MP3 + speedometer?

[Bikemad]

Hey, I had no idea these things even existed last week, and now I find out that they are cheap and easy to get.    I found some 5V GM replacements, with 6 costing $15 US!!!!  Thanks for the education.

Hi Dennis,

Unfortunately my psychic powers are not a good as they used to be, so could you please give me some more clues to help me determine which "these things" you are referring to?

Alan
 

[MP3test]

I think "These things" = stepper motors

[Morgen 3Eman]

Hi Alan

Sorry about the lack of specificity, we were talking about stepper motor speedometers.  I just never twigged to the fact that D'Arsonval meter movements have been replaced by digitally driven analog looking output displays.  The whole idea is just brilliant:  People get some information more quickly from analog displays, which is why digital display watches just never became popular, even tho watches became digital devices.  Digital  measurements can be made very repeatable and cheap, which is why watches became digital, and their accuracy improved by huge amounts. 

Hey, rack it up to me being old and foolish:)  But the concept makes economic and engineering sense.  Rugged, reliable, low power, cheap to build, cheap to change, high commonality across a wide range of packaging options.  Brilliant!  And I didn't even know how common it has become...

But MP3test has lodged an idea in my brain about some of the favorite dashboard instrumentation layouts. My favorite is two adjacent big dials with two smaller dials on the outside.  With a stepper motor to move the pointer, that idea becomes useable in a high vibration environment like a bike. It makes packaging trivial, as all you need do is a bit of graphic design work to change what info is displayed on what "gauge" face.  The drive software only needs to address a different output pin to change what is displayed where. 

 

TTFN,
Dennis

[MP3test]

The most important thing is that digital is better than analog (except sound amplifiers) in many reasons and is more accurate. For example - the battery capacity meter of the crap I bought - it shows always "MAX". Before the idea of Arduino + stepper motors (which I guess I can do myself) I was in a trouble to find someone to change something inside of this to make it correct (i.e. to move from MAX to MIN when the battery is empty) as I am completely newbie in electronics.

With digital it can be done that the scale is not linear. Here comes the question - in the linear scale from MIN to MAX of the battery voltage, how this is related to it's capacity. Mine is 56.9 Volts when fully charged and I guess it drops to 48 Volts when fully discharged (haven't measured it so far). Does anyone knows how the voltage is related to the available energy left in the battery? Is there a formula? I guess it is not linear.

[MP3test]

Gosh, I can't remove the first cover of the controller I think I even f**ed one of the screw's head. Anyone had that problem? Have you normally unscrewed these or some magic is needed here...

[Morgen 3Eman]

Hi MP3test

I have to disagree with your comment that digital is better than analog.  They are just different.   Digital CAN be more repeatable, but you have to remember that crap is crap.  And repeatability is not the same as accuracy.  As the old saying goes, a stopped watch is accurate twice a day.

If your analog meter is reading incorrectly, it is probable that a change in resistor value in series with the D"Arsonval movement would improve the accuracy. The analog meter I am using reads 60 volts full scale, and 48 volts at minimum scale.   If the software doing conversion is incorrectly written, the result will be crap as well.  Don't be fooled by the comments of "experts" , (or even genius's like me): When CD music first came out, a very respected editor of an audiophile magazine published his thought that the music from a CD was better when a green Sharpie was used to make a circle on the edge of the disc.......(The edge is not scanned by the laser doing the data recovery)

How is your speedo design coming along?  I'm going to try to talk my grandson into making an MP3 speedo his intro to engineering practical project

TTFN,
Dennis

[MP3test]

Waiting for components (stepper motors) but I stuck with the problem of removing the cover of the controller - can't remove the screws! Going to buy another tool now.
I will connect first an LCD screen to monitor the values and to be able to adjust the software.

[Bikemad]

Gosh, I can't remove the first cover of the controller I think I even f**ed one of the screw's head. Anyone had that problem? Have you normally unscrewed these or some magic is needed here...

