107mph go kart on 28S/18P pack of Molicel P26A

G

garolittle

10 kW
Joined
Mar 3, 2018
Messages
509
Location
Augusta, GA U.S.A
107 mph electric gokart at the dragstrip….

https://www.facebook.com/247184812650883/posts/985572405478783/?d=n

Components:

AC-9 motor from HPEVS
1238E controller (650A max)
28S/18P lithium ion battery pack consisting of Molicel P26A cells connected with .25mm pure copper bus bars (pack assembled by Vextrek in Augusta, GA)
Thunderstruck BMS and Charge Controller
 
Possible to show a vid that is visible to non-facebookers?
 
liveforphysics said:
Possible to show a vid that is visible to non-facebookers?
Click to expand...

Yes sir. It’s actually good to know that not everyone is on Facebook. I need to do the same :). Here’s the last few seconds of 105 mph run.

https://youtu.be/P5kUjMHM3Qs

736035D3-77BE-461F-A410-9FE624755717.jpeg9905CA10-8B84-4619-A0B8-ABD771CAACB2.jpeg5CE75A30-48A9-48D1-AA4E-B8742AACCCE2.jpegD9FA56D0-8630-4E28-AE9D-5AA69FC8F892.jpeg
 
Can you share the 60ft, 330ft, and 1/8th?
 
liveforphysics said:
Can you share the 60ft, 330ft, and 1/8th?
Click to expand...

Yes sir. Here you go. These times were not so good. Going to try a larger sprocket on the rear axle to improve the lower end acceleration. I am still accelerating at the 1/4 mark so I believe I can keep the same top speed and improve the lower end acceleration.
09E2A4F7-0A65-4205-8626-6F67C4D83BEC.jpeg
 
Nice kart! I see a lot of ET to be dropped in shorter gearing my friend.
 
liveforphysics said:
Nice kart! I see a lot of ET to be dropped in shorter gearing my friend.
Click to expand...

I think you’re right. Will try again this Thursday and hopefully will lower the ET. In theory, I could get a slightly higher TopSpeed since I was no where close to the maximum RPMs with the other sprocket. Definitely will keep you guys posted. Thanks so much for all the great info on this forum
 
Hahaha way to go Gary.
 
Last week, we were allowed to race against some vintage and modern two cycles at the Lamar County Speedway in Barnesville, GA recently. Really great group of people. They did not have to let us race but seemed interested in the project so they let us run with them. Hopefully will get to run against some tagged court scenes. Ultimate goal is a 52 second lap time at the Atlanta Motorsports Park in Dawsonville Georgia. Extremely challenging track with a very talented group of drivers.

Here’s a brief video of the Barnesville race.

https://youtu.be/mvEb7VQAIZk
 
When it comes to aero improvements, the back half is as important as the obvious front half.

I'd look at the "aero civic" website where builders try to improve gas mileage. Take their optimum shape and squish it a bit flatter...
 
spinningmagnets said:
I'd look at the "aero civic" website where builders try to improve gas mileage. Take their optimum shape and squish it a bit flatter...
Click to expand...

Excellent idea. Really appreciate the suggestion. Will do.
 
Hillhater said:
Here is an example of a “lay down” aero kart..
https://i.pinimg.com/originals/9b/d6/f3/9bd6f31122e77b322aafe1d49ba96655.jpg
Click to expand...

Now that is what I call “low wind resistance”. Nice!!
 
Update: 110 mph but still slow on the 60ft and 1/8 mile times. Will try a 2-to-1 sprocket ration next time. Thanks for all the good advice from this forum. 👍 7F49F4FB-07A0-4943-BEC1-9DA00C51C263.jpeg
 
Great job getting faster! Your trap speed shows you've got the HP/weight ratio of an 11sec vehicle.

The 60ft time is around the 15-16sec vehicle range.

The most time critical part of the track to have speed is at the beginning of the run, this is because you spend so much time there.

From the 1/8th to 1/4 you spent 4.459sec and gained 22.7mph
This is impressive but it's got surprisingly low ET impacts.

The 2.503sec 60ft should be ~1.8ish with your HP/weight.
Time shaved to the 60ft plays out at about 3x that amount off your ET.
The good news is, getting a 1.8 60' should shave about 2.1sec off your ET, and should run 11s.

Do anything you can to hit the tires harder from the line. Some controllers have slow ramps programmed, fix that if it's a factor. Pre-load with locking your brakes on the line and build torque with throttle holding still, and release the brakes to launch.
 
liveforphysics said:
Time shaved to the 60ft plays out at about 3x that amount off your ET.
Click to expand...

This is great information. Turns out it’s very true. The one time I managed a sub-1.9 second time at the 60 ft. mark, it had a significant impact on the total 1/4 mile time. Thanks so much for the info. Starting to make sense now. 👍 1EE44A6C-D8BB-4965-B33B-8D15C90D274C.jpeg
 
Thinking of drag racing like rockets helped me the most. A big enough starting impulse let's you coast from there to a very low ET.

You really want to deliver HP sooner than later. My old drag crew chief for ICE racing used to tell me to hit the tires like you're dropping a house onto your axle. It took a couple years to understand what he meant exactly, but when you're in a prepared dragstrip, the tires couple power better when shocked hard and in a dynamic friction transient. You gotta overwhelm the tires, but only by 10-20% slip rate, and your couple for maximum thrust. The longer you can hold that slip rate from the starting line, the lower your ET, because what happens after that just isn't occurring for that long.
 
liveforphysics said:
Thinking of drag racing like rockets helped me the most. A big enough starting impulse let's you coast from there to a very low ET.
Click to expand...

Thanks. It’s starting make sense now. A few years ago I had a less powerful kart and I remember gearing it for the best 1/8 mile time possible. I was shocked that it actually gave me the best 1/4 mile time as well (at a much lower top speed). That proves you can “coast” to a lower ET just like you said. Excellent explanation. Thanks 🙏
 
Really pleased with how the Vextrek pack remains well balanced even after wide-open throttle tests in high ambient temperatures. We are using a 28S/18P pack of Molicel P26A cells connected with .25mm pure copper. The pack does not utilize any active cooling techniques and was exposed to 90+ degree (F) heat for several hours during which we pulled 600A - 650A for about 15 seconds each time. After the final test, the difference between the “highest series cell voltage” and the lowest was only 12mV. We hope to reduce the voltage difference even more after allowing the Battery Management System (BMS) to to apply active and passive balancing over time.

5BD5CD4E-C77B-4AD1-ABBF-07741FC5752B.jpeg
 
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