Tacho Set A Failure
Justina Ky
The tachometer of my two months old (1200 km) V11 Naked has started to do odd things. When I ride with stedy gas for example at 3000 rpm, the tacho jumps suddendly to 4-5000 rpm and then comes rapidly back. The problem was first occasional but is getting worse and worse all the time.
The only thing I know about that is that if it fails, look to a relay. One relay covers the tach and something else (I dunno) mabe the headlight? Also keep an eye on the speedometer cable where it enters the motor on the right side, it will work loose. Rosso's have had a problem with breaking speedometer cables lately.
If the tach and the speedo all work the same way there's a gear that sits at the end of the relevant cable. The gear will be stripping itself. It's a pretty common problem on the bikles with the Veglia clocks, i heard that it was pretty much eliminated on the newer ones though oh well some things will never change.
It's the case. Seriously. The mounting posts on the tachometer case are press-fit and when they start to work loose, the tach starts to behave EXACTLY as you have described. It can be fixed if you're willing to open the unit. Since I have a broken one (actually two) at home awaiting this exact same fix (I've done it twice before), I will try and get some photos of the process and post the whole shebang on my web page. I'm through with Guzzi schematic diagrams for the time being (47 of them enough?), so it's time to do something else. The tach won't fry or anything like that for the time being (I ran one for two years doing that), so if you're willing to wait, I'll try to get to it within the next couple of weeks.
The Veglia instruments, especially the tachs, are prone to the mounting studs detaching from the instrument case. The stud from this one is inside clinging to the magnet on the meter movement. Prior to it's complete detachment, it was just a touch loose and the tach was erratic. Adding the extra wire isn't a bad idea, but I suspect that eventually, the mounting studs will come loose simply because they weren't that well installed to begin with.
As the plastic casing is identical on both sides, the only big difference that I could see between the tacho and the speedo cases was the big hole in the side of the speedo clock where the trip meter reset shaft goes through.
The tacho pickup on the 912 engine is an electromagnegtic coil. A magnet on the flywheel induces a pulse in the coil when it passes by. This produces a pulse which has a positive voltage spike at one end and a negative spike at the other end. Which polarity spike occurrs first is dependent on which lead of the coil is cconnected to ground.
This next part is speculation on my part. I expect that the input to the tacho gauge probably has a capacitor in series to allow the spikes to pass, but blocks the DC component of the signal. As such, the tacho looks like a very high impedance load (virtually an open circuit) to the pickup coil. With no load on the pickup coil, the spike voltages can go quite high (I've seen estimates of around 100volts). These high voltages are causing a breakdown. In the circuitry inside the tacho which is causing the erratic behaviour. With a 220 ohm resistor across the pickup, the voltages never get that high and the tacho behaves itself.
What I've found: the Aviasport gauges supplied by Rotax, are a D'arsonval movement meter driven by a Microchip PIC microcontroller. The microcontroller senses whatever input it is designed to sense, in the case of the tacho, it counts engine pulses, in the case of the temperature gauges, it reads the resistance of the senders, and then the microcontroller translates that measurement into a scaled analog voltage for the meter movement.
With benign signals like those from resistive temperature senders, the microcontroller is quite safe and reliable. However with an active signal source like the inductive tacho pickup, the micro needs to be protected from overvoltage situations as I described earlier.
Given that these gauges have been designed to specifically work with Rotax engines, I think Aviasport should revisit the tacho circuitry. In the mean time, if you use these gauges on your homebuilt and have the same problem with the tacho, try putting a low value (220 ohms) resistor across the tacho pickup leads and see if that fixes the problem. But before you do that, make sure you don't have a loose connection somewhere causing the problem.
