How did you deside your PPM on Rostra setting

semo97

Joined
Oct 14, 2008
Messages
46
Location
colorado eastern slope
Bike
06 ST1300
I have several questions on your pulse per mile (ppm) setting. Some have used the divide by 2 others and myself have used the divide by 4. Does this have any bearing on the ppm setting? Some have set it at 24000, 16090, 19300 and 38600. Where did you come up with this and how did you figure it? I have read every post referring to the Rostra and some just seem to change things around trying to get something to work. I set mine at 38600 and it works well but going back over several posts this was used with the divide x 2. 1911 uses 24000 and has the divide x 4 and it seems to work well for him. I changed mine to 24000 and will try it out when every it stops raining and I can get out the 2 miles of dirt road. It may not change a thing. I would sure like to know how it figures into the setting you use.
Paul
 
I did test today setting my ppm to 24000 from 38600 and not good. I did the down hill only from 7900 to 6900 in 6 miles. Set the cruise at 45mph 3rd gear. It would not hold at 45 + 2 or 3 mph. it would run up to 60 mph and then I would not let it go any more due to the curves being 35mph. I reset back to 38600 when I finished the 6 mile down hill. I used it some more and it held very well so my settings will stay as I posted.
 
I based my numbers on, I read somewhere the St has 8xxxx pulses per mile. That is why I did divide by 4 and @24000 pulse on CC.
 
KTD1911, That is the way I figured but why not use 19300 it is closer to the 20000? I had to go back to the 38600 because the CC would not back off the throttle, the bike just kept picking up coasting speed from going down hill. Set at 38600 it would roll the throttle back to the set speed.
 
There is a wide range this runs over. I have mine set to 16090PPM, since I have VSS / 4.
I think the another question here is: what is your minimum engagement speed?
The Rostra manual says it won't engage below 33mph. Mine is very close to that speed, maybe 35mph.
If your Rostra PPM is set higher than actual, then it won't engage until higher than 33mph is reached.
If your Rostra is set lower than actual, then it will engage at lower speeds.

To answer your question: I assumed 27 pulses per revolution of the driveshaft, which results in 61,629 PPM of the VSS.
Why did I assume 27ppr? Because I think I read somewhere that the Goldwing and VFR are 27ppm, so I used that number.
I did not verify it when I installed my cruise, and I should have. The original estimate of 80,000 ppm I believe came
from PDFRuth when he designed his GPI. So I could very well be wrong with 27ppr. Still works quite well though.
 
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Lets look at anther thought. Does the RPMs have any effect with the setting of the ppm? Or does every thing go off of the ppr. I prefer to set my cruise when I will be at or over 3K rpms. doesn't matter what gear. It seems to be the best minimum rpms for the response of speed adjustment to the speed setting. I was running 4.5K in high gear I think my speed was 80 or 85 and the CC reacted to up and down hills very quickly. I did try and engage at 35mph and it would not but would engage at 40mph. I did not factor in the 7% the speedo is off, just went with what the speedo said. There should be a sticky on the settings every one used and how it performs it could save a lot of time if there was a majority having the same settings when you install one. I could drop down to the 16090 and give it a try, it would take several minutes and the down hill test I do from my place would tell me right away if it performs better and if not, doesn't matter.
 
"Does the RPMs have any effect with the setting of the ppm?"

I am sure the answer to that is 'NO'. You do not need the tach wire connected to make the Rostra work, it only needs the VSS input. The Rostra manual describes the tach connection as only a safety against engine overrev.

What pulse divider do you have? What is its ratio?

And the following is my speculation, from the standpoint of an electronics engineer:
Other than locking out low speed engagement, the Rostra really shouldn't care what the VSS PPM is, as long as it gets a good signal under 38000 PPM. Think of it this way, you set a speed and the Rostra captures the VSS pulse frequency for the set speed. All the Rostra does from there on is modulate the throttle to to maintain that same VSS frequency, and therefore constant speed.

The reason why PPM matters for low speed lockout, is that the Rostra is programmed for an absolute 33mph lockout. I am assuming the Rostra calculates speed by counting the pulses it receives for a certain time. If that works out mathematically to less than 33mph, then it won't engage. So, if the Rostra PPM setting is lower than the actual VSS PPM, then it will think you are going faster than you really are, and allow engagement at a speeds lower than 33mph. Conversely, if the Rostra PPM is set higher than actual VSS PPM, then it will think you are going slower than you really are, and therefore you would need to go faster than 33mph to get it to engage.
 
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I've connected an oscilloscope, and counted 104 VSS pulses with approximately one revolution of the wheel.
The wheel makes about 805 revolutions per mile, so there is upwards of 83000 VSS PPM, and PDFRuth is correct.
I also calculated the VSS PPM from my GPI "learned" IPG to VSS ratio, and the result is approximately 82,000 PPM.

I suppose I should reset my Rostra to 19300 next time I have the fairing off.
 
I am running the rostra divide x 4. I have tried the 24000 and it did not do well, I went back to the 38600. I have easy access to the servo under the passenger seat so I will try other settings and see what I get. Changing the settings is only for information for all on what may work the best. There is a lot of info on the rostra on here but very little when it comes down to the brass tacks. Your testing is very interesting on the working of this unit, this is the kind of information I like. I will post results when the muddy roads dry out some.
 
I test ran today with the setting at 19300, it responded the best of three settings 24000, & 39600. I thought the 39600 was very good. 19300 works outstanding. I did the test same as the other settings doing the down and up hill 6 mile with 1000 ft. alt. change and the high way flat and small hills. I set the cruise it responded right away at backing off or pulling hills very little to no mph difference. It will engage at 35mph. This is my settings with divide x 4 and the Rostra control not the GW control. 1 on, 2 off, 3 on, 4 off, 5 on, 6 on, 7 on, 8 off, 9 off, 10 on, 11 off, 12 off. I hope this will help some on here and thanks to nsxt for is input.
 
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