Two-wheel drive wonder

Story: Nikhil Raghavan

In the book ‘The True History of Rokon Motorcycles’ author Bob Gallagher writes: “The history of the Trail-Breaker two-wheel-drive motorcycle can be traced back to around 1958 when Charles Fehn of Thousand Oaks, California began work on his invention, a "Motorcycle for slow cross-country travel over obstructions and in mountainous regions, and over snow and soft ground". Long-winded, yes, but it was the birth of the Trail-Breaker. Charlie Fehn applied for his first patent for this beast on April 13, 1959. His second application, abandoned like the first, came on August 31, 1962. It wasn't until his third patent attempt, now titled ‘Motorcycle having two driven wheels’, filed August 20, 1963, that Charlie would finally get his patent. By the date of the third filing, the bike was in full-fledged production and it would be August 23, 1966 before the patent would be granted.”

Yamaha's 2 Wheel Drive Bike

Much later Yamaha displayed a prototype, the Deinonychus at 'The Art of Engineering' at the 39th Tokyo Motor Show. It leveraged in-wheel motors and offered a completely new type of two-wheel-drive Electric Vehicle. The bike included 'Stretch & Shrink' functions in the vertical and horizontal directions allowing the rider to adjust the riding position and also the silhouette of the chassis to fit the rider's body size, riding environment, road surface conditions and personal preference.

After Yamaha with this 2-wheel drive WRF450 motorcycle, Austrian motorcycle manufacturer KTM got ready with their version of an all-wheel drive motorcycle.

Many major companies specializing in producing off-road motorcycles have experimented with various designs and methods of transferring power to the front wheel, the most common being the hydraulic drive. Some have tried using cable drive, but all these are still in the development stage and not in regular production. This is mainly due to the many flaws inherent.

Hydraulic drive is convenient due to the hoses being flexible, but the problem is with weight, fluid leaks and losses due to low efficiency of pump and motor. Cable drive was also good theoretically, but the losses due to friction, especially because of the more acute angles while turning, made it phenomenally inefficient.

The technology

Unlike a car, where it is easy and efficient to fit a mechanical drive from the side of the wheel hub, a motorcycle is essentially two-dimensional and requires complicated mechanical transmission to drive the front wheel, necessitating overly complex and awkwardly styled front suspension members and frame elements.

For two-wheeled vehicles such as motorcycles and bicycles, the term 2x2 is used to describe vehicles which can power the front as well as the back wheel. The term 2x2 is also used, to denote two total wheels with both being driven. 2x2 vehicles are typically either mechanically driven via chain or shaft or are hydraulic driven. This scheme greatly improves offroad performance, but is quite complicated and requires more power to operate, thus most 2WD machines are either "exotic" bikes for enthusiasts or created with special uses in mind.

Manufacturers who have one in production include Rokon. Manufacturers who are working or have worked on a prototype include ZID, Suzuki, Yamaha and Honda. Drysdale Motorcycle Co. is developing a chain drive 2WD that will be a 'bolt-on' conversion. It is inspired by the original 70 year old FN design but will be more sophisticated. It uses 2 chains and a custom "banana gearbox" to drive the front wheel; conventional front forks are retained. It is currently being developed on a Honda 750 Africa Twin and will then be fitted to KTM 620 single. The design is suited to all chain drive bikes with narrow motors - so singles and V twins.

On home turf

While all this was going on in the world of mobikes, a student quartet from Madras-based Hindustan College of Engineering (HCE), undertook an unusual project for their final year – a two-wheel drive motorcycle!

BIKE India caught up with the foursome at a nearby rough terrain where they were putting their machine through the paces, amply demonstrating the prowess of the bike.

Four years ago when the fresh batch of students from various parts of the country converged on HCE, four like-minded guys became friends. Rachit Aggarwal from Delhi, Arpit Tandon from Muradabad, UP, Pawan J B Rana from Nepal and Lakshman Sreedhar from Chennai dreamed of becoming outstanding automobile engineers when they graduate from HCE.

Today, four years hence, the foursome has passed out of the college and is realizing their dream, partly. Pawan wants to go to Germany and become an automobile mechanic. Arpit wants to start working immediately, while Rachit was desperately trying to get into Cranfield University, UK to do his masters in automobile engineering. Sadly, he did not get selected and instead is going to City University, London.

Project two-wheel drive

When the foursome started working on the two wheel drive bike, they found themselves up against numerous hurdles. Not much data was available on mechanical transmissions for such bikes. The ones already done used hydraulics. But, they were determined to make it mechanical to cut down on costs.

“We designed and developed a unique system to transmit power to the front wheel even during extreme wheel travel and turning, using a combination of shaft and chain drive. This ensures minimal losses, the ability to select single wheel drive or two wheel drive as per conditions and adequate turning radius and continuous drive irrespective of wheel position,” says Rachit.

Some serious homework resulted in a decision to use Jeep transmission parts. Fortunately, some Jeep_Thrills enthusiasts came to their rescue and introduced them to the ‘Jeep spares’ market from where they were able to pick up the transmission case and mechanicals.

