Robs Stupid Electric Gocart Page

 

This is Robs Stupid Electric Gocart Page. It is Stupid.

Mar 09, 2022
Went to gocart place with some friends. Oops.
Its been awhile since Ive had an actual gocart, and riding the supposed 20hp electric gocarts were enough fun that now I need to build me a new gocart.
If I made an electric cart, I wouldnt have to mess with fragile carburetors, oil, gas, etc.

I already have a few electric motors to choose from:
A 250W one from a silly little Razor cart,
A 1.2kW one from a treadmill
And a 4.8kW one that I got for my stupid Tank, and later used on my rototiller

250W Motor

Ok, a 0.25kW motor from a tiny Razor scooter isnt gonna be very impressive.
It wasnt very impressive when it was on a 50lb gocart.

1200W Motor

Even though this is 5 times the power of the other, a 1.2kW motor still isnt gonna be very impressive

4800W Motor

Used this ME0909 on my rototiller to replace a 5.5hp gasoline motor.
At 4.8kW continuous, its almost twice as powerful as the gas motor it replaced.
Using 2 of the 4.8kW electric motors, one on each rear wheel, might be pretty cool.
Also, seems like having a separate throttle for each one might make some awesome power slides.

To power the motors, I Planned on using some LiPo cells that I have left over.
I have enough to do 450A @ 75V, which is about 33.75kW, or approx 45hp, and the batteries only weigh about 10 lbs.
These would be a good match for the 2 motors.

33.75kW of Lipos (from a few years ago)

Picture of the batteries are from several years ago. They arent nearly that pretty now.
Totally forgot that most of the 54 cells I have are mostly all crapped out.
When I tried to charge them a year ago, there was a fire and stuff! OOOPS!

Fire and stuff a year ago

Since the LiPo batteries are so fragile, I dont want to use them any more, Im gonna have to find some other kind of battery.

Lithium Iron (LiFePo) batteries are the latest and greatest type of batteries, but all the ones grouped into 12V packs are limited to 100A, which is not very useful for this application.
100 Amps * 48 volts is only 4800 Watts, or 4.8kW.
Would have to have 8 * 12V 100AH LiFePos, just to get 9.6kW for the 2 motors.
12V 100AH LiFePo batteries are about $400 each!! So would cost $3200 or so! Not a good plan.
They are about half as heavy as lead-acid batteries, but needing twice as many, I might as well just use lead acid ones.

Lead acid batteries weigh more, but are rated to do way more than 100 amps. Some are even rated to do 2000A!!!
So, even weighing twice as much as the same amp/hour LiFePo battery, it can do 20 times more current, which makes for 10 times better power to weight ratio than the fancy schmancy LiFePos!!

1200A or 2000A Batteries

I decided to use 4 of the 100AH Renogy 12V batteries They are rated at 1200 or 2000 amps, depending on who you ask.
Showed both ratings on the page I bought them from. Even 1200A would be plenty.
At 65lbs each, this turns out to be 260lbs of batteries!!
This adds about 250lbs more than I was thinking of when I wanted to put 2 4.8kW motors on a gocart.
9.6kW on a cart that weighs 250lbs with rider would be pretty awesome.
9.6kW on a cart that weighs 550+lbs with rider wouldnt be that awesome.

The batteries can do 48V * 2000A = 96kW = 125ish Hp.
It would be silly to put 125hp worth of batteries to drive 10hp worth of motors. Gotta find bigger motors.

Mar 29,2022
I found an ME1003 motor. It can do 11.5kW continuous, which is about 18hp, and can do about 24kW or 38hp for up to 1 minute!!
Figured since this was more than twice as powerful as the 4.8kW ones, I would only need 1.

11500W motor!!

Gonna need tires that are quite a bit bigger than the usual gocart ones.
Using tires from the tank, at least for the back ones would be about the right size. They are 18x8.5-8.
Having back tires that are 18 inches tall, would like to have a reduction of about 8:1 between motor and tires.
The smallest 40 series sprocket to fit the 7/8in shaft of the motor, has 11 teeth.
In a perfect world, I would just put an 88 tooth sprocket on the wheel. Dont think such things even exist.
8:1 ratio makes a top speed of a tad over 40mph, which is perfect, and turns out to be a bit under 600 lbs of thrust

When I was still thinking of using the LiPo batteries and smaller motors, I was going to do an intermediate shaft to get about 2:1 ratio, and do a 4:1 ratio between that and the wheel, to get 8:1 overall.

