CycleKarts GB
Forums => Tech Forum => Topic started by: Slack Alice on 14 Jul 19, 10:39 pm
-
I need to seriously upgrade my braking system. It will have to be hydraulic...any good recommendations?
-
Why does it have to be hydraulic? That's only the actuating system.
Anyway, the biggest issue is that the master and slave cylinders come from the same unit. There are plenty of motorcycle rear hydraulics.
A disc with the ability to shed heat, so size, thickness etc that's compatible with the caliper, big and thick as you can. The mountain bike one you had/have was going to be a parking brake, or back up had I used one.
BTW David I was with Thunderbug yesterday, definitely yellow and black (not dark blue as we discussed)
-
I’m really envious! Thunderbug in the flesh!
-
It was like being a kid in a candy store. I only watched about 3 cars go up the hill.
Laugh of the day (and OT) was the commentator who said that the White "must have a badly blown head gasket" It's a steam car and the exhaust...
Back to brakes. The Freikaiserwagen, had one cable operated drum brake, always had, always will do. (That's another one to look up :) )
-
I'll second your "kid in a candy store" comment Rhys, Saturday was mind boggling. Photos of Thunderbug, and the rear end of Freikaiserwagen attached.
-
It would be helpful to get a feel for what brake set-ups people are using. With this being such a critical component the more understanding we can get of what works the better. Please could you share the following any information you know about your:
Master cylinder/piston (bore/stroke)
Calliper (make, number of pots, bore)
Pads
Disc diameter, thickness, design (slotted/drilled/dimpled/vented), material and carrier
Number of discs
Any ventilation to the discs
Plus any comments on performance.
What it was designed for
Photos and links to anything you've bought would also be helpful.
-
Check out 20180201151146 on youtube it may help, although I have changed the front brakes to hydraulic as the cables would pull when turning. I used motorcycle clutch slave cylinders to operate the mechanical levers,cheers, Geoff
https://youtu.be/N09ejgUD_Gk
-
Hello all,
Personally I tried both systems (mechanics on my 1st CK then hydraulics on my second)
For my 3rd, I'm planning the mechanical system.
In fact, the braking of our Ck is a false problem, either it is effective and the wheels blocked by our Ck are light enough
Either the braking system is ineffective, and the result is the same
By return of experience:
The hydraulic type is difficult to adjust, and the stroke of the piston is relatively short, which requires a precise adjustment between the disc and the pads (not always easy to obtain with our CK "DIY")...
For the mechanical type to give complete satisfaction, several essential things must be done
1 large brake pads
2 A disc of large diameter
3 A great race that allows a moderately precise adjustment
4 Easy adjustment of the stroke of the brake pads
here is the model of brake caliper which gives me satisfaction for a very correct price
I used this model on 2 other Ck built for friends, and so for my next Ck too
All this is only my point of view, and therefore questionable .... ;)
[attach=1]
PS : This model has 2 cable tie, so 1 for the foot brake, and the other for the parking brake!
-
I've got a Gemini 10inch disc and a Gemini mechanical caliper which is operated by a 6mm rod from the pedal.
It easily locks when only driving one wheel, but with both wheels being driven it hasn't got the power to lock them up, so it would be nice to have just a little more.
-
I have tried whatever has been available!
Remember that either hydraulic or mechanical has no effect on the performance of the brakes, it's just an operating system, and hydraulic is usually more difficult to get right. First up is that the master and slave cylinders MUST be matched as a system, unless of course you are able to get all the maths right without experiment, and that's pretty specialised. So, if you are going to get some old motorcycle parts, get both the master and slave.
Then you have the leverage ratio on the pedal to the system.
Brakes for a CK often need to be different to a go kart type, wheel diameters are not the same, and according to a brake designer that is a huge factor, even with the same weight of vehicle, all relates to the torque applied by the wheel, so our wheels, overall diameter of around 25" are vastly different to a go kart where the overall diameter is about 10", and it's some sort of mathematical ratio, not just a factor of 2.5. I guess that's why motorcycle systems are a better solution?
The disc has to get rid of the heat, again all very well to get cool air to the disc, but unless the heated air can escape you gain nothing. Just like getting cool air to the engine.
