2 x 800w enough power? And legal issues

[Meathead316]

Hi

The biggest motor I can find is 800w 36v (which im sure wont be able to propel me 200lbs and the vehicle itself probs 200lbs at anywhere near the desired speed of 20mph) so could I use two of them together on separate wheels and essentially get double power? (But use batteries twice as fast)

Could one controller control both if wired in parallel?

Also if my kart were to be a bike, would it be allowed on uk roads if i added pedals (so technically and electric assisted bicycle)

Thanks


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[itsid]

Top speed is not an issue

Pm = m * g * Cr * v + 0.5 * Da * Cw * A * v³

See this thread to find out about the math

So let's assume the total weight is 227 kg (~500 lbs)
227 kg * 9.81 m/s² * 0.02 * 9 m/s + 0.5 * 1.2 kg/m³ * 0.7 * 0.9 m² * (9 m/s)³
= 676.4 W

that'd be the power needed to keep you and your kart at top speed of 9m/s (~20mph) on a levelled asphalt road.

but if you read the linked thread you'll find you want more than just 800W most likely.

double the power.. okay..
but not on individual wheels!

that's a bad idea, especially if you run them off ONE controller

better force synchronise the motors with a fixed shaft (i.e. attach both to a live axle)
that way none of them can run faster than the other because of different load.

'sid

PS please read a few other threads in this forum, most of what you asked has been answered already

 

[Meathead316]

Hi
Thanks for the quick reply
I think I will go for two motors, both on the rear wheel

Will I NEED a controller for each? Will I NEED a controller at all? Cant you just have an on/off switch (relay) and get all or nothing in terms of power?
(Or would i blow something up doing that?)
I want this project to be cheap and cheerful, but most importantly, as simple as possible. (Not in a nooby way, but the more complex a machine is the more there is to go wrong!)



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[itsid]

Well the on off switch will have to withstand an excess of 60 Amps
(switch peak will be somewhere around 75 to 90 Amps I guess)

So if a contact welds shut.. it's ON until the batteries are drained.

Or just assume this:
you show the kart to a friend, and he's all "oh cool.. what's this switch for? *flick*"
And off it goes.. without someone in it...

Full power all the time is a fun way to TEST a motor (bench tests), nowhere near a safe decision on a kart you want to drive.
And even that is kinda scary

Yes, you'll need at least one controller.. (60A or more)
if you mechanically force them to run synchronously;

running a motor (or two in your case) without any controller to simplify things is running a kart without a steering wheel to simplify it

if you want the two motors to run on individual wheels you need two controllers, with the throttle synchronisation based on steering wheel position (and maybe speed)
Otherwise you will run into troubles sooner or later.
That's of course possible, but it'll be quite a task and it requires a third programmable controller basically (a small microprocessor and some code) but you'll have to make that yourself.

So it's actually quite the opposite of what you want

Just run a jackshaft with both motors and the axle from the jackshaft,
or attach both motors directly to the rear axle
(one wheel drive with two motors of that size is just insane)

We take safety seriously around here,
so you might find we give some overcomplicated advice, but do not underestimate what even an 800W kart going wild can cause

'sid

 

[Meathead316]

Very good point about the whole runaway kart thing!
If using two motors will that mean I need a 1600w controller? Or can one controller with two motors in series work?

If not im assuming id have a motor, each with a controller but one twist throttle leading to both.

Anyone know what a copper would likely say/do if i were to ride a homemade electric bike on uk cycle paths or roads?




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[Felineman]

First off e-scooter motors are 3 phase and have hall sensors in them so using them in pairs NOT going to work. Second e-scooter is 300 lbs and and my father is darn near close enough and with extra battery 60 volts to a 48 volt system I was able to propel his FAT (CENSORED) up to 30 Mile per hour. You do a SHUNT MOD on the controller.

 

[Meathead316]

Right, so you saying those motors i chose are crap as i need 2? Or one will work if i overvolt it to 48v and mod the controller?

My mother in law has a mobility scooter and it defies physics how such a small machine can haul her rotund *** around!

Im not looking for mega acceleration, but i do want it to be able to move from a stand still without a little push

If 1 motor and one controller can do this then happy days less faff, less expense!

The controller has brake wires, wires for lights. Do i need to use em? I was gonna do braking seperate...




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[Meathead316]

Also what is/how do i do a shunt mod?


