Yet another electric go kart newb

Status
Not open for further replies.
N

Nikmish

New member
Messages
24
Reaction score
0
Location
San Jose, CA
Hello everyone!

As many others here i wan to build an electric go kart and even though i read the stickies i still can't set my head strait.

Having tight budget I decided to go small first and learn as much as possible.

Here is my initial plan:
I have old go kart without engine and few other missing bits.

Looking to buy 1500W 48v motor on eBay, this one
http://www.ebay.com/itm/171475135134?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

The controller is where i hesitate... there are a lot of choices with different options. I don't want to spend much, but i also don't want to buy junk. PLEASE help me make the right choice.

My preferred controller should have option to change speed/output so my 6year old can have a go. Would be nice to connect some thought of monitor to it to see battery health and etc.

The next thing is the charger. Some controllers have port for charger - how does it works?

Thank you in advance!

For those who want to see pictures, i will be posting my progress here: https://www.facebook.com/gokartproject
 
itsid

itsid

Moderator
Staff member
Messages
11,563
Reaction score
238
Location
Ruhrpott [Germany]
well...

48V 31.25Amps are 1500 Watts alright.. but ELECTRICAL watts..
not mechanical watts.

personally I'd rather buy two of those:
http://www.ebay.com/itm/1000-W-48V-...ter-bike-go-kart-minibike-MY1020/151373055761

for that price ;)

those 1000W are MECHANICAL watts btw.. (peak power is twice that IIRC)

controller for both should be around 40 Amps at least (60A would be a better match)
again, peak powerdraw is way above the mentioned Amp-rating.

as a set:
http://www.ebay.com/itm/1000W-48V-w...trol-box-key-lock-Thumb-Throttle/151599802681


check those links...
(the motor you posted, and it's recommended controller)

www.aliexpress.com/item/1500W-48V-B...ic-Scooter/1975765540.html?recommendVersion=1

www.aliexpress.com/item/2014-High-Q...ic-Scooter/1983620672.html?recommendVersion=1

Anyways...
depending on the controller / throttle you pick, you can simply add a resistor or potentiometer to it to limit the top speed, easy to do and reversible in an instant.
Even the cheaper controllers ($30) come with a battery protection, they shut down before the batteries are drained into uselessness ;)
well, I haven't seen one without that is.

charging port is what you'd expect.. but the chargers are expensive, and if you have a charger for your car battery.. there's no need to get one IYAM.
but its convenient... plug in, wait for a green light, ride on.
the charger provides the power, and the controller prvides the correct wiring to the batteries, that's all there is to it.


'sid

PS facebook ... nope; I'm out.. either post here or I'm not interested at all ;)
 
N

Nikmish

New member
Messages
24
Reaction score
0
Location
San Jose, CA
now that's what can't get in to my hard head - where/how do you see that mechanical power? Pm = 0.8 * Pe - the motor 1500w, it have to be better then 1000w.

Also, the higher RPM gives me hope that with higher gear ratio i will be able to get better torque. Am I wrong?

Thank you for the reply. You found time to share the wisdom, I'll do my part and find time and post pictures here.





 
G

ghost civic

New member
Messages
254
Reaction score
0
Location
maine
if 2 motors are the same physical size, same type and both run on the same voltage....the one that spins at slower RPMs will have more torque. If you have a higher rpm motor and want more torque, you decrease the gearing (pinion or output on motor) or increase the driveshaft input (spur gear to me) Either of those changes will make 1 revolution of the motor turn the wheel less...so more motor power is applied to torque rather than to speed.
This will sacrifice top speed, but increase acceleration.
So, you can get a higher rpm motor and gear down...or a lower rpm motor and gear up. or get something in the middle and have a little bit of play either way with the gearing.
Im not a go kart expert by any means, but RPM and gear of electric motors works basically the same as with RC cars/trucks.

This is with brushed DC motors and also the same with brushless motors.
 
itsid

itsid

Moderator
Staff member
Messages
11,563
Reaction score
238
Location
Ruhrpott [Germany]
very nice kart.. shifter chassis...

make sure to keep the shifter levers and such, just in case you ever want to go back to gasoline.

very nice indeed...

Anywhoo; BTT.

just as ghost civic said;
if two motors have the same power but at different rpms, the slower turning motor will provide more torque.

brushed motors tend to provide more torque than a 'similar' brushless motor for some reason
(something I cannot wrap my head around completely)
and brushless turn faster.

But back to the question shall we.

electric motors, just like gasoline engines, do not provide a fixed amount of power,
and worse, they do not draw a fixed amount of power either.

the amount a motor draws (V*A) is always higher than the amount it can provide mechanically (torque * rpm)

And even worse, the ratio varies drastically based on the load, voltage, amperage and speed.

so electrical power is nothing you should get fooled by, not even peak mechanical power should blind your sight.
those values are not too important for a qualified judgement.

peak power efficiency is ALWAYS below 50%!
all the rest is converted to heat, and that harms the motor.

In fact.. without a diagram a motor is impossible to judge.

I had one for a my1020 (can't find it ATM..) IIRC it's peak power out is 1800W
(again.. really bad efficiency.. and worse could die within minutes because of the heat)

SO, not knowing what the 1500W are meant to be really... personally I'd go for the motor I know, especially since it's less than half the price ;)

'sid
 
G

ghost civic

New member
Messages
254
Reaction score
0
Location
maine
itsid...it is strange you say that brushed provide more torque than brushless. considering that a 24 gram brushless outrunner provides greater power than a old 380 sized brushed motor did...the outrunner being much smaller in physical size and a good deal lighter. also, in rc planes brushed motors were often had to use a gear drive...where as nearly all brushless motor planes are direct drive.

but, Ive never worked with brushed/brushless motors in the size required for a go kart.

It is annoying how watt, power, voltage input, kv, rpms ect are not used the same way universally. Once rc motor may be rated by watts, another by KV (which somehow stands for rpms per volt) and another by turns (which somehow represents KV!) Its like the companies make it hard to understand on purpose. They don't all use the same terms, some will list peak watts, other will list constant. same goes for amperage. And then in terms of RC planes, some simply list the static thrust it can provide with a given size prop.

Peak power is related to peak rpms. I know some brushed motors if run full throttle with no load can heat up quicker than they might with a load...since they will be spinning at max speed (faster than with a load) and the brush/comm friction is increased as the speed increases.

While it is confusing how motors are rated, I am very impressed by what electric motors can do. 10 years ago you needed a large nitro powered motor to make your rc go over 50mph. Today, a 540 sized brushless motor can push a average rc truck to 60-75mph. If setup just for speed runs, some 540 sized motors will push a truck to 90mph. The RC speed record is now around 200mph! Electric motors have left nitro motors in the dust. Their power to weight is soo much higher. Plus, they are quieter and don't bug the neighbors as much...lol
 
itsid

itsid

Moderator
Staff member
Messages
11,563
Reaction score
238
Location
Ruhrpott [Germany]
KC is artificial.. and it does not stand for rpm/V really..
that's a misconception.. it is the amount of rpm needed to generate a Volt and the (mostly false) assumption it'd be a synchronous transformation ...

It's on purpose.. companies like to sell their products with frosting and sprinkles.
So the "highest" values are the best selling ones.. not only for motors.

when there are two motors the same size and price one stating it provides 1400W and the other one 3000W which one would you buy?
... see?...

And yes, older brushed motors are NOTHING compared to newer motors, (neither brushed nor brushless)
the reason is simple.. neodymium magnets instead of rare earth ones.
get an old 380 remove the black magnets and buy a set of neodymiums and put them in.. run it ... grin ear to ear :D

Anyways, we slip off topic.
So slightly shifting this conversation again..
Think about a GX200 engine.. it's "THE" 6.5 HP engine!.. new GX200 are rated 5.5 HP..
but in fact the newer ones are NOT providing less power than older ones,
the only difference is, Honda decided to label the engine with a 24/7 power out instead of the peak power it's capable of providing unaltered.

