Questions about building kart from "A Simple Guide" Sticky

[WaitWhat4355]

Recently I decided I want to try an build a go kart. I would really like to build a high-powered, electric go kart, but budget may be an issue.

After reading the "A Simple Guide" thread (http://www.diygokarts.com/vb/showthread.php?t=9700), I may be able to get my hands on a semi-truck starter motor. The issue with this is how I would control it. I can try mounting a load and measuring the amp draw and try to calculate what wattage it would be with a go kart load, but I might just try it out only running 12v instead of 24v.

I would definitely not want to do the on/off switch for control, but the progressive switching is plausible, only downside is uneven battery drain. I could, possibly, fashion a "shifter" of sorts where I have multiple(4?) 6v or 12v batteries and the first "gear" puts them all in parallel at the lowest voltage for lower speeds, 2nd "gear" puts them in series/parallel for mid speeds, and 3rd" "gear" puts them all in series for high speeds/full blast. Maybe have a 2nd switch with On1/Off/On2, where On1 connects a car starter battery for launching and then immediately switch to On2 for the running batteries and the "shifter" from before.

Made diagrams in Multisim for picturing the wiring. https://imgur.com/a/F5J9HXd

Another possibility would be making a crude controller, or modifying one for higher amperage. Hopefully that would mostly be a lot of MOSFETs and some heatsinks, no?

If anyone has thoughts and ideas they could share, it'd be nice.

Edit: Also, I believe diesel semi starters can do 1000 amps when the engine is very cold. So, considering that the max, peek watts at 24KW which is 32 HP, should I assume the motor can be rated as 8HP running? At least 4?

 

[itsid]

why not just buy a 24V controller? (kelly has some)

Anywhoo, the issue with starter is that you need to KNOW what you are dealing with;

truck starters are usually series wound (with a sep ex option mostly)
not PM motors, so you will throw some serious amps their way in order to make them chooch.
(ever wondered why car batteries have a so called "cold cranking amp" rating in the hundreds of amps?)

since I still have the link from the other thread:
http://kellycontroller.com/kdz4840024v-48v400aseriespm-p-955.html

that'd be a mid size (other models up to 650Amps are available for 24V)
that'd be good for starters up to 12.5kW of mechanical power

the biggest I know is the Letrika MS77 (AZG4689) 9kW electrical (6.5kW mechanical)

but most importantly you need to find a starter with bearings not bushings (still a thing in starters)
and once that's checked you still need to modify it,
the contactor needs to be replaced since it's not designed for constant loads,
then you will need to modify the shaft,
the retraction mechanism has to go, and the pinion gear with it...
sometimes those are bolted on inside a case extension
and thus can be removed with just a few bolts,
but sometimes they are not and once removed the shaft will no longer extend out the casing, which may or may not allow to be shortened.

So you want to be sure you spend money on the correct starter first.

A good size would be anything between 2kW and maybe 4kW (rated electrically)
that should give you ample power for an average kart.

Don't go the other way around and buy an unknown starter (at worst a 0.7kW version)
in which case it'd be easier to buy some other motor instead (like the brushed my1020)

'sid

PS no they cannot draw 1000Amps,
and if they would that would NOT be 32hp (it'd be 26.1hp roughly)

 

[WaitWhat4355]

I wouldn't be buying the starter motor, but my father may be able to procure one. He's a steward and truck driver and has lots of friends so he might be able to procure one. He usually is able to procure somewhat strange stuff like this. This is only a might scenario though, as I am still researching the whole go kart thing, too.

The main issue I'd have with starters is that I couldn't find anything saying what they're rated for and the 1000 amps is just max speculation. Most starters pull about 250-300 amps and in the winter it takes more to crank due to the oil getting "thicker". Also, diesels have a much higher compression ratio, too, so they need more power, right? Again, just a top of the barrel max from assumptions.