I had the same problem removing one of the six screws from the fan/disc mount to access the controller because it was done up so tight that the hexagonal end of my Allen key was starting to turn inside the head of the bolt. After hammering on the end of the Allen key bit to "shock" the bolt loose I was able to undo it without causing further damage to the hexagon inside the head of the bolt:



I find that repeated firm taps with a small hammer usually works best.

If the hexagon is badly damaged, you might have to find a suitable Torx bit to hammer into the head and hopefully remove the damaged bolt.

If it's the actual screws in the controller you can try the same technique with one of these:



If the shock treatment doesn't help, you may have to carefully drill out the offending bolts.

Alan
 

[MP3test]

Using WD40, and a hammer didn't help... I think some welding happened because of a corrosion. If I drill the heads I doubt I will be able to get out the bottom of the crews and I will end with no ability to put the cover back. I will try to solder the tool into the head but lead is weak then may be I have to go to a welder to weld iron to heads and to try to unscrew that way..

[Morgen 3Eman]

Hi MP3test
Hey, don't try to solder the hex bit into the screw. It will not get hot enough to bond.  I have had success using high strength epoxy to make the screw/tool bond.   You have to make sure that you clean all the WD-40, dirt, sweat, etc from everything.  Good luck

TTFN,
Dennis

[MP3test]

So far 2 screws are removed. The other 4 are killing me off. One is a little damaged as Bikemad's case. The epoxy is a good idea, I will try to clean all the wd40 now as everything is greasy. May be by heating it with a butane torch will burn it.

[Morgen 3Eman]

Hi MP3test

You have to have the screw head perfectly clean, or the epxoy will not adhere properly.  Burning probably wont do it.  Soap and water with a small brush will do it; let the water dry well.

TTFN,
Dennis

[MP3test]

I did it with 99% alcohol Actually I think it doesn't have to stuck to the screw - the goal is to fill the gaps between the tool and the screw's hole - it doesn't fit exactly and that's why it damages it. I have 4 of them, all seems to be the same size, so these screws has a little larger holes (not sure if they are cheap and deffective, or all the holes in the world are not 3.00 milimeters but 3.30 or something). Or may be they are 3.50 and I am using wrong tools?

While the epoxy is drying, another question arised - I want to put a disk brake at this wheel (front MP3) but because of the fork it is supposed to be at the right side. The default for MP3 is left side. So the question - is there any difference (in torque, acceleration, regen, etc) if the MP3 is set in reverse mode so I can turn the wheel 180 degrees and the disk brake mount become at the right side?

Regarding the speedometer's battery capacity meter - I have a plan to create trough arduino a) voltmeter b) ammeter c) temperature measurement and while driving from full charge to full discharge to store all data once per second and then to analize it and create the relation between all of these data. The problem I found is that at some point the voltage is almost constant (between 10% and 90% of the capacity?) and it depends also on the temperature, so to show correctly the battery capacity (if possible at all) some maths and statistics has to be involved

[MP3test]

The epoxy didn't solve the problem... the tool got twisted (it is supposed to be strong), but the screw didn't get out!

Do you know if I can get out the big cover of the motor together with the controller and the small cover or the problematic screw tighten the big cover as well? Because I need access to the hall sensors not the controller itself this would be OK - the screws of the big cover can be removed easily.

[Morgen 3Eman]

Hi MP3test,

Are we to understand that the tool you epoxied to the screw is now twisted by the torque you applied, the epoxy is still bonded, but the screw didn't rotate?  I have trouble believing that even a tiny Posi-Drive bit would twist without breaking the head off the screw.  They are really small, rather soft screws!   By the way, you are using a Posi-Drive, not a Phillips bit, aren't you?  Phillips bits are just about guaranteed to damage Posi-Drive screw heads.

I have no idea what you can do at this point, other than hiring a machine shop with an EDM tool to get the screws out. 


TTFN,
Dennis