steerable tag

[davidbrady]

(03-17-2013 15:40)gondolaguy Wrote:  What I remember from past reading on the subject is that the steerable axles, while a good idea on paper, caused the unit to be tail-happy and wander when on inconsistent pavement. This would likely be due to the added potential for play in all the moving parts that allow the steering. It would also explain why they would weld the axles straight versus just relying on the pin to hold it firm. You should check to see if yours is welded as that would make it much harder to restore the feature.

No matter what the current thinking as to being able to restore it or maintain it, I would question the fact that the factory saw fit to weld them straight. That is a pretty radical fix and one that would make me suspect that there is no perfect mechanical fix. I will agree that there could be several series of steerable axle, that could make a difference.

Although this is probably common knowledge, it took me a while to figure out how to easily tell a steerable tag versus non. It turns out it's very easy. Steerable tags have "front wheels" on the tag versus deep dish rear wheels on the non tags.

Corey,

I'm inclined to take the opposite side of this argument.

We're still learning about the Ridewell steerable tag axle used in the LXi, but I think it's safe to assume that it's a caster adjustable suspension system where a linkage allows the axle's caster angle to change for steerability in both the forward and reverse directions.

The axle itself would look like the Dana steer axles on the front of our buses, complete with kingpins, steering ball joints, and a crossbar connecting the ball joints. These parts allow the steering of both tires in unison.

There's also a control mechanism that uses speed and direction signals from the transmission to engage multiple air cylinders at the axle. One set of air cylinders controls the caster angle and another set controls the steering locking mechanism. The caster control needs to lean the axle in the proper direction to allow the tires to self steer. The steering lock control needs to unlock and lock the steering at speeds less than and greater than 15 mph respectively.

I think, although I haven't actually seen the Ridewell system, that the suspension is connected to the the frame carrier via four trailing torque arms (similar to our Ridewell steer and drive axle suspensions); in addition, there may be panhard rod (dogbone) controlling arm to limit lateral movements.

If you've taken a look at the design of our steerless tags you can appreciate the bulk and heft built into the structure in order to handle the tire scrubbing in tight radius turns. You can appreciate the scale of these lateral forces even though they act at zero caster angle. IOW's there's no additional moment created by the offset of the tire contact patch with the kingpin pivot axis.

I wonder if Ridewell was consulted when the Wanderlodge service facility decided to weld the locking pins in place? The intended operation of the axle feeds little if any lateral scrub into the suspension system as the tires steer into the turn. Now imagine what happens when BB came along and welded the locking pin. As the bus is steered into a tight radius, the Ridewell steerable tag is trying to do its job - it wants to steer the tires but it can't because the welded locking pin won't let it. Now all these lateral forces are fed thru the tire contact and into the steering knuckles, into the ball joints and the crosstube, and finally resisted by shear and bending forces at the locking pin, the torque arms, and the panhard rod. I'm inclined to ponder whether Ridewell designed these components to withstand the slow speed, tight radius turning forces induced in a locked pin state?