For you Nerds
03-03-18, 03:53 PM
#1
What??? Only 2 wheels?
Thread Starter
Join Date: Apr 2010
Location: Boston-ish, MA
Posts: 13,434
Bikes: 72 Peugeot UO-8, 82 Peugeot TH8, 87 Bianchi Brava, 76? Masi Grand Criterium, 74 Motobecane Champion Team, 86 & 77 Gazelle champion mondial, 81? Grandis, 82? Tommasini, 83 Peugeot PF10
Mentioned: 189 Post(s)
Tagged: 0 Thread(s)
Quoted: 1222 Post(s)
Liked 645 Times
in
232 Posts
For you Nerds
Something for you Nerds (with a capital N). I was curious about the effect of bumps on a bike's behavior so I did a little experiment and spent some time mulling over the data. It was informative and surprising.
There is a marvelous little device called Pocketlab (thepocketlab.com) which contains a whole bunch of sensors, including 3-axis accelerometer which has a range +/-6g's and a resolution of 0.008g. It can run for 8 to 12 hrs on its internal rechargeable battery and talks to a smartphone via Bluetooth. So I acquired a Voyager model and attached it to the fork of the '87 Bianchi Brava that I use for much of my commuting.
Then I recorded parts of my commute at its highest data rate 50 samples/sec (20msec). Depending on the terrain I ride between 10 and 20mph; 10mph is about 9mm/sec so the spatial resolution longitudinally isn't good enough to measure the shape of the response to most bumps. That's a messy problem (see below) and also what I'd really like to see, so I may try this again riding much slower. I also recorded distance to the ground using its IR rangefinder which has a resolution of 1cm, but it didn't show much interesting.
Here are some interesting graphs (created with OpenOffice). Most show vertical (orange) and longitudinal (blue) axes; a few show all three axes, vertical, longitudinal, and lateral. You can identify the vertical because its average is -1g instead of 0, with a negative sign because the sensor was pointing down for the rangefinder.
First a large-scale view of what appears to begin with waiting at a stoplight. It's easy to see when I was moving in the last third. It appears that I let the handlebar flop to one side while stopped because the lateral (orange) and vertical (gray) lines are not at their normal at-rest positions, -1 and 0 respectively.
Here is a stretch of bumps about 3sec long. The details of the last bump (starting about data point 120) are especially interesting.
First, the downward pulse in the vertical line (orange) means I hit a raised bump rather than a dip. (Remember, the sensor's Z axis was pointing down.) The vertical stress exceeded 3g's, a pretty high number though not unusual.
The longitudinal curve is surprising. The upward peak means the axle accelerated forward, not backward, and the magnitude also exceeded 3g's! It then decelerated and eventually settled down to its background oscillation (which we will discuss later). So you have to ask, how can hitting a bump shove the axle forward?? And by that much! Surely I didn't stomp on the pedals to accelerate that hard, impossible since the rear tire won't sustain that much grip with the road.
The answer is in the fork geometry. Look at this slightly exaggerated picture.
The thrust line of a bump's force can only be radial, i.e. on a line running through the axle. Depending on the height of the bump that line may project to the headset above or below the lower bearing race which acts as a fixed location. If the line projects above the headset then the force of the bump will be to bend the fork upward, pushing the axle forward. The headset itself experiences an impulse backwards even greater, so the bike will be slowed. There is one height at which the axle experiences no longitudinal impulse at all.
Consider some numbers: For a hypothetical 350mm radius and HT angle 73deg with no rake, the thrust at first contact with 1.53cm bump goes through bottom of headset (HS). The thrust angle (TA) would be the HT angle, 73deg. A bump smaller than this will always deflect the fork forwards as the fork bends in an arc centered at HS. A real bike has a rake of, say, 4.5 to 5cm. This means the first contact with a 3.3cm bump goes through HS, for a TA of about 65.0deg.
