Best Motor for parking-lot-drifter kart

[CheatingBoy6890]

Hello,
I recently bought a shifter kart frame to which I'd like to attach an electric motor.
I'm running the kart at 20S lifepo4 so 64V norminal. The battery has 100Ah of capacity. My whole battery assambly is pretty heavy. Almos 40kg.
Now my question is what motor is a good choice?
I've had a look on Alibaba and found three candidates:

Qs 165 50h
Qs 138 90h
Qs 180 90h

Since I've got a pretty big capacity I want the motor to not overheat even when used for quite a long time.
The kart doesn't need to be crazy fast like 60 km/h (40 mph) is probably enough. I'd also like to use a vesc based controller
like the flipsky 75450 since I like to tinker around with things.
Sorry if I posted this in the wrong thread, I'm knew to endless Sphere and the whole karting scene in general.

 

[j bjork]

It is not that easy ta answer I think. The way I see it you have 2 limitations that affects the motor choice a lot.

1 You have low voltage that limits the output of any of the motors. The one with highest kv would probably be the best choice I guess, as it would have the highest rpm/volt.

2 I suppose your controller is for 75v nominal and 450pA? Then you are quite limited in Phase Amps, a low Kv would probably be best as it would have the most torque/amp.

But it wouldn't make much sense to run a big motor with such limited pA anyway, so I suppose 138 90h is the most reasonable choice. I would expect the controller to overheat before the motor.

 

[dominik h]

Tourque = Phase Amps
For a drifter I would choose the controller with highest amps I could afford.
450A is definitly on the lower side.

For the QS165 60H they recommend 850A Phase current

The QS180 90H will shure be a number to big. QS also has a QS155 series with up to 29kW, they are bigger than the 138 and lighter than the 180
If you don't need integrated gearing in the motor there is also a QS138 105h.
But they all need more phase amps.

 

[CheatingBoy6890]

Maybe I'm wrong but I thought I could get the fsesc 75450 running at 500 to 600 phase amps at least for brief periods. I also don't need all the power. My biggest concern is the motor overheating when run for a long time.

 

[dominik h]

For the 72450 they claim up to 1200A burst and user says they see up to 1000A.
Somewhere is said the current measurements is designed for 500A only.
Give it a try and report back.
Hope you head for the watercooled version.

The 138-105h is 8kw rated

 

[CheatingBoy6890]

I think I will order the QS 180 since it's only 70€ extra on Alibaba and try the 75450 with it. But it will take a while for the things to arrive.

 

[CheatingBoy6890]

Do you think it is possible to do a shunt mod to be able to measure and therefore use higher phase currents? Since the firmware is open source it should be as easy as adding a few resistors change a constant in the code and upload the new firmware.

 

[dominik h]

I think you can not use higher phase currents for longer than a few seconds.
Your problem will be the generated heat in the fets.
When it is designed for 450A and you try to reach 900A for a few seconds then you generate 4 times more heat in the fets.
I burnt a mosfet amplifier which is rated for 5,5kW music signal in 3 seconds with a sinewave signal at 50Hz. A 100ms burst signal was no problem for the power stage, but 3 seconds burnt all the fets, long before the heatsink temperature went critical.

 

[CheatingBoy6890]

I thought the current sensing was the limiting factor because I read somewhere on facebook that at currents over 500A there was an imbalance between the phases. I think with the ability to meassure higher currents it should be possible to get maybe 600 phase Amps. But maybe also the fets are the limiting factor.

 

[eee291]

A shunt mod is something you do to a 20 dollar controller, not to any VESC or any FOC controller for that matter.
If you want high phase current for cheap then get a Fardriver.

 

[Zambam]

A shunt mod is something you do to a 20 dollar controller, not to any VESC or any FOC controller for that matter.
If you want high phase current for cheap then get a Fardriver.

Why should FOC controllers not be shunt modded? Thx

 

[eee291]

All if not most foc controllers don't use shunts anymore. Secondly, in order for the foc algorithm/math calculations to even function properly it needs to know the current(s)

 

[ljbred08]

Why should FOC controllers not be shunt modded? Thx

There's no point. Shunt modding is to trick a controller into providing more current than it's designed to do. With programmable controllers, if you want to run past what it's rated for, you simply use the firmware version without limits and enter your bigger values directly into the software.

