Motorized Mobility Scooter

Discussion in 'Introduce Yourself' started by ByronRACE, Feb 16, 2008.

  1. ByronRACE

    ByronRACE New Member

    Hello all,

    I'm new here, and I'd like to get some input about motorizing an electric mobility scooter with a gasoline engine so my father can get the range he needs without having to worry about whether or not he'll make it home in the evening.

    I'm an engineer. I have a mill and a lathe, and can build most anything. I've built engines, cars, and a Go-Ped ESR electric stand-up scooter that does 40mph.

    However, I'm completely new to these motorized bicycle kits and am hoping you guys can help me understand how they work, and help me select a motor for the job at hand.

    First, a bit about the mobility scooter. It is powered by a 1.5hp 24V electric motor that is coupled to a 17:1 transaxle and 10" tires. At 4000rpm (no load max), the motor moves the scooter approximately 7mph. I'm not looking to greatly improve speed; it would be fine if the scooter went no faster than this. 10mph would be great too; no more than that.

    The electric motor shaft protrudes and is used for an electric drum parking brake. This will be removed, and a sprocket will be fitted such that I can attach the gasoline engine. The scooter will be fitted with a mechanical disk brake from a mountain bike.

    So, I simply need an engine and sprocket ratio that will spin that sprocket 4000-5000 rpm. Judging by the amperage consumed by the electric motor when hauling a full load, I believe I need approximately 0.4hp on flat ground to do this.

    I wish to bump-start or drag-start the gasoline engine. My father is unable to pull a cord like that.

    I prefer four-stroke engines for obvious reasons. (noise, smoke, CARB approval, etc.)

    I'm attracted to the Dax Titan 50cc 4-stroke and if that turns out to be a good candidate, I wonder if I can do the following:

    1. Defeat the freewheel on the output sprocket; use a regular fixed sprocket instead.
    2. Defeat the centrifugal clutch (turn a hub on the lathe, weld it in place)
    3. Use the disengager to either engage or disengage the engines gearbox from the electric motor shaft discussed above.
    4. To start, stop the scooter, engage the disengager (connect motors gear box to electric motor shaft), start the scooters electric motor moving (simply accelerate forward on electric power), thus drag-starting the engine. Once it starts, proceed on electric+gas, or just gas...whatever you please. There is up to 1.5hp worth of electric power available to apply backwards through the gearbox to drag-start the engine. I would not need to bump-start, it would drag start.
    5. To stop, squeeze the disengager, apply the brakes. If you forget to disengage, the brakes will be enough to stall the engine (safety/emergency only). Usually, you'll just disengage and the motor will stay running. To use gas power again, it would be necessary to stop the engine and drag-start again, or perhaps you could get good at rev-matching things close enough where you could simply engage at a proper rev-match rpm. Would you destroy the disengager if you did this?
    6. With the disengager disengaged, the electric scooter simply works as usual. The only additional drag is the sprockets which freewheel since they are disengaged from the motors gear box.

    What's wrong with this idea? Can I drag start the motor in this manner or is the mechanical advantage of the gearbox too great to turn the motor over by back-feeding power into the gearbox in this manner?

    Is there a 4-stroke kit better suited for this duty?

    Should I be looking at 4-stroke engines without the gearbox? I could likely achieve 4000-5000rpm and get enough power even if I were to direct-drive or 1:1 sprocket drive.

    If this won't work, then I always have the 2-stroke looks to be simpler and more intended for this sort of bump-start application. I prefer the 4-stroke however. Quieter, more integrated, and an over-all nicer package given the application at hand.

    Thanks for any help!

    Sorry for such a long first post; I'm just excited and want to order the parts asap before I get too busy to finish this project for my dad.

  2. cooltoy

    cooltoy Member

    Would it not be best to just have one of those tiny $200 generators charging his battery? You could even use the low voltage output to power the motor directly with a bit of electrical tinkering, I wrong?
    This has always been one of my "dreams", you have a "push-trailer" with a generator powering an electric bike. This way you are "legal" and never have a dead battery.
  3. That would be the worlds first hybrid mobility scooter.
    Do some small generators have electric start though?
    If so, that sounds like your best bet.
  4. cooltoy

    cooltoy Member

    Good point, I forgot that he could not pull start. I just looked around a bit and there are cool honda/electric start generators (eu3000 honda) but they cost a bundle, about 800 bucks. You can even get a remote start that even puts the choke on for you but even that is around 400 bucks.
  5. One good option would be some of the bigger (49cc) chinese 2 strokes, as
    they have 12V electric start as well. They are only like $100-$150ish

    Hook one of those up to an alternator for charging, and split the
    drive to use it to power the wheels.
    2 jobs in one!
  6. gone_fishin

    gone_fishin Guest

    good stuff happening here...but let's not hide all this good tech-talk in an intro...someone please start a new topic in the garage about this cool idea, i suggest the "electric" forum...great intro,'ll fit right in 'round these parts.

    welcome to MBc :cool:
  7. ByronRACE

    ByronRACE New Member

    Generator idea

    I implemented the generator idea some time ago, and it works. However, it does not package well. I've built two versions of the generator approach. The latest one used an automotive alternator from a BMW Mini and a weedwacker motor. This packaged OK, but was very inefficient. The first method used a chinese generator head with a 2.5hp motor and I modified the field control circuit so it generated 28VAC, rectified that, and fed it to the batteries to charge. Both work. Both are heavy and bulky. Both must be pull-started by someone other than my father since he can't do it. Both are terribly inefficient, wasting tons of energy in conversion instead of propulsion.

    I've come to the conclusion that it would be far more fuel efficient (not to mention performance enhancing) to directly propel the scooter from a gas motor, and you could still optionally use the spinning electric motor to trickle charge the batteries at the same time. A spinning permanent magnet DC motor is a generator. Step 1 is to get the motor propelling the scooter. Step 2 would be to fit a regulator and use the motor output to charge the batteries.

    So, I'll go open a thread on the topic in a different section and we can continue if you want to help me address the unknowns.
  8. gone_fishin

    gone_fishin Guest

  9. wavygravy

    wavygravy Guest

    supurb intro byron! welcome to mb.c ,
  10. azbill

    azbill Active Member

    welcome to MBc ! :D
  11. mickey

    mickey Guest

    Welcome aboard Byron
  12. More batteries or lithium polymer would do the job great, also both 49cc and electric motor can drive the common shafts with one way clutch bearings rated accordingly you could also use the gas 49cc 4 stroke preferred to spin the original motor and short it now it's a charger on the go. Two sets of matched batteries would give them same time into the woods as back out on reserve set. Sounds like fun, good luck.