If the headset does not move upward in a bump, i.e. remains at the same height, the maximum thrust will always occur when the axle is directly over the bump (DOB), i.e. 90deg TA. Actual behavior is complicated as it depends on the bike speed w.r.t. the spring rate of the fork accelerating the mass of the bike and rider upward. A slower bike speed means more upward movement of the HT (normalized for the lower impact), effectively moving the centroid of the thrust point forward toward first contact as the tire deflection diminishes through the course of the bump over what it would have been were the HT not moving vertically. On a typical bike maybe 1/3 the mass of bike and rider are over the front wheel, but wheel and fork together are significantly less. So for a short duration bump event a stationary HS is a reasonable talking point.
Regardless of the speed, the first significant movement of the axle will be somewhere between first contact (65deg TA) and DOB (90deg TA), and the first detectable acceleration of the axle will occur as soon as the tire has deformed enough that the contact patch has moved forward. Thus any bump smaller than about 3.3cm will deform the fork so as to push the axle upward and forward even though the thrust at the HS will be upward and backward. In principle we can detect whether a bump in this data was taller than 3.3cm by whether the longitudinal acceleration was forward or backward. Both types are visible in the data. Here is another example.
In this example the fork is knocked forward by the bump at data point 24, rebounds by decelerating a lot as the movement of the bike upward unloads the weight from the fork, then accelerates forward again as the weight falls back down to flex the fork forward.
This example shows the bike hitting a dip. It briefly releases the load on the front wheel of the rider's weight, and this allows it to move backwards w.r.t. the bike. When the tire hits the upward slope on the far side of the dip it knocks the axle forward again by flexing the fork forward and up.
Finally, note how the background movement seems to involve a consistent up/down or forward/backward acceleration. This suggests a forward/backward resonance of the fork. the fact that it changes direction on every data point suggests that it is close to the Nyquist frequency, in this case 25Hz. I picked up the bike and thumped downward on the front wheel and obtained this pic.
The pattern isn't quite every other point though. So I thumped the wheel while measuring the frequency with Kewlsoft's accelerometer and came up with about 17Hz. So the fork is quietly resonating when driven by the random noise of pavement irregularities.
There is a marvelous little device called Pocketlab (thepocketlab.com) which contains a whole bunch of sensors, including 3-axis accelerometer which has a range +/-6g's and a resolution of 0.008g. It can run for 8 to 12 hrs on its internal rechargeable battery and talks to a smartphone via Bluetooth. So I acquired a Voyager model and attached it to the fork of the '87 Bianchi Brava that I use for much of my commuting.
Then I recorded parts of my commute at its highest data rate 50 samples/sec (20msec). Depending on the terrain I ride between 10 and 20mph; 10mph is about 9mm/sec so the spatial resolution longitudinally isn't good enough to measure the shape of the response to most bumps. That's a messy problem (see below) and also what I'd really like to see, so I may try this again riding much slower. I also recorded distance to the ground using its IR rangefinder which has a resolution of 1cm, but it didn't show much interesting.
Here are some interesting graphs (created with OpenOffice). Most show vertical (orange) and longitudinal (blue) axes; a few show all three axes, vertical, longitudinal, and lateral. You can identify the vertical because its average is -1g instead of 0, with a negative sign because the sensor was pointing down for the rangefinder.
First a large-scale view of what appears to begin with waiting at a stoplight. It's easy to see when I was moving in the last third. It appears that I let the handlebar flop to one side while stopped because the lateral (orange) and vertical (gray) lines are not at their normal at-rest positions, -1 and 0 respectively.
Here is a stretch of bumps about 3sec long. The details of the last bump (starting about data point 120) are especially interesting.
First, the downward pulse in the vertical line (orange) means I hit a raised bump rather than a dip. (Remember, the sensor's Z axis was pointing down.) The vertical stress exceeded 3g's, a pretty high number though not unusual.
The longitudinal curve is surprising. The upward peak means the axle accelerated forward, not backward, and the magnitude also exceeded 3g's! It then decelerated and eventually settled down to its background oscillation (which we will discuss later). So you have to ask, how can hitting a bump shove the axle forward?? And by that much! Surely I didn't stomp on the pedals to accelerate that hard, impossible since the rear tire won't sustain that much grip with the road.
