Article by Alexander Popovich
Light amphibious all-terrain vehicles have their own place within a broad spectrum of modern self-propelled machines. The demand for a machine capable to commute through rough terrain and wetlands regardless of the season and weather conditions was always high since early XX century. Apart from obvious military applications, that kind of vehicle can be used for various civil purposes, including, but not limited to, minor cargo and personnel delivery through undeveloped areas, rescue missions, hunting and entertainment. Many practical applications do not require heavyweight vehicles and, moreover, the minimal size and weight could be essential due to maneuverability, safety or nature protection requirements. Mass production of light amphibious ATVs in theory could be a large segment of the global industry but in reality it is still a niche product manufactured in relatively small quantities.
Many companies all over the world tried to design that kind of machines for military or civil applications and several models are being built in series. Limited success of those attempts has a deep reason behind it: the requirements for a lightweight amphibious vehicle are complex and sometimes controversial. An attempt of a simultaneous fulfillment of all requirements usually ends in high costs, too complicated and thus unreliable technical solutions or losses in functionality. Most notable controversies are:
- being effective all-terrain vehicle and steady floating vessel on the same time;
- high demand for energy and torque and limitations for weight and size of the powerplant; - complicated nature of the drivetrain control for effective off-road operations and simplicity of controls requirement.
All of the above are just different aspects of a major contradiction between advanced technology high costs and the price which the market is currently ready to pay for it. On a certain level of general technology development this controversy couldn't be resolved.
Very high torque requirements at low speeds and at start are typical for the class and produce a major problem for the ATV transmission design. The torque of an internal combustion engines is minimal at low rpm so a transmission with some gear changing mechanism is necessary to get the vehicle started and moving. Unlike for the road vehicles, to move the ATVs (especially on rough terrain - snow, swamp or wet dirt) the top torque at low rpm is needed not for a short period of time but, in fact, continuously. As the whole transmission operates under high load its resource and reliability are decreased dramatically and maintenance costs are very high. Service after intensive off-road exploitation may take up to 1/3 of movement time as a standard practice.
Also should be mentioned that the mechanical transmission (either CVT or gearbox and clutch system) once based on an internal combustion engine, has low overall efficiency and is a very difficult object for automated control as well. The hydraulic transmission could be considered as an appropriate alternative as it is much more suitable for "high torque - low rpm" applications as well as for automatisation but it has even higher production and maintenance costs. Both transmissions as well as internal combustion engines (Diesel and petrol) are quite heavyweight and increase of the power results in accelerated growth of the total vehicle weight, which makes power-to-weight ratio even worse or takes the vehicle out of lightweight class. Practically, there wasn't much progress in that class of vehicle in the last decades: serially manufactured amphibious ATVs of today are not much different from their 30-year old counterparts neither in performance nor in functionality.
Does it mean that the concept of light and inexpensive transporter in not working? No. Nowadays the technology has made a giant leap from the previous level based on the achievements of mid-XX century. It just means that most of the modern lightweight amphibious ATV designers seem not to utilize the new possibilities given by progress in materials, engines and electronics.
The largest breakthrough in the automotive industry blossomed from the early XXI century comes from electric motors and means to control them. Compact size, efficiency reliability, high torque (especially on low speeds) makes them extremely attractable for automotive designers. Progress in batteries brought back pure electric vehicles which were first on the road over a century ago and then pushed aside by internal combustion engine. More and more electric trucks, cars and motorcycles are seen on the highways and city roads, various electric utility vehicles and AGVs are widely used in industry, there are electric boats and snowmobiles. Nearly every vehicle type is now available with pure electric electric powertrain or some sort of hybrid one, but we haven't heard much about ATVs and nothing about amphibious ATVs. Are they an impossible to build? Why they are not available on the market along with thousands of other electric vehicles?
