Need more help with electric go-cart

Regenerative braking is where instead of using break pads that waste energy as heat, when you apply the breaks it runs a generator (which your driving motor might be able to double as) which charges the batteries. Depending on your setup this may only require adding some electronics, but could also be very complicated.

Multi speed gearing is just like the transmission in your car. You can change gears so you have acceleration at low speeds but you can also achieve and maintain higher speeds.

I run a blog called Workbench Creations here on CR4 about projects myself and others have done. When you are done with this project perhaps you could take some pictures and post a few details on my blog about what you did.

I'll check our current controller and see if it has regenerative braking or if it can be added easily.

I understand that different gears and gear ratios can cause different effects such as higher top speed but less acceleration, so what my students would like to do is create something like a ten-speed uses where you can change gears depending on the competition. Is that something we should look into or not?

We'd love to take pictures and post the project on your site. We'll try and send them in within a couple of weeks.

Thanks for the advice,

Lakeside Physics class

Different motor and axle sprocket sizes may be used

Multi-speed gearing,

These two are the same thing.

The motor will have a speed at which it produces most power, it will also have a speed at which it is most efficient. They will probably not be the same speed.

Choose a gear ratio or ratios for effect you wish to obtain (max power? or max efficiency? or a compromise?)

Surely you must have some basic understanding of gear ratios?...if not borrow a bicycle with gears and ride uphill! Basically ,gearing for maximum top speed will give poorer acceleration. Gearing for maximum acceleration will give a lower top speed.....

The key is...do a bit of maths..and experiment! (You don't even need the cart to learn and experiment with gearing)

(Pencil in all the usual safety disclaimers etc)

Regenerative or dynamic braking .

This isn't something you can easilly build yourself...if it isn't built into your controller, you should forget it.

But...Instead of friction brakes like on a car, the motor is used as a brake. e.g. in simple terms (don't actually do this) disconnect the battery and short out the motor it will become hard to turn...you can try this with a small DC motor as a lab experiment*. Or use the current which the motor drives through the short circuit to recharge the battery.

*Also if you turn the output shaft of a small dc motor (fast) it will produce a voltage which you can see on a 'scope or a mutimeter.

For maximum distance run your motor at it's most efficient speed, don't go too fast as wind resistance is proportional to velocity cubed... decrease your rolling resistance by using narrow hard tyres of relatively large diameter. (dont use these at speed, as they won't have good grip).

My students want to do something complicated (I think at least) where they can shift gears like on a 10 speed during competition. Different gear ratio for acceleration competition compared to speed competition. I'm thinking just have 2 seperate gears and we just physically move the chain from one gear to the other between the competitions. Right now the gear ratio is set for a middle results for acceleration and speed. We'd like to be able to create both top speed and top acceleration though.

We're checking our controller to see if it has regenerative braking or if it can be added easily - if not, I'll take your advice and forget it!

Thanks as always for your great advice,

Lakeside Physics class

My students want to do something complicated (I think at least) where they can shift gears like on a 10 speed during competition.

This would probably be lethal! As the chain could fly off.

Maybe a 2 speed system with sets of sprockets and two chains both permanently on the sprockets but somesort of sliding dog to engage one or other sprocket, as per a 'constant mesh' gear box.It would take a skilled designer/fabricator to make such a system, so unless one is available 'off the shelf', I think your idea is far simpler and safer.

Good luck and have fun

Del

Gears the larger the drive sprocket(motor) in relation to the axle sprocket the faster it will go.

Problem is if too large will have poor acceleration. The motor will labor from start until it gets up to speed. Will all so draw down the batteries if a lot of stopping and starting.

Ways to over come this is by one shifting gears. Two would be a torque converter.

A torque converter is a hydraulic device that indirectly couples the drive motor to the drive gear. Produces a lot of torque from motor speed to increase acceleration. Pretty complicated to build. Expensive to purchase

Gear changer from a ten speed bike could be adapted to improve acceleration and increasing top end speed. Note that the gears on the cart and the ones on a bike most likely of different size. The bike chain being smaller may not handle the forces put on it for any duration. Bring spares.

Most electromotive controller have internal regenerative charging circuits. During deceleration and braking the circuits change the motor into a generator using momentum to charge the batteries

Could you post a copy of all the rules, CR4 will put our 'criminal' minds in motion to see how far the rules can be bent.

