Archive for June, 2007

Safety Factors for Designing and Building Go-Karts

Published by
Stephen Burke 
at June 28, 2007 in Chassis Design and Kart Safety. Closed

Introduction to Factor of Safety

Recently, a person emailed me (kartbuilding[at]gmail.com) asking about the “factor of safety” (FoS) required when undertaking calculations to design and make a go-kart. The “factor of safety” is the maximum force and stress a kart can possibly undergo, multiplied by a suitable factor/multiplier. Ideally if the maximum force and stress a kart can endure is calculated, then this factor gets multiplied by the factor of safety.
Having a FoS of 1, means that a Go-Kart is not “overengineered”, and nothing extraordinary will occur. It is when the “extraordinary” or unthinkable happens, that the FoS comes into effect.

Quantifying the Factor of Safety

Quantifying the FoS for a Go-Kart is not an easy task! It certainly cannot be applied to the entire Go-Kart, but parts of it, e.g. the chassis, transmission, brakes, etc. The same FoS cannot be applied to the chassis in every Go-Kart. The purpose and category of Go-Kart must be firstly determined. I.E. is it a racing kart and in what category of racing kart? Once the category and type of Go-Kart is determined, then a FoS can be obtained.

NatSKA – Classes of Racing Karts, and Safety Regulations

NatSKA LogoNatSKA (The National Association for School and Youth Group Karting) governs the sport and activity of karting in schools throughout the United Kingdom. The association holds race meetings run under strict regulations of its governing body (Motor Sports Association), and periodically publishes a Handbook and Regulations. The most recent Handbook and Regulations (2007) outlines the various “classes” of karts, and range from Class 1 (50cc Single Ratio Open) to Class 16 (Honda C70, C90 and C90 Cub Gearbox). Specific specifications (including safety) are outlined for areas of the kart. The following is an edited exerpt from the NatSKA Kart Regulations on chassis design:
The chassis in general shall be of safe, sound and adequately strong construction and shall not include any components of a temporary nature. Specifically, the wheel base is to be a minimum of 101cm and maximum of 127cm. The maximum length of the kart, including bodywork shall not exceed 210cm. No kart is to weigh more than 100kg without the driver.

I highly recommend that the NatSKA handbook and regulations are read and followed, especially if other people are driving and racing your Go-Kart. At the very least, excellent safety guidelines are outlined.

More Technical “Factor of Safety” etc. – Formula Racing

CAD Stress Tests on a ChassisIf you are designing your own Kart on a CAD system etc. some software will allow you to carry out “Stress Analysis” of components. Some examples of CAD software packages are: Solidworks and Cosmos, Pro-Engineer and Pro-Mechanica. These software packages will allow you to carry out simulation of kart components, allowing you to place particular loads throughout, and calculate a FoS automatically! If you are heavily involved in design and analysis of karts, this CAD software will speed things up, and provide a wealth of information.

Stress Test and Factor of Safety Analysis of a Front Stub Axle from a Go-Kart

Stress Test Result Image on a Front Stub AxleAs an example of the amount of information and the ease at which CAD software can calculate the FOS, a stress test was carried out on a Front Stub Axle from a Go-Kart, as can be seen in the image on the left. The entire CAD HTML Stress Analysis is also available. The plans for this “Front Stub Axle” are contained in the Complete Set of Racing Kart Plans.
This test, taking a total of 10 minutes to model and analyse, found that, if a loading of 50 kilograms were placed onto the steering arm, that the resulting Factor of Safety would be 1.466. Therefore, this Front Stub axle is slightly overdesigned. An in-depth knowledge of the individual forces involved in a Go-Kart would be required for an entire Stress Analysis.