Now that I have a much more powerful motor, I dont think I need an intermediate shaft.
Simply connecting the motor with an 11 tooth to a wheel with 60 tooth sprocket I already bought would be a ratio of about 5.45:1, and would give a top speed of just under 60mph, which is stupid, but would make the power transfer much simpler, but only gives a bit over 400 lbs of thrust.

400lbs of thrust in a 500lb gocart isnt really that awesome. Its only about 0.8G of acceleration. I have at least a couple cars that can do that.

I could replace the 60 teeth sprockets with 70 tooth ones to get a more reasonable ratio.
That would give a ratio of 6.36:1, which would make for a top speed of about 50, and about 475lbs of thrust.
475lbs of thrust is still slightly less than 1G, and 70 tooth sprockets are pretty expensive.

I would probably just do that, but I am concerned that the motor isnt gonna spin full speed at only 48V.
Might need to add another battery or 2 just to get to top speed.
Would be crazy to have 600lbs of thrust, but a top speed of 25mph.

For a little bit more money, I could just use 2 of the big motors!
That would be 800lbs of thrust, while using the existing 60 tooth sprockets, for nearly 1.6Gs of acceleration!
If it only does 40mph, Im probably not gonna be sad... Probably.
One on each rear wheel sounds perfect somehow :)

Apr 16, 2022
With 76Hp, and weighing 500+ lbs, everything gonna have to be heavy duty.
Front tires may need to be much larger too, depending on where the batteries need to go to make it controllable.
Haha, I just realized I typed controllable, trying to describe a 76hp gocart!!!
Told you I was stupid.

Speaking of placement of stuff, I want to put the motors behind the axle, with a couple batteries in front of the axle, and one one either side of the driver.
The seat wants to between the side batteries, and up against the other ones.

Rough draft of layout (havent gotten the other motor yet)

The motors, batteries, and driver are nearly all the weight, so Im gonna ignore the weight of the frame and front tires.
With 150ish lb rider, the center of mass will be roughly a bit forward of the seam between the 2 middle batteries, which is about 1 foot forward of the axle.

Wild guess on the center of mass

Im stupid, but 800lbs of thrust is 600ft/lbs of torque on the axle. and I imagine if there is 400lbs centered 1 ft forward of the axle that has 600ft/lbs of torque, the front tires are gonna fly off the ground at a great rate of speed if it ever gets traction!
Sounds like fun, but being able to steer can be fun too.
Will probably have to make it so I can slide the side batteries another foot or so frontwards to get a good balance between traction and steering. Might have to put one or more of the batteries all the way in the front. Will see.

Dang, Im getting anxious to go weld some stuff together.

Before I drive this monster, Im gonna need a couple REALLY manly motor controllers!! I planned from the beginning to build my own from scratch. 2 x 500+ Amps is ALOT different than the 200ish Amps that I was planning on when I first came up with this crazy idea.

I gotta have at least a 60V controller, and 72V would still be less than desirable. If I were to buy one (two), its pretty easy to spend over $1000 each. I saw one (dont remember the specs), that was nearly $3000, and I need 2 of them!!

Prototype Motor Controller

This is a super basic controller that I made, with no filter caps on the supply (the green capacitor is just for the CPU regulator). It only has a 1A diode to control motor flyback. It still worked fine controlling the monster motor running off 12V and no load, and REALLY woosy wiring between battery and controller.
Pretty much worst case example for 12 volts.
Maxxed out at about 60Amps for a really short time when going full blast from stopped.
Really suprised that it could handle the spikes from such a goofy setup.
Not suprisingly, it vaporized nearly instantly when I tried it on 24V!

Basic Motor Controller

This is a schematic for a basic speed / motor / buck controller.
I see that I left off the wire between the AMP and the MOSFET, but I dont feel like changing it. Sorry.

