Serial Hybrid Go-Kart / Junkyard Scrounging

[calvin1]

I have a couple pieces of OPE sitting around not doing much and I have this project (read: backyard mad-scientist experiment) in mind that could use some brainstorming help. I'd like to build a go-kart that used a serial-hybrid powertrain: gasoline engine turning a generator that sends the electricity to motors at the wheels. This only needs to be big enough for a child and won't be seeing terain rougher than a sidewalk or yard. I'd like to get all the powertrain parts from the junkyard or surplus vendors and use one of the engines I have sitting around.

The engines I have sitting around are: 2-stroke McCulloch trimmer (?hp), 2-stroke Lawn-Boy (4hp), 4-stroke Craftsman (sticker says 6hp but I think that might be a little optimistic). The trimmer motor is in the best condition and will run in pretty much any orientation but obviously it's also the lowest power output. The Lawn-Boy motor is also in reasonably good shape but it will only run right-side up or up-side down AND I'd have to make some kind of muffler for it since that's integrated into the deck. The Craftsman is in the worst shape with lots of blowby, can only be run in a single orientation but is also probably the highest output and quietest.

My first idea is to get a one-wire alternator for the generator driven by the trimmer motor and use electric window motors at the wheels.

Possible problems:
1-Will the trimmer engine put out enough power
2-Can I throttle this at the gas engine or will I need to build a chopper circuit to do that much? Could a two-wire alternator's voltage be throttled externally or will it really only produce useful output in the 10-16v range?
3-Is a window motor able to take the side-loads that would come from having the wheels mounted directly to them or will I need to have a real axle? Is there another motor available that is both CHEAP and AVAILABLE that would be better suited?

 

[bepperb]

1hp = 750 watts. If you can find a car alternator that's 80 amps, that would take roughly (14 * 80) 1200 watts assuming no loss. So the string trimmer may run the smallest alternator you can find.

I would probably start this project by doing everything else and charging a battery, and then move on to onboard generation.

Why not just get a power wheels and double the voltage?

 

[calvin1]

Originally Posted By: bepperb
1hp = 750 watts. If you can find a car alternator that's 80 amps, that would take roughly (14 * 80) 1200 watts assuming no loss. So the string trimmer may run the smallest alternator you can find.

I would probably start this project by doing everything else and charging a battery, and then move on to onboard generation.

Why not just get a power wheels and double the voltage?
It's a powerwheels that I'm trying to replace. I doubled the voltage and it lasted a season before the portal-gears blew out. But you're right, I'm trying to build something that's half-way between a powerwheels and real go-kart with the experimentation and DIY as a bonus.

 

[calvin1]

I should add that maybe "go-kart" isn't exactly the word I'm looking for. As bepperb said this is more of a toy, akin to a powerwheels. The primary user will be my 8 year old son so 10MPH is plenty right now but some room to grow built into the design - 15MPH, 20MPH MAX - would be nice.

 

[SuperDave456]

I have a friend who visits "how to build your own battery powered car" forums all the time.

These folks go out and get a junked honda and yank everything but the transmission out of it. No AC, no heat, no coolant or radiator systems.

Only breaks and a tranny, then they build the car from that.

I will see if I can get the forum name from him and they will be able to point you in the right direction.

 

[meep]

you can direct drive the 2hp 2stroke to the alt, probably by clamping heavy rubber radiator hose from the clutch to the alt axle/pulley. simple, cheep, reasonably sturdy.

Window motors not best solution IMO. I'd look for 2 blower motors and rig a belt drive.

You need a motorcycle battery or something to buffer the voltage or the surge-volt drop on motor turn-on will kill V needed by the alt for the field coils.

awesome project!

 

[meep]

consider gearbox from a lawnmower or electric golf caddy drivetrain for mechanicals.

 

[javacontour]

What about a power chair? You know the kind advertised on TV for seniors? Maybe find one of those that's wacked and see if you can pick it up for cheap. Depending on what's not working, you might have a good portion of the goods needed to make such a cart.

They certainly have the power to move a person around, so that's not the issue. The issue would be integrating the gas engine/alternator into the system.

I've been thinking of a recliner that rolls and was thinking of using a power chair as the power train. This morning on a local TV news show, they had gas powered recliners a local home theater store uses in parades as promotional items.

So an electric power chair, or as other have suggested an electric golf cart would make a good basis for such a cart.

 

[eljefino]

Surely you've been all over modifiedpowerwheels.com

I am a rank noob, having used drywall screws to put BMX tire "gator skins" on my kids Peg Perego ATV, and a larger, but still rated voltage battery.

+3 on the electric wheelchair; they often come with fancy speed controllers and estates often sell these for pennies on the dollar. If you're "lucky" the previous owner was bedridden but the chair still got new batteries and maintenance as part of a service contract.

For the price of a one-wire alternator, you can get a harbor freight 2 stroke generator (Under $100!) Then use an old computer switching power supply for gobs (30+ amps!) of 12 volt semi-clean power.

I would consider putting all this stuff on a trailer, with a small battery on board the main car so it could be operated with the trailer detatched for whatever reason.

I would not have anything with a belt and pulleys around little kids unless you had some serious shrouding.

 

[calvin1]

Well I disassembled a couple of the electric window motors that I have in my stash and I don't think any of those will work. The ones I have are all worm drive so cutting power input to them would immediate lock the wheels unless I used some kind of over-running clutch. Engine braking is definitely a desirable feature here so those are out. Also, the worm is in the middle of the shaft with the bearings on the ends. It's not like you could just take an angle grinder to the casing.

I'm going to look at some windshield wiper motors to see if they would work.

 

[meep]

they are typically worm drive also.

 

[Cujet]

I think this is quite simple. A pulse width modulator will drive the motors without issue. Just like a Makita battery drill.

The generator needs only to be an engine driven automotive alternator with internal regulator. A small 12v battery (lead acid) is all that is necessary. Something like a lawn tractor battery is probably the correct size.