More mass in the brake disc(rotor) will absorb more heat and radiate it more quickly so less fade, bigger pads = less fade, slots, cross drill etc also help dissipate heat, but not as well as more disc mass. More diameter helps too. Extra calipers on the disc is a negative help, as it simply shields the disc more.
-
Agreed.
Hydraulic also has the issue of fluid contamination with water and heating of the fluid, but can provide some advantages in terms of efficiency of transferring force and gaining mechanical advantage.
Wheel radius and brake disc radius are absolutely relevant with regard to "stopping power" and torque is of course directly proportional to the radius. The bigger wheels however also carry a larger angular momentum. However, whilst cyclekarts are generally a bit heavier that go karts, go karts typically travel much faster and as the kinetic energy increases with the square of velocity, I suspect the energy that needs to be dissipated is in the same ball park if not higher for go karts.
Rhys, you say you've tried whatever has been available. Have any of them worked well in your opinion and assuming they have, it would be helpful if you could give some details of a system that has worked well on a cyclekart you've built and driven.
-
"Hydraulic also has the issue of fluid contamination with water", the cure for that is silicone brake fluid, I used it many years ago on my Scimitar, https://www.ebay.co.uk/itm/Dot-5-Silicone-Kart-Brake-Fluid-250ml-Why-Pay-More-BEST-PRICE-on-Ebay/401728080201?hash=item5d88dc0949:g:ML4AAOSwqCJciBps.
-
What I have tried has yet to let me down, I guess because I come from a background of old cars I have never really expected too much of brakes. Lifting off the go fast pedal will slow you down too!
The double cable kart brake, just as Fabrice showed worked well, disc was about 250 mm and 5 mm thick, both levers pulled with a bridle as you would find on a cycle. Both pads need to be working to "squeeze" the disc rather than one rubbing.
The hydraulic kart one which was on Kim was great, hydraulic, matched master and a very thick (10 mm?) cast iron disc. That was a set ex the hire kart. I did spend a fair bit of time making sure that the caliper could "float" to make sure both pads were working.
The very basic cable or rod ones as you can buy in the US from every kart supplier are adequate for a few stops, then they fade, when you know that you drive to the ability of the system.
I do know that the mountain bike ones, as Dave had on Thunderbug, go from OK to nothing in a heartbeat, and that's terrifying which is why I would only ever suggest as a secondary.
The one I'm using next has been previously used is from a Honda CB400 master and calipers (rear) with aftermarket race pads. I'm not yet sure about the disc itself, that's a large "fun kart" one, but it does match the diameter and thickness of thee Honda, but simple steel. (I know that on Austin 7 race cars the steel drums are not as good as the cast iron ones)
I know this seems odd, but if there is someone with fantastic brakes , and who drives that way, could well be a danger to others who may run into the back of that one?
-
My experience is limited to the cable operated drum on mine, it's spongy (cable stretch?), and lacking in bite (new shoes probably don't help). Hopefully it'll improve when I get the pedals moved and a straighter run for the cable, currently a bit of an s shape.
When it comes to the next one I'll use the front calliper off the scooter, paired with a pit bike rear cylinder, with a wheel mounted motorbike disc.
My feeling is that we need to use automotive brakes, be it kart, or motorbike, whether cable or hydraulic, anything else is unlikely to be up to stopping 100+ Kg of kart plus the driver.
-
I'm just back from the Motorsports industry symposium and exhibition in Germany. While there I took the opportunity to ask 3 of the brake companies who have staff I know, all asked a question whether we had return springs on the brake pedal. Now I have never done that on a cyclekart, but they all, independently, suggested it, and a relatively strong one too, so that amongst other things of benefit, you know you are pressing.
I had a good look at a few pedal box systems, and it was notable how much spring load is on the accelerator too. Without attachment to anything, cable etc, they were around 500 gm push", more than I have used, but the industry seems to thinks that's about right, or even more!
-
That’s interesting Rhys, I think I’ll try adding a return spring on my brake pedal. Thanks for sharing
-
Coincidently one thing at Stretton I noticed was, with my new trainers on I couldn't feel the throttle pedal, previously
with my old ones (exactly the same make and style) I could, and I was wondering what to do to improve the situation.
-
Thinner socks?
:)
-
Seriously folks, brakes are a very serious issue and as I understand it, Slack Alice was lucky to get away with a few days in hospital following his crash at Stretton. I hope your OK matey?
