Gas Beating Electric Race Kart

Intro: Gas Beating Electric Race Kart

Invented in the 50's and race tuned over the last 60+ years, the kart is the training ground of F1 drivers and the simplest and purest driving experience on 4 wheels. What could make it better?

Arguably the weakest link is the noisy engine that needs regular and expensive rebuilds to keep it competitive. Why not keep the finely tuned frame, wheels and steering and replace the motor with something modern.

To improve on the experience and excitement of the original, the electric go kart will need 20+HP, a light weight battery pack and a minimum 20 minute ride time between charges. Here's how we did it....

Video of Kart being put through its paces

STEP 1: Choosing an Electric Drive

A rotax 125cc gas powered kart engine puts out 21kW (29hp) at 11,500rpm and 21Nm at 8750rpm, weighs 24kg (60lb) and costs around $3,500 rrp. To keep the gas karts honest we need an electric motor and battery pack that is not too much heavier to keep the handling sharp and a power output of at least about 15kW. With a much higher torque output and a wider torque band, an electric motor with a slightly lower power output will beat gas in pretty much every situation except top speed.

A popular high output, smallish electric motor is the Motenergy (previously Mars) brushless motors. We thought they were about the best electric equivalent to Rotax, so we selected the ME1114 which will deliver over 20kW (27hp) on 78V, a peak torque of 98Nm at 0rpm, weighs 16kg (22lb) and costs around $900. A cheaper option is the ME1117 with 20kW peak weighing 10kg and costing about $600.

You can get high power RC model motors with euiqalent power ratings that are lighter and cheaper, but the Motenergy motors will reliably run all day in a small electric vehicle, where as the RC model motors need to be derated for gokart use and are more prone to overheating and failures.

As well as the motor, you still need a controller and a battery pack. We're using a brushless PMAC (permanent magnet alternating current) motor which means instead of brushes, you need an electronic controller to turn the coils in the motor on and off. These give greater efficiency, power, control and reliability in a very compact package, but they do require a more expensive motor controller which is likely to be at least as expensive as the motor. In this case we are using a Sevcon size 2 controller which is reliable european brand and is fully programable which retails for about $700.

So for about half the price of a new Rotax motor, ($1600) we can buy a new electric motor and top spec controller with a similar power output to the Rotax.

STEP 2: Battery Selection

The battery pack for the kart comprises 24 Headway cells, weighs 12kg (26lb), has a nominal voltage of 78V and a peak current output of 300A

The battery pack needs to be matched to the electric motor to ensure we can get the maximum output from the motor, we don't damage the battery by drawing too higher current and provides a reasonable range.

To keep the performance in line with gas karts, lead batteries, although being cheaper are not going to cut it. Apart from affecting the handling with their weight, they will also blunt the power output of the motor. This is because lead acid batteries are not only much heavier for their storage capacity compared to lithium, but they also have much lower peak current outputs, this means that we will need to size a much larger battery pack size so that it can handle peak current bursts. And lets face it, we don't carry around lead acid batteries in our phones. Lithium batteries are the obvious choice. I will leave to other websites or instructables if you want further info on battery types.

There are a few different lithium battery formats available including pouch cells (common in RC models), large format prismatic (usually used in car conversions), 18650's (this is the AA of lithium cells and is found inside the 18v Makita Li-on battery and other cordless tools or headway cells. Pouch cells can be ok, but are more prone to damage and it's harder to be sure of the quality. They can be the cheapest option, but probably the riskiest. The large format cells are not suited unless you are racing enduros as they do not have as high peak discharge so you will end up with a pack that has much greater range (or kWh) than you need for a the required peak current capacity. 18650's and Headways have similar power density and are both suitable, but the headway cells are a lot larger so you will need a lot less of them, making for a simpler battery pack.

There are a couple of different size Headway cells. We selected the 15Ah 40152 cells which are 3.2V, 15Ah capacity and can deliver a 300A pulse. At $30 each the 72V battery pack (to suit the Motenergy motor) requires 24 cells and costs $720. The battery pack also requires battery management and a charger, so the total pack cost was around $1000.