The answer is in the fork geometry. Look at this slightly exaggerated picture.
The thrust line of a bump's force can only be radial, i.e. on a line running through the axle. Depending on the height of the bump that line may project to the headset above or below the lower bearing race which acts as a fixed location. If the line projects above the headset then the force of the bump will be to bend the fork upward, pushing the axle forward. The headset itself experiences an impulse backwards even greater, so the bike will be slowed. There is one height at which the axle experiences no longitudinal impulse at all.
Consider some numbers: For a hypothetical 350mm radius and HT angle 73deg with no rake, the thrust at first contact with 1.53cm bump goes through bottom of headset (HS). The thrust angle (TA) would be the HT angle, 73deg. A bump smaller than this will always deflect the fork forwards as the fork bends in an arc centered at HS. A real bike has a rake of, say, 4.5 to 5cm. This means the first contact with a 3.3cm bump goes through HS, for a TA of about 65.0deg.
If the headset does not move upward in a bump, i.e. remains at the same height, the maximum thrust will always occur when the axle is directly over the bump (DOB), i.e. 90deg TA. Actual behavior is complicated as it depends on the bike speed w.r.t. the spring rate of the fork accelerating the mass of the bike and rider upward. A slower bike speed means more upward movement of the HT (normalized for the lower impact), effectively moving the centroid of the thrust point forward toward first contact as the tire deflection diminishes through the course of the bump over what it would have been were the HT not moving vertically. On a typical bike maybe 1/3 the mass of bike and rider are over the front wheel, but wheel and fork together are significantly less. So for a short duration bump event a stationary HS is a reasonable talking point.
Regardless of the speed, the first significant movement of the axle will be somewhere between first contact (65deg TA) and DOB (90deg TA), and the first detectable acceleration of the axle will occur as soon as the tire has deformed enough that the contact patch has moved forward. Thus any bump smaller than about 3.3cm will deform the fork so as to push the axle upward and forward even though the thrust at the HS will be upward and backward. In principle we can detect whether a bump in this data was taller than 3.3cm by whether the longitudinal acceleration was forward or backward. Both types are visible in the data. Here is another example.
In this example the fork is knocked forward by the bump at data point 24, rebounds by decelerating a lot as the movement of the bike upward unloads the weight from the fork, then accelerates forward again as the weight falls back down to flex the fork forward.
This example shows the bike hitting a dip. It briefly releases the load on the front wheel of the rider's weight, and this allows it to move backwards w.r.t. the bike. When the tire hits the upward slope on the far side of the dip it knocks the axle forward again by flexing the fork forward and up.
Finally, note how the background movement seems to involve a consistent up/down or forward/backward acceleration. This suggests a forward/backward resonance of the fork. the fact that it changes direction on every data point suggests that it is close to the Nyquist frequency, in this case 25Hz. I picked up the bike and thumped downward on the front wheel and obtained this pic.
The pattern isn't quite every other point though. So I thumped the wheel while measuring the frequency with Kewlsoft's accelerometer and came up with about 17Hz. So the fork is quietly resonating when driven by the random noise of pavement irregularities.
__________________
Real cyclists use toe clips.
With great bikes comes great responsibility.
jimmuller
Real cyclists use toe clips.
With great bikes comes great responsibility.
jimmuller
Last edited by jimmuller; 03-05-18 at 05:30 AM. Reason: Correcting a few stupiditities
03-03-18, 04:18 PM
#2
Still learning
Jim,
Are you planning to audition for a part as a professor on Big Bang Theory?
Actually it is very interesting data, and I will try to put my dormant high school physics to work. Thank you for sharing Jim.
Are you planning to audition for a part as a professor on Big Bang Theory?
Actually it is very interesting data, and I will try to put my dormant high school physics to work. Thank you for sharing Jim.
