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Directory:XR3 Hybrid by Robert Q. Riley Enterprises, LLC

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From Robert Q. Riley Enterprises:

"The XR3 Hybrid is a super-fuel-efficient two-passenger plug-in hybrid that achieves 125 mpg on diesel power alone, 225 mpg on combined diesel and electric power, and performance like a conventional automobile.
The XR3 is more than just a build-it-yourself vehicle. It’s a design statement, and its success with consumers is likely to influence the designs and product lines coming from the world’s carmakers."
Do-It-Yourselfers can either buy the kit or the plans. The engine is a 3-cylinder Kubota Diesel.

Note: Some US states do not allow insurance coverage of DIY vehicles that run on 3 wheels.



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Official Website


(.54 Minutes) XR3 Plug-in Hybrid gets 225mpg!!!

  • The XR3 is a diesel-electric hybrid that gets 125mpg on diesel-only mode and over 225mpg on hybrid mode. (YouTube; August 14, 2008)

How it Works

From Robert Q. Riley Enterprises website:

"At just 1480 pounds, this high-performance design combines fast acceleration, a maximum speed of 80 mph, and fuel economy of 125- to over 200-mpg.

Its clam-shell canopy and three-wheel platform boldly differentiates the XR3 from conventional passenger cars. The vehicle’s hybrid power system, diesel engine, and low curb weight are the main ingredients of its super-high fuel economy and excellent performance. Acceleration equal to that of a conventional car and a maximum speed of 80 mph make the XR3 Hybrid equally at home on freeways and surface streets.

Plans enable people with common building skills to build a duplicate of the XR3 Hybrid prototype or convert their own car into a significantly more fuel-efficient vehicle. Readers will understand the factors that influence fuel economy, and learn how to make any car achieve greater fuel economy. The XR3 Hybrid gives enthusiasts and experimenters the opportunity to significantly reduce their transportation expenses and have fun doing it. On a broader level, the vehicle is a highly visible example of the kinds of vehicles that could help reduce personal mobility energy.

Power Systems

The two front wheels are powered by the combustion engine, and the single rear wheel is electric powered. The two power systems are not integrated within the vehicle. The connection between the conventional power system and the electric power system is provided by the ground. Proper phase-in between the two power systems is handled by a simple throttle mechanism and a dash-mounted switch to select between ICE power, electric power, and dual power modes. In the dual power mode, the XR3 will have lots of burst power for quick acceleration. If you were to use this acceleration potential to its fullest, fuel economy would be reduced to something on the order of 150 mpg over a 70 mile trip. Fuel economy will also vary according the particular components chosen for the power system, and how heavy you are on the throttle pedal. Performance figures quoted here are conservatively-driven vehicle having a system configured just like the prototype. Plans provide the information necessary for you to select different components if you want to.


The canopy and the entire front of the body are removable. Removing the front body section provides complete access to engine and suspension components for major servicing.

This removable front clip can be restyled and extended to provide additional forward space for a more powerful engine. With a larger engine you can have big-engine performance and still retain the ability to run on battery power alone. The existing 65-pound (29.5 kg) transmission will handle up to 300 horsepower (223 kW).

The removable canopy provides another level of freedom. A different windshield can be installed to create an open-air roadster effect.

Safety Features

The front portion of the front clip is foam-filled to absorb low-speed frontal impacts. It also serves as an easily replaceable sacrificial element in the event of a frontal collision. The sides of the vehicle are filled with foam to provide side intrusion protection. This foam-filled region, varying in thickness from 5 inches to more than 10 inches, extends from the front wheel wells to the rear bulkhead of the passenger zone, and vertically from the canopy parting line to the bottom of the passenger zone. The design is significantly more resistant to side intrusion than the doors of conventional cars.

A composite roll bar is built into the perimeter of the panel that defines the rear of the passenger zone. In addition, the canopy is equipped with a tubular steel perimeter frame which is reinforced by steel “A? pillar members. This provides excellent rollover protection.

An open interior having no conventional instrument panel or steering column provides forward excursion space for occupant deceleration during a frontal collision. Controlled deceleration is provided by conventional seat belts.

There is no conventional steering column. The steering wheel is supported from the side. The supporting structure is designed to break away in a frontal collision. It is not designed to resist/carry the loads that would typically be imposed by the forward excursion of the driver.


The XR-3 Standard Plans Package is $170. The package includes eighteen D-size (24 x 36 inch) drawing sheets, one 32 x 64 inch full-size template sheet, and a 149-page construction/technical manual with over 200 photos and illustrations.

The XR-3 Deluxe Plans Package is $200. The Deluxe version includes everything from the Standard version plus two CD-ROMs and one DVD.