This project seems to be designed for wider participation than physics. (stress management, food, maths, etc)

The track should be analyzed to determine the optimum choice of acceleration vs top speed. If the track could be replicated the drivers can test and practise. An optimum drive path must be established. The corners should be flattened as much as possible.

The choice of driver(s): The weight must be kept low as possible without compromising other essential requirements (strength etc). The hunks in the school might not be the best choice for drivers because of their weight.

Changing the wheel or sprocket size may be counter productive. The current performance of the car must be analyzed first to determine improvements.

The current acceleration must be measured for different situations (drivers, gears, slopes etc): I hope acceleration measurement is part of the physics curriculum.

My choice for a track with many curves would be more acceleration and less top speed. (I would increase the driven sprocket sizes and not decrease) the drive path can then be selected for sharper corners. In the race the other drivers will notice the fast acceleration round bends and will follow your race path to their determent.

How about something like this? The motor shaft drives a cone and this cone drives another cone via a rubber (maybe) disk ratio-changer. Depending on where the disk is positioned, the drive-to-driven ratio will change and allow something like a stepless gear changer.

This is highly experimental and I wouldn't exactly vouch for its reliability but it would be a nice thing to study and develop.

You can position the ratio-changer mechanically. The driver would have to have lots of practice to find the right position for every situation though.

This sort of system is very elegant. But getting one going properly takes lots of development and has a poor efficiency. Using bike chains/gearing is cheap, reliable and has higher efficiency. Jeff

getting one going properly takes lots of development and has a poor efficiency

I'm not proposing this for manufacturing. It's just something they can use. I'm not sure if I agree as to its poor efficiency. It looks efficient enough though your definition of efficiency might be different from mine .

Using bike chains/gearing is cheap, reliable

This system looks cheap enough. Reliability is questionable though. If you apply this to cars, it would be more appropriate to computerize its function. All you do is step on the gas and drive (stepping on the brakes is also useful). The computer does the rest. If you do this mechanically (via linkage from driver input), it would take lots and lots of practice to get the hang of it.

Nice one Vuc' that would be fun to try and make make as a wooden mock up!

A bit like the DAF Variomatic, which has a sort of V bet to join two...blimey a picture is worth 1000 words.

Wikipedia have a nice digram if you (Lakeside Phys') care to have a look!

I am sure I saw a limit of $1000 for improvements somewhere but cannot find it now.

I suggested some acceleration test in a previous post. it would be appreciated if the results could be posted. (It may enable better advice).

§ Different motor and axle sprocket sizes may be used (I'm not sure what sizes and could use help here)

You need to know the rated torque and current of the motor, the mass of the vehicle and driver, and calculate the reflected torque on the motor. The motor may be overloaded for a short period of time, but if you're having trouble with the concept of changing sprocket ratios to increase speed, you may have trouble calculating the acceleration of the vehicle and WHEN the motor will no longer be overloaded.

§ Regenerative or dynamic braking may be used (Not sure what this is or why it will help - anyone have info on this?)

Regenerative braking pumps current back into the batteries, thereby offering the potential to run longer.

§ Multi-speed gearing, transmissions, or torque converters may be used. (Not sure what this is or why it will help - anyone have info on this?)

Do you take off in your car at a red light in high gear? If you have an automatic transmission, then it starts off in a low gear and automatically changes to higher and higher gear ratios, resulting in lower engine speed to drive wheel speed ratio. Related to 1st question about matching torque/HP/current to load.

§ Dual-speed switching is allowed (Not sure what this is or why it will help - anyone have info on this?)

If you run a motor rated for 24 volts, for example, on 12 volts, the armature current will be half as much as it would when starting from zero with a given load, which is A way to control how much current is delivered to the motor. Using a large power resistor to reduce current is another way, but wastes energy in the form of heat.

We're still reading all the posts and discussing what we want to do - thanks again for all the posts.

Here are all the rules that were requested earlier (happy reading!)

The objective is to constuct an electric vehicle that matches the following specifications. These specifications have been developed by consultants, advisors, and instructors of EV Master, Inc. and the EV Education Program, Inc. as a result of research, teaching, and competitions. They provide a high standard of safety, reliability, and academic value.