03-03-18, 04:35 PM
#3
Senior Member
Join Date: Jun 2006
Posts: 20,305
Mentioned: 130 Post(s)
Tagged: 0 Thread(s)
Quoted: 3464 Post(s)
Liked 2,829 Times
in
1,995 Posts
Interesting.
I guess where I would want to take this would be to instrument the fork ( essentially at the axle) and say the top tube immediately aft of the steerer. To get a feel for the absorption of the fork.
There were the bike shop mechanic arguments about how quick the radius of the fork is related to road feel, then there are additional arguments over straight blade forks...
And my personal observation of twin plate crown forks vs "box" crown units.
Then the whole can of worms regarding tire cross-section and pressure and rolling resistance...
I guess where I would want to take this would be to instrument the fork ( essentially at the axle) and say the top tube immediately aft of the steerer. To get a feel for the absorption of the fork.
There were the bike shop mechanic arguments about how quick the radius of the fork is related to road feel, then there are additional arguments over straight blade forks...
And my personal observation of twin plate crown forks vs "box" crown units.
Then the whole can of worms regarding tire cross-section and pressure and rolling resistance...
03-03-18, 04:42 PM
#4
Freewheel Medic
Join Date: Oct 2005
Location: An Island on the Coast of GA!
Posts: 12,882
Bikes: Snazzy* Schwinns, Classy Cannondales & a Super Pro Aero Lotus (* Ed.)
Mentioned: 140 Post(s)
Tagged: 0 Thread(s)
Quoted: 1452 Post(s)
Liked 2,195 Times
in
962 Posts
@jimmuller, Sharon needs to find a new project for you to do. This is way above my seminary pay grade!
__________________
Bob
Enjoying the GA coast all year long!
Thanks for visiting my website: www.freewheelspa.com
Bob
Enjoying the GA coast all year long!
Thanks for visiting my website: www.freewheelspa.com
Last edited by pastorbobnlnh; 03-03-18 at 08:44 PM.
03-03-18, 04:44 PM
#5
Banned.
Join Date: Jul 2009
Location: PAZ
Posts: 12,294
Mentioned: 255 Post(s)
Tagged: 0 Thread(s)
Quoted: 2588 Post(s)
Liked 4,824 Times
in
1,709 Posts
My head hurts now 
DD
DD
03-03-18, 04:45 PM
#6
Senior Member
Join Date: Dec 2014
Posts: 546
Bikes: colnago titanio oval master, pinarello treviso es, centurion prestige, tomac ti 26er, lemond buenos aires, mbk 753, vitus 992 and zx1, rocky mountain hammer disc,bd century titanium, specialized venge expert
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 130 Post(s)
Liked 39 Times
in
20 Posts
This was appreciated..cool bit of info. Now it would be interesting to do the same with a bike you consider the best rider and note the different resonances in the sine wave. It would be kinda hard to do everything in a controlled environment, unless you were using a lab with consistent variables for each.
03-03-18, 05:07 PM
#7
What??? Only 2 wheels?
Thread Starter
Join Date: Apr 2010
Location: Boston-ish, MA
Posts: 13,434
Bikes: 72 Peugeot UO-8, 82 Peugeot TH8, 87 Bianchi Brava, 76? Masi Grand Criterium, 74 Motobecane Champion Team, 86 & 77 Gazelle champion mondial, 81? Grandis, 82? Tommasini, 83 Peugeot PF10
Mentioned: 189 Post(s)
Tagged: 0 Thread(s)
Quoted: 1222 Post(s)
Liked 645 Times
in
232 Posts
A different approach would be simply to compare oscillation frequencies and bump rapidity on the road. Running the same stretch of road at exactly the same speed would be tough though.
But this shows why road tests like riding down a set of speed bumps is so meaningless. Real roads don't have such continuous equally-spaced bumps. And no matter what the bump spacing, the bike's response and the rider's speed and weight will affect how the fork oscillation sets up in phase w.r.t. the bumps. Maybe I'll try it. Don't hold your breath though.
__________________
Real cyclists use toe clips.
