Mobility Scooter upgrades

Discussion in 'The Projects Forum' started by iONic, Aug 24, 2008.

  1. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    I am looking for a solution to my current troubles with my mobility scooter.
    Right now there is a POT to vary the speed of the scooter and a rheostat to both vary speed and direction.

    The trouble is that have to hold the rheostat arm at a specific position to maintain a constant speed, if I let go I come to a screeching halt. I had already replaced the speed POT from a 10K to a 20K for a bit more flexibility in control.

    What I'd like to do is replace both mechanisms with a digital POT version.
    I found an IC by CATALYST Semiconductor that allows for up or down pulses to vary the speed and I think it could be wired as a rheostat to enable forwards and backwards (see below).

    There are other tweaks I;d like to make as well.

    1) The controls would be 3 momentary switches. Stop, Down, Up.
    the first press should latch the circuit on so as to place the scooter in a sort of cruse control until you press down or Stop. Essentially the scooter's motion is hands free. Revers occurs when you press the Stop button and then press the down button or if consecutive presses crosses the no power zone.

    2) The Digital POT is a 16 Tap POT. I'd like to change it to 4 Taps. I'm not sure how I can accomplish this as I believe I'd need a "Multiply by 4" counter.

    Maybe a 555 could do the counting for me. Holding the momentary button in the on position for 5 seconds or so could get me to full speed, maybe beep on each pulse...

    Any suggestions would be appreciated!
     
    Last edited: Aug 24, 2008
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    I realize this doesn't address your questions, but it seems to me that the present arrangement is a safety feature. Can you add something to your digital mods that will shut down power if you lose consciousness or control?
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Beside Ron H's concerns, there is the matter is power handling in DPOT's. They are relatively fragile devices, and probably cannot be swapped in for conventional pots. Using them might require a considerable redesign of the existing control circuitry.

    Can you post the control section of the circuitry?
     
  4. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    The only option the circuitry would have is the "Stop" button, which would need the user's intervention. Maybe a pressure switch on the seat as an alternative "Stop" would do it.

    The safety mechanism, the constant holding of the speed lever, is what gives me trouble. Holding it for periods of time bothers my hands.

    I knew the safety issue would come up, and I was hoping it wouldn't stop people from offering advise towards my goal.

    bellow is a preliminary circuit of how I might be able to make 4 taps on the Digital Pot at once.
     
  5. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    If it's the control circuitry of the scooter, I do not have the schematic.
    The datasheet for the Digital pot can be found here:

    http://www.catsemi.com/datasheets/5115.pdf
     
    Last edited: Aug 24, 2008
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,694
    904
    Will your digital pot at 5V work with the motor controller? I assume the battery and motor are 12V. Pay particular attention to the voltage and current specs of the digital pot.

    John
     
  7. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    There are 2 12V Batteries in series (24V). I will check if the Pots are actually controlling with the full 24V or Logic via some PWM circuitry.
     
  8. HarveyH42

    Active Member

    Jul 22, 2007
    425
    5
    Maybe not as fun or interesting, but have you considered changing the positioning on the control handle. Haven't really taken a close look, but seemed like a lot of adjustments and options. Maybe a simple extension...

    You should very much consider a safety cut off, not just for your safety, but for those unfortunate souls in your path. I drive and electric pallet jack at work, and use the emergency stop many times each day. If all else fails, it's a good thing to have.

    You might contact the manufacturer, maybe they have a quick fix, or upgrade. Maybe they might share a schematic or a few details to help you. After all, you are a valued customer, and they don't want to lose you, nor do they want you complaining about their product. They want you to advertise positively for them. It's worth a shot, might be a little better than blindly messing around with the control circuits.
    Oh, if they are the ones who make the carts Walmart lets pretty much anybody crash around the store, could you suggest some sort of 'foot-sensor', got me twice so far (bastards).
     
  9. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    I took a look "Under the hood" so to speak, and found the following:

    Battery total voltage - 26.05V
    Voltage at motor with full throttle - 25.82V

    I believe the motor is PW driven.

    Speed Pot - 10K
    Forward/Reverse Pot - 5K Voltage on this Pot was 2.5V to 5.04V(Forward) and -2.5V to -5.04V(Reverse).
    Thus my guess is that the little SOT-23 package can do the job.

