EKartGo Project

This will be somewhat of a rambling thread as I work out the details of my first EV Kart build. Please bear with me if I’m not clear or may wander down some rabbit holes as I think/type out loud. LOL. Yes this is less about racing, and more about engineering. I just happen to be an engineer (by degree in telecommunications) that has always liked speed. Competition isn’t that big of a deal to me. I mainly want the adrenaline rush, and building something yourself is always a fun challenge.

In the fall of '18 I was inspired by what Kolme Faasiline had created. Unlike most of the YouTube electric karts out there that have crazy huge battery packs to burn up tires or just go quick in straight lines, his was serious and designed for sprint racing. If you don’t follow his channel and are interested in electric karts you really should:

At that time I had just completed my first year in karting with a “starter” 80cc shifter running in the shifter kart class at the local track (with mostly 125’s). I of course was never as fast, but showed up most weekends and raced at all but a couple where I had issues (carb setup on a really cold day and a faulty coil). Never having experience with small engines (other than lawn equipment) left me frustrated at times with my pit crew of one (me). With perseverance (and some competitors being no shows or at other races) in the end I managed to somehow finish in 2nd overall for the season. While it was fun, the tight parts of the track I found less so than the sweepers and planned to go 125 for 2019 and just run road course tracks. I bought front brakes for that and put them on, but stuff happened early in 2019 that took my play money away, so no racing last year.

But you can always plan right? That costs nothing but time. So could I build an EKart for road races with 125cc speed? Much research and spreadsheet equations later… Short answer - with current battery technology - you cannot. To make the 30 kw / 40.5 HP of power for 32 minutes with the most efficient controller and motor I could find I would need 1,904 cells for an 18.1 kwh pack. Those 18650 cells by themselves weigh about 95 kg. Add to that the battery case, controller, BMS, cables, motor, etc and the weight is crazy. Not to mention the space required for all those batteries. So until battery technology improves energy density greatly, that is a non starter.

Fast forward to this year. With too much time on my hands (TMTOMH) I went back to looking at sprint races and why I disliked them. It was really those miserable slow corners with a shifter kart engine that was rarely in the right rpm. Well, that’s certainly something that is not an issue with an electric motor. Maybe I should give sprint another shot…

I considered which class I should aim for (of course as a non-scoring provisional). Adult TAG class looks reasonable. I’d only need to produce 20.9 kw / 28 HP for 8 minutes, a much easier target. Although I have to use much higher C rate cells that lowers the capacity, it’s not that horrible. That will only require about a 392 cell pack with a cell weight of 18.5 kg. OK, actually two packs - one for couple lap qualy and the heat race. A second for the longer main. A third would be nice for practice so I don’t have to recharge in-between. With all the other required hardware it should now not be only somewhat heavier than a normal TAG setup so given more torque and no clutch slip loss, it should be about equal.

To be continued… have to run a honey do now.

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I’m always keen to see EV kart projects. I did napkin math a few years ago and more or less figured what you did in that you’re looking at 8 min runs or so.

There was a series in California (I think( that ran electric karts as arrive and drive race rentals. Lap times were in between TaG and Shifter. I keep forgetting the name of the series.

Other electric kart topics here (hint we need more): #electric_karts

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Hey Brian I’ve been considering the same fate for my practice kart - 2014 Energy Kinetic.

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@hallkbrdz so it’s still 18650 batteries that are being used? I use these in my vape units. They are insanely powerful but fairly old tech. I assume that these batteries are the only economically viable solution? I think the batteries are usually like 10 bucks for 2. That’s a lot of money for batteries.

Most things are still based on 18650 cells. LiPo technology hasn’t really changed and most people don’t have the scale to justify custom packaging. Even the Tesla Model S batteries are just a bunch of 18650s. I believe the newer Teslas use a 2170 which takes the same cylindrical form, and just makes it a bit bigger.

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Volvo have moved away from cylindrical cells, I can’t speak to the chemistry though.

With 30 to 60 minutes between sessions, is there enough time to fully recharge the batteries?

I’m planning on using 18650 cells, Sony VTC5A cells at this point for this since they have a max 30A discharge rate for a 12C rating. I won’t normally draw more than 3.5A (controller efficiency dependent), but over a very short time of about 8 minutes so it will normally be about a 7.5C use. A “push to pass” feature for short bursts of extra current is certainly an option. Currently looking at a S30P12 arrangement.

A hour, probably. That would be charging at a 1C rate, which is normal. I am planning on making the packs to easily swap so this is not an issue. It would stink to depending on recharging and then having the time cut short such that you could not make the distance at speed. Two packs will probably do it, since I could run pack one for early practice, put it on the charger. Then put on the qualify / short race pack. Then swap back to the first pack for the final.

Of course at tracks that have a lot more entries this would not work with more heat races, but we’re usually happy to have more than a handful in non kid and 206 classes.

While I will miss the engine sounds and lightness, if this is our future, it’s pretty decent. Fast but quiet.

First purchase - the motor. I decided to go with a DHX Hawk 60. It’s a compact liquid cooled motor that should easily output what I need without being too heavy. I believe that liquid cooling will avoid the heat problem with the Zero motorcycle air cooled motors. Time will tell.

Next I need to nail down the controller and get that ordered.

https://www.dhxmachines.com/hawk60.html

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Damn. 74HP peak :hushed:
How much does the motor cost? Looks like about $2500?

consider my interest in this highly piqued!

i think the Hawk 20 costs $2500. The 60 looks to be around $6300!

Though, given the maintenance intervals and initial cost of a KZ2, it might work out?

The thought of having a motor that could last for seasons is a serious boon.

I bought one used for a test session, so I paid significantly less than a hawk20 is listed for. While I don’t plan on pumping anywhere enough power through it to push 74 HP for now, having margin in a part that frequently overheats and leads to derating is good.

That said, getting the rear tires up to temperature on a cold day will not be an issue.

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Just delivered! Yes - that motor will fit nicely once I make a mounting bracket. Now to find a water pump to cool it, a sprocket (and put a keyway in the shaft), a controller to run it, and build the battery pack. Sorry the picture is poor, but I don’t have time to get it out of the garage today.

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Here’s a comparison between the size of the former Honda 80cc 2-stroke engine that makes about 21 HP tops to the Hawk60 that makes up to 74 HP peak, 46.3 HP continuous. It’s about half the weight by itself, although that is without everything else needed to power it.

Still working on the mount design to distribute the torque.

I am intrigued by your propaganda and would like to subscribe to your newsletter. :thinking:

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Possible kart rail mount design

are those the only mounting points that are available on the motor - on that face around the shaft?