With great bikes comes great responsibility.
jimmuller
Real cyclists use toe clips.
With great bikes comes great responsibility.
jimmuller
03-03-18, 05:21 PM
#8
Senior Member
Join Date: Oct 2010
Posts: 8,515
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3241 Post(s)
Liked 2,512 Times
in
1,510 Posts
Very cool!
I would donate $20 to the fund to purchase a 2nd device so you could continue the tests for the forum. That would be worth it for the discussions it would generate.
I would donate $20 to the fund to purchase a 2nd device so you could continue the tests for the forum. That would be worth it for the discussions it would generate.
Thanks. Instrumenting both the axle and HS was my original intent, but I'd have to buy a second Pocketlab (it was whimsical enough to buy this one) and also synchronize their data manually in OpenOffice or Excel. Maybe... The problem is, 50Hz sample rate isn't quite fast enough for what I'd really like to see.
That is the hard part. I can measure the response of the fork here at home with my phone, but not while riding. I suspect the Bianchi is pretty representative though the decay rates and resonant frequencies would vary bike to bike. Some of my bikes don't have mounting holes on the fork.
A different approach would be simply to compare oscillation frequencies and bump rapidity on the road. Running the same stretch of road at exactly the same speed would be tough though.
But this shows why road tests like riding down a set of speed bumps is so meaningless. Real roads don't have such continuous equally-spaced bumps. And no matter what the bump spacing, the bike's response and the rider's speed and weight will affect how the fork oscillation sets up in phase w.r.t. the bumps. Maybe I'll try it. Don't hold your breath though.
That is the hard part. I can measure the response of the fork here at home with my phone, but not while riding. I suspect the Bianchi is pretty representative though the decay rates and resonant frequencies would vary bike to bike. Some of my bikes don't have mounting holes on the fork.
A different approach would be simply to compare oscillation frequencies and bump rapidity on the road. Running the same stretch of road at exactly the same speed would be tough though.
But this shows why road tests like riding down a set of speed bumps is so meaningless. Real roads don't have such continuous equally-spaced bumps. And no matter what the bump spacing, the bike's response and the rider's speed and weight will affect how the fork oscillation sets up in phase w.r.t. the bumps. Maybe I'll try it. Don't hold your breath though.
03-03-18, 07:06 PM
#10
Phyllo-buster
Join Date: Jan 2010
Location: Nova Scotia
Posts: 8,847
Bikes: roadsters, club bikes, fixed and classic
Mentioned: 133 Post(s)
Tagged: 0 Thread(s)
Quoted: 2298 Post(s)
Liked 2,054 Times
in
1,254 Posts
I wish I had enough 'little gray cells' and education to follow the discussion but those of you with this capacity should should get a copy of Bicycling Science from MIT press for much more of the same. This thread would likely be a worthy entry in the book. I enjoy it even as a layperson. Frame materials, rolling resistance, it's all in there.
03-03-18, 08:01 PM
#11
Veteran, Pacifist
Join Date: Dec 2004
Location: Seattle area
Posts: 13,328
Bikes: Bikes??? Thought this was social media?!?
Mentioned: 284 Post(s)
Tagged: 0 Thread(s)
Quoted: 3898 Post(s)
Liked 4,833 Times
in
2,229 Posts
I'm only a nerd (little n), so ya lost me.
But at least it sounds like you enjoyed the experience.
But at least it sounds like you enjoyed the experience.
__________________
Vintage, modern, e-road. It is a big cycling universe.
Vintage, modern, e-road. It is a big cycling universe.
03-03-18, 08:05 PM
#12
Banned.
Join Date: Jul 2009
Location: PAZ
Posts: 12,294
Mentioned: 255 Post(s)
Tagged: 0 Thread(s)
Quoted: 2588 Post(s)
Liked 4,824 Times
in
1,709 Posts
DD
03-04-18, 02:10 AM
#13
Senior Member
Join Date: Nov 2011
Location: Port Angeles, WA
Posts: 7,922
Bikes: A green one, "Ragleigh," or something.