    24V or in this case 26.06V is available up front for the horn, battery meter, and lights.


    P.S. I understand the safety issue, but just like the seat belt law in VT I do not like someone telling me to do it, or else.
    Bottom line is, I want a pseudo cruse control, at least for a mid range speed. The scooter's top speed 1s 5mph.
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,694
    904
    Did you notice that it powers on at mid-scale? Will that be zero or mid-power?

    Also, the pins must remain essentially positive relative to ground. Your negative voltages during reverse might present a problem.

    John
     
  11. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    I guess the 10K Speed Pot just set the max speed possible. The Foward/Reverse Pot defaults in the center position, no motion.

    O.....O.....O (Pot connections)
    R.....N.....F (Reverse/Neutral/Forward)
    -5V..?..+5V

    It might have been 2.5V to 5V but I just reversed the meter leads. I'll have to recheck that, but I think it's correct, isn't that how a PWM Motor system works?
     
  12. HarveyH42

    Active Member

    Jul 22, 2007
    425
    5
    Yeah, I agree the seat belt laws aren't right either, since wearing one, or not wearing one has no effect on anyone else. It should be left to the individual. Kids and car seats are a different issue... they should be restrained with chains and gags, so they don't distract the driver, or throw crap out the window.

    Your scooter out of control might be another matter. 5mph is still plenty of momentum to do some serious damage to other people and property. Personal safety, should be the individual's choice, and I agree with you there, but you should show a little responsibility toward the people around you.
     
  13. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    You do affect other people, to the extent that injuries cause insurance rates to climb, or worse, if you have no insurance. I have no idea of the actual monetary significance of this.
     
  14. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    The digital pot won't work with a negative voltage, but I suspect you reversed the meter leads.
     
  15. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    It's funny how I searched for a scooter that had a particular ground clearance so that I could get up bumps and ride on the lawn, but the then the scooter mfg. put the safety tip wheels on the back so I couldn't pop wheelies, and in the end I didn't really have the ground clearance specified and ended up getting caught on things. So I bet you can guess what I did!
    It was surely a safety issue they had in mind, but was poorly designed given the quoted ground clearance.

    It's like the infamous STOP sign. Does it make it any safer to stop at one if there is not car, pedestrian, or and other living creature withing a mile from the intersection. When I am close to people with my scooter I am more alert and "responsible", but if there are no concerns I may "roll through the stop sign" so-to-speak. In other words, when there are other people around, or when there is a safety concern I do act responsible.
     
  16. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    The following circuit need some tweaking but I think it will get me started in the right direction.

    I need to find a way to change directions from forward to reverse using the flip-flop. I need to be able to press one button and activate two momentary switches at the same time so that if I want to change directions I can change the state of the U/D pin of the CAT5115 Digital Pot. Any help here would be appreciated.
     
    Last edited: Aug 25, 2008
  17. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Cd4013 has maximum clock rise and fall times of 15usec, so you can't use your simple RC network to debounce the switch. HEF4013 from Philips has Schmitt trigger clock inputs, so it would work in your circuit.
     
  18. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,694
    904

    The answer is "yes." How certain can you be there is not someone around? Do they know you don't know they are around?

    Routine procedures and checklists are the best way to ensure low failure rates. Pilots and doctors both use them, even though they may have done the same procedure 1000's of times.

    Ironically, there was an accident on my corner just last year. It was very early in the AM and involved two cop cars. There is a stop sign, but at that time, the cop with the sign "knew" there was no one around. The crossing cop (no stop sign) saw the other cop, figured he would stop, sped through the intersection, and got T-boned. Fortunately, no one was hurt, but the citizens had to pay for the damages to both cars, so it was not harmless.

    John
     
  19. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Used to be the standard trick question in the old british driving test.

    "It has been snowing heavily and all the marking on the road are covered in snow and the signs are also obscured.
    You are approaching a road junction and all you can see is the snow covered sign on a pole. How do you know if it is a 'halt' or 'give way'? "
    (In the UK we used to call them halt not stop signs.)

    Incidentally to say "stop anyway" was not acceptable.
     
  20. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    Thanks for the tip on the 4013, hopefully I have one lying around.
    Ave you given any thought as to how I could press both the 4013 and the 555 when slowing down or going in reverse?
     
Loading...