Then came the designing part. The toughest was not of applying the drive to the front wheel, but how to make it work while at the same time steering it. “As our base bike we used a Kawasaki Bajaj 100 RTZ. On this we modified the nut securing the driving sprocket in order to fix a selector mechanism obtained from a Jeep’s transfer case,” says Arpit.

“We chose Jeep parts due to the unavailability of any other transfer case for our selector mechanism. The process used here is a dog clutch that pulls and pushes the selector on a splined shaft. This selector engages or disengages the connection between the two shafts,” explains Pawan.

This is then used to drive a propeller shaft with two integrated ‘Birfield type’ CV joints. The gear on the end of this shaft gives power to another mounted on a bearing and along the turning axis of the steering mechanism of the bike. “We used a Maruti half axle shaft as it was the lightest available and the most suited to our application as it had the necessary CV joints,” says Rachit. This was selected because it has two Constant Velocity joints in-built thereby reducing the problem of fixing two CV joints on two separate shafts and aligning them to transfer power smoothly.

After numerous attempts of different sorts and a lot of brainstorming, the foursome decided to fix the transfer case shaft onto the gear output shaft by first cutting the shaft to shorten it, then welding the securing nut of the driving sprocket onto the shaft. After this, the Maruti 800 half axle shaft was mounted longitudinally along the axis of the bike.

“On one end we had a differential sun gear welded on, which meshes with the planet gear. On the other end the shaft had to be extended in order to reach the full length. We did this by welding another shaft to the end of the half axle. On the end of this shaft another planet gear was welded.

In order to accommodate the mechanism without disturbing the steering mechanism we mounted another sun gear onto the axis of the steering mechanism. This is basically an idler gear mounted on the steering axis on a bearing to let the steering handle turn smoothly without being disturbed by the power transmission. We did this by mounting a bearing onto the frame on the underside of the triple clamp mounting and fixing the gear onto this. We could now take the drive from the other side without disturbing the steering. This was secured using a single bolt in the centre which had to be fabricated to suit our purpose,” says Arpit. This is one of the most important aspects of their designs as it allows the drive to be transferred to the other side, essentially the driving sprocket for the front wheel, without interfering with the steering mechanism.

“In order to provide the final drive without disturbing a lot of the existing mechanism, we decided to use a chain drive. To obtain power for this, we had to weld a driving sprocket onto a planet gear. This was secured onto a bracket and takes drive from the sun gear mounted between the triple clamps. This sprocket drives the chain which then drives the front wheel sprocket which has been bolted onto the wheel hub,” explains Pawan. But, they had a problem getting the chain to drive the sprocket, as it would slacken under situations like turning and shock absorber action. “We could not rectify this in time so we decided to cease the suspension action,” says Rachit. (The reader must remember that the quartet was undertaking this job as part of their final year assignment and therefore, had limited time and money.)

“Finally we have been able to successfully drive the front wheel of the Kawasaki Bajaj KB 100 with hundred percent mechanical linkages. The steering works properly while running the front wheel. Our idea of having a two wheel drive motorcycle for the pure purpose of off-roading has been successfully transformed into a practically working model with some scope for improvement,” choruses the foursome.

The design they worked on incorporating chain and shaft drive gave them a system that is selective and can therefore be efficient. If refined properly the entire assembly won’t have to be heavy or rough at all. The system devised also ensures minimal losses in terms of friction. “Given a chance, a lot of improvement can be made to make it lighter and ready for road and off-road use. It’ll surely make life easier for people living in extreme weather conditions,” says Rachit.

How it benefits

Here is an example of how two wheel drive utilizes traction better than single wheel drive. Each of the two tyres on a vehicle has traction (the friction between rubber and ground). Let’s assume that each tyre on dry surface has a traction value of 100; hence, a total of 200. In a single wheel drive, only the traction of one tyre is used (100) to create a forward movement. The torque of the engine is using the resistance (traction) of two tyres to get you moving. Let’s say a torque value of 60 is needed to move the vehicle. The traction value 100 is used up by 60 torque units. A margin of safety of 40 units remains.

Let’s say due to slippery ground the traction value drops to 50 per tyre. That gives you only 50 usable units on the one tyre. But with 60 torque units your traction account is overdrawn by 10. This results in spinning tyres and you cant get the vehicle moving.

In a two wheel drive system the engines power is not sent to one tyre; the power is sent to both the tyres. Therefore on a dry surface with 200 traction value and 60 torque withdrawal, a safety margin of 140 units remains. On slippery ground with a traction of 100 and torque of 60, a safety margin of 40 remains. The tyre do not spin and forward movement is guaranteed. As you see, in a two wheel drive, the traction account is twice as high as in a single wheel drive.

The foursome feels that there is great scope in the development of two-wheel drive motorcycles not only for off-roading and motorsports but also for regular commuters. “As was proved by Yamaha using their 2-trac system in a road bike on a race track, it was demonstrated that the bike had better grip and traction under wet conditions and didn’t lose traction. Our design is therefore viable provided the infrastructure for fabrication and production is proper. We have done the best we could, and honestly, owing to limitations of time and finance, this is not the best possible two-wheel drive,” admits the four of them. Nevertheless, a great achievement from four just-passed graduates.

END