And we're back at vehicle moving :D
An electric motor is only slightly more confusing than a gasoline engine..
if they put on a wattage sign.. without further explanation it can be anything...
from
Max power input (or the analog of WORST mpg for a gasoline engine)
Max power output (not even half of that)
over
ideal power input (the analog of BEST mpg for a gasoline engine)
ideal power output (the highest efficiency ~80% for most of our contenders)
down to
Min power input (analog to idle speed or precisely min amount of fuel to keep engine alive)
Min power out (the amount of wattage needed to turn the shaft)

None of those values are a lie.. so they can use it on a label.
without a diagram it can be anything.. that's why good companies sell their product with a diagram (even some rc companies do AFAIK!)

the only thing WE can do is to do the readings, and learn the basics to try not getting fooled by misleading labels ;)

'sid
 
N

Nikmish

New member
Messages
24
Reaction score
0
Location
San Jose, CA
yes, that part i understood - it's all very confusing :)

Lets try this way - i want to compete at autocross, but i can't afford those $1k setups.
I need your help on choosing optimal kit to get me to my goal.

I would like to keep the battery setup 48v and under, controller should be good enough for different motors (in case i want to experiment and switch).

Please HELP!
 
itsid

itsid

Moderator
Staff member
Messages
11,563
Reaction score
238
Location
Ruhrpott [Germany]
autocross competitive set up...
tough!

no really, you want some grunt in your motor and that will be expensive!
you will have a much better (cheaper) solution with a conventional gasoline engine
I'm afraid.

Read my essence-thread
you can find some math to get an idea of what power you may need.

competitive means you will need serious acceleration and I'm afraid that in turn means serious mechanical power;
I think roughly 6kW and that's not cheap with an electric set up.

Your best chance (if you insist) is an electric golf cart as a donor vehicle.
with a bit of luck you can find one for not too much,
but you need one that comes with a capped motor, or you need to machine a cap / have it machined.. and that's expensive again...

a controller for a motor that powerfull alone has a midsize three figure pricetag,
roughly what you'd have to pay for a 420 predator engine...
or, since you have a shifter chassis.. maybe a used 250cc motorcycle engine
(the much better choice here)

So if you cannot find a cheap 6kw (or more) golf cart or forklift of other equipment that comes with a motor and matching controller...
as much as I like electric karts..
I wouldn't bother much and go gasoline.

you can't have it all ..
a cheap competetive racing kart that's suitable for an untrained 6yo to have safe fun...

even two of those things (cheap and competetive) will be hard to do.
even more so if you go electric (which indeed would add the option to throttle it down for a 6yo)
controllers and batteries can eat you alive... not even mentioning the motor.

I'm sorry.. but what can I say?!

'sid
 
N

Nikmish

New member
Messages
24
Reaction score
0
Location
San Jose, CA
It helped, thank you! At least i know where i stand.

Now with that info i can go back to my original plan - parking lot family fun. (I will keep dreaming though about autocross).

Right, back to the controller. Which one i can get that will serve me well with ONE 1000w my1020 AND will work well later with TWO 1000w my1020s?

Also, there is MY1020 and ZY1020 - brushed & brushless?
 
D

drm

Member
Messages
73
Reaction score
0
Location
USA, TN
Nikmish said:
It helped, thank you! At least i know where i stand.

Now with that info i can go back to my original plan - parking lot family fun. (I will keep dreaming though about autocross).

Right, back to the controller. Which one i can get that will serve me well with ONE 1000w my1020 AND will work well later with TWO 1000w my1020s?

Also, there is MY1020 and ZY1020 - brushed & brushless?
Click to expand...

Yeah the my1020 motor listed looked like it had zy on the sticker.

Buy a programmable controller rated for the power of 2 motors and adjust it when using one motor.

http://kellycontroller.com/kdz4820024v-48v200aseriespm-p-951.html
 
G

ghost civic

New member
Messages
254
Reaction score
0
Location
maine
that motor looks impressive. pretty heavy for its size. not only is it 2.5hp at 12v...but 8,000 rpms as well!?
 
itsid

itsid

Moderator
Staff member
Messages
11,563
Reaction score
238
Location
Ruhrpott [Germany]
look at the diagram!

that's Bulls shirt..

max PowerOut ~1400 Watts best efficiency ~53% :ack2:

but hey it surely drains your batteries faster than the my1020 ... :D

'sid
 
itsid

itsid

Moderator
Staff member
Messages
11,563
Reaction score
238
Location
Ruhrpott [Germany]
sepEx controller.. hmm

(seperated excitement)

means, the controller is meant to run on four terminal motors (three terminal motors sometimes)
if it can be used on a small common (two terminal) brushed motor IDK..
(have't read that manual tbh!)

if it can.. go for it, if not stay clear ;)

'sid
 
Status
Not open for further replies.
Top