First Electric Go Kart - Need Advice

[fionnwhelan]

Hi all,

So I was thinking about making my first Electric Go kart, as I was considering doing engineering in college, and I think it would be great to have some experience with electronics before starting. I am completely new to this, but have read a good few posts on here and elsewhere as well. I have a rough idea of all the components I need and how they fit together, but I still have a few questions, and need some advice.

Here are the components I've found:

48 volt 2000 watt brushless 3 phase motor

https://m.ebay.ie/itm/Electric-Brus...-chain-drive-for-New-MAF-X2000S-/232169152820

48 volt 2000 watt brushless motor controller

https://m.ebay.ie/itm/Control-relay-Electric-E-scooter-2000-watt-48-volt-MAF2000RS-etc-/262801932357

4 × 20 Ah SLA 12 volt batteries

https://m.ebay.ie/itm/12V-20AH-SLA-Batteries-x-4-12Volt-20AH-/181313828136

12-48 volt 60 amp circuit breaker for car audio/marine

https://m.ebay.ie/itm/12-48-Volt-60...eaker-Car-Audio-and-Marine-IP67-/132397301213


I already have a pedal-powered kart to attach all these components on to.
As well as this I will probably be using 6 gauge wire. I am aware I need a potentiometer of some sort as a throttle, but I have no idea what kind of rating I need for my circuit.

Here are the calculations I've done so far. If I've made any mistakes don't hesitate to tell me.

2000W=82% efficiency
2440W=power going in

P=IV
2440W=I(48V)
I=50A
So at max speed there will be 50Amps in the circuit.

Engine RPM=4500
Wheel Circumference=1.88 metres
40km/hr=11.1 m/s

11.1÷1.88=5.9 axle revolutions per second
5.9×60=354 axle revolutions per minute

Therefore gear ratio for 40km/HR

354 : 4,500
1 : 13(12.7 to be exact)


20Ah batteries in series stay at 20Ah
20A=1 hour
50A=24 minutes (according to this, my kart would only last at top speed for this short amount of time)
I know there is the peukert effect, but I think there must be something drastically wrong with my calculations, as I was having a look at the website of the electric scooter that this motor is designed for, and it has 12Ah batteries, and yet it says it has a range of 26 km. If I was running my kart at full speed , it would go 40 km/hr for 24 minutes = 16km range, even though my batteries are almost double the capacity of those in the scooter. Here is a link to the web page of the scooter:
http://www.mafscooters.com/product.php?PID=814

So basically if that's all right, then my questions:

1) what rating of potentiometer do I need to properly control my motor

2) will there be enough torque from the motor considering the gear ratio, if I mostly want to use this kart for off road

3) have I done something wrong with the battery calculations, and if so can I get batteries with smaller capacity(the 20Ah hours are very expensive)

4) is there a way I can add a reverse button into the circuit and if so how

5) need some advice on how the speed controller is hooked up to all the different components

6) will the components I have shown above all work together

7) the 1 : 13 gear ratio is not ideal, as there is a sprocket already attached to the axle, and I can't weld, so that will probably have to stay there, if possible. It has 24 teeth. This would mean the motor sprocket would have to be 2 toothed(1.8 exactly), which is not possible. So I am wondering, other than getting a much bigger sprocket and welding it to the axle, is there any other way of slowing the motors RPM down enough to get the kart moving at reasonable speeds?

 

[itsid]

Well.. there's a major flaw in that I'm afraid, tucked away inbetween the sentences...
40km/h on a pedal kart.. NOPE! 40 km/h on a pedal kart OFF ROAD?? Nope nope nope...

That reads "massive injury by chassis failure"

Other than that,
not much to say..
I don't have and cannot find the motors specsheet wich is important to answer some of your questions..
since IT is what draws the amperage not the controller.

1) potentiometer is unlikely to be needed at all, a 0-5V hall effect throttle is way more common.
(and yes, I know some still allow for a poti instead... don't bother)

2) 13:1 on a 48V 2kW motor will surely have the torque to get you through nearly any terrain on a small kart.
there's not much we can say about the torque without having the motor specs, but I'd say around 5Nm is reasonable to assume 65Nm should be okay to move you through rough terrain IMHO.

Now.. Functional Artist runs IIRC exactly that BOMA motor, maybe he can chime in and fill in some gaps.

3) Sure, you can buy motorcycle batteries they start at around 9Ah usually are around 12-15Ah and top out at about 24 or so... everything in betwwen should be available.

4) you need a controller that has a reverse functionality;
you could swap two phases o the motor to have it run in the opposite direction, with a very beefy to way toggle switch, but chances are you'll freak the controller out if you do that without switching the controller on and off while swapping phases...soo that's inconvenient.

5) the manufacturer of the motor controller should provide you with a manual for that (corectly color coded) but it's straight forward really, and once you have it, we can talk you through

6) NOPE
as above.. a pedal kart powreed by a 250W motor is fine IMHO.. by a 2kW motor is stupidly asking for injury!
I haven't read the auction details (lazy-pre-christmas-state) but if it doesn't come with reverse it doesn't suit your needs. but it should fire up that motor otherwise ..

7) get rid of that pedal kart NOW!
and yes, you would need a jackshaft to compound gear that thing
(10T on the motor-> 54T on jacksahft In, 10T Jackshaft out to the 24T axle sprocket
12.96:1 overall gear ratio ... but don't bother either)

7a).. the Controller FunctionalArtist used has a governor circuit, throttling the motor down for kids or beginners (many have such circuit) ... but since it's electric you could also just limit throttle movement to achive the same

'sid

 

[Functional Artist]

Yup, I agree

...it's best keep the pedals on pedal karts

...most brushless speed controllers have reverse, if the one your looking at don't have reverse capabilities, it's simpler to look for another

...I have used 12V 12AH SLA batteries, on many different karts, for ~30 - 45 minute runs many, many times

...you can go with bigger batteries but, your just lugging around more weight (which affects maneuverability & uses more power to carry the extra load) (not much additional benefit)

FYI; here is a wiring diagram

http://www.diygokarts.com/vb/showthread.php?t=37537

Yup, a 48V 2,000W motor will run off road easily


This kart !Arriba! is set up for (2) 48V 1,000W motors

...it only has (1) motor on it currently

...but, it's so torquey that it lurches to the right when first accelerating

...& easily, goes OFF ROAD

https://www.youtube.com/watch?v=xJo3M6KGN34

 

[Crotchrocket]

Here’s a foot pedal
https://www.ebay.com/i/112136095025...3D711-117182-37290-0%26rvr_id%3D1400113178533

Most of the electronics are in the motor controller. A fun project might be to build your own motor controller, but might be a bit much for someone with no real electronics experience. Also building your own Lithium battteries would be a good lesson on how those work, but the welding machine to put them together is like $100, a bit of an investment for a single project, but on something like an e-bike it’s more important to be able to have more power in the form factor you desire

https://m.youtube.com/watch?v=TY7FwffZ5vc

 

[fionnwhelan]

Thanks for all the help so far, I'm looking into finding an ideal kart, doesn't seem like there's too many out there!