he claims
  lol
 me: F = ma, so 1000 lb-ft/s2 = ma
4:51 PM hpidriver: 8lbs average weight of head
 me: figure weight of the head about 40lbs.. since you can hit horizontally and throw some of you rbody into it
  ok, we can do 8lbs
 hpidriver: plus helmet is 2 at most
 me: round to 10
 hpidriver: yea thats fine
4:52 PM me: means 100 ft/s2
  ~36ft/s2 = 1g
  so thats 3g
  takes 70g - 90g to cause a concussion (on average)
4:53 PM Kevin: my grandma got hit with over 9000 g's and didnt get a concussion ^^
4:54 PM me: you'd need a 1000*(70/3) = 23,000 lb pressure sensor
  and assuming you only headbut something.. if you hit something more horizontally the Mass of the head will be affected by the mass of the body.
4:56 PM wait, I'm way off.. its more
4:58 PM my numbers are right, nm
5:01 PM hpidriver: well i am pretty sure we found that 1000lbs on the head is enough to cause injury
  not sure why we need to make it ft-lbs/s2
5:02 PM me: Also, if you use pressure sensors, you have to have the entire inside of the helmet covered since you can get hit in any direction
  Force is lb-ft/s2
5:03 PM hpidriver: no i know
  either way, it wouldnt be that hard to line the helmet with these
5:04 PM they are small strips 2 inches long
5:05 PM me: just used google tools to figure out pounds exactly.. to cause 70g on a 10lb head is 70,059.45 lbs
5:06 PM either way, I don't see presure sensors working. I believe we have to stick with accelerometers to get accurate readings
5:07 PM Alright I gotta get going. I'm going to keep looking for accelerometers. We've got a call in to some company reps to see if they will donate some acceleromters or direct us to one that is affordable.
 hpidriver: alright ill ttyl
5:08 PM me: later, bud
 hpidriver: we'll try to get everyone else on next time
 hpidriver@gmail.com has left