Now I don't know if I am right or I am wrong but I guess a sudden loss of brakes was the cause of the crash. It was certainly the cause of Rhys' crash and of course, he was driving the same car.
I remember looking at the braking arrangement following that and I thought the brakes were not capable of converting the kinetic energy of the cyclekart travelling at perhaps 15mph, into the equivalent heat energy, within the few yards the driver was perhaps hoping for. I'm sure Slack will rethink the brakes now but that's not what I am writing about.
I am of the firm opinion that we need some sort of simple 'standard' that we, as builders and drivers, should adhere to and that the standard should include brakes and anything else directly related to the safety of the Cyclekart.
Now this will take some thinking about I know (and I don't expect anyone to retrofit anything) but for new builds its a necessity I think and I would personally welcome a meeting of members specifically to discuss the subject.
-
I think meeting and working on the question of braking is a good idea Adrian
-
Thanks Stefan.
I would like to know if everyone feels the same?
We all know how important safety is but perhaps we don't always know how to 'build it in' as it were.
There are other things too, of course, all of which I am confident would come out were we to have such a meeting.
We have some good designers in our little group and we have people with 'senior' racing experience as well as good machinists, all of whom could contribute I'm sure.
The sort of thing I have in mind is a small A5 size booklet which is given to all new and potential members to help them on their way to building a safe and successful Cyclekart.
-
Sounds like a good idea to me Adrian.
-
Chris mentioned Silicone fluid, now everything I've read about it sounds excellent.
The one thing I can't seem to find a definitive answer to, can you use it in a braking system that has already had normal brake fluid in it? Is just draining the old fluid out enough or do you need to replace parts? Any ideas gentlemen?
-
You need to at least drain and flush the system through with the Silicone fluid. Ideally strip and clean everything thoroughly to get the full benefit.
-
Thanks for that info Chris.
-
Hi guys...when I started this thread I wasn’t thinking of my current situation!!
Hospital says rest and come back in 4 weeks. There won’t be much engineering done !
Having studied brake maths for the last few days, I believe the problem was lack of braking pressure in the system. It seems that a 6:1 ratio is ideal at the pedal, increasing say a 50lb foot pressure to 300lbs at the master cyl. Mine is only 2:1.
I am using a small bore M/C of 1/2” dia and this puts the effective pressure up to 500psi.
I believe this should be between 1000 and 1200 psi available for use.
Add to this the relatively small dia (200) of the disc and the width of 3mm, fade was probably the culprit.
Having said that, they did work for half the time before failure??
The basis was a matched pair, for the rear of a 650cc Suzuki bike. A 1/2” bore M/C and a single cyl. Slave of 1.5” dia. The slave was unusable however because it needed a large aluminium bracket to support one end of the pads.
I changed it for a bike M/C with 2, 1” pistons. ( slightly smaller area overall).
My first change will be to the pedal ratio, to get psi higher.
Next post will be the formulae I believe are required and the application to Thunderbug.
See you later......Dave.
-
http://www.engineeringinspiration.co.uk/brakecalcs.html
This is the site I used for the formulae.
I first calculated the ck weight....W = ck mass + driver x9.81.
In my case. 130 + 85 x 9.81 = approx 2150N.
Calculate deceleration rate. I assumed an initial rate of 33mph and a terminal speed of 7mph, stopping over 5 seconds. This is 15m/sec to 3m/sec.
Therefore 12/5 = 2.4m/sec/sec. x 2150 = 5160N.
The torque on the wheel...( I used 560mm for the wheel dia., 280 for half ).
T = F x Rad. T = 5160 x 0.28m = 1445Nm.
Calculate clamping load on wheel. C = T/ eff rad of disc x coef of pad x no of pads
C = 1445/0.1. = 14450 N.
Calculate system pressure required P = C/ A ( slave piston area)
P = 14450/982 mm2. = 14.7MPa. Megapascals
7 MPa = 1000psi.
Since I need 2000psi and only have less than 500, the brake doesn’t work!
Solution, more pressure and probably a bigger disc.
Please check my thinking/calcs. Dave.
-
Dave,
Nice work on the calculations.
