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Post by Roger on Dec 9, 2014 11:55:51 GMT
I'd be a little wary of using mountain bike calipers/discs without a bit of testing first. They're brilliant for what they're intended for, don't get me wrong, my bike is gravity based so I wouldn't leave home without 'em But my concern is that they're meant for stopping 75-100 Kgs. Ok, you might get the occasional heavyweight rider, but a train of five passengers may be somewhere in the region of half a tonne in weight including loco and carriage - would they be up to the job? Maths: 5 Passengers at an average weight of 75KG (11st 11 ish!), loco weight of 50kg (0-6-0), carriage of 30kg - 455kg total. That, and the pads are bloody expensive, costs me as much to replace a set of pads on my brakes on the mountain bike as it does to replace them on the average car, and they're only the size of a 50p piece each! I hear what you're saying but I don't think the maths does justice to it. If you think about it, the torque on a mountain bike disk is massive because it's near the hub and the braking effect has to reflect on the full diameter of the wheel. That's got to be a multiplier of x5 and don't forget that tyres don't slip easily on tarmac. The situation on a riding car is very different, the multiplication factor is much less and if too much braking is applied, the wheels will slip. I'd say it's more than adequate for the job. The cost of pads is another question though, but how often are they going to be changed? Do the brakes get a hard time?
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Post by GWR 101 on Dec 9, 2014 14:34:23 GMT
Hi thanks for your input on the brake discs I did look at the options of buying them but they are too big as the wheels are only 4" diameter (don't think the club would be happy with the brake disc cutting through the sleepers) . Just to clarify its a two axle drivers truck which will have a disc brake on each axle, the reason for four discs is that two are for the 7 1/4" axle set which will drop into the same frames when using the ground level track. They are only intended to brake the engine and drivers truck as the passenger coaches have separate braking, apologies if my previous post caused any confusion please feel free to comment if you still consider this not a suitable method. Regards Paul
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Post by Roger on Dec 9, 2014 14:48:38 GMT
I don't know how big the pads and calipers are, but there's no reason why you couldn't use them on any diameter you like. I'd ignore what they use them on it's not relevant to your application. It might be that you can't get the caliper close enough to the axle anyway but it might be worth nipping down to Halfords and having a good look at some.
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Post by Rob on Dec 9, 2014 16:09:21 GMT
That's a good point Roger, I'd not considered the diameter of the wheels - 26" compared to 4"! They certainly have the ability to lock 26" wheels, whatever the surface. I once warned my brother not to use the front brake when he was having a play with the suspension down a set of large steps, human instinct is to grab on hard if something doesn't feel right and sure enough, over the handlebars he went! He was doing brilliantly to that point considering he doesn't normally ride bikes down stupid things!
The calipers themselves are pretty small, I can take a photo of mine later for a size comparison. They are quite expensive, being roughly equivalent to the entire price of typical Halfords bike, so might be a little over the top. I've had some experience with the cheaper mechanical variety of disc brake and found the modulation to be poor - pretty much off or locked, could have just been a poor setup though.
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Post by Deleted on Dec 9, 2014 18:25:54 GMT
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Post by Deleted on Dec 9, 2014 18:46:22 GMT
Tut-tut young Mr Glade that is green-------go back to page 5 and my last but 1 posting ...........For what it is --it's a bit expensive ( apparently --- maybe ----perhaps --- )... but the principle is easy to copy...Just make sure the whole body is free to float on those pins and thus re-act and bring BOTH pads into play....
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Post by Deleted on Dec 9, 2014 18:49:14 GMT
ahh...sorry chaps.....put it down to a senile moment.....
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Post by GWR 101 on Dec 9, 2014 20:47:48 GMT
I am using some of the ideas from a drawing sent to me by a fellow contributor from the other side of the world so it's not entirely my design. However the braking system was a lever with a block of wood onto the wheel od, so I just thought I would go for something different, having said that there are suppliers in this country that sell complete disc brake kits for our application. Regards Paul
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Post by Rob on Dec 9, 2014 20:57:51 GMT
These are my calipers: Front disc is 7". When it wears out i'll replace it with an 8". Rear disc is 6": Prices range from about a tenner for the most basic of mechanical calipers, through to about 500 quid each.
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Post by GWR 101 on Dec 9, 2014 22:36:29 GMT
Thanks for that Rob, I think a trip to local bike shop is in order. Regards Paul
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Post by Roger on Dec 9, 2014 22:44:05 GMT
That's pretty compact Rob, it might do the job.
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Post by Rob on Dec 9, 2014 22:45:59 GMT
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Post by Deleted on Dec 10, 2014 0:25:48 GMT
Blimey matey ---- that's almost up to the 9" on my Honda CG125....( which also has an AXLE, so I'm just "On-thread" )........
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Post by Oily Rag on Dec 10, 2014 1:46:32 GMT
Could not be bothered As you were
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uuu
Elder Statesman
your message here...
Posts: 2,814
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Post by uuu on Dec 10, 2014 7:52:42 GMT
Talking of doing the maths... The energy to be dissipated by stoppng is mass times the sqare of the velocity. So a biker stopping from 30mph has 36 times the energy to radiate away than stopping from 5 mph. So I think bike brakes will not have overheating issues being used on miniature trains.
Wilf
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pault
Elder Statesman
Posts: 1,497
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Post by pault on Dec 10, 2014 10:07:11 GMT
when i was taught to drive miniature locos I was taught to let nature do as much work as possible, ie coast to a stop where ever you can, it wastes lass fuel and creates less wear on everything. Bearing in mind that locos do not roll anything like as freely as a bike I would see no problem using the bike calipers. Making the disk from aluminum however I would suggest is not such a good idea, I cant see the disks lasting long at all. I guess you could hard anodize them but then you would have an abrasive disk that would probably kill the pads or the anodizing would wear through fairly quickly so back to square 1
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Post by GWR 101 on Dec 10, 2014 10:48:15 GMT
Hi Paul yes I did consider that might be a problem so the discs are 8 mm. thick so dropping the axle and skimming in situ is not a problem. Also as they are bolted to a steel hub refurbishment is not a major issue, and I was considering rubber for the brake blocks so they would possibly wear out first and replacement of those would be an even easier and far less costly option. Thanks for your input it is much appreciated and as I keep stating I have absolutely no experience of loco driving so it's all a case of learning as you go. Regards the other Paul.
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