You could use the following approaches:

• Construct a vehicle that complies with these performance and dimensional specifications. Components need not be purchased as part of a kit from EV Master, Inc. Note that a vehicle constructed to compete in this class must be designed from the "ground – up" as part of a comprehesive engineering design process following these guide specifications. Due to the unique nature of the EM-TV and the high loads imposed, modification of a manufacturers' go-kart cannot be accepted. For safety, reliablity, and liability, conversions are limited to racing go-karts. Refer to the E-Kart class specifications.
• Use components provided in the EV Master Teaching Vehicleä (EM-TV) kit to construct a vehicle (All specs. included)

All EM-TVs, regardless of approach used, will be inspected prior to any competition and must adhere to the following rules and specifications.

VEHICLE

1. Vehicle Type

Vehicles shall match all the performance and dimensional specifications of each section of these specifications or shall be assembled from an EV Master Teaching Vehicleä (EM-TV) kit (All specs. Included). As stated previously, conversions of manufactured go-karts does not comply with these specifications.

2. Dimensions

The vehicles shall not deviate from the stock measurements

· Track – center-to-center of tire, front = 37" (95 cm)

· Track – center-to-center of tire, rear = 39" (99 cm)

· Overall length = 80" (203 cm)

· Wheel base = 60" (152 cm)

· Distance from pedals to seat back = 36" to 42" (91 to 107 cm), adjustable

· Weight (minimum, with batteries, without driver) = 300 lb. (136 kg)

Following measurements are for reference and are based on standard 15 x 6.00-6 tires front and rear with 14.6" (37 cm) diameter.

· Ground clearance (minumum) = 4" (10 cm)

· Height – front bumper = 8.75" (22 cm)

· Height – rear bumper = 12.5" (32 cm)

· Height – center of steering wheel = 24" (61 cm)

· Height – top of roll bar = 40" (102 cm)

3. Minimum Ground Clearance

No part of the vehicle shall be less than 2" (5 cm) above the ground with all tires removed from rims (vehicle sitting on the rims).

4. Modifications

All modifications must be designed with safety as the principal concern. Modifications must not interfere with safe operation, result in frame modifications, or pose a safety risk to other participants. All modifications must be described in writing by email to Luis Romo at lromo@EVMaster.com. Modifications will be closely inspected during tech inspection. It will be the discression of the GAEVR staff to accept or reject modifications. To avoid disqualifications due to non-compliant modifications, it is strongly suggested that you discuss your plans ahead of time. Prior to the rally, modifications will be treated in confidence.

No modifications of the basic design and construction or substitution of components will be permitted except as listed here or by specific written permission from GAEVR staff following the procedure outlined above.

· Drive system

§ Single and dual motor drives are allowed

§ Different motor and axle sprocket sizes may be used

§ Regenerative or dynamic braking may be used

§ Multi-speed gearing, transmissions, or torque converters may be used.

§ Dual-speed switching is allowed

· Tires

§ Tire inflation pressures may be varied provided the manufacturer's maximum inflation pressure is not exceeded.

§ Non-standard tires may be substituted – subject to speed, load-carrying, clearance, and design considerations.

· Batteries

§ Only commercially available rechargeable batteries shall be permitted. Batteries shall be "sealed" (valve-regulated) type. The propulsion battery pack voltage shall be a maximum of 48 volts nominal. Total maximum battery weight shall not exceed 100 pounds (45 kg).

· Body

§ Vehicle numbers at least 6 inches high and in a contrasting color shall be displayed on the seat back. It is preffered to also attach number plates or other vertical surfaces suitable for displaying vehicle numbers and sponsors' names on each side of the vehicle. (Consider numbers plates on the battery box lids.)

§ Vehicles can be equipped with body panels or other vertical surfaces suitable for displaying vehicle numbers and sponsors' names on each side of the vehicle.

§ Vehicles may be equipped with body shells provided that:

§ Sharp edges, corners, or protrusions that could cause injury are avoided.

§ Fins, spoilers, air dams, and other aerodynamic devices must comply with the vehicle dimension requirements and not present sharp edges that can be a hazard to drivers and crews.

§ Bodywork, including windscreens, fairings, and canopies must not interfere with driver egress or access to the battery disconnect switch.

§ The driver must be able to exit the vehicle unaided within 20 seconds.

§ The disconnect switch must be operable from outside the vehicle without the removal of any bodywork

SAFETY

1. Roll Cage

The factory-supplied side bars, roll bar, and bumpers (or dimensional equivalent) must be in place. The roll bar must extend above the top of the driver's head and shall be wider than the driver's shoulders. Side bars, designed to provide side impact protection shall run the length of the vehicle at a height greater than the driver's legs. The side bars, roll bar, and vertical steering support post closest to the driver shall be padded with at least ½" thick foam.

