E-Kart
 

My son and I have been working on an electric racing kart for a high school competition.

We got it going the other day for the first time and hit 34 mph on our 35 mph gearing. For the competition it will be geared closer to 45 mph.

It uses a Mars ME0909 motor, Alltrax SPM 48400 controller and 3) 12V batteries in series for 36V. 75# of batteries and 25' of cable.

Still need to finish a roll cage for it.

http://i132.photobucket.com/albums/q...g/874e77f5.jpg

http://i132.photobucket.com/albums/q...g/b8d0abe3.jpg

http://i132.photobucket.com/albums/q...g/0fe6b62a.jpg

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Jay

What blast (on a closed course) your cart must be.
It looks very professional, is it made from a modified gas sucking go-cart ?

Yes. The frame is a "Trick" (now "Trick Olympic") brand 4-cycle kart. The chassis and fairings were donated for the project.

Our work so far involved designing and fabricating a mount for the motor and a system to securely support 75 pounds of batteries.

A roll cage of 4130 chrome moly tubing still needs to be completed.


Jay

Excellent! Are there races? Formula class for the electrics?

The Electrathon (Welcome to Electrathon America) is a national competition with regional events.

Although we tried, we couldn't complete our vehicle for this year's final competition at Road America, held today. The 4130 chrome moly tubing we ordered for the roll cage was delayed, and I still don't have it...

Here's a photo of the start of today's Electrathon competition - (attachment below)

Oh yeah. Electrathon. Modern soap box derby. I studied the art form when my daughter's high school bought a chassis. They never found the money to do anything more than look at it.
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To Bad the electrathons got totally rained out from even showing up on the Saturday I was competing at Watkins Glen. I was looking forward to checking them out. World champ C. Michael Lewis was there navigating in a diesel engine swap Insight. He didn't bring his electric.
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How much loss is there in a wide open controller? One idea I had would be to set your wide open gearing to the predicted average speed and have a boost button actuate a starter solenoid which would by-pass the controller whenever there was no traffic to eliminate the heat loss.

Thanks. My son is going to look into that.


Jay

The live axle and sticky tires are also a little less than efficient in the turns but it will still be a blast to run and get it dialed in as good as it can be.

Looks like great fun there. Too bad you don't get to compete. Next year?

The kart set-up does have a few drawback, which we have tried to address. The solid axle does scrub when turning, but we have thinner tires at a higher PSI to help reduce it as much as possible. It's very noticeable when turning tightly, but the steering geometry is designed to pick-up the inside rear tire to let it scrub less, and we've moved the rear wheels in as far as we can as well. Fortunately the turns are huge and it shouldn't be too big of a handicap. We fitted the motor with a custom clutch so it will coast freely, and it seems to coast very well. There were only 2 cars that carried any amount of cornering speed - the overall winner and the fastest car. Most were very slow in the corners, but with spoked bicycle front wheels you couldn't push too hard. I did see a car in the pits with one of its front wheels folded over. Our theory is to keep corner speeds way up in order to help conserve energy - that's the theory...

The other plan is to P&G on the straights. Bringing it up to max speed (45 MPH @3000 RPMs) and coast down from there. Not sure how far would be the best to coast down to though before full power back up to 45 - maybe 35 MPH?

He really just wants it to be one of the faster cars and not compete for overall honors. Overall honors includes the quality of your monthly and final reports and also requires we add 60 pounds of ballast to compete in class. We will most likely just run Exhibition Class and not worry about some of the overbearing rules.

They have 2 other events besides the RA one. Pretty sure they are both at stockcar tracks. Some of the Electrathon cars have suspension, which would be nice at at least one of the tracks because of the bumpy surface.

I just picked up the roll cage tubing today, and we will continue to work on getting the car completed for the first event after school starts later this year.

Thanks for the compliments and tips.


Jay

Well... it's been a while since I updated this thread...

The E-kart has taken us a bit longer to complete than we expected (like a year) - but it's done! My son was in a full leg cast for 4 months, and had rehab for another 4, so we got behind on the project. The shop that was bending the 4130 Chrome moly tubing last year screwed-up, and didn't get us the tubing on time, but I don't think there would have been any way we could have gotten it all cut and fitted in time anyway.

It took quite a while to notch and fit the cage tubing to satisfy the rules, but it should be legal. We had it professionally TIG welded, and that alone took the welder almost 4 hours.

We added another battery (behind the seat) for 48V, and picked-up another 1000 RPMs and more power. Top speed has been 48 MPH, but that was in the neighborhood. Should be faster on the track's 1mi+ straights.

Here's a picture from today -

http://i132.photobucket.com/albums/q...psdf6d253a.jpg


Competition is this Monday (5/13/13) at Road America. I'll post results as soon as possible.


Jay

Beautiful. What are the rules for the formula you are competing in?

Thanks.

There's a bunch of safety rules that we had to comply with (tubing type, size, and wall thickness and opening size in the cage), but we will be competing in the "Exhibition" Class - hence the "E" designation in our number.