It consists of 5 basic parts. Well, 4 parts apart from the motor we are controlling.
The AMP takes a weak signal from a CPU, or other logic type thing, and amplifies it to turn the MOSFET on and off as fast as possible.
The MOSFET is the workhorse that does the actual switching. It turns on and off thousands of times per second at various duty cycles to achieve various output voltages. It can turn partially on and would be really simple to do it that way, that would be way too inefficient for anything larger than trivial amounts of current.
The DIODE prevents the collapsing current from when the motor is switched off from making overvoltage that would damage the MOSFET.
The CAPACITOR serves 2 purposes: The main purpose is to provide instantaneous current to the motor when it turns on.
The other purpose is to smooth out the potentially damaging pulses from the inductance of the power supply.

When I made my stupid controller, I purposely used really small wires everywhere, and didnt include a CAPACITOR at all.
Was just testing limits.

A real controller would have 10s of 1000s of uF of capacitance, and 100s of amps of diodes to protect the MOSFET.
Capacitance values arent the whole story though.
Mostly the ESR rating of the capacitors are what determines how well they are gonna protect the MOSFETs.
Some high end controllers will have a bunch of main stream bulk capacitance to supply the current surges, but use super high quality, low value capacitors to protect from supply surges.

As far as diodes go, alot of people will insist on having as many amps of diodes as the controller can handle. Problem with this, is that high amperage diodes are rated for RMS current, which is the average current, but the spike from the motor is mostly a fixed duration, and is usually less than 10% of the cycle time, depending on switching speed, and subsequently only needs 10% of the current rating of the controller.
For instance, even with the crappiest setup ever on my prototype controller, a 1A diode was enough to control 60A of motor current.

May 07, 2002 Sorry for all the geeky stuff, but I was bored with feeling crappy and having crappy weather outside
Slow start, but finally got started making real gocart parts. Spent a few hours making the parts that the motors will bolt to

Fairly complicated Motor brackets

Two of these brackets will be bolted to each motor, with some supporting steel to make the motors able to pivot to tension the chain.

Motor brackets bolted to one of the motors

I was worried about the brackets sticking out too far and interfering with the chain.

Is the chain gonna hit the brackets?

NOPE!

Really observant people may have noticed that the first picture of the brackets bolted to the motor shows the ends sticking out different distances.
I made all the brackets the same, but the bolt holes arent in the middle of the bracket.
Since half the brackets are bolted to the motor in the opposite direction, the distance from opposite ends of the brackets need to be the same to weld the brackets into a square.
So, the brackets arent really finished, but not too hard to fix.

May 13, 2002 Got motor mount frame thingies done.

Stupid mounts to hold the motors

Was gonna mount the motors in a way that they could pivot on an axis to tension the chain. Ended up making them slide instead. Dang stupid people!
Had to wait to make the rest of the motor mount thingies until I made enough of the frame to connect them to.

Made significant progress today. Got a big portion of the frame made, and the brackets to bolt the axle bearings to.

Axle bolted to beginnings of frame

Just enough room for the chain

The motor mount brackety things arent ready to be bolted to the frame, but easy to see where they are supposed to end up.

Looks alot like porn to me

Motor mounts for one of the motors is done! Turned out kinda goofy, but whatever.
Nuts at the bottom right and bolt on the far left allow bracket to slide when loosened.
Nut in the middle tightens the chain when tightened.

Stupid motor mounts

Stupid cheesy rear slidy bracket

The rear slidy bracket doesnt need to be very strong, but will probably at least add a washer to clamp down better.

Chain tensioner

Ran the motor off a big battery charger just to see the wheels spin.
The wheel spins almost 3 turns per second, which means almost 10mph at 12V.
So, it should do nearly 40mph at 48 volts.

Click here for 7 second video

May 25, 2022 Tried using 24 volts and batteries went everywhere.
3 batteries make 36v and fit alot better

3 batteries fit real nice

26 second video of violent 36v launch

Holy noodles, that is crazy! 48v is likely to be significantly more violent. Should probably wear a neck brace.
After I fasten the batteries down better, will have to see how much dirt it moves from under the tires.
This is what it did to the asphalt:

Couple of little peel out marks

June 07, 2022 Made a cage to hold the batteries better and got the seat mounted.

Kinda funky

Trying to figure the steering. Wanted to use a front end from an old riding lawnmower. Thats not gonna work.
The rear of the frame is a couple inches higher than I wanted, and the batteries are 2 inches higher than optimal.
The seat is several inches higher than I wanted, and now the front of the frame wants to be several inches higher than I wanted. Arrrggghh.
Even if I built a bridge between where I want the frame to the steering block, there are several issues

Steering rod in the way of feet

Cant turn the assembly around because the Ackerman would be all messed up.
The setup has everything else wrong with it too.
The wheels are too close together, so wouldnt be able to turn very sharp before tires hit the frame.