Factors of Safety for Go-Karts in Amusements and Funparks

In doing some research on Factor of Safety for Go-Karts, I came across an “Amusements Devices Act” which makes specific references to Go-Karts and the required Factor of Safety! Although the act (legally binding),  has been superseded by a later document, the numbers and references are interesting to see. Part IV of the above act, pertains specifically to Kart Design! An excerpt of its legal requirements are:

  • The speed of an adult kart shall be limited or governed so as not to exceed 45 kilometres per hour.  R.R.O. 1990, Reg. 20, s. 40 (2).
  • The seat, back rest and leg area of every kart shall be so designed as to retain the driver inside the kart in the event of a collision at the front, rear or side of the kart.  R.R.O. 1990, Reg. 20, s. 41.
  • Rotating, moving or hot engine parts of a kart that may constitute a hazard to an occupant of the kart shall be shielded to prevent burns to the occupant or the entanglement of the occupant’s hair, hands or clothing.  R.R.O. 1990, Reg. 20, s. 42.
  • The wheels of a kart shall be so enclosed or guarded that the wheel of one kart cannot interlock with or ride over the wheels of another kart.

Factor of Safety on Formula Racing Cars

Various universities are taking part in “Formula Student” lots of readily available information about building advanced racing Cars is available. Two excellent reports on designing formula racing cars can be found here and here. The latter document has a section on “Factor of Safety Development”.

Conclusion to Factor of Safety when Designing Karts

The materials used, and the forces involved make the calculations for FOS quite difficult. CAD software makes things much easier, allowing you to select the materials from a drop-down menu, and allowing you to apply forces wherever you require. CAD software will also allow you to change material thicknesses to achieve an optimum FOS, and weight balance.
Using your common sense, and reinforcing areas which would potentially fail in a collision will go a long way in having a robust Go-Kart.
If you have any queries or questions, drop me an email or leave a comment below.

Using a Centrifugal Clutch and Chain Drive

Published by
Stephen Burke 
at June 26, 2007 in Kart Transmission. 71 Comments

For a long time, the transmission and drive webpage on the kartbuilding.net website has been lying idle, and unfinished. This article covers one of the unfinished articles, “One single gear, using a centrifugal clutch, and chain drive.”.

About Centrifugal Clutches

Centrifugal Clutch OverviewThe Centrifugal clutch is one of the most popular and simple methods of transmitting power from the engine to the rear wheels in a go-kart/go-cart. This type of clutch is fully automatic, and works depending on the speed (revs) of the engine. If the engine is turning over very slowly, then the centrifugal clutch is disengaged, and the kart comes to a stop. If the engine speeds up (increase Revs Per Minute rpm) then the automatic clutch will engage, and the kart will move forward.

There are two parts/components to every Centrifugal Clutch:

  1. Bell Housing & Sprocket
    This bell housing, with its small sprocket connected to the rear axle via a drive chain, spins freely on the engine‘s output shaft, and as a result will need some grease and oil to keep it in good running order. With the engine turned off, the kart can be pushed forward, driving the chain, and spinning the bell housing freely.
  2. Center Shaft with Weighted Friction Shoes
    This Center Shaft/Unit is directly attached to the engine‘s output shaft. It is attached to the output shaft via a “keyway” and “grub screw” as will be discussed in the Fitting section in this article. Once the engine speeds up, this Center Shaft will expand and grip the bell housing, and in turn drive the chain.

These types of clutches can get very technical, in terms of power and speed ratings. There are numerous types of clutches available, with various “inner bore diameters”, “horsepower ratings”, “RPM engage\disengagement ratings”, “sprocket & chain sizes”. It is advisable to find out the essential information for your engine, if you are going to buy one of these centrifugal clutches. The small sprocket which comes attached to the “Bell Housing” needs to match the pitch and width of your large rear sprocket on the rear axle of the go-kart.

Buying/Sourcing a Centrifugal Clutch for a Go-Kart/Cart

The best places to get/buy these types of clutches are: your local karting arena, ebay, www.northerntool.com, www.cometkartsales.com. Don’t go and buy the first Centrifugal clutch you see. Shop around for a cheap quote. Also – try and get a typical and well known clutch (especially of you are buying a brand new one), as the “friction shoes” tend to wear quite quickly depending on your gear ratio. Comet type centrifugal clutches are the most well known brand.