First of all, what can the electrification contribute for the ATV design? Obvious advantages of electric motors are their high torque available even in "stall" conditions and compact size. Electric powertrains are relatively easy to control by modern computers and they require much less maintenance. Less obvious are new possibilities in vehicle composition, opened by compact and flexible transmission (wires) and elimination of shafts, chains, gearboxes and other bulky mechanical powertrain parts. Same applicable to hydrostatic transmissions, however unlike hydraulic liquids electricity does not freeze in winter and requires almost no time to travel from source to destination within electric circuitry, allowing much faster system reactions and higher rpms. Another advantage comes from digital computer control over the vehicle operation and behavior. Endless number of features could be programmed into the system, ranging from musical entertainment to autopilot, which are seen in street cars. With complete electronic control over electric transmission and various data available from the onboard sensors (including driver's input) sophisticated motion algorithms can be implemented to provide better road and off-road performance then achievable under manual control.
The said advantages are widely used in street cars but what prevents them to shine in small amphibious tractors? The answer is quite obvious too. Most widespread electric powertrain solutions are high voltage (100+ Volt) or even very high voltage (over 400 Volt). They are quite safe if remain intact as well as timely and carefully serviced, but even minor isolation fault turns a car int a death trap once its wet enough. Modern street electric car's safety is not affected by rain and all circuitry is well away from any reach of humans onboard. Can we expect same level of safety in small off-road tractor? Definitely not. Amphibious all-terrain vehicle deals with much more water than any road car. Due to usually extreme nature of its movement as well as lower maintenance standards risks of accidental electric system isolation damage are very high. Together this facts make driver and passengers immensely vulnerable to electric hazard. Any voltage exceeding 48V is commonly considered to be deadly dangerous to water-related applications and is definitely not acceptable for amphibious ATV. 48V battery powered utility vehicles are well known but their powertrain hardly can be called lightweight due to massive batteries and power circuity adopted for high currents (which are inevitable coming with low voltages).
Another critical problem is the energy supply. Although the best batteries are still about 50 times worse than ordinary gasoline in energy-to-weight ratio and recharging process still takes considerably long time, battery powered vehicles found their place on the market and are competing with traditional ones. Unfortunately that's not the issue for off-road machines, as they typically operate quite far from power grid infrastructure. Recharging battery powered vehicle stuck in swamp or on a snow slope is incomparably more difficult than refilling fuel tank with petrol.
Not everything is good with available electric motors too. Obviously a reduction gear is needed to connect "fast" electric motors with "slow" drivetrain. Extreme torque requirement for vehicle start demands a certain reduction ratio at low rpms but that ratio is not effective for high speed movement. Both construction constraints and low voltage requirement limits revolution speed of modern BLDC/PMSM motors at a relatively low level. So to put a typical electric motor available today a CVT or gearbox is still necessary, bringing abroad extra weight and complications. Not surprisingly, there are no appropriate (compact, efficient and intelligent) CVTs available on the market to install onto the hypothetic all-terrain EV.
Is that an end of the story? Not yet. Low voltage hybrid system could answer all of the challenges mentioned above. A combination of pure electric drivetrain with petrol or diesel generator known as "series hybrid" once made safe and efficient enough can be an ideal solution for amphibious all-terrain vehicles. Long operating range, independence from power grid and high torque performance of electric motors are definitely good factors for ATVs, but so far no-one was making them for the market. The reason for that is quite simple: there were no low voltage powertrain components suitable for off-road applications. Despite huge variety of motors, controllers, alternators, rectifiers and ultracapacitors being available its not easy if not impossible to find a working low voltage equipment combination suitable for harsh environment, wet conditions and extended temperature range. Thats where the Vanquisher story starts. Keen to build an electric transporter for all-weather and all-terrain applications we were faced with the necessity to build almost everything by own hands.
