Tuesday, July 26, 2011

Hub Design & Selection ( Part 1 )

SHELL Eco-Marathon
To build the most efficient vehicle in the world.
Like the current Guinness world record holder of most efficient vehicle in the world, the PAC-Car II: 5385km/L of gasoline, Ladoux, SEM Europe 2005.
Prototype vehicles are light, low drag, low rolling resistance, compact, efficiency-demanding. Beside custom building all the part for a vehicle, we could always salvage for commercially-available product, such as those from hi-end bicycle, as they provide the right thing that we need, just at some cost of our wallet thickness T_T. Well, it pays for any fast and proven workable things.

Sheldon Brown
Sheldon Brown's page contain a vast amount of data about bicycle part's technical terms, from daily-seen-MTB ( mountain bike ) in Malaysia to very-rarely-seen-tricycle (which is fairly common in European country ). Below are the page for some common hub for bicycle from several manufacturer. Basic yet informative webpage for any cyclist.
Sheldon Brown's Hub Page [Link]

Spoke Holes
Commonly seen hubs in Malaysia have fixed spokes hole number of 24, 28, 32 or 36 with the holes arranged radially in a plane on a flat or slightly tapered flange.
Hubs for 16" rim have only 20 holes, while some BMX bike's hub have up to 140 holes. Generally, more spokes = higher strength = more weight = less aerodynamic.
Expansive bicycles have little spokes with high strength made from titanium alloy, etc.
A perfect aerodynamic wheel would theoretically have zero spokes, an easier alternative would be adding a wheel cover on the spokes. This will reduce the drag produced by the spokes cutting through wind while rotating.

Figures: covered wheel
( & maybe a disc wheel if money is not a matter )

Figure: 20 holes hub

Figure: 28 holes hub

Figure: 140 holes hub
( Misc. New BMX bike's usually utilize sealed bearing hub or cartridge bearing hub for longer hub life )

Flanges of hub hold the spokes that connect to rim. Spoke holes on the flanges often have some degree of countersink to provide easier mounting of the spokes.

Figure: typical hub flanges

Figure: Shimano XTR hub

Figure: Cannondale Lefty Hub
( Lefty's hub in specially designed for cantilever load, see [link] for more details on Cannondales Lefty Bike. ##around 80 pounds per hub!! )

Some cheapo aluminium sheet hub have steel ball in between the wheel axle and the hub and acts as bearing which is very unsuitable for heavy normal load and cantilevered load scenarios. In the development of hi-end bicycle, bearings are essential in terms of reducing friction, increase drive train efficiency, increase coasting range and reduce energy wastage. There are several types of hub which incorporated with ball bearings which are getting common in local shop these days, as people are slowly coming back to less-emission lifestyle.

Bearing serves a vital role in increasing energy efficiency, imagine 50% of your paddling force goes to vibration, noise, heat, etc. We would never know our true potential then. The same goes to the vehicles, an environment-concerning engineer would never like to see the low efficiency in any terms. The bearings seem strong and rigid, but it is delicate in terms of the ball's micro structure, we would like to have a 100% working bearing to unleash the vehicles full potential, so proper handling ( do not drop the bearings, do not run bearings without proper lubrication, do not pull or knock the outer and inner ring in opposite direction, do not burn the bearing, etc. ) are very important. A prototype vehicle with good efficiency can easily coast for over 1.5km with engine turn on by only a few second.

Figure: Hubs with angular contact ball bearings.

Figure: Loading in angular contact ball bearings.
( Tapered roller bearings can carry a higher load than deep groove ball bearings but it is noisy and less efficient, while angular contact ball bearings combines the good of both: quiet, high load capacity, axial load capability and smooth )

Figure: Sealed bearing hub.

Figure: Cartridge bearing hub (yes, the bearings are exchangeable).

