Electric goKart for SCCA solo2/autocross

Hi all,

I'm new to these forums and hope this is the proper location for this post.

I'm looking into building an electric kart for my 9 year old daughter to use in our local SCCA solo Junior Kart program and hoping to tap into the knowledge base here.
My current plan is to use the following Motor: Mars ME0909 PM pancake motor. http://www.cloudelectric.com/productdetails_popup.asp?productcode=MO-PTX-0909

One of the requirements I have set for myself in this build is to have the capability to remotely(I'm into RC planes and cars, so I have the transmitters/receivers) shutdown the kart in the event of an emergency. Preferably being able to use regen braking to quickly slow it down and not just cut all power allowing it to coast. I called Alltrax and spoke to tech support and apparently they do have a controller that I could make work by remotely activating the key switch, and the controller would go into regen braking, but it only works on shunt motors like the D&D, but those may be far to heavy and a bit over my overall budget. I couldn't find a number for Kelly Controllers, but I think they may have something that would work with the Mars Motor above. Any ideas?

Ok so that is my basic question, if you would like some more background info feel free to continue reading below.

For those that are not familiar with autocross... well I think wikipedia describes it best.

An autocross is a timed competition where drivers navigate one at a time through a temporary course marked by traffic cones, rather than racing on a track with multiple other cars, as in road racing or oval racing. Autocross tends to place more emphasis on car handling and driver skill than on sheer horsepower, and events typically have many classes which allow almost any vehicle, from economy sedans to purpose-built vehicles, to compete. Speeds are slower in absolute terms when compared to other forms of motorsports, usually not exceeding highway speeds, but the activity level (measured in discrete turns per minute) can be higher than even Formula One due to the large number of elements packed into each course. Autocross courses are typically 40 to 70 seconds in length, with speeds limited to 70 mph for insurance purposes.

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Currently the SCCA Junior Kart classes only allow a limited set of gas 4 and 2 stroke motors, namely the Yamaha kt100 and the Briggs and Straton World Formula. To keep speeds down restrictors or smaller carbs are used, but the kids still can get speeds up to 40 mph in FJB (9-11 year olds) and upwards of 50 mph in FJA(12-14 year olds). I would like to keep the electric motor on par with these gas engines as the ultimate goal here is to get the SCCA to allow two new electric kart classes. So parts need to be off the shelf and readily available and at a reasonable price. A Briggs and Straton World Formula motor that is race ready runs about $1000, so I've set that as my budget for Motor, Controller, and other misc items minus the batteries. Of course if I can come in under $1000 even better as this would probably appeal to more parents in our sport. I think this format of competition is ideal for an electric kart because we only need enough battery power to make four runs. Each run rarely goes over 60 seconds in length so total run time per event is maybe 5 to 6 minutes.

Here are the weights I have to work with. A rolling kart chassis minus engine and fuel tank comes in at around 105 lbs. The rules for FJ classes stipulate a minumum weight of 250 lbs with driver. My daughter weighs 60 lbs. So that gives me 85 lbs to play with. The Mars ME0909 weights 24 lbs, a 300 amp Kelly controller 6-10 lbs? That gives me 50 lbs for batteries. I'm not sure I want my daughter surrounded by heavy AGM, or SLA batteries at 12 to 20 lbs each. Instead I'm thinking of the same Lipos I use for my RC airplanes. HobbyKing has some 6S1p 8000 Mah batteries that weight about 2.5 lbs each. Four of those setup as 12s2p at 16AH would weigh 10lbs. After 6 years of flying with lipos in my planes I think I could comfortably come up with a safe way to use them in my daughters kart.

So that is my novel, If you read all that I really appreciate it and would welcome any advice you may have.

Thanks,

Paul

So my main objective is to be able to accomplish this safely.

Hi turt1e, Welcome to the forums.
I hope you can get approval to run an electric kart in autocross, its the ideal situation to use electric power...
. IE, low speeds, high torque , and short duration.
With your experience in RC and LiPo, you are in a good position to make it work well.
I suspect your problem will be finding a suitable controller, and battery package within the cost limitations.
I am not an Expert on these sized motors, but i know the Agni 95r motors have been preferred over the Mars units for various technical reasons, such as heat dissipation, and i seem to recall controllers can be tricky to find a suitable unit at a sensible price.
Kelly certainly do regen controllers though. This may be a useful link.
http://www.mavizen.com/build_your_own/parts.html
I will try to find you some info..
Cheers

Hillhater said:

Hi turt1e, Welcome to the forums.
I hope you can get approval to run an electric kart in autocross, its the ideal situation to use electric power...
. IE, low speeds, high torque , and short duration.
With your experience in RC and LiPo, you are in a good position to make it work well.
I suspect your problem will be finding a suitable controller, and battery package within the cost limitations.
I am not an Expert on these sized motors, but i know the Agni 95r motors have been preferred over the Mars units for various technical reasons, such as heat dissipation, and i seem to recall controllers can be tricky to find a suitable unit at a sensible price.
Kelly certainly do regen controllers though. This may be a useful link.
http://www.mavizen.com/build_your_own/parts.html
I will try to find you some info..
Cheers

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Unfortunately the Agni motors are just not in my budget at the moment. I'm trying to approach this build as an alternative to the current gas karts so spending $2000 for an Agni + Controller just doesn't make sense when a World Formula motor can be had for $1000. I want to be able to go back to the SCCA kart community and say "For $1000 I was able to setup an electric kart with these easily attainable parts, lets make a new class around this". The batteries I see as an extra expense, just like fuel is an extra expense on a gas kart.

I guess what I really need is some ideas for is how to setup a remote kill switch. I thought of using something like this Electronic PWM Controlled Relay but being only 24 amp and up to 30 v I'm not sure if I could wire this in somehow. But this still only shuts the system down and would still allow the kart to coast at speed. Ideal I would like some way of remotely applying regen braking into the equation as well. I was hoping there may be a controller available out there that would allow it to be remotely controlled for some features.

Thanks for the reply,

Paul

Forklift motor! Cheaper than agni. Really heavy but can power small cars and can be overvolted.

I understand your motives for keeping costs down,.
This Kelly controller may suit your needs.
I believe it says regen/braking switch input is available, and a good price.
http://kellycontroller.com/kd7220024-72v200aseriespm-p-48.html

You have RC knowledge and your not looking at the large airplane motors, ie turnigy 80-100 or even the smaller one 63-74...why?

Min weight of the go kart is 250lbs meaning even just one of the smaller motors like the 63-74 with a go kart CVT will rocket the kart from 0-40mph very fast, even without the CVT and just a clutch. That little motor has ~4-5kw of peak power, same as the gas engines. You start talking about the 80-100 and a 9yr old child will have a grin from ear to ear

Seeing as we're all trying to find new sellers of the 80-100 motor your best bet for a kart that decimates all comers in the short term is 2x 63-74 200kv(http://www.leaderhobby.com/list.asp?type=searchlist). a pair of Castle creations HV controllers(any 12s controller would be good, castle just has a reputation for surviving) = same rpm or close enough to a stock kart so easier to gear etc. Mount both motors on the same shaft. Link the shaft into a CVT drive system with a clutch setup for ~1000rpm engage and the kart will launch very well and make full use of the gears.

Motors plus controllers should be ~$500 shipped.
misc fab work $200
Batteries for 6min run time 6/60x4kw = 400wh. http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16706 Each pack will have 100wh, if you buy 6 for $350 and you will have plenty for your kid to have a ball

http://www.youtube.com/watch?v=vwODx028_Jw&feature=player_embedded this on a smaller scale, get a clutch designed to handle to torque too

fizzit said:

Forklift motor! Cheaper than agni. Really heavy but can power small cars and can be overvolted.

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I did look into forklift motors, but way more weight than I want to put on a kid kart chassis. Also, probably way more torque than a 9 year old should have starting out.

Hillhater said:

I understand your motives for keeping costs down,.
This Kelly controller may suit your needs.
I believe it says regen/braking switch input is available, and a good price.
http://kellycontroller.com/kd7220024-72v200aseriespm-p-48.html

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Actually that's a nice find. $199 seems reasonable, although the 80amps continuous is worrisome. Having no good idea of how many amps the Mars ME0909 will pull under my application, I was thinking of going beefier on the controller. I keep getting the impression that the Kellys pop pretty easy when run near their limit, but that the Alltrax are pretty bullet proof. Is that perception correct on my part?

Bluefang said:

You have RC knowledge and your not looking at the large airplane motors, ie turnigy 80-100 or even the smaller one 63-74...why?

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Haha... yeah I know right! I would love to be able to use one of those outrunners on my daughters karts! If you or any one else can show me a brushless controller that won't fry instantly on a kart without CVT or a clutch I'd probably try one. CVT are not allowed in our Junior Kart classes and I would like to stay away from having to use a clutch. If I'm going to have any luck getting other parents onboard with going electric I need to show that those annoying items they have to deal with on a gas setup are not a factor with electric.