All up the battery pack weighs 12kg or 26lb (480g per cell)

STEP 3: Building the Battery Pack

78 Volts DC from this battery is unlikely to harm you if you touch it with your finger but don't connect them to your jewellery, pacemaker or little brother. These cells will deliver huge currents if you short them out so be very careful not to accidentally short them. They will melt tools, cause nasty burns and can self destruct. Have a system in place to ensure you do not drop a tool or a tool across terminals of the pack and insulate your tools just in case.

Building a lithium battery pack is not difficult if you head the above warnings, go about it systematically and purchase a suitable battery management system. The battery management (BMS) can be daunting but you need it to avoid damaging your battery pack and to prevent the risk of a battery meltdown. The BMS monitors and limits charging currents, peak current draws from the battery pack and may also monitor the temperature of the pack, thus protecting your cells and leaving you to race your kart as hard as possible without worrying about your cells and we would recommend BMS as essential.

To build the pack, all you need to do is to connect each battery in series, i.e. positive to negative with a suitable connector. Our battery supplier, EV Power provided terminal lugs and plastic clips with the batteries to connect the cells together and the batteries come with screw terminals, so the first step in assembling the pack is as simple as clipping and screwing 24 cells together. There were a few decisions to make such as what was the best way to package the cells, a task reminiscent of using lego and finding the best way to package the power bricks together and fit them on the kart.

After connecting the cells together, the battery management will need a connection to each cell. The instructions for this will come with the battery management board that you are using. The BMS board from EV Power that we were using required one wire be connected to each positive cell in the correct order, so we started from one end and connected each wire in turn to the next positive terminal in a methodical fashion to avoid confusion and mistakes or ending up with a large tangle of wires.

The photographs show a BMS cell connector that was used in the pack for this kart. There is also an example wiring diagram for BMS (for a smaller capacity system than we used on the kart) showing connections to cells, charger and motor.

STEP 4: The Controller

We are using a brushless motor so we require a suitable brushless motor controller. The controller takes 78 volts power from the battery pack, a 5v input from a throttle and inputs from position sensors in the motor (often referred to as hall sensors) and delivers power directly to the coils in the motor, rapidly switching the coils as the motor rotates.

The controller selected for the kart is a Sevcon Size 2 controller. Sevcon make a compact and reliable controller that is highly programable and the size 2 controller can be configured to 78V and will deliver up to 180A. We are running the motor within the 14kW capacity of the controller and a fair bit less than its 20kW+ peak that the motor will produce.

The Sevcon controller was sourced from EV Power along with the battery and motor and cost just under $700.

STEP 5: The Chassis

This project is about building an electric drive train and fitting it to a Kart.

There are heaps of good second hand gokarts out there for under $1000, cheaper without an engine. We are using a sprint kart which originally ran a 100cc Yamaha J class engine for this project, but any style of Kart is going to go just as well with an electric drive train.

STEP 6: Putting It Together

Putting it together just involves mounting the electric components on the kart chassis; motor, battery, controller and wiring it all up.

Motor

The electric motor has a face mount where as a standard kart frame has a foot mount for the motor. To mount the motor a 90degree angle bracket was made out of 8mm aluminium plate. One side bolts to the motor, the other bolts to the motor mount on the frame.

A small auto timing belt pulley (toothed belt) was fitted to the motor and a large pulley was fitted to the rear axel bolted up to the standard gokart sprocket carrier. It would be possible just to keep the regular kart rear sprocket and fit a chain sprocket to the motor, but chains are more noisy than a belt and we didn't want the quiet buzz of the electric motor drowned out by chain clatter.

Battery

The cells were assembled in two rows sitting vertically and a clear acrylic box was made to fit them in. The battery box was just thin enough to fit in the space between the kart seat and the side pod and was bolted to the kart frame using aluminium brackets front and rear. It is taller than the side pod so it sits higher and can be easily seen in the kart.