Figure: Loading in deep groove ball bearings.
( Recommending SKF's energy efficient bearings: at least 30% boost in energy efficiency; hybrid ceramic bearings: lubricant-free, silicon nitrite material which is only 40% density of steel, low inertia, high load capacity, long life, quiet, low thermal expansion, expansive ( 4~5x for hybrid: steel case with ceramic balls, 15x for full ceramic compared to a good quality steel deep groove ball bearing )..phew~

Figure: Standard Bearing Dimension
( some standard bearing size from SKF, ID: Internal Diameter, OD: Outer Diameter, H: Height )

Continue in Part 2..

*composed and produced by: Si Tzen ( sitzen_ng@yahoo.com.tw)
*All links are accessible on 26/7/2011

Saturday, August 21, 2010

How Design Wheel Hub

Mechanics Mens et Manus Series- Wheel hub design

Wheel hub design is a basic knowledge for every mechanical designer. How to make a super low rolling resistance wheel? What kind of bearing should I choose? What feature is a must in my hub design? These doubts will be answered after you read this post.

I come from a mechanical engineering education background. Been working hands-on on various project in university, from design to fabrication. I have been working on cars, karts, engines and recently electric motors. This is my first engineering/design post to share my experience and knowledge.

Choosing the size of your wheel

The first thing that has to come in mind is “What size I want for my wheel?” Normally bicycle comes in 16”, 20”,21”,24”26” diameter wheel size. Do check with local repair shop for these sizes, and the spokes length available. You would want a hub designed and you can't put into a rim because you’ve got no suitable spokes for it. Do design a hub with minimal post machining work.

Big Wheel or Small Wheel?

Big wheel needs a bigger torque to initial the rolling but possesses larger rolling momentum once it rolls on a specific speed.

Therefore, designer needs to play around with the torque formula-Torque=Force x Radius and find the compromising values from these parameter.

Normally, when deciding the wheel size for the vehicle, driving wheel should be as close to sprocket size for minimal force required to drive the veh

icle and driven wheel should be as big as possible to be driven at ease.

Choosing the right type of bearings

What makes the wheel roll? Bearings of course. Normal bicycles use ball bearings; some wheel chairs use sealed bearings. When designing a wheel hub, it is necessary to think what type of forces will be exerted on the wheel. A steered wheel will experience radial force from reaction force from ground, lateral force when the car steers. Hence we need to choose bearing which design for these two predominant forces. Normal seal bearing will only withstand radial force and could not handle lateral axial force. In this case, angular contact bearing is recommended.

There are 2 steps from the ends which are meant for bearing resting. Some design does include a sleeve which synchronize the rotating of the opposite 2 inner race of the bearings. A sleeve looks like a hollow cylinder. It is axially through for the shaft or axle.

During machining, care must be taken when determining bearing tolerance. Remember to make taper for ease of bearing fittings. Press the outer race of the bearing when fitting it into the hub.

Below is my machined wheel hub for my ceramic bearing fits hub.

author: david chew
email: cvk33@msn.com

A Legacy to be Hold

USM Shell Eco Marathon Team embarked a tough journey to Sepang International Circuit on the last July. They finished fabricating their cars just before the race day and only done some testings on the cars.

The journey started early in the morning, we traveled to Sepang Circuit with our restless mind and body due to recent round the clock work. During the race day, we were still working on some minor furnishes and double all the linkages and wirings.

At last, the cars still managed to go on track after both cars passed the inspections.

Actually, things were getting smooth during the inspection. USM GEN2 passed the inspection quite early among the Malaysian teams. We also been selected for the parade during opening ceremony. This car possessed an unique feature of having natural jute composite as material for the shell of the vehicle. It also has a special design of rear wheel steering which catches the attention of all visitor to our pit.

During the track run, we suffered a major blow which prevents us from finishing the laps. Sepang Circuit has a challenge which Europeans competition doesn't have. There is a steep slope for after the second turn. We are lacking gear ratio hence we cant climb the slope. It was disappointing and the team manager- David did not feel good all day long so did Horizon our prof.

It was a great competition after all, the team has a better plan for the next years, in the aspect of technical designs and team management. After all, it was a great education platform. The manager is determined to have a better entry next year with a more solid team and the year coming after, we will show off our true colors in 2012. This is a legacy to bear, a mission started as David, accomplished as a Goliath.