Hi Scott, yes I had exactly the same problem and went thru two aviasport gauges before I stumbled on the solution you describe. It may not be widely known as Floods had no idea. I needed to fit the smaller 2 1/4 gage due to space requirements. My first one lasted a couple hours and pegged out. The second one worked for a while and then would go off scale after 5k rpm or so. I then tried the 3" gage and it worked perfectly, but I needed the 3" hole for something else. I imported an American 2 1/4" gage and it helpfully had the instruction that if the gauge becomes erratic at high revs, to fit a resistor as you describe and it works perfectly. I can only presume the larger 3" gage has room enough to have a resistor inside? It's interesting you should make this post as when I was having my issues with 2" gauges, I saw on your plane at Watts and noticed the smaller tacho and I was wanting to ask how you were going with it. I agree that aviasport should address the issue as the gauges are not cheap.]regards, mark
I had a problem early last year with my vdo tacho. The hr meter would glitch during flight. I was about to remove the gauge and send back to an authorised repairer. I have since had a total failure of my voltage regulating device. ATSB incident report and raa report completed after an emergency landing at Naracoorte. I no longer have any problems with my vdo hr meter since a new vrd has been installed. It's only now that I attribute the glitch to the faulty/failing vrd. Early warning sign of failure?
If the battery went completely flat it would have the effect of showing as no current to the tachograph, when the current is disconnected from a digital tachograph it will show an error message, so as Santa said it will need to go to the tachograph centre or dealer to be reset.
I understand electrics at a basic level, but am quite a newbie at electronics. This is my first real Arduino project. I'm, though, a software developer (currently web development, did C/C++ some 15+ years ago), so hopefully will have less trouble in the programming department.
I'm working on a temperature-sensitive automatic fan speed controller for a fan that is cooling my lathe's motor. I decided to approach this step-by-step, so first thing I'd like to do is to be able to control the fan speed using a potentiometer, and also read the actual RPM reported by the fan's tachometer. I will deal with the lathe motor temperature measurement later.
After hooking up a potentiometer to the Arduino, I followed this article. I've set the PWM frequency to 25 KHz as mentioned in Noctua's pdf. This worked without any issue, the fan can be controlled with the pot from almost 0 to max RPM.
I wanted to be able to measure the fan's RPM, mostly to be able to tell if the fan is not working properly for some reason. So I tried to hook up the tachometer output, based mostly on this instructable. I didn't quite understand why the tachometer signal is pulled up to the 3.3V pin. I modified the code based on other snippets I found, I also tried the original code and several different variants.
The problem is, I'm getting really strange readings. Only with PWM set to 100% duty, I'm getting something that seems somewhat reasonable - around 1760 RPM (the fan is rated at 2000 +/- 10% RPM). At 0% duty I'm getting 0 RPM, and everything is between displays around 20000-30000. It seems that the interrupt is firing really often for some reason. The fan is new so I'm guessing something is wrong either with my code, or with the wiring of the circuit.
Connections:
Arduino UNO, powered via USB
Fan power connected to a 12V bench power supply.
Fan PWM connected to pin 9 on the Arduino.
Fan tachometer connected to pin 2 on the Arduino (directly, internal pull-up resistor enabled).
Power supply's ground connected to Arduino ground.
Attached is a screenshot from Noctua's pdf. It mentions "Vcc for 12V fans: 13V", while I have 5V from the Arduino. I am wondering if this 13V is just the max allowed Vcc. If I understand Arduino's INPUT_PULLUP pin mode correctly, I should have the same circuit as prescribed by the picture.
Is this how you greet first-time posters on this forum, by nitpicking some minor detail, and offering nothing truly helpful on the actual topic? I've had some coworkers like that, who would write comments about some code style issues during code review, but not take the time to look into the substance regarding architecture, possible bugs etc. I thought Arduino was created with beginners, students and hobbyists in mind, for many it can be a first start in programming. Many (most?) tutorials I've seen (including official ones) have rather primitive code which could be called amateurish.
I thought that by reading the "How to use this forum" topic and following the advice in there, I would get some friendly help. I didn't think I would find some professional snobbery attitude as my first experience on this forum.
I see that you have a lot of posts in here, 4 stars (whatever that means), and a lot of karma points. So it seems you are a knowledgeable and helpful person. But I can see that you didn't actually check the links I've posted, or compared my code to the code in the links. Instead, you jumped to conclusions and undeservedly criticised instructables, and accused me of copy&paste coding.
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