Mentioned: 194 Post(s)
Tagged: 0 Thread(s)
Quoted: 1627 Post(s)
Liked 630 Times
in
356 Posts
tl,dr
[/humanities major]
"They can put a MAN on the MOON, but I sure as hell can't."
[/humanities major]
"They can put a MAN on the MOON, but I sure as hell can't."
__________________
● 1971 Grandis SL ● 1972 Lambert Grand Prix frankenbike ● 1972 Raleigh Super Course fixie ● 1973 Nishiki Semi-Pro ● 1979 Motobecane Grand Jubile ●1980 Apollo "Legnano" ● 1984 Peugeot Vagabond ● 1985 Shogun Prairie Breaker ● 1986 Merckx Super Corsa ● 1987 Schwinn Tempo ● 1988 Schwinn Voyageur ● 1989 Bottechia Team ADR replica ● 1990 Cannondale ST600 ● 1993 Technium RT600 ● 1996 Kona Lava Dome ●
● 1971 Grandis SL ● 1972 Lambert Grand Prix frankenbike ● 1972 Raleigh Super Course fixie ● 1973 Nishiki Semi-Pro ● 1979 Motobecane Grand Jubile ●1980 Apollo "Legnano" ● 1984 Peugeot Vagabond ● 1985 Shogun Prairie Breaker ● 1986 Merckx Super Corsa ● 1987 Schwinn Tempo ● 1988 Schwinn Voyageur ● 1989 Bottechia Team ADR replica ● 1990 Cannondale ST600 ● 1993 Technium RT600 ● 1996 Kona Lava Dome ●
Last edited by Lascauxcaveman; 03-04-18 at 02:14 AM.
03-04-18, 03:38 AM
#14
Master Parts Rearranger
Join Date: Mar 2015
Location: Portlandia's Kuiper Belt, OR
Posts: 4,403
Bikes: 1982 Trek 720 - 1985 Trek 620 - 1984 Trek 620 - 1980 Trek 510 - Other luminaries past and present
Mentioned: 221 Post(s)
Tagged: 0 Thread(s)
Quoted: 1556 Post(s)
Liked 2,024 Times
in
989 Posts
I will have to read this again when it's not 1:30 AM, but I like what you are doing and analyzing here. Resonant frequencies of various steels, to say nothing of putting this on vintage aluminum forks (Cannondale et al) or carbon-fiber. I would imagine, given my experience with steel and aluminum in this context, that aluminum will give a higher frequency, or at the very least, a more rapid response/oscillation.
03-04-18, 04:21 AM
#15
Bianchi Goddess
Join Date: Apr 2009
Location: Shady Pines Retirement Fort Wayne, In
Posts: 27,858
Bikes: Too many to list here check my signature.
Mentioned: 192 Post(s)
Tagged: 2 Thread(s)
Quoted: 2930 Post(s)
Liked 2,924 Times
in
1,491 Posts
Interesting. I presume you’ve heard of the International Roughness Index pertaining to roadways?
https://en.m.wikipedia.org/wiki/Inte...oughness_Index
https://en.m.wikipedia.org/wiki/Inte...oughness_Index
__________________
“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk
“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk
03-04-18, 06:47 AM
#16
Senior Member
When explaining anything to me, beyond thingamajig, whatchamacallit, doodad, thingamabob,and doohickey, it becomes too technical for me. But thanks for the effort.
03-04-18, 07:56 AM
#17
SE Wis
Join Date: Apr 2005
Location: Milwaukee, WI
Posts: 10,515
Bikes: '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400, 2013 Novara Randonee, 1990 Trek 970
Mentioned: 40 Post(s)
Tagged: 0 Thread(s)
Quoted: 2747 Post(s)
Liked 3,395 Times
in
2,056 Posts
https://wisconsindot.gov/rdwy/stndspec/ss-04-40.pdf
03-04-18, 08:15 AM
#18
Senior Member
Join Date: May 2008
Location: Fredericksburg, Va
Posts: 9,579
Bikes: '65 Frejus TDF, '73 Bottecchia Giro d'Italia, '83 Colnago Superissimo, '84 Trek 610, '84 Trek 760, '88 Pinarello Veneto, '88 De Rosa Pro, '89 Pinarello Montello, '94 Burley Duet, 97 Specialized RockHopper, 2010 Langster, Tern Link D8
Mentioned: 73 Post(s)
Tagged: 0 Thread(s)
Quoted: 1607 Post(s)
Liked 2,216 Times
in
1,103 Posts
I have not thought about the dynamics of the geometry to that level. Thanks for sharing!