I know all of you mean well, and I'm not trying to shoot down all your suggestions. I really do appreciate the advice. But if I'm going to have any chance of getting an electric kart class formed in our organization I have to approach this build as if I was building a kart for a "spec class". That means I can create a list of easily obtainable off the shelf parts (that don't have to be modified to make work) and describe how they all work together so that other competitors can build the same "spec" kart. Yes, this means I'm not going to have the fastest, most expensive, and bleeding edge electric kart out there, but that's OK since this is just for Junior kids. Believe me if this was for me I would be taking a different approach, as my competition car in SCCA autocross is a Z06 Corvette, so I like performance. But, my 9 year old daughter doesn't need that yet!

Thanks again guys for all the feedback, it is appreciated. Although I still haven't seen any ideas out there for a remote shutdown/slow down system!

Paul

TheSuperKids has a nominally-rated 1500W motor and Crystalyte controller for ~$300. I've bought got the pair; unused as yet. The information I have is that the controller will handle 72V and 55A (~5 HP), which is my goal for it.

Forrest

turt1e said:

Thanks again guys for all the feedback, it is appreciated. Although I still haven't seen any ideas out there for a remote shutdown/slow down system!

Paul

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Even without regen, a geared ( 5:1 ? ) dc drive will have a lot of "off throttle" drag that would slow the kart pretty quick.
so a straight forward RC operated throttle control voltage (5v) cut out switch would work .
Have you asked Kelly ?

Yeah don't you keep the tire pressure low for grip? It doesn't seem like they would coast very far in the first place, and it doesn't seem like a good idea to throw your daughter into a panic stop without her having control over it.

McDesign said:

TheSuperKids has a nominally-rated 1500W motor and Crystalyte controller for ~$300. I've bought got the pair; unused as yet. The information I have is that the controller will handle 72V and 55A (~5 HP), which is my goal for it.

Forrest

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Now that is an interesting find. Do you know of any threads were people have used that setup? 55A on the controller seems a bit hard to believe. My RC planes are pulling 40 to 50 amps and those don't have near the loading that this 1500W motor and controller would be seeing with a kart that weigh 250lbs minimum. But man that would almost be the way to go if that controller really is able to handle it.

Hillhater said:

Even without regen, a geared ( 5:1 ? ) dc drive will have a lot of "off throttle" drag that would slow the kart pretty quick.
so a straight forward RC operated throttle control voltage (5v) cut out switch would work .
Have you asked Kelly ?

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Having never built an electric vehicle I really don't know what to expect from a setup like this, so I'm glad to hear that it should have a lot of off throttle drag. It would be a lot simpler to remotely activate a kill switch, rather than having to somehow integrate it with the controller for regen braking. Not needing to add regen braking to the controller would be even better since it would save some money!

And yes, after a little google searching I did finally find a phone number for Kelly, but got there voice mail. I'll give them a try again tomorrow.

fizzit said:

Yeah don't you keep the tire pressure low for grip? It doesn't seem like they would coast very far in the first place, and it doesn't seem like a good idea to throw your daughter into a panic stop without her having control over it.

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I'm not real sure what kind of tire pressures the karts run, but I do know that they are not low enough to cause less rolling resistance. We reducing tire pressures on a race tire either to compensate for the heat buildup from the initial turns of the course or to insure we have an even contact patch across the width of the tire. And sometimes we increase pressures to keep the tire from rolling over on to the side wall.

And yes you are correct that it would not be a good idea to cause a panic stop situation. My goal would be a gradual deceleration in a safe manner. Guess I'm just going to have to decide on a motor and controller combo and start testing!

Thanks again guys,

Paul

turt1e said:

fizzit said:

Yeah don't you keep the tire pressure low for grip? It doesn't seem like they would coast very far in the first place, and it doesn't seem like a good idea to throw your daughter into a panic stop without her having control over it.

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I'm not real sure what kind of tire pressures the karts run, but I do know that they are not low enough to cause less rolling resistance. We reducing tire pressures on a race tire either to compensate for the heat buildup from the initial turns of the course or to insure we have an even contact patch across the width of the tire. And sometimes we increase pressures to keep the tire from rolling over on to the side wall.

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Generally for the short Autocross runs in a low powered kart (<20bhp) , the tire pressures will be higher than normal ( 15-25psi ) in order to get heat into the tires quickly for grip. Cold kart tires are like running on ice. Tire warmers are not allowed i think ?
Sprint karts running 15 min or more races will run 8-12 psi depending on track temp.

Did you consider to switch the motor windings to a braking resistor? It'll not be a "controlled" braking, but you could check some resistor values untill you get your desired emergency braking curve.