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[Felineman]

1 motor is fine some e-scooters can weight up to 500 lbs and carry 400-500 lbs riders. your problem is attacking the motor to the axle. I would go through the electric build threads we have here. OR get yourself a motorcycle engine with a quiet exhaust. Electric builds can get expensive as soon as you want speed and distance. Don't be afraid to do at least a month worth of research to weight out the pros and cons.

 

[Meathead316]

Motor to axel will be a chain, no?

I defiantly want to proceed with an electric build, I have no intent on using a petrol engine.



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[itsid]

*sigh*

No, e-scooter motors are NOT 3 phase!

Well to be honest, very few are indeed, but most are not;
most are simple brushed motors and most of the brushless are 4 phase.
And only the very expensive ones come with hall effect sensors
(cheaper ones use the back emf instead

I'm quite certain that Meathead is referring to a UNite MY1020 36V 800W..
and that is a brushed motor! (two terminals)

Anyways.. you cannot run two brushed DC motors safely in series;
IF you run them off of one controller wire them in parallel!

And yes, the controller should provide an absolute minimum of 1600W
I'd suggest a 60Amp controller that'd be 2200W @36V

brushed controller that is..
if you indeed intended to get brushless motors you'll have a hard time running it off one controller.

since you'll need to synchronise the coils first, and that requires a lot of time to do it correctly.
Doing it incorrectly will result in a fatal loss of at least one motor and the controller
So brushless.. forget about the second motor or get a second controller with it.

'sid

 

[Meathead316]

Sorry my bad, i meant parallel!

This is the motor I have my eye on
http://bit.ly/17i2U6z
Just two wires, + and -
I think i should try one motor and controller, but while building keep in mind i may need to add another to allow room, then if need be get a second lot

As for a controller, none ive seen on ebay list the amp rating...

Another question (excuse me if its stupid) but is there a way to electronically brake using the motor? Although probs a bad idea if electronics fail....





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[Felineman]

Sorry I guess you didn't read my post right I had said E-scooter not scooter E-scooter motors are 3 phase but if you want to use 24-48 volts brushed motors yes you can run them in parallel BUT they will drain at about 2.5-3 times faster, Don't ask me why but they always drain faster the more load you put on them. You can search craigs and kijiji and ebay for motors and controllers from mobility scoots for the best price per build. They have good power and decent travel distance. and most are only 24 volt so the weight is not bad with only 2 batteries 4 if you want backups. A decenttly made cart with 2 24 volt motors and 4 batteries should only weight about 200-300 lbs and should be able to handle 22-25 inch tires for access to those more swampy areas. I've done a few electric quad builds. But I'll let Itsid direct you towards the controller and motors that you would need, he seems to be very knowledgeable in these electric builds. I'm off to work on some foam board insulating my new shop before I can do anymore work on my TANK. Have about 3 days worth of work before I can do the electrical for the lights and heater.

 

[itsid]

Meathead, that's a My1020.. brushed DC motor (as expected )

Feline:
that's an escooter:

and this is an e scooter:

And guess what.. completely different motors
a brushed DC in the first (my1020 48V 1000W)
and a brushed hubmotor (48V 500W) in the second.

so yeah... I read your post
You're talking about electric senior scooters (which aren't scooters at ALL!)
and you're right some of them use 3 phase motors..
but some of them don't!

'sid

 

[Felineman]

This is an e-scooter those things are toys and not legal for the road. To be legal it must NOT exceed 32 kmph have peddle and not exceed 500 watts least here in Canada. Not sure about the states.

 

[itsid]

okay, that's also an e-scooter.. and it also has a hub motor..
what's in there IDK.
the revoluzzer (500W) is roadlegal in germany (25 km/h)
other models have up to 2000W (look the same) and are still road legal up to 45km/h
scooters like the one you pictured can be had roadlegal with motors up to 4kW (80 km/h)

And the next step is a road legal motorbike with well whatever fits into the frame (biggest I know is 65kw and is doing 220km/h)

Anyways.. my point was: just because the scooter itself looks somewhat similar, it doesn't mean the motors are.
The 500W Hub motor on "your" scooter
and the 500W Hub motor on "my" second scooter might be identical, or something completely different, without the spec sheet you'll never know!

'sid

 

[Felineman]

Meathead please fill out your location in profile so we know by what legal rules you have to follow.

 

[itsid]

Feline.. read closely.. UK rules!

'sid

PS but true enough, a proper location in the profile helps us to provide good informations