Fitting a Centrifugal Clutch for a Go-Kart

Once you have obtained a suitable Centrifugal clutch, and depending on whether it has the correct “inner bore diameter”, fitting will be relatively straight forward. As mentioned earlier, there are 2 pieces/components to the Centrifugal Clutch: the Bell Housing, and the Center Shaft.
The bell housing goes onto the engine shaft first, with its concave bell housing facing outwards. This bell housing spins freely on the engine’s shaft, so make sure to put some grease between the inner bore diameter of the housing and the outer diameter of the engine shaft. Push the bell housing in on the engine shaft as far as possible (until it hits the flange on the engine).
Keyway on Engine ShaftGrubscrew on a Centrifugal ClutchKeyway on a Centrifugal ClutchThe Center Shaft with its Friction shoes is placed onto the engine next. There should be a “keyway” cut into the inner diameter of the clutch shaft which should align with a keyway in the engine’s shaft. This keyway makes sure that the “Center Shaft” will rotate with the engine. To stop the “Center Shaft” from slipping out off the engine shaft, there is a hole to allow a “grubscrew”. A grubscrew is where a threaded small bolt will screw through the Center shaft and tighten in on the engine shaft. You may or may not receive the rectangular metal “key” with the centrifugal clutch or not. I suggest you visit a lawnmower repair shop or a hardware store to obtain a suitable “key”. Below is a photo of the Centrifugal clutch transmission complete. A plastic chain guard can also be seen. If your engine does not have a keyway, and perhaps has another PTO (power take off) Shaft Type(s) as can be seen here, then you may have to resort to welding the “Center Shaft” to the engine’s output shaft. This should only be done as a last resort.
Centrifugal Clutch Transmission on a Go-Kart complete

Typical Gear Ratio and Chain Drive Setup

Large Rear Go-Kart SprocketOn Centrifugal Clutches, the small sprocket attached to the “Bell Housing” has typically 10 teeth (although this can vary). As a rough estimate, a gear ratio of 5:1 is needed for a standard/typical go-kart/cart, with a 5hp engine running at 3500 rpm, and with rear wheels of diameter 300mm or 12inches. The speed of the go-kart can be calculated based on this “gear ratio” combined with rpm of the engine and diameter of the rear wheels (Calculate speed of go-kart). A large sprocket with 50 teeth for the rear axle can be difficult to obtain. Ask for this large sprocket at the time you are buying the centrifugal clutch and it will save a lot of looking.

Centrifugal Clutch from a Chainsaw

Centrifugal Clutch from a Chainsaw EngineInstead of buying a purpose go-kart centrifugal clutch, it is also possible to get similar centrifugal clutches in “chainsaw engines” and “mopeds/scooters”. Although these types of clutches were not designed specifically for a go-kart it is possible to adapt these to suit a different engine. As can be seen in the photo on the left, a smaller “inner bore diameter” will be found in clutches from chainsaw engines. Also, instead of a small drive sprocket attached, there will be a special star shaped sprocket, which typically drives a cutting chain. A small drive sprocket will instead have to be welded to the “Bell Housing”.

Centrifugal Clutch from a Moped/Scooter

Centrifugal Clutch from a Moped/ScooterInside mopeds/scooters there are also centrifugal clutches, however these are slightly different in the fact that they are “wet clutches”, where the “Bell Housing” and “Weighted Center Shaft” run in an oil bath! It might seem impossible at first that a clutch can run in oil, however the oil keeps the clutch cool and free from maintenance. Again similar to the chainsaw type centrifugal clutch, there will have to be adaptations done, as there will be a “Splined” inner bore which will need to be drilled out to suit the engine’s output shaft.

In some mopeds/scooters there are 2 centrifugal clutches each which engages at different rpm of the engine. Therefore when the scooter is going slow and the engine is slow, the first centrifugal clutch engages. This provides a high gear ratio giving extra torque at low speeds. When the moped is moving at an average speed, and the engine turns faster, the second centrifugal clutch with a lower gear ratio kicks in and changes the gear ratio. This setup is very complicated involving a ratchet type free wheel system and is not feasible for use on a kart. It is possible to adapt and use one of these clutches however on a kart.

