Has anyone measured the resistance of the feedback signal from the servo motor to the PGM in the various states?
I believe this would be one of the main causes of blown PGMs and stuffed servo motors if your actual RC valve position is completely different to the feedback position.
Don't think it's a feedback error so much as carbon deposits on the power valves which make them harder to turn.
The great / bad thing with DC motors is that the more resistance there is, the greater the torque they develop but of course this means more current flow.
That's why they use them in diesel / electric trains - massive torque.
In our application, the motor will try to turn those valves as directed until they shift or the PGM goes pop as it cannot supply the current the motor is drawing.
The answer is an inline fuse / circuit breaker, and is something I've never got round to doing though I've had it in mind for far too long! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
I agree with you there, that carbon buildup is one main cause of the valves jamming, but is it probable that another cause is that someone has not calibrated the feedback position to RC valve actual position? So when the actuator drives to the end, the feedback says it's not in the correct position, starts building up the torque (and current) and eventually pops?
I've thought about fuses, but could a fuses give us the accuracy required? The theory behind it sounds good, as the I2t characterisitcs can be calcultaed but I don't know if a manufacturer would put that much precision into it considering they are designed for significant overcurrent.
CBs or a TOL type device I think is a good way to go, but like you I haven't put much more thought into it.
Good to see someone else has these thoughts simmering in the background
I've no idea how you'd go about calibrating the motor, but yes I can see what you're getting at.
As for setting the current draw, I'd suggest a trial with an ammeter in line to see what the unit draws in normal use. Once you have a feel for it, add half and amp and off you go. That way, at least you'd know your valves were due a de-coke when the CB tripped! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
I've had a few of the servo motors open, and all the feedback sensor is, is a 5k trim pot. I think one rotation = 0=>5k. It has no end stops (so you can turn the thing as many times as your want either direction), and just goes through the resistance range.
so say 5k Ohm = fully openRC valve feedback. Some numpty has stuffed around with the trim pot and it's set to 5k Ohm. You install the servo motor, assuming all is good, and have the RC valve closed.
When you turn the bike on, feedback says fully open, actual position is fully closed, motor tries to drive feedback (and valve) to closed position. Since valve is actually closed, motor is pushing hard, draws extra current and either throws a tooth off the gearbox cog or pops a PGM.
The servo motor is actually a little 280 sized motor, I haven't had much luck finding out what sort of current draw those things have.
I was thinking about a dog clutch on the pulley like RC servos have on them to stop overload, but the fuse is better in every way.
Would be interesting to see how much difference there is between servos, they probably have different start/end positions compared to each other. I have a pic of mine in open position if anyone wants to compare.
zxcvbnm wrote:Would be interesting to see how much difference there is between servos, they probably have different start/end positions compared to each other.
How do you mean? Between different bikes? I doubt there'll be any difference - a standard unit buiilt on an assembly line and fitted to every bike regardless. _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
It's funny when people look for things to "fix" purely for the sake of it! Just go and buy an RGV if you want something to "cure"!
In 13 years I've never personally heard of an RC Valve servo failing (although I certainly don't doubt it is possible), and for many years now, since we discovered what fried PGM's, I've hardly heard of one of those popping either! Like I've said in a previous thread, the only time you really hear about it now if when a new Member joins with an already fried ECU, asking what to do about it!
A looked after (not even very well looked after) NSR is by far the most reliable 250 2T roadbike out there. Mid nineties Honda at it's finest. Can't you just be happy with the fact it all works and enjoy riding it rather than trying to fix something that is so unlikely to fail, you're simply wasting good blasting time?!
If you want to perform preventative maintenance, fit a new set of pistons and rings once in a while!
Maybe I'm missing the point in all this? _________________ Andy.
NSR-WORLD.COM
Please keep all responses to Forum posts on the Forum so that others may benefit.
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I don't think you are Andy.....Run the bike, with some WOT at times, at the end of the day that should be the reason to buy it! 2T on pipe, worry after the ride?? _________________ Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30
Well you certainly killed that interesting technical disussion! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
Before this topic dies, is there any way of testing a servo motor without connecting it up to the bike? I have a spare, and would like to do some diagnostics on it. Are there any servicing values that I can check?
I have searched, but all the threads appear to be hijacked and no answer is given......
Dave Ett wrote:
Well you certainly killed that interesting technical disussion!
I didn't think my opinion meant that much!