Practically speaking, good ATV is all about the off-road performance. Typical ATV's off-road performance is limited by the geometry of propulsion system and main body. In theory, the bigger wheels are, the better it goes, but in practice both pneumatic wheels and tracks sizes are very much limited by a body design, so they must stay relatively small. Another problem for almost all amphibious vehicles is to provide numerous water-tight and dust-protected sealing for the axes which are typically located below the waterline. As a result the transmission elements usually suffer from bilge water. ATV steering is a complicated task as well. Car-alike turning by wheel steering is often difficult on the rough terrain and strength requirements for the turning suspension and steering mechanism are very high and therefore those parts are either too expensive or not reliable. The alternative, the tank-style turning by side track braking, which is commonly used in most ATV appears to be reliable but limits maneuverability of the vehicle as most of the known mechanical transmissions cannot provide reverse movement for one track. The four track system with individual hydraulic motors, provides better performance but appears to be very expensive. Finally, the hovercrafts, though very effective on any terrain or over water, are not a competitive solution as their energy efficiency and reliability are far below the market expectations.
The original idea behind the Vanquisher was to create an inexpensive and reliable utility amphibious transporter which could be transported in a standard trailer towed by a street-legal car. Apart from fulfillment of a usual requirements for off-road missions (the agility, high land and water speed, significant clearance combined with low center of gravity and low terrain pressure) we focused on implementation of ability to carry up to 4 passengers (not including the driver) or up to 2 long objects (like people laying on stretchers) and a set of remotely controlled and autonomous unmanned operation capabilities.
We have chosen to combine track and wheel advantages by making a 4WD vehicle with "virtual wheels". Virtual "large diameter and low pressure tires" were modeled by a track modules with individual electric motors for the propulsion. That helped us to provide full symmetry of the vehicle, big clearance, low mass centre, high waterline, low terrain pressure and saved a lot of space in the cabin for seated or lying passengers. Serial hybrid scheme with a petrol generator and an ultracapacitor as a temporary energy storage is implemented as a powertrain.
Some more explanation is needed for the concepts above. First of all the best off- road performance is provided by a very large wheels which are not practical in implementation. However, only no more than a third part of the wheel circumference is in fact "working" for the vehicle movement. Thus, the "unnecessary" parts of the wheel could be eliminated. A large low pressure wheel could be simulated by a specially shaped track. The resulting propulsion system made of four track segments may combine the advantages of both track and wheel. A major consequence of the propulsion concept as of above and with an electric transmission instead of a mechanical is a unique chance to build a symmetrical machine body suitable for floating. The heaviest part of the construction, the power source, could be easily positioned in the optimal place with prime concern of weight distribution as there are no longer any chains or shafts connected to it. Also, large virtual wheel diameter moved their axles far above the waterline though which removes problem with watertight sealing and bilge water as the body has no openings below the waterline. The body of such a vehicle itself resembles a trimaran boat which is considered to be one of the most stable floating vessel types. Low profile with low gravity center combined with considerable ground clearance gives it an extra maneuverability and safety in agile movement applications.
The vehicle composition resembles several successful designs of the past, mainly Soviet battlefield amphibious transporter known as "LuAZ-967" built in large series in 60- ies and 70-ies has just 4 small car wheels but a symmetrical boat-like body with a central driver position. That compact machine was a further development of ideas seen in German Volkswagen "Typ 166 Schwimmwagen" and American Ford "GPA Seep" of the 40-ies. Despite quite different looks there are very many similarities between LuAZ and Vanquisher. The almost symmetrical weight distribution of LuAZ was designed with key concerns of its amphibious features. Apart from standard cargo and personnel transfer missions the car with central driver position could be also used to transfer up to two wounded persons on stretchers installed along the vehicle body on the left and right of the driver. Although practically useless in deep snow or swamp the quick and low-profile machine was very popular in the army as a cost effective supply and rescue amphibious transporter. Even almost 50 years after cease of production there are still LuAZ fan clubs running. Further development of the light amphibious transporter idea by replacing a mechanical transmission with electric one and replacing small wheels with much larger virtual ones has brought us to the current Vanquisher composition. Unique symmetrical composition, with a very low centre of masses, located at geometry centre of the vehicle, ensures Vanquisher's high stability while driving on terrain and afloat. The principal composition and key drivetrain solutions are protected by patents.