Saturday, June 5, 2010

Shell Eco-marathon Asia 2010 - Showcase of Malaysian Teams

Shell Eco-marathon Asia 2010 - Showcase of Malaysian Teams

Date: Wednesday, June 2, 2010

Time: 12:00 p.m. to 1:30 p.m.

Venue: Auditorium Cempaka Sari, Presint 3
(Opposite Palace of Justice)

Kompleks Perbadanan Putrajaya, Putrajaya


11:30am – 12:00pm:

Arrival of Guests

12:00pm – 12:05pm:

Welcome by Emcee

12:05pm – 12:15pm:

Speech by En. Anuar Taib, Chairman, Shell Malaysia

12:15pm – 12:25pm:

Speech by Datuk Seri Mohamed Khaled Nordin,
Minister of Higher Education

12:25pm – 12:35pm:

Video presentation of the Shell Eco-marathon

12:35pm – 12:45pm:

Unveiling of Shell Eco-marathon Asia - Best Malaysian Team Challenge Trophy by En. Anuar Taib and
Datuk Seri Mohamed Khaled Nordin

12:45pm – 13:00pm:

Symbolic Flag-Off of vehicles at the entrance of
Auditorium Cempaka Sari

13:00pm – 13:30pm:

Press Conference

13:30pm – 14:30pm:

Tour of student teams booths showcasing their vehicles designs at the Foyer

Buffet Lunch



We arrive at Putrajaya at about 9am and had the chance to have a look around the place. Here are some pictures taken from the surroundings:

Soon after, a briefing was given to all those that were present on the day regarding the general rules of the SEM.

Symbolic Flag-Off of vehicles then took place at the entrance of Auditorium Cempaka Sari

Then, it was time for the student team booths to showcase their vehicles at the Foyer:

The event ended after all the guests and participants enjoyed a buffet lunch which was held at the Foyer as well.

Wednesday, May 26, 2010

New Race Format

New Race Format: Old Race Format:

4 Laps 6 Laps

Number of attempt: 5 4

Time Limit 23 minutes 35 minutes

Distance Covered: 11.2 Km 18.2 km

Average Speed: 30km/hour 30km/hour

This change was announced on 24th May. This change is to reduce congestion and logistics issues.

No Driver change, no pit stop for Prototype category.

(Less Driver, Less Uniform Cost)

Tuesday, May 18, 2010

Selected 10 for SEM media event

For the upcoming event of SEM on 2nd June at Putrajaya, the name list above is the selected 10 as the representative for Team USM.

These students will have to prepare some poster of our vehicle design for showcase at student booth during the event.

We will be heading Putrajaya by USM bus.

Shell Eco-marathon Asia 2010 - Showcase of Malaysian Teams

Date: Wednesday, June 2, 2010

Time: 10:00am - 11:30am (followed by lunch)

Venue: Putrajaya - exact venue to be confirmed.


9:30 - 10:00 Arrival of Guests

10:00 - 10:05 Welcome by Emcee

10:05 - 10:15 Speech by En. Anuar Taib, Chairman, Shell Malaysia

10:15 - 10:25 Speech by VIP from Ministry of Higher Education

10:25 - 10:35 Video presentation of the Shell Eco-marathon

10:35 - 10:45 Unveiling of Shell Eco-marathon Asia - Best Malaysian Team Challenge

    Trophy by En. Anuar Taib and VIP from Ministry of Higher Education

10:45 - 11:00 Symbolic Flag-Off of vehicles at the entrance of auditorium

11:00 - 11:30 Press Conference

11:30 - 12:30 Tour of student teams booths showcasing their vehicles designs at the foyer/lobby

        Buffet Lunch

12:30 End

TEAM USM Selected 18

The name list above is the selected 18 members for SEM Asia Team USM.
These people have to depart to Sepang Circuit from 7th July onwards.
Only these 18 people are allowed to access to the paddock area, official events of SEM.

Hence, more dedication are expected from these students and are required to stay for the whole June for intensive preparation.