Do you think it is pointless to compare different configurations with this unit? Tires and wheel configurations on the same bike might be interesting even with a somewhat controlled test as you did with thumping the wheel.
Could you describe the challenges with collecting/analyzing the data?
How about increasing the size of the mounting hole to fit the skewer?
Do you think it is pointless to compare different configurations with this unit? Tires and wheel configurations on the same bike might be interesting even with a somewhat controlled test as you did with thumping the wheel.
Could you describe the challenges with collecting/analyzing the data?
How about increasing the size of the mounting hole to fit the skewer?
__________________
Bikes don't stand alone. They are two tired.
Bikes don't stand alone. They are two tired.
03-04-18, 10:19 AM
#19
Senior Member
Join Date: Aug 2009
Location: Berkeley, CA
Posts: 7,244
Bikes: '72 Cilo Pacer, '72 Gitane Gran Tourisme, '72 Peugeot PX10, '73 Speedwell Ti, '74 Peugeot UE-8, '75 Peugeot PR-10L, '80 Colnago Super, '85 De Rosa Pro, '86 Look Equipe 753, '86 Look KG86, '89 Parkpre Team, '90 Parkpre Team MTB, '90 Merlin
Mentioned: 87 Post(s)
Tagged: 0 Thread(s)
Quoted: 834 Post(s)
Liked 2,126 Times
in
555 Posts
When Strava is not enough...
Neat experiment. Thanks for sharing.
Neat experiment. Thanks for sharing.
03-04-18, 10:49 AM
#20
small ring
Join Date: Jul 2012
Location: PNW
Posts: 1,025
Mentioned: 24 Post(s)
Tagged: 0 Thread(s)
Quoted: 438 Post(s)
Liked 925 Times
in
370 Posts
How solid is that mounting tab? I would think that would add significantly to the measured fork resonance.
__________________
59 Allegro Special -- 72 Bob Jackson -- 74 Motobecane Grand Jubile -- 74 Sekine SHS 271 -- 80 Nishiki International
85 Shogun 800 -- 86 Tommasini Super Prestige -- 92 Specialized Rockhopper -- 17 Colnago Arabesque
59 Allegro Special -- 72 Bob Jackson -- 74 Motobecane Grand Jubile -- 74 Sekine SHS 271 -- 80 Nishiki International
85 Shogun 800 -- 86 Tommasini Super Prestige -- 92 Specialized Rockhopper -- 17 Colnago Arabesque
03-04-18, 10:58 AM
#21
aka Tom Reingold
Join Date: Jan 2009
Location: New York, NY, and High Falls, NY, USA
Posts: 40,503
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
Mentioned: 511 Post(s)
Tagged: 0 Thread(s)
Quoted: 7348 Post(s)
Liked 2,470 Times
in
1,435 Posts
I hope this continues somehow and is published and peer-reviewed.
__________________
Tom Reingold, tom@noglider.com
New York City and High Falls, NY
Blogs: The Experienced Cyclist; noglider's ride blog
“When man invented the bicycle he reached the peak of his attainments.” — Elizabeth West, US author
Please email me rather than PM'ing me. Thanks.
Tom Reingold, tom@noglider.com
New York City and High Falls, NY
Blogs: The Experienced Cyclist; noglider's ride blog
“When man invented the bicycle he reached the peak of his attainments.” — Elizabeth West, US author
Please email me rather than PM'ing me. Thanks.
