cheap controller options?

[ghost civic]

considering building a properly powered electric kart.

what are some cheap ways to control the power to the motor? Is it cheaper to get (or make) a stepped controller as opposed to a linear one?

Im very familiar with electronic speed controllers for RC cars, but im sure a go kart will require far higher amperage and voltage. Most RC controllers are rated at 12v with burst amperage ratings around 300-350a.

Also, is there a way to set up a controller so that when no on the throttle some drag brake is applied (motor braking)?

 

[itsid]

well, don't make no mistakes..
it's very likely that an electric kart doesn't need any amperage close to 350 Amps..

(well yes.. technically it's possible to go well beyond that limit.. but occasions are RARE )

There's a HUGE difference in RC motors and kart motors (or precisely any EV motor [electric vehicle])
And the main difference is this:
RC motors are rated at there maximum powerdraw, as you might know, some even at there very limits (at amps they can burn out in a few seconds without active cooling)
So a 5000 Watt RC motor for example isn't as hard to find at all...

Now, EV motors are rated at power OUT, the power they convert into kinetic energy,
and not even at their limits.. but instead at a rating that's safe to apply nearly all day.

So their rating is MUCH lower.. and in fact they're powerdraw is too...
a 100W 36V motor for example (quite common size) draws no more than 40 Amps max.

Only if you go into the realms of golf cart motors, or anything way above 10000 Watts, you have a good chance of getting much higher amperage and voltage, otherwise only one of the two will rise...
(depends on your choice)

Generally, you will want to keep the amperage low on an EV..
since you can survive nearly any voltage, but touching high Amps will surely blow your hat

that being said.. there is no such thing as a "stepping" controller for an EV really.
and the reason is simple..
it's much more comfortable (easier to use, control AND BUILD) to have a common mosfet control..
full power, just for fractions of a second at a time.. that way.. the motor is simply "off" for most of your riding time, not drawing any power from the batteries
and the only thing you contol is the intervall.

Much like modern day rc controllers work,
and the good news... within the overall power we're talking about an EV controller can be had even cheaper than a quality RC controller.. at least it's not more expensive than that

So, check twice what motor you want (see the essentials thread to get an idea of the power you want/need)

And then check to see what controller there is.. kelly controllers are cheap, and of good quality for example...

'sid

 

[ghost civic]

so, lets say I get a motor from one of those electric scooters (or something in that size range) are you saying that it wont pull more than 300 amps? Most RC speed controls are rated above 300 amps (burst rating) and between 30-100 amps constant. I find it hard to believe that a 540 sized RC motor could draw more amps than a starter motor or a motor from one of those scooters. I have spare RC speed controls, and I could control them with a modded rc servo tester (basically a potenti-whatever) The only downside is most RC speed controllers are only meant for 12v. some can do 16, 24...but those are typically more expensive and meant for brushless motors and not brushed.

I once had a traxxas emaxx with a 775 sized motor running on 15v...it could pull my daughter in her power wheels (even tho it struggled with traction)

I had once seen a neat "mechanical" speed controller used on a larger RC. It was a heavy duty spring...the wire to the motor was attached to the spring, and the power from the battery was run to the tip of an arm. that arm could move across the length of the spring. the closer it is to the end where the wire was, the less resistance and the greater the power to the motor. Im not saying that would be good for a E kart, but it is still a neat way to be able to control the amps.

 

[itsid]

mechanical speed control is crap... it always involves potentiometers, and those by design DRAW power from batteries converting them into heat..
(still draining the batteries)

electric scooters use very low power, or what reads as such.. a typical kids scooter is 100-120Watts only, adult sized scooters 250W just like adult e bikes typically are..
and yes, within a voltage range of 24-36V (some 48V).. even a 1000W motor will draw nothing close to 300 amps...
again, that's 42 Amps nominal... okay, they will draw up to 60Amps, since mechanical power ratings do not reflect their electrical ratings too well..
but even that is nowhere near 300...

And yes.. RC motors can draw much more amps than any ev motor..
based on their design that doesn't mean they can provide anywhere near the mechanical power an ev motor could ...
with very few exceptions, they'll fail instantly.

And, you should not power an ev motor with an rc controller...
a matching controller for an up to 1000W ev motor is somewhere in the 20-50 dollar range and is more reliable than any rc controller out there.

Again, it's not impossible, it's just utterly impractical, and comes with a bunch of downsides

keep in mind, that most rc motors are meant to turn fast,
ev motors turn much slower with a much higher torque;
and without torque you don't go anywhere

It's a difference if you want to move say 6lbs of aluminium and lexan or 200 lbs of steel and bones ...

'sid

 

[ghost civic]

yep, it was late last night that the RPM of RC motors vs EV motors popped into my mind. That very much explains the difference in amp draw.

A typical brushed RC motor spins between 25,000 and 30,000 rpms. such a motor in my truck will drain a given battery in 25 minutes. However, my larger, heavier rock crawler truck that has 2 motors of the same size...but which spin more like 5,000 rpms (these motors are for torque, not speed) the same battery will last over an hour. And the speed control for that truck has similar amp specs as the one for the single 25,000 rpm motor even tho it is powering 2 motors.

Ill start looking into proper ev controllers...I figured they were more than 20-50 dollars.