I think that for the deceleration calculation, you're using force = mass x acceleration where mass is in kg. So that should be F = 215 x 2.5 = 537N. However 5 secs feels like a very long time - (it's taking us less than that to do the whole length of the straight in front of the pits at Stretton) - so maybe 1.5-2.5sec?
Looks like you also needed to include the pad coefficient and number of pads in the clamping force calculation...
Plugging those back into your calculations:
Calculate deceleration force. I assumed an initial rate of 33mph and a terminal speed of 7mph, stopping over 2 seconds. This is 15m/sec to 3m/sec.
Therefore 12/2 = 6m/sec/sec. x 215 = 1290N.
The torque on the wheel...( I used 560mm for the wheel dia., 280 for half ).
T = F x Rad. T = 1290 x 0.28m = 361Nm.
Calculate clamping load on wheel. C = T/ eff rad of disc x coef of pad x no of pads
C = 361/(0.1*0.35*2) = 5157 N.
Calculate system pressure required P = C/ A ( slave piston area)
P = 5157/982 mm2. = 5,251,527Pa = 762psi
So, it would seem that more pressure would be helpful to bring your performance up to what you're hoping for.
However, I think there's a very important distinction between brake performance and brake reliability. If our brakes don't have great performance but do the same every time, then you can drive to suit that....but based on your description of what happened, what I think you experienced was a sudden change in your brakes' performance. Sudden unpredictable changes are dangerous.
There's been talk about brake fade and "pad gassing" (lots of debate about whether this is real), pad glazing and boiling fluid.
Assuming a 215kg cyclekart incl driver, stopping from 15m/s/s to 0.
Kinetic energy = 0.5 x mass x velocity squared
= 0.5 x 215 x (15*15)
=24,188 Joules
Taking a brake disc of say 0.5 kg (note the Gemini one weights about 1.5Kg so 0.5kg would be very light.)
The specific heat capacity of steel is about 420 J/kg.C. Assuming all the kinetic energy is lost as heat in the brakes, then the temperature rise in that one braking event would be
24,188 / (420 * 0.5) = 115 C
This assumes all the energy goes into the brake disc, and that no heat is lost from the surface of the disc or brake calliper. It also assumes that no heat goes into the brake hub or the rear axle.
But, what temperature does brake fade happen at? I've read and heard all sorts of temperatures, but the vast majority are around 600-700 C and higher. So to me it seems unlikely that the brakes would get up to those sorts of temperatures except for on the flimsiest of disc rotors, through a mechanical problem with the brakes, or the driver "riding" the brake pedal.
Boiling of brake fluid seems more likely than brake pad fade although normally, only a small proportion of the energy goes as heat into the calliper. Also, we'd expect the brake pedal to go soft.
So, for me the jury is still out. Any other thoughts?
-
Impressive work with the numbers you two.
A couple of thoughts about the numbers...
Top speed 33 MPH, that's got to be higher, we know CK's have hit 50 in USA and I would personally add 10 percent for safety on top of that.
Time spent braking, like Stefan 5 seconds seems way too long, from my own driving experience it's more like 1 - 1.5 seconds.
Also should you not be using a terminal velocity of zero, since worse case scenario we would be 'red flag' situation, immediate stop on track?
As Rhys and Stef have both eluded to, not so good braking but reliable/constant is safe, but brakes that start excellent but then degrade not good. I agree with this.
Also just a thought, with your driving position Dave, your knees are heavily bent, this physically push's the end of your foot downwards, are you riding the brakes without knowing it, even if only slightly? I know when we are sitting in the cars stationary it's easy to notice these things, but when we are being bounced around on track different story.
I think we have been looking for the one answer when maybe two factors are involved. Increase both pressure and disc size/mass. Pressure will give you braking force, mass will give you reserve of energy absorption...think that all makes sense???
-
You two have lost me, I'm impressed!
I think if it was me, I would try to find some straight tarmac and run up and down giving the brakes real abuse until they fail again. Trying to narrow down the factors responsible.
-
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.
-
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?
-
No Dave you're not always at the back, that's my perogative when I'm there (at the moment anyway). ::)
-
Hi Chris.....ok, we’ll share last place! How’s your modelling going? Any time for the CK?
-
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.
-
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.
-
http://www.engineeringinspiration.co.uk/brakecalcs.html
This is the source of my data.
-
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.
-
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.
-
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/