2. Fire Extinguisher

Each pit crew shall have at the ready a 2 1/2 pound or larger dry chemical 1A, 10BC fire extinguisher with a positive indicator showing charge, during all vehicle operation and charging. It is not necessary for a fire extinguisher to be mounted on the vehicle.

3. Driver's Seat

A contoured, molded racing seat must be used. The seat shall be mounted on an operable, adjustable seat track to accommodate different size drivers. The seat shall be securely bolted to the seat tracks and seat supports.

4. Safety Belts

A two-inch wide seat belt with standard automotive quick-release buckle shall be installed in the vehicle with the ends anchored to the structural frame as designed.

5. Steering Wheel

A steering wheel with padded rim shall be used.

6. Clothing

It is recommended that drivers were driving suits of fire resistant material that effectively covers the body from neck to ankles to wrists. If such clothing is unavailable, the driver must, as a minimum, be dressed in long sleeved upper body garment and full-legged lower body garment. The upper and lower body garments must meet and overlap. Gloves and shoes must also be worn.

7. Helmet

Each team shall supply their own driver's helmet with a Snell 90 or better rating. The helmet must be equipped with a face shield or separate goggles. A neck collar must be worn.

ELECTRICAL

1. Wiring

All wiring shall be routed to ensure they do not contact moving chassis components. Wiring shall be secured to prevent movement and protected from abrasion.

2. Cables

Cables supplying the motor and controller with traction battery current must be a minimum #6 AWG multi‑strand copper with an abrasion resistant insulating jacket.

3. Wiring devices

All wiring connections, switches, terminal blocks, and connectors shall be designed for the full-rated current of the application (e.g. quick-disconnects used on battery cables shall be designed to handle the controller's maximum current draw.)

4. Shock Protection

All voltages greater than 14 volts shall be insulated and protected from incidental contact. No exposed propulsion battery voltages shall be permitted.

5. Safety Devices

The manual disconnect switch, speed-limiting governor with interchangeable plug, and main fuse must be installed and in proper working order. (It is not necessary to use a speed limiting resistor in the governor plug for competition.) Control circuit wiring should be separately fused with a fast-acting fuse rated rated for 5 amps or less.

6. Traction Battery Fuse

Batteries must be current-limited via a DC rated fuse (250-Amp maximum rating) placed halfway through the battery string such that it divides the pack Voltage in half.

7. Instrumentation

At a minimum, instrumentation shall include means of measuring battery pack Voltage and current while the vehicle is operating. Such instrumentation shall be visible to and operable by the driver. Additional gauges and instrumentation including data loggers and energy meters (kWh or amp/hour) are recommended to help in understanding the efficiency and operation of the electric vehicle. They are not required for competition.

8. Contactors

Contactors or power relays should be enclosed.

9. Batteries

Batteries shall be commercially available rechargeable, "sealed" (valve-regulated) type. The propulsion battery pack voltage shall be a maximum of 48 volts nominal. Total maximum battery weight shall not exceed 100 pounds (45kg). It is recommended that batteries be placed in the vehicle to minimize polar and roll moments of inertia and provide even weight distribution front-to-rear and side-to-side. The battery pack shall be isolated from the chassis (i.e. a floating ground). Batteries shall have less than 5 milli-amps current from both the positive and negative high voltage terminals to the chassis ground.

10. Battery Enclosure

Batteries shall be contained in the marine-type battery boxes as supplied with the kits. The cover shall be removable to allow access to the batteries and battery terminals. The battery boxes shall be secured to the vehicle frame and be of sufficient strength to retain batteries in the event of collision or roll-over. It is recommended that the batteries be secured inside the boxes to prevent shifting.

11. Spare Battery Modules

Replacement of failed battery modules shall be permitted prior to or subsequent to competition using spare battery modules. Replacement of modules will not be permitted during an event. Modules shall only be replaced after consulting the GAEVR staff.

BATTERY CHARGERS

To use on-site charging, chargers must comply with this section. If you opt to charge off-site, compliance is recommended but not mandatory.

1. General Regulations: Vehicles shall be brought to each event fully charged. Vehicles will operate throughout the day on a single charge. Charging will not be allowed at the location of any competition, except as directed by event officials.

