Coupled Wheel Geometry (Fusion 360)

At least on a tractor unit it would have spring brakes so it would fail safe but I expect there might be a big kiss pressed on the windscreen at head height!

Mark

Thanks Geoff. I might have guessed someone else got there first,

Dave

Dave, That sounds suspiciously close to a dynamic motion analysis - perhaps Murray can enlighten if this is available in fusion?

If it is not, you can probably get all the information you need from section properties dialogues to allow hand calculations (perhaps in excel, given your comments about not wanting do the maths) to be made.

Mark

I know it's not what you are saying but there is a related urban myth that air brakes are fail safe because once there is insufficient pressure for the service brakes to work, the handbrake will come on. But you need the best part of 10 bar for full retardation via the service brake yet you only need ~2 bar to get the hand brake off. That leaves a gap where you may have only minimal braking before the hand brake finally comes on. I can tell you this from experience, having taken a 12t bus down a steep gradient at Millbrook with a failed compressor - quite a stimulating experience.

Murray

Murray, I can also confirm that when you are about a mile and a half from the gents (a wind sheltered wall would not cut it) and the only vehicle to get you back is a Scania prime mover with an air leak, getting the breaks off takes an eternity.... on the plus side, they do get a move on with not trailer!

Mark

I'm guessing that you can probably EITHER do FEA on a rigid assembly (eg spring-mass) OR make a moving assembly (dynamic motion analysis). But unless I've missed something, I don't see how you can sensibly implement a blade spring in a dynamic assembly.

Unless you want to make a breathtaking animation, I can't see any benefit in trying to use CAD for this kind of design work. The FE analysis (resonance) would help to dimension the mass and spring elements but I suspect that beyond that you'd be better just modelling the parts as a static assembly.

Murray

Murray, That is what I was getting at. You could always do a full blown dynamic simulation but cost of equipment (not just the software) would be a serious investment and the skill would be past my pay grade I would think.

I take it then that fusion does not come with dynamic simulation?

Mark

Thanks Murray and Mark. Good advice.

John S, yes, I've seen this in truck racing. On one occasion it ripped off the rear axle which cartwheeled over the track with the propshaft flailing.

Geoff

I once spoke to someone who had seen a coach propshaft come up vertically in the aisle...

Neil

Thankfully not very often, the result is usually a spectacular derailment. It's happened once in preservation that I know of. There the little end pin became dislodged on a bullied Pacific running on the main line down south, the connecting rod dropped and very fortunately landed on top of the electrified third rail, so the crew managed to bring it to a stop. Net result was a major panic care of the ORR and RAIB (which considering I'm one of several fitters who sign these things off as fit to run on the main line for a large UK preserved railway lead to a bit of stress in my day job). Had the third rail not been there it had the potential to be a repeat of a identical accident in the 60's where a Britannia Pacific (similar sized engine) ended up on its side, with the train pilled up behind it.

As part of any main line fitness to run examination (FTR for short) I perform all the motion pins (usually secured with collars and taper pins) and all the crank pins with their caps securing the rods are examined for slackness, missing cotters, taper or split pins (delete as applicable), damage or signs of movement. Annually all the rods are stripped off and dye-pen NDT'd for signs of cracking along with the crank pins on all our locos (having just finished doing this on a BR standard 4MT 2-6-0).

Owain