Wont be able to turn very sharp

The kingpin inclination is about half of what it should be. The camber is way off, and the wheels want to be inside out to clear. Other than that, it is perfect.
While trying to figure what to do about the steering. I figured since it pops a wheely, it doesnt need steering to try to drive it.

15 second video of kinda riding it

Actually rode it a few times. That was one of the funnier rides. Alot less violent on dirt.
The sticky-out parts of the frame make for some of the best brakes ever, when they embed themselves into the ground a couple feet!

70hp self propelled lawn dart

Noticed from the video that the seat bent back several inches when accelerating.
Had to add a brace behind the seat to keep it from breaking off.
May have found a place for the 4th battery too

Seat bracing and possible battery home

Had to remove the seat to keep from catching it on fire while welding, but 4th battery fit ever so barely

4th battery has a place!!

Can hardly wait until I can try it with 48V.
Its probably gonna peel out like mad, or do a crazy wheelie!
Did I mention that I can barely wait?

Jun 10, 2022 Couple of things to do first:
Make longer cables to be able to actually sit in the seat while riding the monster.
Make sure the cables cant short to other cables by running through some old garden hose.
Add a bar across the front to prevent pokey frame pieces digging into the ground and making violent stops
The bar will eventually have parts connected to it for front wheels

Made more battery cables

Battery cables way long

First Launch on 48v. Might be a little scared...

First 48v launch `This is stupid`

Peeled out ALOT on the dirt. Decided to try launching on asphalt.

Slightly smoky burnout!! Click to see (all glorious 6 seconds)

It doesnt pop a wheelie much any more. It loses traction too quick.
Even with around 500lbs on the back tires, traction is still a problem.
Even starting on the asphalt, its only pulling about 0.75G.
The tires spin just under 5 times in the first second, which is a bit over 23 ft.
It only travels about 13ft in that time. Thats only a bit over half of the tire rotation translated into movement.
It would likely be much better if it actually had front tires that could roll, instead of plowing the ground.

Sometimes get a cool spark

Now I wanna try 60volts! Motors are rated at 72v. Its probably gonna make traction worse, but whatever.
I have a battery I could steal from my robot Booby thats about the same size as the ones on the gocart.
Hmmmm...

June 20, 2022 Not used to needing such large tires on the front of a gocart.
Tried to figure way to mount front tires, but all was too funky without making front too tall.
Had to add a step up part to the front of the frame.

Few more inches to work with

Other view

Now seems like a more natural place to mount steering.

Perfect

Almost perfect. Still pretty tough to get geometry right.
Maybe these wheels will work better?

Taller, skinnier tires make geometry easier

Maybe Ill just weld them like this?

Steering is so overrated

Just kidding.
Got the king pin part of the steering made

King pins!

1 inch pipe has 1 inch inside diameter. 3/4 inch has outside diameter that is fractionally larger than 1 inch.
Grinding the outside of the 3/4 inch makes it fit inside of the 1 inch really nice.
Shiny part spins inside of not shiny part

Spinny vs not spinny

5 pairs of Vice-Grips to hold stuff in place for welding

Jigetty Jiggety

Setting up for welding the spindle on

The front wheels are mounted and supporting the weight, and place for the tie rods to connect to
Not used to doing the steering bar in front of the front axle. When they are behind the axle, they need to be slightly pointed together.
In my mind, that means that to have the same geometry, they need to angle way from each other when in the front.
I temporarily made the tie rod connecting points bolt to the top of the king pin.
Theoretically, the nut can be loosened and angle adjusted to get the right Ackerman effect
Then I will weld them in place.

I got spindles attached to the king pin

Just 1 more piece before tires follow each other!

Jun 25, 2002 Got the steering done.
First ride (on 12v) made it apparent that it was WAY too hard to steer. Extreme caster is fine on smaller carts, but this one is too heavy for that.
Cut and turned the axle to get rid of about half the caster. 2nd ride was much easier.

Less extreme. Easier to steer

Took several low speed test runs before finally working up to 48 volts.
12 volts is only slightly more fun than a stock electric barbie car. 24 was pretty exciting. It usually popped a little bit of a wheelie on takeoff. 48 was a whole different level of crazy!

