driving truck suspension

[Andy G]

Hi Folks,
I have bought a driving truck.
It is the design of a long low sided truck.
It has 8 wheels, set on 2 individual bogeys.
This type seems quite common among the GL5 membership.
I wonder if anybody could provide me with the set up and some photos, of how 'if any springing' is utilised to keep each wheel in contact with the rail.
The bogeys on my truck are free to swivel and flex (when the truck is upside down.
When the truck is the right way up and on the track, it keeps de-railing.
This is due to the 8 wheels all now being forced up, to constantly ride in the same orientation as the flat bottom of the truck.
There is no springing arrangement to force the individual wheels down onto the rail (when the rails are uneven), causing the wheel flange to ride out of uneven track as the rail drops away to a low point.
Any help, especially photos of any springing arrangements utilised on these trucks would be much appreciated.
Best Wishes.
Andy G.

[Dave Noble]

Hi Andy,

Am I right in thinking that each bogie has two separate sideframes pivotted on a central bolster, so that they can pitch up and down, thus keeping all four wheels on each bogie in contact with the rails when the bogies are detached from the underframe. These then would be compensated bogies with no springing.

If the problem arises when you fasten the bogies to the underframe, then you are not alone, this is a common problem.

I'm guessing that each bolster is pivotted in the middle on a bolt, and has a roller or some sort of support near each end riding on the bottom of the underframe.

Is this correct? If so, I'll get back to you.

[Andy G]

Hi Dave,
Thanks for your reply.
Nice to hear from you, hope you are o/k.
Yes your description of what I have is spot on.
I hope if this is a common problem, somebody has thought of a cure for it.
I hope you or another GL 5 member can enlighten me as to keeping on the rails.
Best Wishes.
Andy G.

[Dave Noble]

Right, the problem is that the supports prevent the body from rolling relative the bogies, ie rotating about the vehicle's longitudinal axis, like a ship rolling from side to side.

What you can do is allow one bolster to support the body with the supports/rollers which are already there, but give the other bolster some freedom by removing the supports/rollers, and only supporting the body from the middle of the bolster. You will probably need to add washers to the bolt, between the bolster and body, though a better solution would be to use a small thrust bearing. If you do this, looking at the end of the vehicle, the body should follow one bogie, but allow the other bogie to roll under the other end and follow the track. This is probably the simplest solution and gives a fully compensated vehicle.

An alternative would be to replace the rollers/supports with sprung ones, this should give a less harsh ride, but would be more involved.

Full size bogie vehicles do have supports similar to what you have, but the difference is that they have springs over the axleboxes as well, and these give the flexibility required to keep the wheels on the track.

Let us know how you get on.

[Andy G]

Hi Dave,
Thanks for your suggestion. It sounds an easy fix (thankfully).
I will try it out and let you know how I get on.
It all sounds to make perfect sense.
Cheers
Andy G.

[Scrat]

Hi Andy,

on my first driving truck with two unsprung, rigid bogies a simple washer between bogie top and frame did the trick. It allows the bogie to tilt in any direction. The truck has run fine ever since.

[Andy G]

Thanks for your input also 'Scrat,
I have now made the two axle end rollers the same size as the axle material and spaced the bolster to the same distance as it was originally with a thick washer ( as you suggested Dave).
The bolster does still not flex about freely.
This seems to be because the bolster is about 3/4" square.
The pivot pin holding the bolster to the underframe, and passing through the 3/4" bolster material is a reasonably close fit, (thereby) preventing its angling ability.
I plan to machine the bolster thinner where the pin passes through so that it can re-angle easier.
I guess I will reduce it gradually until it appears to angle sufficiently.
I do not want to take the bolster material too thin, otherwise it will lose its strength and bend in service.
Does this sound to be the solution Gents ???
Another thought would be to leave the bolster at full thickness, and drill the hole for the pin slightly larger in diameter for most of its thickness, leaving a small amount the original diameter.
I think the second thought is the best and easiest !!!
Any thought's.
Cheers.
Andy G.

[Dave Noble]

Your second idea (over drilling) is definitely the way to go.

[Andy G]

Cheers Dave,
thanks for the encouragement.
I will let you know how it turns out.

[Westernkid]

Hi Andy,
I think what Dave did not clarify, is that the bogies need to be able to roll on the longitudinal axis in order to accommodate changes in cant of the track. If they cannot flex then you get exactly the problem you describe of derailments as the flanges ride up.
Exactly the same problem also happens with models of Diesel Locomotives which can be up to six feet long if the suspension is not correct and that is without the weight of a full size driver sitting on it.

[mickfearn]

Hi Andy the nut that holds the side frame on the square bar that you describe needs to quiet loose on the axle,to allow the movement as described by
Westernkid.
.

[Dave Noble]

Andy,
Did you get a PM from me a few weeks ago?
Dave.