MP3 + speedometer?

[MP3test]

The epoxy got broken at some time, the tool's head is twisted let say 30 degrees. It's one of those with L shape, should be "chrome-vanadium" type. What I've noticed that it is 3mm exactly but it is a little loose in the screw's head, so the holes there are more than 3mm, like 3.2 or 3.3 which allows the tool if more force is applied to damage the hole... This may be is my fault because this type of tool doesn't apply force uniformely.

Anyway now I can try to put with force a torx bit to see if this would help. A last step before going to a welder

[Morgen 3Eman]

Hi MP3test

It sounds like the screws on your MP3 are a different type than on mine, or we are talking about different areas.  Good Luck with this mess.

TTFN,
Dennis

[MP3test]

Here it is and the twisted tool:



On almost all videos where they remove that cover I see one and the same "CLACK" sound like the screws are glued - may be because the screw and aluminum are from different metals and some type of corrosion happens there and they are micro welded who knows. Same happened with the two I removed successfully, but it seems the other 4 want me to commit suicide

[Morgen 3Eman]

That is just amazing.

[MP3test]

Hey Morgen,

I plan to use these stepper motors for the speedometer:
http://www.aliexpress.com/item/NEW-10pcs-Japan-Nidec-Mini-stepper-motor-micro-stepper-motor-2-phase-4-wire-D6mm-stepping/1590283900.html
They are just 6 millimeters, but I guess they will have enough power to rotate the arrow. Because they are so small I think I can connect them directly to the Arduino w/o using any driver - Arduino can provide up to 40mA to the output ports and I guess this is enough for the motors like these (I can't find any data sheet, this is the manufacturer's page http://www.nidec-sankyo.co.jp/cmi/english/product/stp_m_01.html )

But you mentioned not to forget to put diodes - as electricity can be generated in the motor and go back to Arduino and damage it. Is this possible to happen with so small motors? What kind of diode I should use (I guess I will need 4 diodes per motor - for every wire?)

Thank you!

[Morgen 3Eman]

Hi MP3test

I hope you haven't bought the motors yet,  because they are not a good choice.  At 5 volts, they will draw about 125 milliamps, which is way, way above the 50 mA limit of the Arduino.   They are also  4 wire, which means they need to be driven by H-switches, so the current flow can be reversed through the coil.

Regarding the diode, you need one across each winding that you drive.  I'll see if I can find a schematic that shows how to install them. 

I saw an a good choice for the steppers when I Googled something like "stepper motor speedometer GM"... and found 5 for $15?$20?..

If I get a chance I'll see if I can find it again.

TTFN,
Dennis

[MP3test]

Hi,
I saw at the web a person has measured them and they have 20ohms resistance which should mean that at 5 volts they will draw 250mA. Yes too bad, yesterday when I got 0.25A I thought about it as 25mA
I found a schematic for the required diodes - they should be 8 not 4, there are some chips with 8 diodes compiled but any way it is a lot easier to get a stepper motors with a driver and not to scratch head about current, adding diodes etc
I haven't ordered these yet so I am looking at other options. But the "GM replacements" are way too big I'd like to get something in the "micro" range.
Thank you for your help.

[MP3test]

I finally decided what to order for the steppers - 10mm motors ($0.70 each) and a small driver ($2.30 each):

[Morgen 3Eman]

Hi MP3test,

It looks like you found a bargain!  I was wondering why having them so small was important?  I'd like to see your proposed layout. 

Have you started figuring out your flowchart/ scheme for data acquisition and translation yet? 

Have fun.

TTFN,
Dennis

[MP3test]

Arrows are extremely light so I don't need much power, but I wanted to be sure that I will be able to put two motors in the speedometer - one for the speed and another which will rotate the odometer...
I am almost ready to start collecting data (I will collect voltage, ampers, speed and temperature) for the statistics - after I read that these batteries produce almost constant voltage in 80% of the time the measurement should be very well calibrated (if possible at all) - this is for the battery capacity meter to have linear conversion of its voltage.
BUT before that I have to open that cover!!!
I'll try some other things tomorrow before I break it

By the way no one suggested if this will be OK:

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 MP III is left side. So the question - is there any difference (in torque, acceleration, regen, etc) if the MP III is set in reverse mode so I can turn the wheel 180 degrees and the disk brake mount become at the right side?

[Morgen 3Eman]

Hi MP3test,

I will tell you that from a hardware point of view, electric motors don't care which way they rotate.  The software may change things a bit, but the actual motor will give exactly the same performance, no matter which way you spin them.

TTFN,
Dennis

[MP3test]

Thanks! But this motor has 3 hall sensors to detect motion and to manipulate it and from that point it's up to the motor's designers if they did it in a way that it is reversable?

Good news! I finally got that cover out! Nothing worked but this method - (I don't know the word in English) but a "chisel" (a metal bar that is sharpened at the end) nailed at the end of the screw's head, hit several times with a hammer to the direction to unscrew it and it worked finally!

Now where are those cables...

[MP3test]

OK, the bad news is that the so secret "For meter display" connector has nothing but ground and battery+, the other 3 wires don't go to the controller; the good news is that I'm not using the pedelec, and for the speedometer signal I will use it's wire! Pfew.

I did some pics and marked all the wire colors and relation between a wire in the controller <-> a wire from the connectors. Plus added Bikemad's hall sensors info - the wires in the controller are A,B,C etc, the wires in the conectors are 1,2,3, etc:

[MP3test]

Finally the solution is:

- open the controller
- unsolder the yellow wire
- solder it to the pin corresponding to the yellow wire from the hall sensors connector

As a result you will have hall sensor's 0V-5V ticks at your pedelec signal wire.

Of course this is if you don't use the pedelec.


My yellow wire was exactly the length needed to be soldered to the desired pin. I forgot to take a picture and already assembled the controller...

[MP3test]

OK now the signal problem has been solved, come the problems with phisics and Ohm's law I guess So please help...

So far I can measure the value in Volts of the hall sensor with the Arduino. I can see when I rotate the wheel BY HAND that the value goes from 0 to 4.5V. But this is so if I rotate it by hand!!!

When I try to rotate it trough the throttle - nothing happens. Even if I disconnect all the wires of Arduino! So some fuse or any protection switches ON there as I guess I am draining all the power of the +5V measuring the voltage of that line? As earlier I was concerned by specs Arduino can (will?) drain up to 40mA trough the input pins while MP3 has 50mA for the +5V circuit to work. And if I drain all of it, it stops working as it shuts itself down.

To fix the problem I have to switch the main power off, wait 2 seconds and switch it ON - and the MP3 is resurrected. Good I didn't blew it.

But now comes the new question - how I can make a connection to Arduino that will drain just small part of MP3's 50mA +5V of electricity trough it's hall sensor? To add a resistor or it should be more complex?