Conclusion to Centrifugal Clutches, Chain Drive and a Single Gear Transmission for a Go-kart

Having a clutch in a kart allows for great freedom, where the engine can be started and the kart can remain stationary. It also allows the driver to stop the kart without having to turn off the engine. Depending on the weight of the kart, the speed and power of the engine, a centrifugal clutch may not be ideal, but it will work. It is the most effective and simple Single Gear Transmission for a Go-kart. It is referred to as a “Single Gear Transmission” because there is only 1 speed and 1 gear ratio that the kart can go at. As a result of there been only 1 gear ratio, there has to be a hard line drawn between fast take off speed and high end speed.

If you have any comments or queries on this article, feel free to contact the author at: kartbuilding [at] gmail.com

“Making a Racing Go-Kart Vanish” – Magic Trick Revealed

Published by
Stephen Burke 
at June 25, 2007 in Karting Fun. Closed

A person attempts to drive a go-kart fast enough in order to make it disappear! The go-kart, ontop of a parking garage in Las Vegas is driven towards three people with fire extinguishers, and as the CO2 is discharged, causing a cloud of smoke, the go-kart vanishes into thin air!

Incase you were fooled in the above video, the go-kart didn’t disappear. The following website shows how a mistake in the camera angle, combined with slow motion playback, reveal the true outcome of the go-kart. 

http://members.cox.net/thinkcrazy576/Criss%20Angel.htm

Pitman (drop) Arm versus Bell Crank

Published by
Stephen Burke 
at June 23, 2007 in Steering Setups. Closed

Introduction 

Both these methods transfer the rotation of the steering wheel into linear movement of the track rods, which then turns the wheels right or left. At high speeds, it is essential there is fine control of the turning of the wheels, and the Pitman Arm/Bell Crank plays a crucial role in ensuring that when the driver turns the steering wheel even slightly that this movement is transferred into steering of the wheels. Any play or movement is not acceptable, especially at speeds above 30 mph.

Pitman Arm – commonly known as the drop arm

Pitman Arm type SteeringThe Pitman Arm method used on the kartbuilding.net steering plans #2, #3, where a simple drop arm welded to the steering column connects to the track rods via a 10mm HTS (High Tensile Steel) bolt, moving them from right to left.

As can be seen in the photo on the left, the Pitman arm is attached to the steering column, and the other end of the arm is connected to the track rods. To compensate for the angles and movement in angles, rose-end bearings are used at the ends and middle of the track rods. This allows for ease of movement.

The length of the Pitman/Drop Arm can be adjusted to make the steering easier, or more abrupt and sudden.

Bell Crank

Bell Crank SteeringThe bell crank method is found to be a more efficient and precise method of steering, however this method can be a bit more difficult to setup on a go-kart. Typically bell cranks are L shaped levers, which can move track rods from side to side. As the bell crank is essentially a lever, there is more room for tweaking the gearing/leverage required, allowing steering to be made easier or more abrupt. The connection in the photo on the right however, does not connect up with the steering column. In order to adapt the bell crank to work on a kart, or off-road kart, the setup as outlined on the image below is required (thanks to theo).
In this case a universal joint was used to transmit the rotation of the steering column to the bell crank, which in this case is T shaped. As a result the bell crank provides for more positive steering than the pitman arm.

Final Points 

Just to point out, steering racks, in a car for example, do not operate on either of the above principles/ methods, as gears are used to transfer the rotation of the steering wheel to linear movement of the track rods. The steering racks in a car can weigh quite heavy, and can add unnecessary weight to a kart, even when adapted to suit a kart.

For the purposes of karting and general karts, the pitman offers a quick, easy and effective solution. Its more of a realisation of the bell crank, that I wrote this article, and to mention its existence. Whatever method of steering is chosen, it needs to be firm, positive and strong enough to withstand heavy driving.