03-04-18, 11:03 AM
#22
Disraeli Gears
03-04-18, 11:21 AM
#23
Senior Member
Join Date: Feb 2008
Location: Peoria, IL
Posts: 4,476
Mentioned: 86 Post(s)
Tagged: 0 Thread(s)
Quoted: 1829 Post(s)
Liked 3,376 Times
in
1,580 Posts
some some quick thoughts & questions about the instrumentation:
how much noise is there? what is the rms or peak value of the G readings while at rest?
Has the scale factor been checked in a basic way? i.e. place the sensor on a level surface in all 6 orientations (with the sensor's X, Y, and Z axes placed so that they are oriented with, and then against, the gravity vector), and verified that the reading is 1G in the selected axis, while the other axes read 0 G.
The size of the bumps encountered when these measurement were made wasn't disclosed, but I'm wondering if it makes sense that the longitudinal acceleration was nearly as great as the vertical acceleration. Would that mean that the wheel had encountered a slope of roughly 45 degrees? Or would it be different because the net force was accelerating only about half the mass vertically, while the longitudinal acceleration acts on all of the mass??
Or does it get messier because of the mass & spring effects, requiring the use of differential equations?
I'm an electrical engineer, and try my best to avoid these sorts of mechanical discussions, but still find them interesting. Any chance that some standardized bumps could be fabricated and see how the results match expectations? It would also be an opportunity to check the consistency/repeatibility of the sensor, and to mount it on different locations on the bike as you make repeated passes over the standard bumps.
Regardless, it's always fun to make some measurements and see if they matched your expectations!
Steve in Peoria
how much noise is there? what is the rms or peak value of the G readings while at rest?
Has the scale factor been checked in a basic way? i.e. place the sensor on a level surface in all 6 orientations (with the sensor's X, Y, and Z axes placed so that they are oriented with, and then against, the gravity vector), and verified that the reading is 1G in the selected axis, while the other axes read 0 G.
The size of the bumps encountered when these measurement were made wasn't disclosed, but I'm wondering if it makes sense that the longitudinal acceleration was nearly as great as the vertical acceleration. Would that mean that the wheel had encountered a slope of roughly 45 degrees? Or would it be different because the net force was accelerating only about half the mass vertically, while the longitudinal acceleration acts on all of the mass??
Or does it get messier because of the mass & spring effects, requiring the use of differential equations?
I'm an electrical engineer, and try my best to avoid these sorts of mechanical discussions, but still find them interesting. Any chance that some standardized bumps could be fabricated and see how the results match expectations? It would also be an opportunity to check the consistency/repeatibility of the sensor, and to mount it on different locations on the bike as you make repeated passes over the standard bumps.
Regardless, it's always fun to make some measurements and see if they matched your expectations!
Steve in Peoria
03-04-18, 11:39 AM
#24
Senior Member
Join Date: Aug 2014
Location: Capestang, France
Posts: 1,341
Bikes: Lots of French, some British and a couple of Italian
Mentioned: 35 Post(s)
Tagged: 0 Thread(s)
Quoted: 247 Post(s)
Liked 130 Times
in
65 Posts
.Milo
03-04-18, 11:52 AM
#25
Senior Member
Join Date: Feb 2008
Location: Peoria, IL
Posts: 4,476
Mentioned: 86 Post(s)
Tagged: 0 Thread(s)
Quoted: 1829 Post(s)
Liked 3,376 Times
in
1,580 Posts
That brought out my pedantic side. The G it's measuring is dynamic so it would be 0s all round until it moves. Similar to pressure in diving - although atmospheric is 1 bar, your starting pressure for a dive is considered to be 0 at surface, 1 bar at 10m etc. I think .
Milo
.Milo
There are a number of interesting applications articles about accelerometers from the manufacturers, such as those in the lower part of this web page from Analog Devices...
Accelerometers | Analog Devices
The graphs presented show the nominal 1G offset for the vertical axis, and I'd expect to see the same in the other axes as the sensor was rotated.
Steve in Peoria