Wednesday, August 12, 2009

Some Cycling Results

OK, I took Chuckette out for a bike ride. The rig is pictured below. The trailer is a Burley Solo, about 2004 vintage. It was converted for K9 use a while back. It has a suspended floor above the regular bottom floor – sort of a mesh hammock. This is not unlike the original seat, which is a mesh sling suspended just above the floor.

Baby TestBed

Chuckette was strapped into a Combi child carrier and the carrier was strapped into the trailer, rear facing, using some mountain climbing webbing secured to the aluminum uprights you see pictured here. This snugged the seat as well as can be done in a car, using webbing that’s about half the width, but twice as thick. (Any force that could break this webbing would not be a force that anyone involved with this setup, either Chuckette or me, would be likely to survive.)

Baby TestBed

Below you can see that in such a configuration, Chuckette has a double rollbar: the first being the trailer itself, the second the bar of the child seat.

Baby TestBed

 

The trail behind our home has a huge variation in surface. It goes from smooth blacktop to concrete sidewalk slabs to smooth gravel to chunky gravel to potholed dirt road back to blacktop crossed by tree roots. Some of it is downright uncomfortable, but it doesn’t go on for very long that way – or no one would ride it at all.

The results weren’t very surprising to me, but I think they are interesting. (Click the chart to get a bigger view.)

The annotations explain most of what you see. The little bit of sidewalk I ran to get to the trail generated some bumps in excess of 3 Gs. Thereafter, you see that the smooth blacktop generated very little above 1.5 Gs. And remember, you get your first G “free.” That’s what you pull just sitting still, courtesy of your friend gravity.

The gravel and rough pavement produced plenty of jiggles 2 Gs and up, but, to my surprise, there were only 46 samples greater than 3 Gs. If that sounds like a lot, consider that the accelerometer is sampling at a rate of 20 samples per second. In other words, the occasional 3 G bumps don’t last very long at all, less than 5/100ths of a second. (This file has more than 14,000 samples across 26 minutes of running around.

I confirmed using Excel that, in fact, there were no consecutive samples >3 Gs. So, if anyone out there worries about 3G exposures, keep in mind that these are occurring for tiny fractions of a second.

whole bike ride

Mean: 1.10
Median: 1.07
Max: 5.16
Minimum 0.03
Standard dev. 0.51
samples >3 Gs 46.00
consecutive samples > 3Gs 0
 
Keep in mind that this is a completely unsuspended bike trailer, too. Burley’s newer trailers in this range utilize small, elastomeric (IIRC) suspension systems which would make them even smoother than this.
 


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