In order to actually compete in class, we would have to add 60 pounds or ballast that needs to be removable so it can be weighed with the driver. Rules say the driver needs to be 180 pounds. My son is 120. There are numerous other rules that would be impossible to comply with using our current set-up.

There's also a max battery weight that we are now over.

To really be competitive in-class we would need a "purpose-built" chassis. My son plans to do some other improvements for next year based on how we do this year, but after that they could use the motor/controller/batteries to power a purpose-built chassis if they wanted to. That would be up to the teachers/advisers. We built this one the way we wanted to in our garage (with plenty of our own money...).

We are planning to keep it at the house over the summer so he can race a few SCCA-type solo slalom races in the area with a couple mods.


Jay

Here are a few photos from the Electrathon competition at Road America May 13/14 2013.

We weren't competing in a class, but we did have the unofficial fastest slalom time, fastest lap time, and fastest top speed at just under 60 mph on the GPS. Last year a team from Canada had the fastest speed at 50 mph using Li-Po batteries.

We knew we wouldn't be competitive in the endurance part of the competition, but did complete 3 full laps - about what our testing predicted. The winning team in the open class with Li-Po batteries did 7. Plenty of vehicles did 6. Coasting was nowhere near as good as some of the enclosed 3-wheelers with bicycle tires, but our cornering speeds were way up. When he was running with the lead pack at the beginning of the event he consistently had to add power to keep up while they were still coasting.

We learned quite a bit about batteries. Some of the top teams are getting 18V from their 12V batteries by deep cycling them. That's a big part of it that we didn't know about or do before the competition.

He was happy after the last heat of the day where he just wanted to open it up without concerns about efficiency. We went with our tallest gearing. He figured he would get one good hot-lap and that's it, but was able to do 2 at full speed. He lapped some of the cars before coming in. We did get a fair amount of compliments on our set-up and fabrication, and the kart was the probably one of the safest and easiest to drive vehicles there.

http://i132.photobucket.com/albums/q...ps509b54ac.jpg

http://i132.photobucket.com/albums/q...psc4a7446c.jpg

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Awesome fun!
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A hot battery is a full battery. The best electrathon class teams use battery heaters and hard charging to run to the car with the race battery still bubbling as they install it just before the race. I believe C. Michael Lewis still holds the record at 62 miles in an hour with his beautiful luge style streamliner.

how about using scooters 10 or 12" wheels and tires next time ?
I can't see them being less FE friendly than go kart items ...

I have seen them use wheels from a Yamaha PW50. Not sure the exact size, but pretty small.

They would require a bit of mods to the bodywork to use, but it's not a bad idea. It would reduce the scrubbing while cornering significantly and I'm sure the smaller contact patch would give better coasting. The small/wide kart slicks are definitely a big disadvantage for rolling resistance and also limit our gearing.

I don't know if he'd go for it though - he really liked the fast cornering!


Jay

Not my project but more efficiency in the drivetrain = more speed ...

I'll be sure to mark that event on my 2014 calendar. You have one of the best looking machines in all the pictures, that has to be worth something, right?

Are you able to put Lexan over the 'windshield' part of the cage? Maybe some underbelly sheeting?

Thanks. We felt good about the performance and execution, even though we didn't really win anything with it.

We have considered a pan and windshield, with a full body pan being first on my son's list.

I'm not sure about enclosing the roll cage and adding a windshield - would it increase the frontal area and create more drag? Seems like it would punch a much larger hole and produce a larger wake - but I don't know for sure.

Thanks for the ideas everyone!


Jay

I agree with you : wind shield like hooked to the bars sounds like more drag to me : you increase S without improving Cx enough.

On the other hand, closing the air path behind the driver does not increase S but improves Cx.

I'm thinking Stiletto2 design :
http://i1183.photobucket.com/albums/...ps8d12d4cb.jpg

But I wonder : up to 45 mph, is the SCx this influential ?
I'm thinking weight, weight distribution and rolling resistance are of paramount importance.
Also, as I understood, the potential for your top speed / acceleration is to be seeked in the controller / batteries area, right ?

I agree - I don't think any minor improvements in aero will be noticeable at our speeds. Min sustained speed is probably around 30, max around 60, average is about 40 (EDIT: My son said the GPS registered 45 MPH average for 2 laps from a standing start), and it's not at the max for that long - less than 20% of the time (maybe more like 10%). Those would be more "speed-run" numbers. To get more endurance you'd need to drop it down from there. The more we drop it down the less of a factor the aero will be.

I think rolling resistance is the major mechanical factor limiting our endurance. Coasting is the key in that area. From what we learned, the biggest gains are in battery capacity. We probably had only 60-70% of the capacity of the top teams even with higher voltage overall. We needed to up our voltage to get more RPMs out of the motor due to our small dia tires and gearing limitations.

The weight is about where it has to be, and we are lighter than most because we didn't add 40 pounds of ballast needed to compete in-class.

Our controller is top-notch and completely programmable via laptop. Motor is also pretty good and commonly used by top teams.

To really be competitive we would need to build a chassis specifically around the rules with low-drag (rolling resistance mostly) being the major goal. Overall, what made us fast held us back in endurance - and the driver has a heavy foot...


Jay