(Also, as @eee291 said, doing so would likely wreck the controller's functionality because it's much higher tech than a normal non-FOC controller.)

I agree with the above recommendation to use a Fardriver for big phase currents; that is currently the cheapest option for high power. For Flipsky VESCs, they are rated close to the hardware limits, so if you put more current through than they are rated for, they will break. One can push it a little with really good cooling (running a 75100 at 120 phase amps is a common instance of this), but in general they are rated accurately and don't have much component headroom. (There's a reason they're so small).

For the OP (@CheatingBoy6890) I would say that:
1. The Flipsky 450 is more than enough if your expectations are set accordingly. It's about three, possibly four times the power that is needed to hit 40mph on a small EV like this. For decent acceleration on a gokart, it's probably about right.

2. If you want more power (who doesn't ) get a Fardriver (cheap, non-VESC though) or a 3shul (expensive, VESC).

 

[Zambam]

Is this cheap controller from the iScooter i12 FOC type? The manufacturer says it is, via an email response to my query. There's a 48 pin MCU. There's also a shunt that you can see in lower right corner of the circuit board pic.




The harness from the motor shows (from top to bottom), phase wires (yel, blu, gn), single white wire (1 pin connector), then 5 wires to 5 pin connector. Is this info useful in determining whether it is FOC or not?

 

[CheatingBoy6890]

I think you are right. Shunt-modding really isn't something you do to an (kind of) expensive ESC. I thought of doing it, because I read people use the FSESC75450 with phase currents as high as 600A or more. But the shunts can only measure up to 550A or so. My thoughts were that the FETs are capable of more current but the measuring hardware isn't able to get accurate values. When modding the shunts say to half their original value and custom firmware (shouldn't be to hard for a VESC, I think), I could release the full potential of the hardware.
But cheap ESCs probably don't have much more potential in them than written on the outside.
Besides I'm busy trying to get the ABI encoder to work.

 

[CheatingBoy6890]

I had to open up my ESC because it is fried. I guess you get what you pay for on Alibaba. However my shunt-mod idea doesn't seem to be that stupid because the manufacturer actually has left two shunt slots without a shunt. My guess is that the same ESC (same transistor board, different Control-Board) is sold as FT85RS with a 550A rating.
So if I am able to fix this ESC I can also add one or two shunts per phase to allow for higher current sensing.

 

[forcefed86]

None of those motors IMO, if you have sleeves on the drift cart. You need little to no power to blow the back wheels off with sleeves. Run something super cheap and easy. 1020 motor is MORE than enough. My drift cart with a 6.5 briggs was way too much. it was 10x more fun with a 3hp motor on it. Same with EV. No need for power when u have little to no traction out back.

 

[CheatingBoy6890]

I mean I've already got a QS180. I'll probably have to turn back power in software.

 

[forcefed86]

Or keep that for something fast an not a drift project.

 

[scianiac]

I don't fully understand the logic of thinking about shunt modding a controller you just blew up. Sounds like a great way to immediately blow it up again. At these current levels the Mosfets are not the problem, sure they can probably handle a ton of current and they probably did not blow from too much current or overheating. They blew because it's a shit ESC design that can probably barely keep the current stable, adding more shunts is only going to make the probably barely passable current sensing worse. With these cheap VESCs it's down a lot to luck and tuning skill. You get lucky your motor and tune runs stable at very high current or you spend a lot of time tuning it so it runs stable.

Technically you can't just install a no limits firmware and change the current to whatever you want, you'll run out of ADC range at some point. Technically a shunt mod gets around this but also decreaes the current precision at the same time which makes it harder to run well. I also think you may need to change the firmware so it knows you changed the shunts but not sure on that one. More importanly though you are shoving tons of current around a poorly designed board which casues all sorts of noise any problems that makes it hard for the controller to run in a stable fashion.