Controller

The controller bolted to the frame of the kart just in front of the motor and a small box in front of the controller houses an on/off switch, forward and revers switch an contractors. The controller has a power feed in from the battery pack, inputs from the battery management (BMS) which can turn the power off if the batteries run too low (or any other battery fault is detected), input from the throttle and sensor inputs from the motor. Three heavy gauge power wires connected directly to the motor.

Probably the most complex part is building the battery pack. Bolting the cells together is easy, but there are 24 BMC cell connectors that must be installed across each cell. Its not that difficult, but you do need to be very careful to follow the wiring diagram correctly or you will damage your BMS.

Throttle

The throttle cable that normally goes to the carburettor in gas kart is attached to a throttle pot or electronic throttle (see photo). The electronic throttle has a +5V input from the controller and puts out a 0-5V signal back to the controller.

Big Red Button

The big red button is attached directly to the battery pack and can isolate the pack in the event of anything going wrong.

Contactor

The a small on/off switch in the kart doesn't directly switch on the power to the controller and motor. A small switch operates a contactor (large amperage relay) which switches on the power. The contactor enables low voltage switching in the BMS to turn off the power if required to protect the batteries.

STEP 7: Cost Summary

A frequent question on Instructables is what does it cost, so I've summarised the costs below.

Second hand race kart - varies a lot but you should be able to pick one up for under $1000 without an engine.

Kart $800

Motenergy motor $900

Sevcon size 2 controller $700

24 headway cells $720

BMS $300

Contactors, switches and wiring $150

TOTAL $3,570

STEP 8: The Future of Karting

Racing Karts can be expensive to run with frequent engine rebuilds to stay competitive. With the electric karts other than the obvious no need for fuel and oil, the motor requires virtually no maintenance.

The battery pack installed on this Kart will be good for racing for around 45 minutes and the lithium cells will be good for up to 1000 cycles. It can be recharged in 30 minutes and if you absolutely can't wait 30 minutes for a recharge, a second battery (worth about $1000) can be easily swapped over.

Some controllers such as the Sevcon have the ability to program or tune the motor, but it is not the same as a gas kart which needs precise tuning of carburettors, exhaust, air intake, valves and timing to stay competitive. Tuning an electric motor involves plugging the controller into your computer and fine tweaking the torque delivery curve, throttle and regen mapping, so you spend more time having fun in an electric kart.

Karting, the Future is Electric.

This Instructable is a collaboration between Roddilkes and Ganhaar. Kart concept and development by Roddilkes. Written and photographed by Ganhaar. Electrical system supplied by EV Power.

Comments

[tkjcan]

Hi, I really enjoyed reading about your original kart build. I have few older gas karts, heavy concession karts with gas engines. I get frustrated by Lack of honesty from these Companies selling conversion kits, and not disclosing that You get very short driving time, which means a mountain of spare batteries, or spare karts to keep even small track going. I am wondering, in these years since you built kart, are there any quality kits that would give 1or 2 hours, more run time before charging? Any help is much appreciated

[Hgcdesign]

What's the gear ratio you used

[Ganhaar]

Hi Sorry if I missed your comment. I don't think I have that info written down and I no loger have the Kart, sorry don't think I can give you that info. You may be able to get a good estimate from scaling from photos.

[Ganhaar]

I can't remember what the exact gear ratio was, about 1:3 I think

[PatrickT4]

How close does this build come to meeting cams specs? This would be a great idea for hillclimb, they take almost any vehicle that applies. I'd love to run an ev kart at hillclimb. Im from brisbane and live right near a really good hillclimb circuit. I reckon if I could build one in the last 12-18months they might just be ready for it!

[JeffR135]

I am working on a electric harness for hang glider. Currently I am working with direct drive brushless motor prop. I would pay for someone to fabricate motor mount / driveshaft and reduction pulley as this go cart. know. Thanks Jeff

[Ganhaar]

Hi Jeff,

Being a hang glider, I imagine you would want the parts out aluminium where possible to keep weight down. I'm not sure where you live, but is probably best to find a local fabricator / machine shop. Maybe even someone who fabricates bikes if you can track down nearby. They may be more used to working in light weight, high strength fabrication than more industrial fabricators. Also boat builders / repairers will usually have skills in fabricating aluminium.