Much work has been done to build a completely new low voltage power management and control system. As a result of several years of research and development, we are proud to be the first to make a complete power management and control system for low voltage off-road electric vehicles. Our unique system is an integrated solution including reconfigurable central computer, motor controllers, remote control system and, finally, a electronically-controlled continuous variable transmission (eCVT) to balance speed and torque of available electric motors and drivetrain requirements.
How much power transporter need? Surprisingly not too much. Easy calculation shows that a 2 ton tracked vehicle could be moved on a unpaved road at a speed of 20 km/h with just 10 kW (2.5 kW in 4 motors each) of power transformed into mechanical energy. Exceptionally high efficiency of electric powertrain reduces requirements for the generator, so instead of heavy and hot high-power engine a relatively small air-cooled motor with compact alternator could be used. To get available power practically doubled for temporary boost at start and to overcome complicated obstacles an ultracapacitor is a quick and inexpensive solution. Power management equipment continuously dealing with high currents (typically hundreds of Amps) at low voltages (48 Volts) is not something available off-the-shelf these days so we were forced to build it ourselves.
Considering certain reserve needed we decided to build power controllers capable to handle up to 7kW per each motor. The development resulted in dual channel controllers integrated with relays and fuses, generator control and CVT control circuitry to minimize number of modules and cables. We have also developed a specialized onboard computer embedded into driver's panel, which is capable of supporting steer-by wire interface, motion control and advanced remote control features, including First Person View video remote and Follow Me autopilot. Finally the whole power management and control system built with most recent electronic components and state-of-the-art design concepts fits into just 3 modules connected only by power lines and digital network interface.
Essential effort was applied to ensure vehicle safety in any environment. As it is expected to be operated in wetlands and on water, as a boat, the onboard voltage is limited to 48V DC, which is considered safe for humans in case of unlikely but possible event of direct contact of electric drivetrain with water. To achieve that a unique low- voltage integrated power management system was developed as no such products are yet available on the market. All electric/electronic modules are IP67 protected and comply with safety requirements as per ISO 10133:2012. Safety features on terrain are including but not limited to tree-channel braking system, safety belts for all passengers, roll bars, protective frame all around the vehicle integrated with strong front and rear bumpers. There are no openings/holes in the vessel body below the waterline and boards are high enough to give the Vanquisher good floatation capabilities (we still have a bilge pump as a standard accessory for some case). Safety equipment in the Vanquisher complies with up- to-date EU requirements.
It appears to be possible with a modest 24 hp motor seen on lawn mowers, applied to 4-track drivetrain, to achieve huge pulling force of 20 kN at low speeds and agile movement on any terrain type and on water. The resulting machine key technical specification parameters are:
Dimensions: 3282x2051 mm
Weight: 1500 kg
Payload: up to 500kg
Ground clearance: 418 mm
Terrain pressure: 85 g/cm2
Top speed: 26 km/h
Maximum incline: 45 degrees
Base price Euros 42,000
The Vanquisher, a first of its kind multi-purpose amphibious all-terrain transporter, is proving that electric vehicles can operate off-road too. Unique features of hybrid-electric drivetrain, providing excellent off-road performance at very low cost with little maintenance required, if compared to conventional ATV solutions, make it a principal breakthrough, able to change the small-size transporters market completely by opening a large number of new possible applications. Perhaps, in the near future the EVs will find their way on rough terrain as they recently did on the road.
By Alexander Popovich, Development Director at Advanced System Design, Portsmouth, United Kingdom
Learn more at the next leading event on the topic: Energy Independent Electric Vehicles 2017 on 27 - 28 Sep 2017 in TU Delft, Delft, Netherlands hosted by IDTechEx.