speedometer function on motor controller

Discussion in 'General Electronics Chat' started by robo5050, Dec 30, 2007.

  1. robo5050

    Thread Starter Member

    Dec 6, 2007
    15
    0
    I was wondering if anyone on this forum could give me a source for information
    regarding how the speedometer transducer circuit works as being part of
    a pmdc-1 phase-electric scooter motor controller???
    All I want is a link to the theory/function of an electric speedometer
    circuit which is part of a generic motor controller.
    Thanks in advance!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Since nobody has replied yet...

    I've not heard of such a thing, but they could exist.

    Are you repairing a scooter, creating a new design for one, or just theorizing?

    Were I to build an electronic speedo circuit for a scooter, I might use a Hall-effect sensor to detect the revolutions of one of the wheels, or the motor if it were direct drive. The Hall-effect sensor could trigger a one-shot multivibrator (such as a 555 timer) to put out a fixed-width pulse to a speedometer. The more frequently that the speedometer received a pulse, the higher it would read, giving a MPH or KPH indication.

    Of course, it would need an odometer as well. This could be a simple divide-by counter circuit with static memory, or a microcontroller. A 12" diameter wheel travels roughly 37.7 inches per revolution, 1680.7 revolutions per mile - so a divide-by-168 counter counting the pulse train would give reasonably accurate 1/10 mile indications.
     
  3. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    http://martybugs.net/electronics/speedo.cgi

    You can in theory count the breaks in the motors turning and using that measure speed. That would require careful measurement of the distance rotated between breaks. The above circuit is much simpler.
     
  4. robo5050

    Thread Starter Member

    Dec 6, 2007
    15
    0
    Thanks for the reply,SgtWookie;I am interested in building the motor controller with voltage
    doubler and speed circuitry integrated with it,I would like to have the controller sense the motor speed(4-brush DC motor) like the original motor controller does,but do not know how the original one senses the scooter speed!!
    I appreciate the digital speedometer article link,rmevil,but the speed sensor setup uses
    external magnets mounted on the driveshaft-I would need to install the magnets on the driven wheel-with a coil to sense these for the switching;I would prefer,if at all possible,to user any of the original scooter circuitry!
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    What's this about a voltage doubler? That would only make sense for a low-current high-voltage application; not a situation like this where you're powering a scooter. You need to match your motor and power source.

    Do you know if your scooter's motor is in working condition? How about the battery or batteries; is it/are they good as well?

    Your PWM circuit could probably be quite simple, but there would need to be some safety features added in case of circuit failure; like a cutoff switch in case the throttle gets stuck, and a PWM override (cutout) when the brakes are applied.

    There may be useable components from the prior circuit, such as a pot driven by a throttle twist grip, or perhaps an accellerator pedal on the floor - or is there nothing left of the original controls?

    Can you post some photos of it?
    What is the make, model and year of the scooter?

    OK, now things are making more sense.
    In my original response, I mentioned using a Hall-effect sensor. These are quite inexpensive, easy to use, reliable and they will sense the rotating magnets on the driveshaft very easily. There is no need to change that. You DO need to figure out how far the scooter moves between magnets passing the point where you will mount the Hall-effect sensor, as that will be used in the calculations for MPH or KPH and miles/km travelled.

    There may already be a Hall-effect sensor mounted near the magnets - look around for it. It will likely have either two or three wires. One of them will be a signal wire, one for power. If there is a 3rd wire, it will be the ground wire - but it may be simply grounded at the mounting point.

    Need more information here. I'm having to guess too much...
     
  6. robo5050

    Thread Starter Member

    Dec 6, 2007
    15
    0
    The original motor controller has built-in overcurrent,overvoltage,and brake cutrout circuitry,so I may just leave it on the scooter.
    The throttle that came with the scooter is a 3-wire throttle,but I couldn't find where the
    hall effect switch or magnets are located;this controller is sensing the scooter speed
    some other way!

    As for the voltage doubler circuit tentatively planned,I was looking for more of a
    speed increase,and thought that the voltage doubler would help-not that it needs to
    be a pocket rocket,but to have maybe 5 mph faster than the top speed of approximately 20 mph.

    I would like to post some representative pictures of my scooter-looks very similar to the Xtreme X-360 scooter,but only has 2 SLA batteries-to this forum,but go not know how to post the scooter/part pictures!!
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Is the original motor controller working? If so, you should probably stick with it.

    Voltage doubler - well, since the controller has built-in overvoltage/overcurrent protection, it would keep your increased voltage from doing much good. Besides, running the motor at speeds above what it was designed for may cause it to fly apart, or the windings may get cooked. At the very least, your scooters' reliability will be negatively impacted by increasing the voltage supply.

    If your scooters' motor is on the axle with the driven wheel, a Hall-effect sensor may not work there due to the amount of interference by the motor. It may need to be on the other wheel.

    You need to use the "advanced" mode in order to upload pictures to this site. Click the "Go advanced" button on the bottom for starters.
     
  8. robo5050

    Thread Starter Member

    Dec 6, 2007
    15
    0
    I think I will probably stick with the OEM motor controller for now since it already contains the speed sensing,over-current,under-voltage circuitry;may upgrade the motor if I use the voltage doubler circuit(which would be switched in/on by the motor controller output connection);I am mostly concerned with
    designing a simple relay-switched regenerative braking circuit due to the OEM controller not equipped with a regenerative braking feature!

    BTW,here are some representative pictures of my e-scoot
     
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