General Discussion (Classic Trains)

To Deggesty and any knowledge engineers I am a new member I am curious about when adding a counter weight to a wheel as such like in steam locos does this weight improves the forward momentum somewhat as the speeds increases. I know that the counterweight main purpose is to offset the propulsion rods energy on the wheels, that  a side, does the weight adds to the forward motion. I welcom your feed back.

Lemlakit   lemlakit@yahoo.com

Although the counterweights comprise a small portion of the total weight of the entire mass of the engine, they at first contribute to inertia during the acceleration, and then the momentum during deceleration, just like all the rest of the mass.

So, really, no, the counterweights don't add to forward motion....they take more energy to get rotating around the axle as any mass would, and could therefore be counted as hindering the forward motion of the engine...at first. 

What they do is to offset the torque that the rods and cranks impart to the rotating masses as they move about the axes of each of the axles.

-Crandell

The counterweights also offset the weight of the rods and crankpins, thus smoothing out the rotation. Ever drive an automobile with unbalanced tires? The crankpins and rods add weight to one side of a wheel. The locomotive would jump around and also damage the rails. The weights balance the wheels. If you look at the main drivers of a steam locomotive, where all the rods connect to and has the biggest crankpin, that wheel also has the biggest counterweights.

Lemlakit, welcome to the Trains forums. Feel free to ask any question you have--and to share information that you have.

Selector and pjrr have made excellent points. 

Ideally, the weight of the counterbalances will exactly counter the weight of the main and side rods and their pins, and the weight of the valve gear that is attached to the drivers, so that the net effect of the weight of all is zero. However, in operation, the exact downward force of the mass of the various parts varies continuously, and there is also variance with changes in speed--and there are differences between the effective weights found when under steam and when drifting (moving without admitting steam to the cylinders); I noted this last difference just now, when I checked in the 1922 edition of The Locomotive up to Date. In practice, it is impossible to have perfect counterbalance at all times.

I hope we have helped you in understanding just what counterbalancing accomplishes, and what it does not.

Johnny

Thanks Crandell for your message, I am in descory mode in a project: by having a hollow space - a hollow tube place on the  the side and around the circumference of the wheel partially fill (50%) with a heavy liquid, as the  rpm increases the liquid would be trap by check valves at one solid location, within the tube, creating a counterweight thus adding to forward motion, or  needing less horsepower to generate the motion, this is not relating to locos in particular but the physics of motion.

Your input is appreciated   > Lemlakit >

For application on a locomotive, the check valves would need to be place so that the liquid ended up in a position such that it offset the reciprocating mass of the moving rods - in other words, in the same place as the cast counterwights normally used.  In this application, I think that the simpler cast weight would be more practical.

In other than locomotive applications, the concentration of weight at a single location along the circumference, in the absence of  drive rods to offset that weight (the reverse of the situation on a steam locomotive), would result in a hammer-blow effect with every revolution of the wheel.  This could be mitigated by cross-counterbalancing with the wheel on the opposite end of the same axle, but this would also negate any potential increase in the forward rate of motion.  Also, the addition of weight would, I think, increase the amount of power required to impart motion in the first place, and, without counterbalancing, any power increase realised from the rotating weight would occur for only one half of a revolution, with a corresponding decrease for the other half.

Of course, I never studied physics and perhaps I don't fully understand your premise. 

Wayne

I hope I understand your last post, Lemlakit. 

As long at the locomotive is required to deliver its own weight, and presumably some other revenue-generating weight, elsewhere along the linear axis of the rails on which it is meant to move, it will require energy transfer to effect that motion....forwards or in reverse as the case may be.

You can place a fluid offset from the central axis of each driver pair along the rim so that the weight of the mass acts like a counterbalance and imparts a torque around the axis.  In a drive-train with low resistance, and on level or near level track, the torque could be sufficient to move the locomotive.  However, you would need masses of something approximating 0.5 neutron density to deliver sufficient torque at the distance from the axis of rotation that we can afford on a steam locomotive to move revenue tonnages.  Moving such fluid weights, and fluids of such density, would take advances in technology applied to steam locomotives that would: a. not make any sense to me, and b; be highly expensive and require a lot of energy.  You would be better to force such fluids against turbines clutched to a transmission and forget counterbalance torque.

However, if you mean "flywheel" rather than "counterweight", you could make the drivers hollow in the rims and filled, not with check-valves, but small turbine blades, and force the dense fluid against the blades to make a fluid drive...they would be their own transmission.

And I am a non-engineer/physicist, too.

-Crandell