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From: Jeff Liebermann <jeffl@cruzio.com>
Newsgroups: rec.bicycles.tech
Subject: Re: Extensive article on Rivendell and Grant Petersen
Date: Wed, 25 Sep 2024 11:09:08 -0700
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On Wed, 25 Sep 2024 11:01:17 -0400, Frank Krygowski
<frkrygow@sbcglobal.net> wrote:

>On 9/25/2024 5:39 AM, Catrike Ryder wrote:
>>  
>> A few weeks ago, after posting about braking, I tested the Catrike's
>> brakes at 15 MPH. I stopped at about 6 feet, keeping the chain rings
>> off the ground.
>
>No you didn't, unless your "about 6 feet" has a tolerance of something 
>like 50%.
>
>For the engineers in the crowd: It's a simple constant (negative) 
>acceleration problem. Acceleration (or deceleration) is given by V^2/2X 
>where V is initial speed, X is stopping distance. 15 mph = 22 ft/s
>
>(22 ft/s)^2/(2*6ft)= 40.33 ft/s^2 deceleration. That's 1.25 times the 
>acceleration of gravity. For that, you'd need tires with a coefficient 
>of friction of at least 1.25, which would be very, very unusual. (0.9 is 
>a typical upper limit.) But more important, you'd need to _immediately_ 
>apply the brakes to the very limit of traction with no skidding; and 
>you'd need no weight on the unbraked rear wheel, so all the decelerating 
>mass was contributing to braking traction. You'd also need exactly the 
>same amount of braking on each front wheel so as to prevent a spin, 
>given that the rear wheel would have to be raised.
>
>Oh, and whether or not the rear wheel would raise to put all the weight 
>into front wheel traction depends on the geometry of the bike+rider. The 
>elevation angle of the total center of mass would have to be precisely 
>right, not too high nor too low.
>
>All this is based on the physics of the real world. Those living in 
>other universes should post their math, or their videos.

You can measure acceleration (or deceleration) using a smartphone:
<https://play.google.com/store/search?q=accelerometer&c=apps>
Measurements are always useful as a sanity check.

I used this app for a while:
<https://play.google.com/store/apps/details?id=com.keuwl.accelerometercounter>
but it lacks a data collection feature.  

This app looks like a better choice, but I haven't tried it yet:
<https://play.google.com/store/apps/details?id=com.kelvin.sensorapp>
The free version will record data and save in a CSV (spreadsheet)
format.  However, the other formats require buying the paid version
for $40/year or $4/month.

I believe that you'll find that the acceleration (or deceleration) is
not constant and varies substantially.  To properly compare calculated
and measured AVERAGE acceleration, you'll need to collect some data
and crunch the numbers.





-- 
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558