Author Topic: Brakes  (Read 20629 times)

Chris Brown

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Re: Brakes
« Reply #30 on: 21 Nov 19, 05:07 pm »
Driving position is part of the problem with my braking, again knees bent making it difficult both to apply full pressure, and fully release the brakes.

Slack Alice

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Re: Brakes
« Reply #31 on: 21 Nov 19, 07:28 pm »
Thanks guys.  I’ll go over those sums Stefan!  I did actually include the coefficient and pad numbers in my attempt. Coefficient I used 0.5, 2 pads, and disc rad at 0.08 then rounded it all up to 0.1. I have no idea what the pad coef is.
 
You guys don’t spend very long braking do you!  I think you are all underestimating the actual time spent braking. However, variations in these parameters don’t affect the end result a great deal. ( no wonder I’m always at the back! ).
You’re right about bent legs/ leg pressure etc. Probably best to err on the low side for foot pressure on the pedal.
 
When I was measuring the pedal ratio, David noticed that it was easy to reach the bulkhead with the pedal under full braking pressure. I suppose it’s possible that during those ‘poor braking moments’ my pedal was actually hard up against the bulkhead and no additional pressure was being created, hence reduced clamping force and therefore no brakes. Probably a more realistic cause than fade, as your sums show.
 So what do we think a realistic foot pressure might be?

Chris Brown

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Re: Brakes
« Reply #32 on: 21 Nov 19, 07:33 pm »
No Dave you're not always at the back, that's my perogative when I'm there (at the moment anyway).   ::)

Slack Alice

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Re: Brakes
« Reply #33 on: 21 Nov 19, 07:46 pm »
Hi Chris.....ok, we’ll share last place!  How’s your modelling going? Any time for the CK?

Slack Alice

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Re: Brakes
« Reply #34 on: 21 Nov 19, 07:55 pm »
Stefan...I think you are wrong with the initial deceleration calc. Referring to the document I suggested, g at 9.81 does come into the equation.

StefanN

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Re: Brakes
« Reply #35 on: 21 Nov 19, 11:05 pm »
Dave, Gravitational force is acting perpendicular to the our direction of travel and so doesn’t have an effect.    It’s different if we’re not on the flat, so it does come into hill climbs.   What’s the document you’ve been reading?  I’d be interested to read it too.

Chris S,  I agree that some testing is key and I’ve even put together some test equipment....frustratingly the maths is proving much easier than finding somewhere to do testing.

Slack Alice

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Re: Brakes
« Reply #36 on: 22 Nov 19, 08:35 am »

Chris Brown

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Re: Brakes
« Reply #37 on: 22 Nov 19, 03:37 pm »
My intention when I go to 4 wheels was to mount a brake disc to one wheel, as I have some to fit, and it'll improve cooling being outside the body.

Now that my second used 17" wheel has arrived, complete with brake disc, I have 4 discs, so I think I'll probably make provision for using twin wheel mounted discs on the next two karts. I'll also allow for twin master cylinders with a balance beam on the pedal.

StefanN

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Re: Brakes
« Reply #38 on: 22 Nov 19, 07:22 pm »
http://www.engineeringinspiration.co.uk/brakecalcs.html
This is the source of my data.
It took me a while but I think I've figured out the misunderstanding.

In the section on Braking Force on that website
Braking Force = Mag
M= mass (kg)
g = the number of "G" 's  (no units) of deceleration
a = deceleration due to gravity. (m/s/s)

so multiplying g and a give a deceleration in m/s/s

which is the equivalent of F=ma and simply using the deceleration (a) 2.5m/s/s in your original calculation Dave.

Slack Alice

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Brakes design info
« Reply #39 on: 22 Apr 20, 10:31 am »
As you all know, the subject of brakes is my priority!   I came across this site yesterday. It’s a 4c4 site but covers the subject superbly. There is a spreadsheet as well, so you can input your own data for personal results. There are some issues....units are imperial and it expects brakes on each wheel!
Have a Look.    http://www.pirate4x4.com/tech/billavista/Brakes/