brushless motor for electric to kart

[GabYoung92]

For a couple of years I've been wanting to build an electric go kart!

Yesterday this idea was sparked again after going to Game Over GC (http://www.gameovergc.com.au/) and riding their electric go karts. However there is not much info about the karts other than "a 20hp DC electric motor that produces far more torque than other kart engines"... I asked the staff there for more info but they had no idea what type of motor it was. The only other think I found out was the chargers were doing 48V @ 100A (well that was written on it anyways)

Looked at a fair few videos on youtube like the Z-Kart, LOLriokart and a fair few others and they seem to use a BLDC motor. The prices off the hobby king's website have made me quite interested in trying to use a brushless motor. After looking through the site, these are the links to the motor and ESC that I think may be useful to my project:

Motor
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=39212

ESC
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=46160

Hoping to go use a Lipo 8S or 33.6V when fully charged system to power it.


I would like to know if anyone has had any experience with doing an electric kart build and if I'm on track with the motor and ESC...

 

[LabSpokane]

That's a 7hp motor if it's 100% efficient. More 6.3 in reality.

1hp = .746 kW

[xthexder]

This seems like a cool project you've got.

Some things to consider from my own experience:

That motor is an outrunner motor, which means the outer housing is what rotates, not just the shaft. For something like a gokart this isn't ideal since you could easily get stuff caught in it.
You'd most likely want an inrunner motor, however those don't tend to come in very low RPM packages.

The other thing is the KV of the motor (rpm per volt). The one you've linked has a KV of 172, which means you'll get just under 6000 rpm at full throttle on your 8S setup.
Depending on your tire size and your gearing this may or may not be ok. If you've got 15cm diameter wheels and a 1:1 ratio your theoretical top speed is ~150 kph assuming your kart doesn't weight anything (and there's no drag from the air). If you can get an RPM closer to 1-2k you'd be using your power more efficiently.


I've actually built a "kart" before by motorizing a plastic tractor. I ended up using the 1KW 36V motor here: http://www.electricscooterparts.com/motors36volt.html
The chain geared it down to about 1000 rpm at the wheels, and I got about 40 kph in practice (on a very flat road).
I used 3x 12v sealed lead acid batteries for this, and a basic speed controller. I think in practice brushed motors work better for this type of thing, but they can be a bit hard to find.

[GabYoung92]

Yup, already aware of being an outrunner.  Was going to cover it go nothing (or no one) can get hurt on it.

I was reading that a lower KV is preferred as higher KV motors seem to burn out...
Also looking for a bit of torque to get up inclines

Looking to do a top speed of 40km/hr anyways so was going to gear it for a bit more torque


Hmmm, that's what I wanna know, why do you think brushed would be better?

[xthexder]

The main reason is that the controller is much simpler. The problem with how BLDC controllers work is that they don't know the motors rotation unless it's moving, so if you stall it (or you're just starting off), it just has to start applying current until it can start to get some feedback. This wouldn't be a problem if you had a sensored motor though.

I hadn't really thought about it until just now, but a sensorless brushless motor would really not work at all for starting off or driving slowly. The minimum RPM for this would be fairly high before the ESC doesn't know what's going on, and when starting off, you would have almost no control over the throttle until you're moving. It's possible you could even end up going backwards a part rotation if the ESC starts off with the wrong motor pole.

It's worth noting that most of my experience with brushless motors is with small quadcopter motors, so there might be some crazy way these larger motors are handling things that I don't know about.
I do know howver that it's really hard to stall a 1KW brushed motor, and if you go up to a 2 or 3 KW motor, you'll easily have enough torque to spin the tires of just about any kart.

Edit: Also on the topic of KV, I'm not really sure if a higher KV would burn out more easily, but it's definitely true that a 1KW 100 KV motor will have more torque than a 1KW 1000 KV motor, so if you're going a set speed, the higher KV will end up using more power, and thus heat up quicker.

[Isad]

Hi
Great project.

This might be dum and usles but couldnt
u use one of those car starters they are dc and are pretty good
idk about the speed that they reach but they go pretty high
And are so easy to find dont cost a fortune buying them used.

[Zero999]

Hi
Great project.

This might be dum and usles but couldnt
u use one of those car starters they are dc and are pretty good
idk about the speed that they reach but they go pretty high
And are so easy to find dont cost a fortune buying them used.

The problem with starter motors is they're only designed to be used for a short length of time before resting. A starter motor would have to be de-rated, otherwise it would burn out if used continuously.

[Isad]

Hi
Great project.

This might be dum and usles but couldnt
u use one of those car starters they are dc and are pretty good
idk about the speed that they reach but they go pretty high
And are so easy to find dont cost a fortune buying them used.

The problem with starter motors is they're only designed to be used for a short length of time before resting. A starter motor would have to be de-rated, otherwise it would burn out if used continuously.

I knew somone would have the answear
well it would be soem work to de-rate it but still
would be cheaper and easyer to controll.