First 48v Ride

I was only coasting most of the time, only giving it power for a second or so at a time, until the roundy-rounds.
It was REALLY scary. In the video, when I first came to a stop, it was because I needed to catch my breath!
At the end of the video, you can see how hard it is to rip the wires apart from each other. Thats even with touching them together at an angle to make the easier to pull apart.
Only issues I had was the batteries bounced part way out of their cage, and one of the chains came off.
Doesnt accelerate very fast with 1 wheel drive.

Not very awesome (14sec video)

I put a strap over the batteries, but havent adjusted the chain yet.
Thinking a 1 wheel burnout on asphalt might be really smoky and awesome.

I REALLY need a better way to control the power.
It would be much more fun to be able to give it power until you need to slow down, as opposed to keep killing power, just to make sure you can.

Since it pops a wheelie on 24v, it seems somewhere between 24v and 36v would be the optimum voltage for the fastest acceleration from a stop. 36v peels out alot, and 48v is retarded.
Having a controller would allow me to set current limit over time to make the optimum power to get going. In the mean time, maybe I can figure something.

June 30, 2022 Going from 48v to 60v would be 25% more speed to the wheels. Would probably make the tires peel out more to make slidyer fun. Would make it 65-70lbs heavier too.
Hmmm.
Changing the sprocket on the motor might just make it overpower the wheels enough to make it slidyer.
Maybe.
I have a pair of 16 tooth sprockets to replace the 11 tooth ones.

45 percent faster?

So... if the 11 tooth sprockets topped out at 40mph, 16 tooth ones could make for a top speed of 58!!!
Thats not stupid, its way beyond that. Cart doesnt even have brakes.
Im actually hoping to lose traction, and make it accelerate slower.
May even make white smoke on asphalt?
Will see what happens.

Made a ginormous spark that scared me.

Crazy spark (Dont click)

Woohoo!! seems quite a bit faster. A bit over 1 second of power applied, gets going pretty fast, and coasts a long way.

Happy Giggles (28sec video)

Made 2 nice black peelout marks, but still no white smoke :(

Made another run to get accelerometer data

1.2 seconds of really bumpy ride!

Looks like the frame is oscillating at about 110mS. When power is applied, it bends the middle of the frame upwards as it tries to pop a wheelie, then it loses traction and relaxes, then repeats when it regains traction.
Adding a couple of triangles to the frame should smooth this out.
Fun Fun

There is a much bigger problem though.
After turning around to come back, the cables welded together and wouldnt come apart.
Made crazy peelout stripes across about 30ft of the grass.
Was probably going 25mph or more when I ran into a space between a riding lawnmower, a fence, and a pile of poky yard tools.
Mostly missed the sharp stuff, but destroyed the riding lawnmower.
Broke the front of it, bent the back axle, bent a rim, and ripped a tire off the rim.
Also managed to destroy a tricycle, and broke the fence in 3 places.
Other than that, it went very well, and the gocart is mostly fine.

July 3, 2022 Decided it was finally time to weigh the monster.
For whatever reason, I kinda thought it weighed about 350lbs.
Was way off. Almost 200lbs heavier, at 530lbs. Scale indicated just under 550lbs, but the chain used to weigh it was just under 20lbs.

Nearly maxxed out the scale

The batteries are specd at 65lbs, which would be 260lbs for 4 of them.
I figured about 100lbs of wheels, frame, seat, etc. Maybe 150, but 530lbs - 260lbs of batteries = 270lbs of other stuff.
I dont believe it. Either the batteries have to be alot heavier than they say, or the scale is whacked.
I took all the batteries off to weigh it without them. Sure thing, it weighs just under 300 lbs without batteries!!
Ouch!

No wonder the cables welded together and tried to kill me!
Just under 2Gs of acceleration, not to even mention the nearly 6Gs of force in the upward direction, meant the motors were putting out WAY more torque than they are rated for.
Not even counting the upward Gs, the motors mustve been taking over 2000A!!! (1100A/1.08Gx2G=2037A)
Rough crazy guess including the Gs in the Z axis, the motors were probably taking over 3000A!

I dont plan on doing that ever again. Gonna smoke the motors, the batteries, or both.