Twin Engine Buggy


Front view of Twin Engine Buggy


This buggy is powered by two computer controlled VFR750 engines, one for each back wheel. It has a few hundred horse power and has great handling performance.

My motivation for designing and creating this weapon is to get the absolute most out of my buggy riding. Secondly it is a lot of fun creating something that is different.

My design philosophy was to create the highest performance design with reliable components. The main improvement on my existing design was the drive.

Buggy performance:

People who have driven a locked rear axle buggy will know that they suffer from understeer. This can be very frustrating under certain conditions, for example coming into negative cambered gravel corners. Because my rear axle isn't locked it doesn't suffer from this infliction. Controlling the power to each wheel positively steers the buggy on it own, let alone the steering wheel. Creating intentional power distribution to each back wheel. A diff does not provide intentional power distribution, my system does. Micro seconds after I turn my steering wheel I am achieving power assisted steering from the rear wheels. By applying more power to the outside wheel and even engine braking the inside wheel I achieve amazing cornering speed and accuracy.



Drive choice:

Pro's and Con's:

Locked axle “My previous design”
Dual engine design with locking Clutch.

Design details:

Each back wheel is driven be an individual engine. The power to each wheel is controlled with a servo system that I created. Extensive feedback is used for intelligent control. The two back wheels are locked through a controlled clutch to ensure straight line power is achieved. The clutch is controlled with a modified Saab hydraulic clutch release bearing. Each wheel has a large disk brake.

The design allows full functionality with either single engine running as a locked rear axle drive. Just turn one engine off and it's just like anyone else's buggy. This feature drastically increases the reliability of the buggy. If one drive train brakes down, no worries, just use the other one.

The feedback includes the following:

Control:

Control is achieved through a micro controller PCB board that I developed . The micro controls two servo motors that offsets the existing throttle cables. Servo position is achieved through a pair of Ford Falcon EA TPS.

Steering wheel position is achieved with a quadrature encoder set up as an absolute encoder. This is achieved by using the index at center steering position to reset position. This eliminates error accumulation.

The drive speed sensors are ford falcon speed sensors. They are mounted to the primary drives.

The revs are from the engine computer. Throttle position of each engine comes from the servo position sensors.

Clutch positions are determined using switches.

The Control chip was programmed using nothing but interrupt driven real time control programming techniques. The display chip was programmed using nothing but standard commands because it didn't require real time control.

I created the PCB using Express PCB Software.

Display:

Display is achieved through a micro controller PCB board that I developed. It controls a standard 16*2 LCD display and up to 16 super large 7 segment common cathode displays.

Info displayed includes:

Parts:

Safety:

Safety is a key aspect of the design. The main safety aspect of the design is the fact that each wheel is controlled individually by a powerful motor. Incorrect power distribution could cause torque steering.

The throttles are controlled directly via existing cable. They are not directly controlled via a servo.

A safety switch is also installed to stop both engines at once.

The braking system is extremely powerful and stays cool under race conditions.


Control Box view of Twin Engine Buggy

Left servo view of Twin Engine Buggy

Display view of Twin Engine Buggy

Rear Panel view of Twin Engine Buggy

Back left disc
This disc is mounted to the primary left sprocket. This brake spins faster than the wheels due to a 18 to 30 reduction. But gearing it down provides more braking power. Off road buggies don't go at road speeds, so it doesn't cause heat problems.


Back right disk
This disk is mounted to the primary right sprocket


Left speed sensor
The left speed sensor worm wheel came standard with the correct spline. Lucky!


Right speed sensor
The right speed sensor worm wheel came standard with the correct bore diameter and key. Lucky!


Locking clutch
The clutch is an essential feature of this design. It provides safety and makes for better power slides.


Hydraulic clutch release bearing
The hydraulic clutch release bearing makes for a neat design. Cable or leaver's, not so neat...


Radiator air deflectors
The 20 degree mounted radiators look good but require air deflection to function well. The design pumps more than enough air in to keep it cool.

Results:

5,000Km +

How am I enjoying it?:

Well I'm really enjoying this buggy. It's such a pleasure to drive. The acceleration is immense, it is fast all the time.

Rally type tracks:

Bliss... When can I go out again! That says it all!...

4 wheel drive type tracks:

4 wheel drive type tracks performance has been a surprise. I am actually getting up the super steep and slippery track better. I believe this is due to the extra weight causing my tires to really dig in. I thought the extra 100kg was going to decrease steep and rough track performance but it's actually better. Because the final drive is only a 30 tooth sprocket and with no disc brake on the final drive, I have gone from 220mm of clearance to 350mm of clearance. This is proving to be very beneficial on the tracks 4WD's have rutted. The torque is greatly increased due to having twice as many cylinders which has resulted in a much more usable slow speed.

Reliability:

I was expecting the chains to be high maintenance, but to my surprise I have only tensioned them once at the very beginning to two of the all thread systems. At this many km I would have had to tension it at least a few times with the previous single engine design. I believe this is due to the fact that the chains are loaded up less because there are now two off them powering the drive, with only an extra 100kg total mass.

The engine clutches are nicely staying at equilibrium due to the fact that as soon as one engine starts taking the load early under power it wears quicker and returns back to equilibrium. Very happy with that!

The control system has not had a single problem, I turn it on at the start of a ride and four hours later it is still functioning perfectly.

Changes:

I have removed the right adjustable thrust bearing that is next to the right sensor. It is not needed because the pillow blocks can easily handle me pushing on it with my foot via the clutch plates.

The drive rims have been strengthened with new inner plates from a Datsun.

I am no longer using the rear mud guards.



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