Free cycle computer - rice krispies
03-14-07, 08:14 AM
#26
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please explain how you can measure speed without knowing the wheel circumference simply by placing a sensor a specific distance from the axle. i agree there may be an issue with having a preset wheel circumference, but placing the sensor a "very, very specific distance from the axle" does not solve the problem. these computers count the number of revolutions. that is constant over the radius from the axle to the tire. the calculation would be: revolutions per hour (from the sensor) x miles per revolution (circumference) = miles per hour. how does your imaginary computer calculate speed with the number of revolutions and the distance from the axle?
it may have a preset circumference that cannot be changed, but the positioning of the sensor does not effect the reading of revolutions. it will just read high if the wheel is smaller than the preset and low if the wheel is larger than the preset.
key, they aren't in the box. you need to mail in for them.
it may have a preset circumference that cannot be changed, but the positioning of the sensor does not effect the reading of revolutions. it will just read high if the wheel is smaller than the preset and low if the wheel is larger than the preset.
key, they aren't in the box. you need to mail in for them.
Last edited by zip22; 03-14-07 at 11:05 AM.
03-14-07, 08:27 AM
#27
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Originally Posted by G60
do you even know what you're talking about?
go ahead, try and prove me wrong
please son, don't give me the rolleyes when you've got no clue what you're talking about.
go ahead, try and prove me wrong
please son, don't give me the rolleyes when you've got no clue what you're talking about.
Speed is only a measure of distance/time. No matter where you put the magnet, no computer can register any more or less than precisely one "blip" per revolution. If this computer truly has a preset and unchangeable tire circumference, then it will take that circumference, divide by the time between blips and output the speed. Which will be wrong, if your tire circumference is not the same as the preset.
NO MATTER WHERE YOU PUT THE MAGNET!
May I humbly suggest that you get your money back from that Holiday Inn Express?
Last edited by specq; 03-14-07 at 08:45 AM.
03-14-07, 12:05 PM
#28
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Originally Posted by G60
do you even know what you're talking about?
so, without being able to input a tire diameter, how else would the computer know to display the correct readings? oh yeah, it wouldn't
since the cheap computers have no way for you to input a different diameter, it has only one preset, and you have to match that up with a very, very specific distance from the center of the axle in order for you to get a correct reading.
you think you can just put a magnet anywhere and the computer would automatically display the correct reading? this is true for computers where you can input your precise tire diameter, but NOT for these cheap computers.
go ahead, try and prove me wrong
if anyone can get their hands on the instructions from this computer, it will say exactly how far the magnet/pickup have to be from the axle.
please son, don't give me the rolleyes when you've got no clue what you're talking about.
so, without being able to input a tire diameter, how else would the computer know to display the correct readings? oh yeah, it wouldn't
since the cheap computers have no way for you to input a different diameter, it has only one preset, and you have to match that up with a very, very specific distance from the center of the axle in order for you to get a correct reading.
you think you can just put a magnet anywhere and the computer would automatically display the correct reading? this is true for computers where you can input your precise tire diameter, but NOT for these cheap computers.
go ahead, try and prove me wrong
if anyone can get their hands on the instructions from this computer, it will say exactly how far the magnet/pickup have to be from the axle.
please son, don't give me the rolleyes when you've got no clue what you're talking about.
I've never seen a cheap computer that didn't have the feature to input the wheel circumference- heck even the cheap $8 computers at walmart/target have that feature. I can't see why this free one wouldn't also have the feature, but who knows. I'm not familiar with EVERY single cheap computer on the market, so I could be wrong.
We'll see when I get my free computer...SUCKERS!
03-14-07, 01:22 PM
#29
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the circumference or diameter doesn't really matter as they are directly related c = pi(d)
it also wouldn't be completely useless. you could buy a bike that had the correct sized tires, or you could figure out the factor it was off by.
it also wouldn't be completely useless. you could buy a bike that had the correct sized tires, or you could figure out the factor it was off by.
03-14-07, 02:18 PM
#30
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Originally Posted by zip22
the circumference or diameter doesn't really matter as they are directly related c = pi(d)
And on pi day no less. Should be the BF official holiday.
03-15-07, 10:38 AM
#31
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Originally Posted by operator
No it doesn't. the rim has a higher velocity than near the hub. The time it takes to make a revolution is the same.
True, but the computer isn't measuring velocity. It measures the number of revolutions by the circumference of the tire.
03-16-07, 10:01 AM
#32
is full of it.
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I'm totally uneducated as far as this physics stuff is concerned but that whole
"higher velocity near the hub" than at the rim seems very counter-intuitive. I suck at explaining things too but I'll try.