For the question of "why not just buy a 24V controller?" is because I didn't know what a starter motor could be rated as, if used as a continuous run. I mostly want power on a budget, and power that won't just go up in flames too easily. The guide said

If you can get one, the starter from a large semi truck is super- most of them run on 24v and are big enough that the load of a go-kart is not going to be a problem from a continuous-operation point of view.

so I thought my father might be able to produce one. Otherwise I'd just do the whole Golf Cart Motor thing and spend $900(from what I found) on a motor and controller and strap it to the smallest go kart I can make/find with $1000 in 4 batteries, or just build what this guy did
https://www.youtube.com/watch?v=RTdbjXOa-BU
$2500 motor and 6 of the $250 yellow tops.

 

[itsid]

I see where this is heading,

if you want it cheap.. go and buy a 212 predator with a coupon for 99 bucks,
you cannot beat that in price!

you will need to spend serious money even with the cheapest viable electric motor.
you need to spend 450 bucks in batteries anyways
(more the more power the motor can draw)
plus a controller, plus wiring, plus contactors (for higher amperage systems)
....
1000 bucks isn't too wrong to assume and you'd better be prepared for that.

'sid

 

[WaitWhat4355]

So, I can only get a good powerful electric go kart for relatively cheap if I keep getting good rolls, so to speak?

 

[anickode]

So, I can only get a good powerful electric go kart for relatively cheap if I keep getting good rolls, so to speak?

Yes, minus the good part.

Using parts for other than their intended purpose isn't going to get you a good anything.

Starter motors typically have very low duty cycles, a bushed armature, no cooling mechanism or even venting. They can (and do) burn up from prolonged use.

The cheapest speed controller would be like the old 48v golf cars used. They had 8 - 6volt batteries connected in series. The speed controller had 8 contact points, each of which would energize a solenoid that was tapped between batteries.

Position 1 was 6v
Position 2 was 12v
Position 3 was 18v
And so on.

 

[Functional Artist]

Yup,
...starter motors are NOT designed for "constant duty"

I tried to use a V8 Chevy starter to power a kart ~10 years ago
...it only lasted ~2 times around the block
…& it was very noisy & very slow

http://www.diygokarts.com/vb/showthread.php?t=34016

It would probably be best (for you) to do some figuring & make some initial decisions, before procuring stuff
...like how fast you want to go
...how big/heavy of a kart that you intend to motivate (total weight including operator)
...how long you want to ride (@ a time)
…& finally how much you want to spend

Because each of those decisions "will" affect your/the bottom line (literally)

 

[WaitWhat4355]

So, I will probably go with the 212 Predator motor to start off with, but I am a little bit greedy. Would it be good, bad, or so so two by two 212cc Predator Motors for $200 and stick them both on the same gokart? Would it be better to go for the 301 CC Predator motor for $220?

 

[mckutzy]

212-common parts and setup, standard bolt pattern and shaft size...
301-The smaller big block... 1" shaft size, more money for a clutch/TC... the same power gains can be sought by upgrading the 212...

Adding 2-212cc engines is for the most part useless...

 

[anickode]

212-common parts and setup, standard bolt pattern and shaft size...
301-The smaller big block... 1" shaft size, more money for a clutch/TC... the same power gains can be sought by upgrading the 212...

Adding 2-212cc engines is for the most part useless...

The 301 is 8 hp, right? Should still be able to use a 1" driver 30 series clone on that without issue.

Not a whole lot of aftermarket for the 301 though. Not like the 212 anyway.

 

[WaitWhat4355]

212-common parts and setup, standard bolt pattern and shaft size...
301-The smaller big block... 1" shaft size, more money for a clutch/TC... the same power gains can be sought by upgrading the 212...

Adding 2-212cc engines is for the most part useless...

I was thinking along the lines of having them run side-by-side, but having a larger gear ratio on both, instead of one you'd have for a single engine, for higher speed as they share the load. Like, instead of a 1 to 8 ratio, have each motor used a 1 to 4 ratio.

Edit: If I want more power on a 212 predator engine, should I just spend money on the intake filter, jet, exhaust header, and vent filters for it? Almost $90...
https://www.gopowersports.com/212cc...ab&utm_medium=Website&utm_campaign=free_plans