Hillhater said:

Generally for the short Autocross runs in a low powered kart (<20bhp) , the tire pressures will be higher than normal ( 15-25psi ) in order to get heat into the tires quickly for grip. Cold kart tires are like running on ice. Tire warmers are not allowed i think ?
Sprint karts running 15 min or more races will run 8-12 psi depending on track temp.

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That is essentially what I do with the Corvette on hoosier race tires. Run them at 32psi front and 28 rear for an autocross, and about 4-5 psi lower if doing a track day. And you are correct active tire warmers are not allowed in SCCA autocrossing. However, tire blankets to help retain the heat you have acquired from prior runs are allowed.

Vaquer said:

Did you consider to switch the motor windings to a braking resistor? It'll not be a "controlled" braking, but you could check some resistor values untill you get your desired emergency braking curve.

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Actually that is an excellent idea! I had not thought of doing it that way. What size braking resistor do you think would be appropriate for a 4kw motor that could be pulling upwards of 100amps?

Thanks,

Paul

Ok guys one more question for you. Even though this Kart will be a 48 volt system, I'm thinking it would be nice to go ahead and get a 72 volt capable controller. Now if I do this and get the 72 volt contactor plus precharger & diode will I still be able to run the system at 48 volts using a 72 volt contactor?

Depends on what controller, the Kelly controllers are all capable of being run from 18v to there max V IIRC. not sure about alltrax, curtis etc...

If you're trying for a budget setup from easily attainable parts I would at least take a look at the brushed scooter stuff. Efficiency isn't a concern when its a single one minute lap. I think the 60v 100a amp scooter parts would be enough to have fun with for kids. How much does a 12 year old weigh? What kind of power do the gas karts make?? Ask mcdesign if he thinks the brushed stuff is too weak for his kid..

Ok guys, here is an update of where I'm at.

I pulled the trigger and went ahead and ordered a conversion package that Carl over at EVdrives put together for me right at $900. Here is what just came in today.

Mars me0909 motor
Alltrax's new SPM 48300 controller.
curtis PB6 throttle box
MZJ 200d 48v contactor and precharge resistor
250 amp fuse holder
24 ft total of 4 awg black/red wire and 8 lugs
two 175 amp Anderson quick connectors

So I'm pretty close to my $1000 price that I wanted to stay at, but will still need to fabricate a motor mount, and a few other small pieces like an on-off switch with a light, and an emergency kill switch.

As far as batteries go, I'll initially be using 4 AGM style batteries that weigh 12 lbs each, just because I have access to about 20 and they are free. But I've already ordered 4 of the Turnigy 8000 mah 6s1p batteries from hobbyking and they are sitting in customs according to USPS tracking. Still not sure about using the LIPOs though....

vanilla ice said:

If you're trying for a budget setup from easily attainable parts I would at least take a look at the brushed scooter stuff. Efficiency isn't a concern when its a single one minute lap. I think the 60v 100a amp scooter parts would be enough to have fun with for kids. How much does a 12 year old weigh? What kind of power do the gas karts make?? Ask mcdesign if he thinks the brushed stuff is too weak for his kid..

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I thought about using the brushed scooter stuff, but it just didn't look like they could match the performance of the gas karts the kids run. The gas motors make from 5hp to 15hp. My daughter will be 9 in November and weighs around 54 lbs. I'm trying to keep the kart with driver at around 250 lbs. I may find out that this Mars me0909 motor is way to much power, which would be nice because then I could just turn down the power with the controller. If that turns out to be the case then I could start looking at the scooter motors. Actually I may still do that because now my other daughter who is 6 years old now says she wants her own racing kart!

Farfle said:

Depends on what controller, the Kelly controllers are all capable of being run from 18v to there max V IIRC. not sure about alltrax, curtis etc...

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Actually I understand that part. What I was asking earlier though was about the contactor. For instance if I decided that 48v is too much power and I want to step it down to 36v system will I have to change out my 48v contactor? My guess is yes I will. I'm thinking that if I run it at 36v then there may not be enough voltage for the contactor to open and close reliably? I was just hoping I could avoid having to buy multiple contactors in order to test the system at different voltages.

kidsonroll said:

Go karts are usually gas type or the one that needs gas in order for one to work. With the innovation of technology some go Kart Company created the electric go karts. These karts run with the power of electricity and produce no smoke at all. Here are some of the advantages and disadvantages of electric go karts. The advantages of electric powered go karts are that it is safe, which is suitable for children and chances for rollover is less. Another is less maintenance cost because it has less mechanical parts.
8)

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Uhhh.... ok.

So what happened to this project?