2. All Chargers: Charger AC input and extension cords shall be a minimum of two wire and ground, outdoor rated (SO) cord. Minimum wire size shall be #12 AWG for 20 ampere service. Cords shall be in excellent condition with no splices abrasions or cuts penetrating the outer jacket. Cords shall be rated for use at 400 volts or greater.

Chargers shall be equipped with standard NEMA plug connectors suitable for the voltage and current requirements of the charger. The charger AC plug shall be NEMA 5‑15P 120 Volts, 15 amps. The AC breaker feeding the receptacle will be 20 amps. The AC receptacle in the charging area will be a NEMA 5-15R. Current will be limited to 16 amps AC. Charging power shall be provided through Ground Fault Current Interrupter Circuit Breakers which will trip free at a ground current (or branch circuit current imbalance) of greater than 5 milliamperes. Chargers shall be capable of operation from this source.

The charger shall be equipped with an output fuse rated for use at 250 volts or greater and an ampacity no greater than 125% of maximum charger DC output.

3. Off-board chargers: It is assumed that all EM-TVs will use off-board chargers. If an on-board charger is installed, refer to the GAEVR Vehicle Specifications for additional guidance.

Off‑board charges shall have a utility ground connection to the charger shell. DC output cord shall be rated for at least 125% of the maximum charger output current. The outer jacket of this cord shall be rated for outdoor use at a voltage of a least 200% of the charger output. The DC connector to the vehicle shall be polarized and rated for at least 125% of the maximum charger output current. Plug and receptacle electrical connections shall be shrouded to prevent contact. Alligator clips or other temporary connections shall not be permitted.

4. Extension cord: Each team shall provide one UL-listed extension cord, designed for exterior use, at least 30 feet in length and rated for the appropriate voltage and current of your charger. If your vehicle utiliizes more than one charger, you must either provide a cord with multiple plug-ins or separate cords for each charger. To avoid excessive voltage drop in the extension cord, a 14-guage cord is recommended for 15-Amps, 12-guage cord for 20-Amps, and a 10-guage cord for 30 Amps.

MOTOR / CONTROLLER

1. Motor Type

Motors shall be of the direct current type.

2. Controller

Controller shall be DC, pulse-width modulating type. Maximum current rating of 400 Amps at nominal 48 Volts DC input. The controller shall be equipped with a high-pedal disable interlock to to prevent energizing the controller with the accelerator depressed or allowing reverse to be energized while the pedal is depressed. Controller bypass switches are not permited.

3. Accelerator Mechanism

The controller shall utilize a foot-operated, low-current accelerator position sensor designed to switch the controller off if the sensor shorts or a wire becomes disconnected. Accelerator mechanisms shall be free moving and shall return to the zero current position when released. At least one energy source (e.g. springs) shall be provided to return the accelerator to the zero current position.

Mechanical

1. Fastners

Fastners for steering, drive, and brake components must use locking nuts, lock washers, or safety wires.

2. Accelerator Mechanism

Accelerator mechanisms shall be free moving and shall return to the zero current position when released.

3. Brakes

Vehicles must have fully functional dual band brakes operated by a foot pedal with mechanical linkages. All brake linkage connections shall be secured with cotter pins or safety wires.

4. Chain Guard

The chain guard(s) shall be in place during competition

You might be able to tear apart one of these for a transmission that will put you under $500

http://www.lrbikes.com/LR.asp

http://bandlbicycles.com/page.cfm?PageID=219

then you would still have another $500 left in your budget to trickle charge the batteries. You will probably only need an extra 30 seconds in the distance race.

Comments must stay within Modification rules.

Example :

Why double motor drive is better or worse than single motor drive.

How can the drive wheels be allowed to distribute power? Differentiate speed? Eliminate spin?

How can differentiated multi speed gearing be controlled?

I am off to a workshop, (Loafshop) see you!

Suggest you recruit Lewis Hamilton to drive...

Here is a link that has torgue converters and other accessories for go karts. You could also set up two sprocket and chain drive or synchronius belt and pulleys configured to the drive ratios you want. One for low speed and torque the other for speed. On both drives on the driven sprockets have an electric clutch (like the ones on an automobile air conditioning compressor) and wire them to a double pole double throw switch. The switch can be labled low and high. When the student takes off the switch will be in low for torque. When he hits the straightaway, he can flip it into high to gain more speed.

The double pole double throw switch should not have the center off position.