Imagine I have a rim that is the size of the solar system. I place a sensor on a spoke end near the hub(sun) and one on the same spoke near the rim(pluto). When I spin the wheel one complete revolution, the near-hub sensor travels the tiny hub circumference in exactly the same time as the near-rim sensor traveled through the circumference of the solar system.
If velocity is speed in a direction, it seems to my uneducated mind, that the velocity is higher at the rim and that this higher velocity at the rim is directly proportional to the distance from the hub.
I've never taken a single physics class or stayed at a Holiday Inn Express, so I may be way off base here.
"higher velocity near the hub" than at the rim seems very counter-intuitive. I suck at explaining things too but I'll try.
Imagine I have a rim that is the size of the solar system. I place a sensor on a spoke end near the hub(sun) and one on the same spoke near the rim(pluto). When I spin the wheel one complete revolution, the near-hub sensor travels the tiny hub circumference in exactly the same time as the near-rim sensor traveled through the circumference of the solar system.
If velocity is speed in a direction, it seems to my uneducated mind, that the velocity is higher at the rim and that this higher velocity at the rim is directly proportional to the distance from the hub.
I've never taken a single physics class or stayed at a Holiday Inn Express, so I may be way off base here.
03-16-07, 10:25 AM
#33
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you are correct, but the small sensors don't measure velocity and i'm not sure how they could. they just tick every time the sensor passes by the receiver - counting the number of revolutions. now, when you're looking at your solar system, one revolution is one revolution. it doesn't matter if you're near the rim or near the sun, they both travel one revolution.
ticking once every revolution is a pretty easy measurement. i'm not sure how you could even measure velocity with one sensor. maybe if your receiver was a bit longer and you calculated how long it took the sensor to travel the length of the receiver. but that would give you the velocity at that point in the wheel. to translate that into the speed of the bike, you would still need to know the size of the wheel. so it would be a more complicated measurement and a more complicated calculation which would still need you to input the wheel diameter or circumference.
ticking once every revolution is a pretty easy measurement. i'm not sure how you could even measure velocity with one sensor. maybe if your receiver was a bit longer and you calculated how long it took the sensor to travel the length of the receiver. but that would give you the velocity at that point in the wheel. to translate that into the speed of the bike, you would still need to know the size of the wheel. so it would be a more complicated measurement and a more complicated calculation which would still need you to input the wheel diameter or circumference.
03-17-07, 10:08 AM
#34
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Originally Posted by zip22
that was my thought as well. i have an older astrale (cc-cd100) and this looks very similar. i had a weak urge to get another wire assembly so i could use the astrale on my daily beater, but this was cheaper. the only thing i'm a bit worried about is programming this one. i'm not sure how or if they will let you change the wheel size.
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This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.
This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.
03-17-07, 11:09 AM
#35
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Originally Posted by dobber
Why would it not have that simple capability? It's not like that ability would add anything to the cost.
03-18-07, 11:43 AM
#36
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Originally Posted by specq
May I humbly suggest that you get your money back from that Holiday Inn Express?
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This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.
This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.
03-22-07, 11:11 AM
#38
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I'm to try as well.
Just stopped by the local stop and shop and they had a current sale for the Kellogg's cereals.
buy four and get $6 off.
now to find my milk and bowl.
Just stopped by the local stop and shop and they had a current sale for the Kellogg's cereals.
buy four and get $6 off.
now to find my milk and bowl.
03-24-07, 03:43 PM
#39
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I think this has already been answered, but just to be sure, the question of mounting the magnet a specific distance from the hub is only important insofar as it must be close enough to the sensor to trigger it as it passes. The modern bicycle computer operates not by measuring the velocity of the magnet on the spoke, but as has been said, by counting blips as the magnet goes by and each blip represents a single rotation of the tire, and travelling the distance of its circumference along the road. This accounts for the calculation of odometer reading. To calculate linear speed, the calculator measures the time interval between the blips, probably accurate to milliseconds on a quality computer, to be able to give an instantaneous speed reading. It calculates the circumference (Pi times the diameter of the wheel which is the distance travelled during one revolution) divided by one mile (or kilometer) divided by the time interval for a single rotation divided by one hour (to derive the fraction of an hour). All this should yield the miles per hour (or kilometers per hour) during that one rotation. It thus calculates the fraction of a mile or kilometer travelled in that fraction of an hour to yield the mph or kph. I hope that helps.
I'd like to have a recommendation from anyone who knows of a decent bike computer which allows you to input the circumference or diameter in 1 mm increments (or ~0.04 inch) resolution rather than the more common but coarse 1 cm scale. Price is a factor, but secondarily. Thanks!