If you have any comments about this article, feel free to email me at kartbuilding [at] gmail.com and I will post them here.

Happy Go-karting!

Technorati

Published by
Stephen Burke 
at June 20, 2007 in Kartbuilding Services. Closed

Technorati is used to verify and read Blogs and their associated RSS feeds.

In order to get this blog and the kartbuilding.net website known, Ive joined.

Technorati Profile

Overview of Kartbuilding, Kart Plans, and what’s to be found.

Published by
Stephen Burke 
at June 20, 2007 in Kartbuilding Services. Closed

Background to Kartbuilding 

Since the kartbuilding website which was first founded in 2000, many changes, updates and additions have taken place. The site started out as, and still remains a DIY and enthusiasts website for anything to do with designing, building and making go-karts, or karts, or carts, or go-carts as they are sometimes called.

The website was originally setup to provide “free kart plans” which there was a huge lack of at that time. Since then, other websites have offered free kart plans, however lack the extra information, tips and help which is required to make a go kart from limited part availability, or on a low cost budget. A plan for the future would be to provide a list of other kart plans available, to catalogue and critique them, providing you with extra resources and how-to’s.

Many people visiting the kartbuilding website do not realise the vast amount of information available. This can clearly be seen from the list of emails sent to kartbuilding [at] gmail.com This blog post is to provide a clear and concise overview of what’s available on the kartbuilding website.

Overview of what’s on the Kartbuilding Website
(in chronological order of their availability)

  1. [PLANS] Off-Road/General Purpose Kart Plans
  2. [PLANS] Plans for a Basic Wooden Kart with provision for a lawnmower engine
  3. Types of Kart Engines
  4. Methods of Transmission for Karts
  5. Calculate the Speed of a Kart (based on rpm, wheel diameter, and gear/chain ratio)
  6. Photos and Details of other peoples karts
  7. [PLANS] Racing Kart Plans in Photographic Format
  8. [PLANS] Complete set of Racing Kart Plans (pdf format)
  9. Kartbuilding Photo Gallery
  10. Archive of FAQ’s and Emails (emails sent to kartbuilding[at]gmail.com
  11. [PLANS] Wooden Go-Kart Plans (soap box carts, or simple push karts)
  12. [PLANS] Build a Highway Street Kart (from Modern Mechanix, 1962!!)
  13. Kartbuilding Blog (frequently updated)


Whats to Come

1. Plans for a “Lawnmower powered Wooden go-kart” will be finalised and completed. Currently the information for wooden karts and lawnmower engines are broken up and segregated. This new set of plans will show how to make an engine powered kart with little or no money using only timber and scrap materials.

2. Updating and Re-designing of the “Build a Highway Street Kart”. Currently these plans are in Imperial (inches), with some dimensions (measurements) quite hard to read. These plans will be remodelled in solidworks, the 2d plans and 3d model of which will be made available for download.

3. An improved and revamped “Transmission of Power” webpage. The current one is very old, incomplete and missing some pages. The transmission is one of the most important parts of a kart. Having a good and optimum transmission is the difference between a fast and slow kart, and can even compensate for having a low-powered engine.

4. Cataloguing and critiquing other free kart plans which are available on the internet, telling which plans are good for which purpose. This tends to be the greatest difference between kart builders. Some people want simple and very cheaply made karts. Others want all the trimmings, suspension, reverse etc. and are willing to spend money to do so.

5. Proper listing of parts and materials which are required. Many people ask what parts and materials are required. How much will they cost me? Can I get these parts online? These questions and many more will be made into a “Sourcing Parts and Materials” section.

For now, the best of luck with building your own karts.
Feel free to contact me and I will post comments, articles and photos as they arrive.

– Stephen

Welcome to blog.kartbuilding.net

Published by
Stephen Burke 
at June 19, 2007 in Kartbuilding Services. Closed

This is the first post of http://blog.kartbuilding.net I hope to keep this blog regularly updated with tips, information, diagrams and photos of various karts and kart building techniques.

Stay Tuned.