Three point acceleration and deceleration curves
 

 

 

 

 

Question: I have a question about the 3-rate acceleration/deceleration that is found in the X-series decoders like the MC2 and T4X, amongst others. I understand the values that make up the acceleration and deceleration rates, it's just the cutoff points I need clarification (so CVs 125, 127, 129, 131). My problem is understanding how these cutoff points work. Are they absolute values in that if I didn't make any change for Vmax and Vmid, my maximum would be 255 and these cut offs are less than 50% throttle. But since in my case (for example i have CV2/start volts set for 50, CV5 set for 150 and CV6 set for 100) the VMax is just over 50% of the maximum (150/255), then will the values in the cutoff CVs be abolute numbers referenced to the maximum possible (255) or will they be fractions depending on the values set in CV5 and 6? The manual suggests using 90 for CV125 and 130 for CV127. I hope this makes sense to you what I'm asking. Perhaps just a bit of clarification in plain English is all that I need. Let me ask this another way. In my example, I have an effective throttle range of 50 to 150. So 10% throttle should supply 60/255 available volts to the motor. If CV125 is set at 90, then the first rate is in effect during this range (so the first 40% of my effective throttle range) correct? Then the next rate (CV126) will be in effect between 90/255 and 130/255, and the last rate anything over 130/255. Now if i change my VMax to 200, my cutoffs should also change because now my throttle has a larger range (50 to 200), right? Answer: The term "transition point" instead of cut off point would better describe what happens at that point when the decoder reaches that speed. The decoder will switch from one acceleration value and use another. For example if you have a value of 50 in CV125, the decoder will use the acceleration value in CV3 until it reaches speed step 25 (internally this is translated to 50), at that point it will stop using the value in CV3 and use the value in CV126. When using Vstart, Vmid, Vmax, the values in the acceleration curves are not affected. However if you have a Vmax speed value that is lower then The transition point you simple will never go into that part of the acceleration curve. For example if Vmax is set for 150 and CV127 is set for 155, you will never Reach the transition point to allow the third acceleration value to be used.
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