I just find it amusing that every now and again someone wants to try and find something to fix on an NSR! There are plenty of 2-stroke failures common to all the 250's, and without doubt this is the highest concentration of NSR owners in one place outside of Japan so it can appear there's a lot of piston/ring/barrel issues at times, but they usually stem from previous uninformed and incompetent ownership (often in Japan!) or from piss-poor "race" setup -- the NSR is unquestionably extremely reliable, probably the most reliable, as far as 2-stroke race-reps go!
The electrical and electronic components are superb, as they are on ALL the modern 90's 250's, and in reality ALL makes and models since the early 90's! Even the MC16 stuff is good, and I personally put the majority of their failures down now to vibration, humidity, and the fact the newest '16 is now 21 years old! How many 21 year old TV's and VCR's are there out there still working that hard under those sorts of conditions?!
PGM's predominantly die when the RC Valves cannot rotate freely due to poor maintenance... I will put 50p on it!
There's nothing to stop you guys discussing it still, but what will the outcome be? Is someone going to manufacture a tiny M-max sized box which will plug in-line between the harness and RC servo that will "pop" before the PGM if it detects a current draw out of range? Are the black boxes going to be mass produced and marketed specifically for each model, and sold at a price that makes it appealing to everyone to go to the trouble of buying and fitting it? The opening post hints at the fact that a solution could be worked on that will benefit the WHOLE NSR community.
Personally I just can't see the point!
I bet if you could magically "see" all the dead PGM's and the reason for their failures, the number that died because of a "feedback signal/resistance" issue is virtually non existent! _________________ Andy.
NSR-WORLD.COM
Please keep all responses to Forum posts on the Forum so that others may benefit.
Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.
Andy wrote:Is someone going to manufacture a tiny M-max sized box which will plug in-line between the harness and RC servo that will "pop" before the PGM if it detects a current draw out of range?
Yes. One day...
Andy wrote:Are the black boxes going to be mass produced and marketed specifically for each model, and sold at a price that makes it appealing to everyone to go to the trouble of buying and fitting it?
No. But I'll show others what I did.
All I gotta do then is replate the barrel, rebuild the engine, jet it, MOT and tax it, insure it and the whole project will have been worth while! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
Middo wrote:Before this topic dies, is there any way of testing a servo motor without connecting it up to the bike? I have a spare, and would like to do some diagnostics on it. Are there any servicing values that I can check?
I have searched, but all the threads appear to be hijacked and no answer is given......
Any help would be appreciated.
If you have a look at the wiring diagram, you can find out what wires go to it. Put a multimeter on the centre arm of the feedback, then I am not too sure which side of the feedback pot to measure! It's all guesswork from here, so good luck!
The service values....what do you mean by that? It's just a 5k Ohm variable potentiometer (variable resistance), so when these things fail, they normall short circuit or open circuit. If you mean, what are the corresponding feedback signals to RC valve position.....again I am not sure and that is one of the questions I was asking.
PGM's predominantly die when the RC Valves cannot rotate freely due to poor maintenance... I will put 50p on it!
There's nothing to stop you guys discussing it still, but what will the outcome be? Is someone going to manufacture a tiny M-max sized box which will plug in-line between the harness and RC servo that will "pop" before the PGM if it detects a current draw out of range? Are the black boxes going to be mass produced and marketed specifically for each model, and sold at a price that makes it appealing to everyone to go to the trouble of buying and fitting it? The opening post hints at the fact that a solution could be worked on that will benefit the WHOLE NSR community.
Personally I just can't see the point!
I bet if you could magically "see" all the dead PGM's and the reason for their failures, the number that died because of a "feedback signal/resistance" issue is virtually non existent!
Andy,
I agree with you that over 95% of failures are related to gummed up RC valves and lack of maintenance. The others......we probably won't find out what it is and don't really care as you would just swap out components and junk the bad bits. In real life, how many people will actually spend quality time looking after their bike and making sure it does work properly. There are enthusiasts like yourself that do that, but also we have those that don't understand that all things need love and attention.
I was recently asked to have a look at an MC21 that had free moving RC valves but was suspected of blowing a PGM. When we put a working one in, it made the working PGM release the "magic smoke". Knowing that the RC valves are free moving you have to try and determine what else is causing the problem, and how to verify the cause without it becoming an expensive exercise.
So my post was intended to get valid opinions and brainstorm, all in a technical context.
Separate to this, I had discussed issues with PGMs and servo motors face to face with someone from this forum, and one of his faulty servo motors actually had sheared off a couple of teeth in the gearbox, causing it to seize.
And yes, if the solution to the problem of blowing PGMs for 9x% of the times can be found by off the shelf components, I am willing to post that up and let others decide if they want to do it or not.
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