Author Topic: Speed Sensor Installation and Calibration  (Read 258 times)

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Offline EmanHeeman

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Speed Sensor Installation and Calibration
« on: September 12, 2020, 09:10:11 pm »
Hi everyone! I have a 71' CB500 that I did a resto-mod restoration into a cafe racer type bike. I have an m-unit blue in it that I had a few questions about:

- Where do you like to mount the little magnetic speed sensor and how do you run the wire? (I have spoked wheels)
- How did you calibrate the speed sensor? I do not have anyone to ride next to at the moment to go precisely 50 km/hour. (I wish we could enter in our tire size in the app and then it could calculate it)

The third question/problem I have is not related to the speed sensor. My battery seems to be slowly trickling out while the bike is sitting until it is dead. Normally in a few days. I have not done a deep dive into trying to trouble shoot this yet but wanted to ask if anyone else has experienced this/ gauge common causes. I wired the bike completely myself in a bit too hastily in a day because I was anxious to get the engine running. I could have a made a mistake somewhere that is causing the battery to discharge into the frame possibly? I thought that possibly the m unit is draining it?

Edit/Update: I did a few checks on the battery this morning. I checked the voltage (12.9V). Yesterday the battery was dead so I jumped with my car and let it run for 10-15 minutes. It could start up, shut off and restart multiple times under its own battery power then. I then checked to see if any current was being drawn from the battery and sure enough there's 0.02 to 0.03 amps being pulled. When I flip the switch to the m-unit blue it goes to 7.1 amps and fluctuates by +/- 0.1 amp. Is that normal current draws?
« Last Edit: September 13, 2020, 06:38:18 am by EmanHeeman »

Offline stocky

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Re: Speed Sensor Installation and Calibration
« Reply #1 on: September 13, 2020, 08:42:40 pm »
On the bottom of the cb750 fork there was an extra hole that I fabbed up a basic bracket that the sensor attached too. The magnet I epoxied/glued to one of the bolt head of the brake rotor bolts. Ran the wire partly up the fork and followed the brake line up into the headlight.

If you have a cell phone with GPS, can just download an app that gives you a speed read out. I have a phone mount on my bar so it wasn't a big deal.

I'd double check your wiring. If everything is wired directly into the m unit I don't think it's supposed to be pulling that kinda amps when it's off, at least mine doesn't.
« Last Edit: September 14, 2020, 03:53:49 pm by stocky »

Offline kanak_atk

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Re: Speed Sensor Installation and Calibration
« Reply #2 on: September 22, 2020, 09:26:51 pm »
One issue might be that it's still connected to your bluetooth, I'm not sure what proximity your bike is to your living space (if at all) but I know that the fast blinking light can draw more power than when it's intermittently flashing.. just a thought.


To piggyback off the magnetic speedometer question, I keep getting a config error when I've been trying to calibrate my bike. the manual says to maintain a constant speed and I'm wondering how dead on it has to be because I'll fluctuate .1-.5 miles and get the error. Could the issue be that I need to nudge the pick up closer to the magnet on the rim? It would be nice to get this solved and if anyone has had this issue, I'd appreciate some input!
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Offline stocky

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Re: Speed Sensor Installation and Calibration
« Reply #3 on: September 23, 2020, 12:43:33 am »
One issue might be that it's still connected to your bluetooth, I'm not sure what proximity your bike is to your living space (if at all) but I know that the fast blinking light can draw more power than when it's intermittently flashing.. just a thought.


To piggyback off the magnetic speedometer question, I keep getting a config error when I've been trying to calibrate my bike. the manual says to maintain a constant speed and I'm wondering how dead on it has to be because I'll fluctuate .1-.5 miles and get the error. Could the issue be that I need to nudge the pick up closer to the magnet on the rim? It would be nice to get this solved and if anyone has had this issue, I'd appreciate some input!

From my experience it doesn't have to be dead on, just won't be that accurate if you're too far off.

I was also wondering before I installed the sensor how far apart the magnet could be, so I hooked up a multi meter and set it to the continuity function with the beep tone and played around with the distance. I can't remember since it was awhile ago but I want to say over an inch apart and it didn't respond that well.

Offline calj737

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Re: Speed Sensor Installation and Calibration
« Reply #4 on: September 23, 2020, 04:53:19 am »
magnet to sensor is maximum 4mm separation.

With the mUnit off, it should drain no power unless you have the alarm function activated, OR, you kill the engine with the HI beam active.
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