I'd like to have a recommendation from anyone who knows of a decent bike computer which allows you to input the circumference or diameter in 1 mm increments (or ~0.04 inch) resolution rather than the more common but coarse 1 cm scale. Price is a factor, but secondarily. Thanks!
03-24-07, 06:50 PM
#40
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Originally Posted by Keith C. Johns
............................snip......................
I'd like to have a recommendation from anyone who knows of a decent bike computer which allows you to input the circumference or diameter in 1 mm increments (or ~0.04 inch) resolution rather than the more common but coarse 1 cm scale. Price is a factor, but secondarily. Thanks!
I'd like to have a recommendation from anyone who knows of a decent bike computer which allows you to input the circumference or diameter in 1 mm increments (or ~0.04 inch) resolution rather than the more common but coarse 1 cm scale. Price is a factor, but secondarily. Thanks!
03-26-07, 03:46 PM
#41
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my order shipped yesterday. it says to allow 30 days (third class mail). i'll post initial impressions and some pictures when i receive it.
you can track your order at
https://www2.kelloggs.com/Promotion/OrderStatus.aspx
you can track your order at
https://www2.kelloggs.com/Promotion/OrderStatus.aspx
04-02-07, 09:01 AM
#42
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"My Cateye Astrale 8, Cateye Double Wireless (CD300DW) and Polar CS200 all allow inputs in mm for tire circumference." --Dogbait
Thanks for the reply, Dogbait. (Is this your ID because dogs like to chase you on your bike?) I was interested in one with wires rather than wireless which have an extra cell to replace more often.
I decided to check out the one for $9 at Walmart, figuring how far wrong could I go for that price? I was surprised to discover one with nice features which also had millimeter circumference input. I would recommend it.
I would be interested to know whether this free cerial box computer inputs also in mm. Thanks!
Thanks for the reply, Dogbait. (Is this your ID because dogs like to chase you on your bike?) I was interested in one with wires rather than wireless which have an extra cell to replace more often.
I decided to check out the one for $9 at Walmart, figuring how far wrong could I go for that price? I was surprised to discover one with nice features which also had millimeter circumference input. I would recommend it.
I would be interested to know whether this free cerial box computer inputs also in mm. Thanks!
Last edited by Keith C. Johns; 04-02-07 at 01:02 PM.
04-02-07, 11:15 PM
#43
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Or ebay it for $5 (+ $20 to ship)
Originally Posted by I-Like-To-Bike
It would be "worth" at least $20 if sold at an LBS though, eh? Maybe $40 with the right brand name. Wonder if there is Rolex brand anywhere?
04-05-07, 10:53 PM
#44
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received it earlier this week. i don't have my cateye here to compare, but i will if anyone is interested. it seems like it will do everything i want it to.
the table of wheel settings seems to match up pretty closely with the mm ratings on the cateye website, but in cm. the table only lists those specific values, but you can input anything from 001 cm to 239 cm
here is the entire manual so you can look over all the modes and settings
https://img90.imageshack.us/img90/1820/manualmv9.jpg
fit and finish is what you would expect for free. the battery door is a bit sketchy, but once i got it seated correctly, it seems like a good fit and it has an o-ring. the unit overall is thinner than my cateye (if memory serves me correctly), the bracket is very cheap feeling, and sliding the unit in and out feels just as cheap, but it is very firm and i'm not afraid of it falling out. pretty much just what i was looking for and $5 was a good deal in my mind.
the table of wheel settings seems to match up pretty closely with the mm ratings on the cateye website, but in cm. the table only lists those specific values, but you can input anything from 001 cm to 239 cm
here is the entire manual so you can look over all the modes and settings
https://img90.imageshack.us/img90/1820/manualmv9.jpg
fit and finish is what you would expect for free. the battery door is a bit sketchy, but once i got it seated correctly, it seems like a good fit and it has an o-ring. the unit overall is thinner than my cateye (if memory serves me correctly), the bracket is very cheap feeling, and sliding the unit in and out feels just as cheap, but it is very firm and i'm not afraid of it falling out. pretty much just what i was looking for and $5 was a good deal in my mind.
Last edited by zip22; 04-05-07 at 11:03 PM.
04-06-07, 07:26 AM
#45
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Originally Posted by zip22
received it earlier this week. i don't have my cateye here to compare, but i will if anyone is interested. it seems like it will do everything i want it to.
04-06-07, 10:13 AM
#46
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That computer totally belongs on my fixed gear!
04-06-07, 06:58 PM
#48
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too bad the offer expired end of march. i would have definitely gotten 1-2 more 
04-07-07, 10:58 AM
#49
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Originally Posted by seriouslysilly
too bad the offer expired end of march. i would have definitely gotten 1-2 more