If you can design the parts you want on CAD from a standard thickness plate, you can also get them cnc cut reasonably economically through an online cutting service.

[JimM238]

I am building one like this

where do I source the belt drive parts?

[Ganhaar]

In my region there are a number of bearing suppliers that also stock belts and pulleys. You may also be able to find the parts online. In the US one of the larger suppliers of belts and pulleys is Gates. Try searching for Gates stockists near you and they will prob stock a range of similar drive parts.

Regards

Wayne

[qais04]

live

[qais04]

do you lie in the States?

[qais04]

Ganhaar is this kart going to be for sale any time soon because I`m looking for a kart and yours is a really good choice.

[JimM238]

Hey

Wouldn't the BMS limit the pack potential 150 amp discharge rate to only 30 amps or so depending on the model?

Thanks!

[JBM7]

I also couldnet find a charger designed for 24 cells only 16...

[JBM7]

Can you please give the name of the BMS that you used? I cannot find the one you used...

[Ganhaar]

Tuning is specific to the controller that you use. Various controllers allow varying degrees of tuning. The Sevcon controllers that were used on this project are highly programmable and well supported by factory trained suppliers. I would suggest you speak to your controller supplier and find a manual for your controller.
One of the disadvantages of the cheaper chinese controllers is the limited documentation available.

Regards
Wayne

[mrgw98]

Thanks! I will definitely do that. Just out of curiosity, would you every recommend one that someone were to use one you can not tune?

[mrgw98]

Are electric go karts allowed to be raced with gas go karts?

[Ganhaar]

generally not which explains why there are so few electric karts around. The challenge with getting them more widely adopted is not their performance, cost or difficulty in building them, rather because gokart racing rules have become very tight to maximise close competition and development of driver skills, it means there is no ready racing classes in which to compete.
There are one or two attempts that I have seen to get an electric kart class off the ground, but I think they haven't been that successful yet but I expect that in the next 5 to 10 years you will see a few classes spring up and then a fairly rapid electrification of gokar racing for the following reasons which mirror some recent experiences with motorcycle racing.
1. Cost - in particular running costs of electric karts and bikes will be a lot less than petrol classes primarily on account of avoiding need for costly engine rebuilds. In addition electric motors, controllers and batteries are continuing to get better and cheaper. When a big supplier produces a cheap high performance gokart electric kart conversion kit this will be a game changer.
2. Noise and pollution - reduced noise and no pollution will allow kart racing back into in city areas such big parking lots and closed off streets with minimal disturbance to residents. This will make kart racing much more accessible to casual spectators and lower the infrastructure cost to be able to hold events.
3. Race Management and Safety - May not be so obvious at first but electric kart lend themselves to simple connection into remote management systems. This will enable race organisers a lot more control over safety aspects, with a press of a button all karts could be put in a reduced power mode or turned off when there is an on track incident and power could be ramped up gradually for the start of a race
4. Closer Racing and Handicapping - The more precise control over engine power outputs will allow much closer racing, a common goal of the often elaborate rules in motorsport. This could simplify a lot of the rules and ensure closer racing through a simple device that will ensure everybody in an event can run with the same peak power. It will also allow the same karts to be used with different peak power for different events and age groups. Another interesting possibility foreshadowed by formula E and the modded electric kiddy car event at Maker Faire is the possibility of additional elements to competition including handicapping, power boosts, spectator involvement and online instantaneous race stats, all delivered through wireless electronic management systems.

Things are a bit quiet at the moment but I'm sure the kart racing scene will get really interesting and be revitalised by electric karts and wireless electronics in the near future.

[gravityisweak]

I'm not sure if I missed it or not, but what is the top speed of this kart? Also, how does it feel to put the pedal down and accelerate full throttle in comparison with a gas kart? Thanks for sharing!