Vextrek Update

Summary: Electric Go kart using a DR Shifter Kart chassis (M99)
Motor: AC-9 from HPEVS (100V)
Controller: Curtis 1238E (650A max)
Battery: 100V/46aHr pack consisting of Molicel P26A cells connected with .25mm thick pure copper

So why post a video of a gas powered kart catching and passing our electric kart? Because this was a test session against a shifter kart at the Atlanta Motorsports Park (Dawsonville, GA). You can not improve unless you race someone faster than you. :slight_smile:

As you can see, the electric kart (Black #6) keeps the lead at first because of its speed on the long straight away. The shifter kart eventually passes the electric kart because of its ability to take turns quicker (less weight) and its acceleration up hill. Since we can not “shift gears”, Vextrek will switch to a higher sprocket ratio (probably 3-to-1 versus the 2.7-to-1 ratio used in the video). Also, we are reducing weight where possible. The electric kart is 305lbs (138 kg) without a driver. Our goal is reduce weight by at least 5 lbs (2.2 kg). Finally, we were only using 90% power in this video. Eventually, we will increase it to 100% power but this will likely require motor controller software adjustments regarding “gear softening” and “max throttle voltage”.

In summary, we identified areas for improvement and we are currently implementing solutions. We like posting our progress and we are always open to ideas. Feel free to message us and thanks for following our story.

Here is the link …

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Thanks for sharing! What kind of lap times are you running with it so far at AMP and what are you targeting?

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Looks like amazing fun. Plenty fast, too.

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Best lap time was 54 seconds. Still have to work to do to reach out goal of 52-second lap times. Really like that track. Very challenging.

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Thanks. Learning more each week. Lots of really long nights in the shop :-).

A few more pics of the electric kart. thanks for all the suggestions from people on this form.




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What kinda of times did it run at the dragstrip? 1/8th mile?

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Have been running 1/4 mile just to see what i can get on top speed. 109 mph at 12.77 seconds. I will find the time slip …. It’s around here somewhere :slight_smile:

Not really relevant from a “go track” perspective since few straight aways are that long. Lots of fun though :slight_smile:

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Whats the weight distribution given the engine and fuel cells?

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Have not had the kart scaled out but hoping to do so before the next trip to the Atlanta Motorsports Park. Not much room to move components around but probably need some caster/camber adjustments. Will definitely post the weight distribution print out when available Picking it up is most definitely a 2-man job :slight_smile:

Here you go…

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And before anyone asks …. No we do NOT have as much electric kart knowledge as Bryan Hall has. :slight_smile: Bryan probably could challenge Elon with his knowledge base :slight_smile: :+1:

LOL. I’m not sure about that, but thanks. He certainly knows more about rockets.

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This is probably a stupid question because i don’t know what your ultimate goal is but…

Why aim for shifter pace? I would think you’d be more likely to sell something that was lo206 or KA pace with bonus that you’d be able to then produce a lighter unit (less power = less weight for similar run time) and people wouldn’t need to shell out on front brakes.

History shows that trying to do something thats too different doesnt sell well, like the wankel engine or the various really fast 4 stroke engines.

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It’s a fair question. The best answer for competing with TAGS and shifters is fairly simple … Because it’s hard. We may end up selling something less powerful but when we saw the electric kart performing well against TAGS we were inspired to compete with a shifter kart. To be honest we may fail (shifters are crazy fast!). However, it’s easy to back off on power and offer something like a LO206. However, competing with shifters is very motivating (and humbling). Short answer … we do it because it’s hard. :slight_smile:

Here is a short clip of Vextrek vs. TAG Masters at the Lamar County Speedway.

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To give you an idea of the difference in energy required between a TAG kart and a 206 kart, Gary has a 46 Ah battery on his kart. For 206, using the same motor and controller, about 40% as much battery capacity is required. Of course that AC-9 motor is overkill for running with a 206, so you could also increase the efficiency more by running a smaller lighter motor in a more efficient window as well as fewer higher capacity (but slower drain) cells.

I agree with Gary in that pushing the envelope is the hard thing to do. You find out what breaks, and learn how to overcome that (such as with his neat welded copper bus-bars instead of higher-resistance nickel). Plus it’s fun. To downsize you still carry over the same design principals and maintain the same reliability, just in a smaller package.

Of course the issue with providing an electric 206 equivalent is that the 206 package is pretty inexpensive to purchase and maintain compared to any 2-stroke motor. Not really a good target market IMHO, but I may be wrong.

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Very well said Bryan. There are many trade-offs at all segments of go karting racing in terms of an “electric kart equivalent”. I agree that the LO 206 market is probably the best series to target in terms of electric karting. That was our original intent and we learned many things. One thing I definitely need to correct was my statement that it’s “easy to reduce the power and target the LO206 market” In my experience, there’s nothing easy about competing with any particular gas powered series. Gas powered go karts at all level have natural advantages over electric but one of the most difficult ones to overcome from an electric standpoint is cost and weight. Regardless of the series targeted, electric karting is always going to be “heavier and more expensive“. It will likely be this way for a few more years.

Very good points about using a more efficient motor and fewer (but higher capacity Lithium cells) for an LO206 build. We’re on our third prototype now and to be honest our performance targets keep moving. It’s a good news story in that the performance has improved over time. However, the moving targets have come at the expense of the corporate pocketbook but I think overall it’s been worth it. Right now I’m in my garage working on a battery balancing issue. I am completely exhausted because I can only start this kind of work after my regular day job… Accountant. however building electric go karts just doesn’t feel like work. Absolutely love it!

Also a sincere thank you to everyone on this and other forums who have provided suggestions. You guys are awesome.

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SS batteries will be the game changing factor - if they can be developed & mass produced.

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100% agree. Solid State batteries would be lighter, safer, and charge quickly. Not sure when they would be available but that would be awesome. :slight_smile: