Barry Olsen said:
Stanley,
Your first four questions are not germane to the hobby. Top speed is not relevant to running trains, crawling ability is much more important.
Barry
Thank you for replying to my questions. This provides common ground to try to effect communications. You and I see things very differently in this regard. We agree that crawling ability is paramount. My K27s crawl at less than 1 smph and will pull a full load at that speed. They accelerate over the entire speed range extremely smoothly. The video I posted long ago shows excellent slow speed performance. And equally important the wheels will slip long before the motor stalls (assuming you can provide sufficient power) These locomotives are the work horses on my railroad and are the ones my operators like the best.
Where we apparently disagree is top speed. You believe it is not relevant, I believe it is fundamental. Some of us are into realistic operation of our trains and prototype speed is important for us. A good performing locomotive in my opinion must have both low end and top end performance. I have one locomotive that has excellent low end performance but no top end speed to speak of. It sits in the shed awaiting a new motor/gear box to gain a reasonable top end performance.
Let me try to answer my own questions for this part and why I asked them
- What is the scale speed of the K27 as shipped with a double lead worm at 18 volts DC with its 1/14.5 gear ratio?
The K27 as shipped has a double lead worm gear and has a speed of 41 Scale MPH at 18 volts DC (this is 1:20.3 scale speed measured with an Aristocraft 10 amp switching power supply)
- What would be the scale speed of the K27 at 18 volts DC be if the double lead worm was replaced by a single lead worm with the same 1/14.5 gear box?
If the K27 had a 1:14 gear box and a single worm then the speed at 18 volts DC would be approximately 21 scale miles per hour
- What would be the scale speed of the K27 at 18 volts DC be with a double lead worm but the gear box was replaced by a 1/29 gear ratio?
If the K27 had a 1:29 gear box with a double lead worm then the speed at 18 volts DC would be approximately 21 scale miles per hour
- What was the max prototype speed of the K27 on the valley line south of Alamosa?
The valley line is one of or the longest straight and almost level section of Narrow gauge track in the country.
I was not there in the 30s-40s to clock it but I have been told that the max speed of the K27 was 45mph and as the K27 aged the railroad did not like the K27 running at that speed which is why in later years they placed the 30mph speed limit sign in the cab which would still be quite a ride considering the condition of the track. I have been in a lot of cabs but the K27 is rather unique in the speed limit instructions to the engineers. Note the Blackstone model also built by Kader in HOn3 has a specified max scale speed of 45MPH, which is the same as that specified for the 1:20.3 model.
I have been told that it is the intention of Bachmann to produce 1:20.3 models which perform across the full prototype speed range. The model as produced meets their criteria.
Barry Olsen said:
Number five gear pitches, have to match.
Number six, your word “currect” is confusing, is it correct or current? Please note that the single thread worms are matched with single thread worm gears and double thread worms are matched with double thread worm gears. I buy my worm gears and spur gears from Stock Drive and they offer each for the worm you are using.
Also they offer the gears in different pressure angles; i.e., 14 1/2 degrees and 20 degrees.
I spent a good amount of money having my worms customized by a shop in Colorado. What they did for my worms solved a series of problems, they created two worms for me single thread and double thread.
Sorry for the typo it was intended to be current production. I agree completely with your statements. Your gears are excellent and I think you will agree the gears in the K27 are way beyond what Bachmann has ever done in the past.
- What is the gear pitch of the production double lead worm and the pitch of a similar single worm gear?
As you correctly point out, the gear pitch of the single lead and the double lead worm are different and they much match the rest of the gear box.
- What would happen to the correct gear box if the double lead worm was simply replaced by a single lead worm?
In short order you would grind up the gear box.
I asked these questions because you and Dave implied that Bachmann had a design defect and that they intended a different gear ratio but changed to a double worm gear and thus unintentionally doubled the speed which was unintended. This set of statements is wrong and has led to a lot of false rumors being spread around based on incorrect information.
Bachmann makes their own gear boxes and as you state the gears must match. You can not simply change from a single to double without redesigning both gears. The gear ratio is selected simply to meet their design constraints for desired speed at various voltages.
Bachmann build a locomotive in 1:20.3 that has the same speed characteristics as the prototype and also apparently the same as the Blackstone model. They chose 18volts DC for this conversion. Now one could reasonably argue that the top speed should have been 30mph (to reflect the speed restriction currently in the Cab), or you can reasonable argue that 20 volts would be a better value for this to be measured at. Reaching a consensus of what we desire for top end speed and at what voltage this speed should be measured helps the manufacturers design product that best meets our desires. And like it or not, not all modelers want prototype speeds, I have visited a lot of layouts and often they like to run them faster. A manufacturer needs to try to accommodate all segments of the hobby.
Perhaps a gear ratio of 1:16 or even 1:18 would have been a better compromise choice as this would still have provided a reasonable top end speed (although less than the prototype) and would have required less torque and thus less amps to reach those speeds. What makes this all work with the current model is that the Pittman motor in the K27 has more than enough torque to handle the load over the entire speed range.
But 1:29 with a double worm, no way. Such a gear ratio would result in a locomotive that would run way to slow and most desire the prototypical speeds. With small layouts prototype speeds often do not look very good but as the length of the run increases, operating like the prototype becomes very reasonable and looks quite good.
I have 3 K27s on my railroad. Even with extra weight they slip long before the motor is over taxed and have a ton of low speed performance. The motor and gear box are well matched and they perform well over the entire speed range.
Barry Olsen said:
If the gearbox in the K-27 is so good, why was it changed in the Mallet? Also the gear ratio has been announced as being 1:28. If you have been so right, doesn't this prove you wrong?
Barry - BBT
Barry coming from you this is a strange statement. Should not a gear ratio be determined by the desired scale speed range, the prototype characteristics, the motor, and the drivers? I have seen a report on the Bachmann site on the gear ratio but nothing on the motors or other operating characteristics. A logging Mallet is not the same as a K27 and I would expect it to function differently. From the photos posted, I can not even imagine how one would get two pitman 9000 motors in this model. Lets wait to see what the final production locomotive looks like before speculating on its insides.
Stan
