# Shifter Kart beating E-Kart.



## ChukenThe3rd (6 mo ago)

Hi guys, 

Long time lurker, I usually always try to get things done on my own but I'm at a point where any help would be greatly appreciated.

We built a racing kart with the following specs.

ME1616 Motor (water cooled and air duct mod, see explanation below)
Curtis 1238SE-7971 900A controller
Custom 26S18P Molicel P42A battery (96v nominal, 109V full)










At 70% power limit from the controller, which is enough to compete with shifter karts, and with proper water cooling we only got 3 minutes of fun before motor temp reached 150c. Quite disappointing.










We decided to modify the motor and force air into it via an air scoop, so we machined the front and back plate and 3D printed an air scoop.
























This mod has proven to be quite good. For comparison:

Prior to the air scoop mod: 40% power for for 5 minutes would raise temps to 112c
After the air scoop mod: 40% power for 5 minutes would raise temps to 74c.

Although 40% is nowhere near the power level we want to be at for a 15min race, the mod was encouraging. However, when we turn the power up, we see that the temperature raises quite quickly regardless.

60% power for 5 mins brought the temps to 130c

I also see that the lower the battery voltage gets, the faster the temperature raises for the same power level, most likely due to the controller increasing amperage draw to compensate for lower voltage, therefor, I am thinking of increasing the battery pack to 30S (111v nominal, 126v full)

I think the biggest problem I have with the ME1616 and the Curtis controller is the fact that RPMs are limited to 5400, which has me running a 2.1:1 gear ratio in order to have a competing top speed, field weakening is also pretty much useless due to the 5400RPM limit.

Do you guys think that swapping to an AC20 motor, which would rev much higher with the Curtis controller, would help with my overall heating issue? I'd be able to use a gear ratio closer to 3:1 and therefore reduce load needed for the same acceleration? It is my understanding that the AC series motors are better optimized for the Curtis controllers than the ME1616, am I wrong?

Thank you for any input or feedback you can provide.

Cheers!


----------



## Functional Artist (Aug 8, 2016)

IMO your overloading that motor with the low GR your running 
& that's causing it to heat up, quickly.

I understand your gearing for a specific speed
...but, IMO it's just too much for that motor 

On my Hell-raiser kart, I'm running a ME0708 
[email protected] a 3:1 gear ratio (16T drive & 48T driven)
...with a 400A Kelly controller 
...& powered by a 48V 50AH batt pack
I haven't had any heating issues with this set up




But, when I tried a My1020 48V 1,000W motor (@ 4.8:1) on this kart (just as a test) 
...it "zipped right along" 
...but, got so hot that it started shooting flames out of the back of the motor (@ ~3:35) 
...so, I'd have to say that I was overloading it, causing it to heat up quickly.


----------



## ChukenThe3rd (6 mo ago)

Functional Artist said:


> IMO your overloading that motor with the low GR your running
> & that's causing it to heat up, quickly.
> 
> I understand your gearing for a specific speed
> ...


Thanks for your feedback, so then you are confirming my theory that running a 3:1 GR with a motor that would allow me to rev higher in order to achieve the same top speed would be a good way to start.

I've come across a few people that tell me they aren't experiencing heating issues with their karts. But I then come to realize they simply aren't pushing it as hard. For example, if I use this kart in front of my house and have fun with it for 15-20 minutes, no heat problems at all, but when I take it to the track, where you actually try to race and get the best lap in, the story is very different and heating occurs MUCH faster.

Not saying this is your case, but just sharing info.

Thank you so much for your input, greatly appreciated.


----------



## kennybobby (Aug 10, 2012)

Lupin3rd, nice looking cart. Looks like fun. Here's some ideas on stuff to check.

What is your coolant flow rate? Assuming an electric coolant pump--is it up to supplying 10 liters/min or more? What is the temperature delta across the radiator? Good airflow across the radiator/need to add a fan/larger coolant lines, etc

Have you checked the alignment/phasing of the encoder with the motor windings? For example, back-drive the motor on the bench with a hand drill while monitoring the encoder and the back emf of the windings on an oscilloscope. If there is a mismatch then the inefficient motor currents may be causing extra heating and reduced torque.

Some 98V test data seems to indicate that the advertised motor specs may have been stretched a bit. Maybe try using 4500 as the max rpm. Look at your track layout to determine if you need high top speed or more low end torque for accelerating out of the corners. i used to race 125gp at Road Atlanta, TGPR, Willow Springs, Roebling, much different tracks require different gearing (plus carb jetting for weather). i would bet the fastest shifter cart guys are geared more for low end torque than for top speed no matter which track you race. You have to do the best you can within the power limits of your machine.










knowing the speed, weight and final ratio from the motor thru the wheels and tires to the ground, then it would be possible to calc the power needed, then determine if the motor is up to the task.

i didn't look at your battery at all to see if it is up to the task, but that is really the most important factor to evaluate with respect to performance, e.g. enough energy supply to provide 15 minutes at the needed power level.


----------



## remy_martian (Feb 4, 2019)

Borrowing a hotrodding/racing term: "There's no replacement for [swept rotor] displacement"


----------



## ChukenThe3rd (6 mo ago)

kennybobby said:


> Lupin3rd, nice looking cart. Looks like fun. Here's some ideas on stuff to check.
> 
> What is your coolant flow rate? Assuming an electric coolant pump--is it up to supplying 10 liters/min or more? What is the temperature delta across the radiator? Good airflow across the radiator/need to add a fan/larger coolant lines, etc
> 
> ...


Thank you so much for your response.

My flow rate is 9L/min, honestly, I find the water cooling on this motor badly designed. The windings get to 150c and the water inside the radiator is still lukewarm. The windings heat up too quickly for the water jacket to be able to dissipate the heat fast enough, if that makes sense.

I have not checked encoder alignment, I guess I naively thought the motor characterization would do a good job? I dont have the knowledge or experience to perform that test, but I'll ask around, maybe someone locally could help me, although I doubt it..

Can you elaborate on your suggestion to use 4500RPM max? From the info I found, this motor is rated for 8000RPM but the Curtis controller is limiting me at 5400RPM. If I used 4500RPM, I'd have to use an even smaller gear ratio to get a decent top speed and therefore increase the load on the motor? Or am I missing something?

The battery is not a concern at all, it is capable of providing the needed power for a 15 min race at the desired power level.

Again, thanks for your time, greatly appreciated.


----------



## kennybobby (Aug 10, 2012)

i don't know if this might be a factor to consider, but the Curtis datasheet indicates that controller is for AC Induction motors, which operate with "slip" between the stator and rotor magnetic fields. 

A PM motor must be driven (commutation) in a synchronous manner that does not allow for slip.


----------



## ChukenThe3rd (6 mo ago)

kennybobby said:


> i don't know if this might be a factor to consider, but the Curtis datasheet indicates that controller is for AC Induction motors, which operate with "slip" between the stator and rotor magnetic fields.
> 
> A PM motor must be driven (commutation) in a synchronous manner that does not allow for slip.


Good point, the Curtis controllers allow you to run SPM motors, however, I do think that they are not as good with them as AC induction motor, which is what I meant when I wrote ''It is my understanding that the AC series motors are better optimized for the Curtis controllers than the ME1616, am I wrong?''.

I think you're kind of confirming what I was thinking, this motor might not be optimized for this controller, or vice versa.

I have an AC-20 motor on the way, so time will tell.

Thanks!


----------



## kennybobby (Aug 10, 2012)

Looking at your data graph, your peak current is hitting 500A when accelerating and if you integrate the current signal then your average looks to be higher than 250A, the continuous motor spec rating assuming with adequate cooling.

Looking at the temperature trace it ramps up immediately and appears there is little to no cooling at all, obviously totally inadequate for the task.

For motor and actuator applications i like to see about a margin of 2 for current. That is to say it will do the required job without getting into thermal issues at the nominal current, but there is sufficient margin in the design to allow overdrive of twice the current for a certain time period and still not exceed the thermal limits. This is important at the component level, FETs or IGBT, plus at the system level for critical applications.

Since you are pulling nearly 50kW at peaks your cooling system must be able to handle that much power also.


----------



## hallkbrdz (Jan 2, 2018)

You might want to talk with Gary Little at Vextrex as he's running a Curtis HPEV motor combo: Vextrek

There'e a recent video of his kart chasing a shifter... almost but not quite possible, with understeer due to weight being a large part of the problem.

Also, here is a good build thread agonizing over some of the same sort of issues you are now encountering. Enjoy... Electric kart - Endless Sphere


----------

