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is there a reason why they don't have the wheels spin separately? Does it make it more complicated? Or there is a disadvantage?
by geokon 4y ago
is there a reason why they don't have the wheels spin separately?
Does it make it more complicated? Or there is a disadvantage?
- nikanj 4y agoIt makes it more complicated. The wheels need to be fixed to the axel for breaks to function, so you can’t just stick a bearing in the wheel and call it a day.
- dredmorbius 4y agoThis seems unlikely.
- geokon 4y agoI'm imagining two half length axels. I guess this creates some torque but the breaks and bearing would be identical
- wiredfool 4y agoThen you'd still need bearings in the middle of the axle somewhere.
- mulmen 4y agoDon’t rail brakes generally act on the rolling surface of the wheel? Why would it be any different with independent wheels?
- bregma 4y agoNot regenerative brakes. Only friction brakes work that way.
- dredmorbius 4y agoRegen braking would operate through the same electic motor which powers the wheels in the first place. https://connectorsupplier.com/regenerative-braking-systems-rail-applications/ https://connectorsupplier.com/regenerative-braking-systems-r...
- brudgers 4y agoMy guess is at a minimum maintaining the bearings would be more difficult. A solid axel allows placing an external bearings between the truck and the axel. Hub bearings are internal and service would require dealing with the nontrivial weight of a loose wheel. See https://en.m.wikipedia.org/wiki/List_of_railroad_truck_parts https://en.m.wikipedia.org/wiki/List_of_railroad_truck_parts
- avianlyric 4y agoThe fixed wheels, plus the bevel create a self-centering effect. As the wheels move off centre, the bevel makes one wheel have a larger effective diameter and the other wheel a smaller effective diameter. Because the wheels have a solid axel, that forces one wheel to start travelling slightly faster than the other, causing the pair of wheels to turn. With the bevel making the wheels larger on the inside, it means that as a pair of wheels drifts right relative to the tracks, the right hand wheel rides up, starts behaving as if it’s larger, and then starts to overtake the left wheel (which has ridden down, and behaves as if it’s smaller), creating a turning effect to the left, correcting the rightward drift. When setup correctly, and travelling at a reasonable speed, the big metal lip on train wheels should never touch the track. The self-centering effect does all the work, the lip is just a backup to deal with overly tight turns, points and extremely slow running.
- geokon 4y agoI get the principle of how it works - though it seems imperfect bc it would vary depending on the weight/load. But why favor such a mechanism to just independent wheels? Or are you saying the whole setup actually tilts the carriage into the turn - helping to prevent it from tipping?
- mulmen 4y agoIf the wheels were independent the lips on the wheels would constantly ride on the inner sides of the rails. That increases rolling resistance and wear.
- RX14 4y agoThere are some trains which use independent wheels, but they need complicated mechanical centering mechanisms to replace the self-centering effect, and these are more expensive to maintain.
- dredmorbius 4y agoAny examples / explanations of which you're aware?
- dredmorbius 4y agoIt's a matter of balancing straightaway and turning performance. For a good explainer see: https://yewtu.be/watch?v=SRsm7mv0Oh8 https://yewtu.be/watch?v=SRsm7mv0Oh8 With separted axles, you wouldn't get the climbing behaviour of the outside wheel. With a fixed axle, the idealised shape of the wheels is of a double-ended cone (see the video for an example) which can ride higher on the outside of a turn. Even with conical wheels, with independent axels there's no way to impart a turning force on the carriage. I'm not entirely sure what the end result would be, but I suspect it would be a far harsher ride, and much more track and wheel wear. Probably a much higher probability of derailments as well. Cone angle varies by type of train and speeds. The video shows both freight and high-speed rail designs and discusses characteristics of both.