You need a bigger car Frederic.
have you looked into those 700 watt motors
they use in electric scooters? May have to add wheelie bars.

 

Well, with the one 24V 300W motor running off a 12V mower battery, it was suprisingly quick with my 170lbs sitting on it. So with my son being 22lbs, the 300W motor is gross overkill. In fact I'm starting to play with the internal controller a bit to see if I can easily limit the top speed for his safety.

 

Kind of like a Top Fuel license.
You get the little one some seat time then step
it up until he gets full power runs.

I started on a times 3 scale of the Big T model
years ago for a RC project, have the 1/2" x 1 1/2"
frame and headers bent up from SS tube but no time
to work on it.

 

Well, as he gets older I have a supply of lawnmower engines I've rebuilt last and this past summer... a 3hp, a 5hp, and a 12hp, the latter two being electric start.

But he has a lot more aging to do before I will power anything he rides to that degree.

Though, I have taken him for lawnmower rides on occasion. What I do is toss the bagger vac system to the side, hitch on the yellow $70 lowes lawn cart, and take him for a ride around the property as well as down the cul-de-sac. I did this today in fact, and he just loves it. He holds on real well and waves to every house as we pass them, which is kinda cool. Huge ear to ear smile too. A week ago I had taken him for a ride, and as I turned into my driveway a police car was pulling in behind me, and I was like oh... no... but the cop got out and asked how old my son was, and we started talking about raising kids in general, my son, and his two boys who are apparently early teens. Then he left saying "be careful" and that was it. And here I was expecting a huge hassle.

Anyway, as far as this toy car goes, I have to device self-actuating electric brakes. Apply power to deactivate, remove power and they clamp. If you have any ideas I'd welcome hearing them. It turns out this thing freewheels much more than I anticipated. I expected it to stop within a few feet, but it really takes off when powered and when power is removed, it gradually slows. Not good!

 

Maybe electric brakes would be an idea. Replace the go switch with a double throw unit and build a circuit to backfeed power from the motor to the battery.

I've seen mention of this idea somewhere before in reference to electric vehicles partially recharging their own batteries but can't for the life of me remember the details.

 

When the throttle is lifted have a switch connect the two motor leads, dynamic braking.

 

dynamic braking is a fantastic idea, except that the motor controller (PWM type) is built into the motor housing, and my test of shorting the motor's power leads did absolutely nothing.

I'm going to have to devise some kind of mechanical brake, unfortunately.

 

ok, thats better. now you can go back to work.

 

While before I said shorting the two motor leads resulted in no braking action, it seems I was mistaken.

Shorting the motor wires with a relay actually DOES provide quite a bit of braking energy.

The problem with my initial test was the SPST switch, which I pulled out of the junk drawer. I attempted to use it to replace the power switch on an appliance today, and it didn't work. Then I decided to try it again, by twisting the wires together and sure enough, it's very difficult to turn.

So I cobbled together a pedal-actuated relay that when the pedal is pushed, the relay is powered and in turn the motor receives full power. Release pedal, the relay goes back to it's unpowered state, and the motor power leads are shorted with 10 gauge wire, and the car stops fairly well.

Not quite like a mechanical brake, but more than enough for my purposes.

Thanks for the tips guys... and sorry I argued. It should have occured to me that maybe, just maybe, the switch I tested with was bad.

 

Now you need to hook a voltmeter to that motor and see what happens when you turn it. I'll bet you produce voltage. Just replace your go switch with a dpdt switch, put a diode or two in place and backfeed the voltage to the battery. Partial recharging and brakes all rolled into one.

 

Reduced reverse voltage that will stop ya, na bad idea for the battery.

 

I do some work on electric fork trucks and they use the regenerative braking setup. Makes the battery last a lot longer and works well. Most use plug braking as well which essentially throws reverse voltage to the motor to slow it quickly. If you want, I'll see if I can find a schematic here at home.

 

Frederic, I wish I were an insanely wealthy man, for if I were I would certainly give you a whole bunch of it, just to see how far your potential would take you.

 

20000+F150.... if you have a schematic handy, I wouldn't mind taking a gander at it. I have the relay disconnecting power to the motor while simultaniously shorting the power leads to the motor (SPDT Automotive Relay - actually a Ford part amazingly enough) and it's working well with the testing I did today. But I am certainly curious as to what forklifts do due to your suggestion.. because this brake thing I have cobbled together now, doesn't provide a complete stop. The faster the motor is going, the more effective the braking is, until it gets very slow then it kinda freewheels at least a few feet. Which is okay of course... just would be nice to take into consideration my son trying to stop on a decline, and keep rolling. Safety first!

HKeifus - Thank you for your comments... and anytime you feel amazingly generous I'm happy to send you me "to buy" tool list heh-heh.

My real problem is lack of time and lack of a job... otherwise I could test out some of my more radical ideas. Though most of them probably wouldn't work well otherwise they'd be patented by now.

 

Working Schematic. Hopefully I drew it correctly... but whatever i wired seems to work fine

http://frederic.midimonkey.com/booto.../schematic.jpg