DecoderPro Comprehensive Programmer

Speed Control Pane

The Speed Control pane looks very complicated, but it can be one of the most significant in improving the performance of your locomotive fleet. Let's look first at the top of the pane:

There are three important CVs here, Start Volts, Mid Volts, and Max Volts. They work together to make a very basic three point speed table.

Start Volts is the voltage at the first speed step. If your locomotive didn't start moving until there were three volts on the track with analog power, this lets you set up the decoder to give it 2.99 volts right away, so it will start moving when you want it to.

Max Volts is the maximum amount of power the locomotive will get from the decoder. If your locomotive looks like Chuck Yeager's X-1 at full throttle, then you can trim the top speed down to a more reasonable level.

Mid Volts lets you configure the slope between Start Volts and Max Volts a bit, so that if your locomotive reaches full speed at 5 volts, you can stretch out the lower end of the curve to get more fine control in a useful speed range.

If you are having problems with unpredictable speeds with your locomotives, check these settings. On any number of occassions I have discovered one or more of these settings have been changed accidentally (usually due to an error in programming with a throttle), leading to very odd speed performance. In particular, if the Mid Volts is lower than Start Volts or higher than Max Volts, results can be highly unpredictable. DecoderPro will not let you make this mistake.

If the full Speed Table is used (which we'll be getting to in just a moment) the Start Volts, Mid Volts, and Max Volts settings are ignored. The "Use VStart, VMid, VHigh" and "Use Table" radio buttons switch back and forth between the two.

I have not seen a model locomotive yet that would run at exactly the same speed forward and backward. The "Forward Trim" and "Reverse Trim" options let you make this adjustment. However, the settings for these are not as intuitive as you might think. A setting of 0 in these CVs turns them off. However, a setting of 128 in either of them will have no visible effect! To make the forward and reverse trim effective, raise the value above 128 to increase speed, and lower it below 128 to decrease speed.

The Speed Table

The Speed Table allows you to fine-tune the throttle response of your locomotive. You might opt to match all of your locomotives so they run at the same speed for the same throttle setting, or you might want to set the table up so that your locomotive runs at the actual scale speed indicated by the throttle. Or maybe you have someone in your operating group that likes to switch the yard at Mach 2.5, and you want to slow them down a bit. There are a lot of ways to use this feature.

The default speed table for most decoders is a straight line. The "Force Straight" button below the table duplicates that.

As you can see, you have both numbers and sliders to work with. Changing eiither one will make the other change to match it. The first and last steps are set to minimum and maximum values.

The "Match ends" button will also result in a straight-line graph, but you can offset the beginning and end by any amount you wish. The function will then draw a straight line between those two endpoints. Below is an example of the result.

If you don't desire a straight-line response curve, there are two other options available. The "Constant ratio curve" gives you a response that increases slowly in the low end, and rapidly at high throttle. This function will also draw the curve between preset end points.

The "Log curve" reverses this response, giving you a logarithmic response curve with high accelleration at low speeds, but topping out quickly. It will also draw the curve between preset endpoints.

The "Shift left" and "Shift right" buttons move the entire speed table left or right one space with each click on the button. The example below shows a linear 0-255 speed table that has been "Shifted left" three times. "Shift right" works in the same manner, moving the entire table right one position with every click.

Of course, you can enter the numbers individually or move the sliders one at a time to create your own fully customized speed table.

One very important thing to remember: No matter how pretty your speed table looks, it has absolutely no effect on the locomotive unless you write it to the decoder!

On to Next Section

Back to Index