One of the CD-ROMs contains SolidWorks 2D CAD drawings and 3D models, along with DXF files necessary for water-jet or laser cutting flat metal parts. The DXF files alone will save many times the extra $30 because your water-jet or laser service does not have to create the necessary files from drawings. (DXF files provide tool-path information for automatic processes.) The second CD-ROM contains a construction manual set up to run in a web browser with click-to-enlarge high-resolution color photos, video clips, and SolidWorks eDrawings 2D drawings and 3D models. You can get a free viewer that will let you view and take dimensions from the electronic CAD files and 3D Models.

The DVD contains over one hour of video of the vehicle being built. It’s a “reality TV? show, not a Hollywood production. The two prototyping technicians who built the XR3 had no prior experience with fiberglass. So the video includes minimally-edited clips taken at various stages of construction along with verbal instructions and comments on the particular operation.

When you purchase plans you will be automatically subscribed to a password-protected update site. Your user name and password will be emailed to you when your plans are shipped. You will receive periodic notifications of updates when new content has been added to the update site. You can unsubscribe at any time, but the update site lets you stay informed on the latest developments and improvements to the XR3 Hybrid plans. New information that will be added includes: additional computer files, new drawings and photographs, new techniques for building, and new resources and vendors.

If you’d like to try the eDrawings viewer, you can download an executable eDrawings file (in a zipped packet) of the Front Wheel and Knuckle Assembly model (4.80 MB) by clicking on the foregoing link. You have the option to either Run or Save the file.


Although the XR-3 can be built just as the prototype was built, kits are on the agenda. Information will appear on this page as it becomes available. But the XR3 can be constructed using the same techniques used to build Tri-Magnum. Click on FRP/foam composite for a document that shows the composite system used to build the body for the XR3.

A knocked-down body kit consisting of pre-molded panels provides the greatest benefit at the least cost. So body kits will be supplied as unassembled panels that builders can bond together. In addition to enabling the lowest price, this type of kit also reduces packaging and shipping costs. Frame kits will consist of a welded-together assembly, which turns the project into mostly a bolt-together operation. The goal is to deliver the greatest benefit at the lowest possible price, and avoid supplying parts that you can purchase locally.

The price of kits has not been established."


"Construction costs are highly variable because of the many choices available due to the XR3’s design. It’s a modular design that lets builders make choices according to their budget and performance goals. More than half the cost of parts for the XR3 prototype went to the electric propulsion system. In other words, the cost of electric propulsion components is greater than the cost to build the entire remainder of the vehicle, including the diesel power train.

At the upper limit, a duplicate of our Li-Ion-powered prototype will top $25,000. If you switch to lead-acid batteries, you can save the difference in cost between the two types of battery systems. Li-Ion batteries in the prototype cost about $7,500 ($9,000 delivered with a battery management module) and a lead-acid battery pack will cost between $1,500 and $2,000.

At the bottom end of the scale, a diesel-only vehicle capable of achieving 125-mpg can be built for less than $10,000. And the modularity of the design allows you to begin with a diesel-only vehicle then add the electric power train components later on. Nothing in the power train has to be changed. It’s simply a matter of leaving off the unwanted components. You can, however, enlarge the 3-gallon fuel tank to 9 gallons and end up with a range of over 1,000 miles on a single fill-up.

Similar options are available with a battery-only vehicle. One can simply leave off the combustion power system, install more batteries in the extra space, and end up with a BEV capable of driving 100 miles on a charge. Li-ion batteries can be recharged in about two-hours.

These cost-related choices also affect the performance of the vehicle. For example, leaving off the electric propulsion system reduces vehicle weight from nearly 1500 pounds to about 950 pounds. This improves diesel-only fuel economy and acceleration. When the electric propulsion system is not installed, the engine is then loaded to only about 41 pounds per horsepower.

Relevant Publications

  • Robert Q. Riley, Alternative Cars in the 21st Century: A New Personal Transportation Paradigm, 1994, pp. 282-283 and 366-367.



Company: Robert Q. Riley Enterprises, LLC

Inventor: Robert Riley

Robert Q. Riley consults for corporate and private clients on new product design and product strategies. He promotes environmentally friendly technologies, and writes and speaks on the subject of alternative automobile design. He has chaired conference workshops and spoken at industry, scientific, and academic events, including the Global Energy Future symposium (Columbia University), the World Car Conference, and the Northwest Alternative Fuels Conference. He consulted on the Different Roads automobile exhibit at New York’s Museum of Modern Art, and was a panelist on the museum’s daylong symposium on the future of the automobile. He was one of the two U.S. technical consultants selected by Delcan Corporation to assist with Transport Canada’s Sustainable Transportation Technology Forecast.

Mr. Riley is the author of Alternative Cars in the 21st Century: A New Personal Transportation Paradigm (Society of Automotive Engineers, 1994 & 2003), and Alternative Fuels for Spark-Ignition Engines (for a volume on Motor Gasoline in the series, Critical Reports on Applied Chemistry, Royal Society of Chemistry & Society of Chemical Industry, U.K., 1995). The Second Edition of Alternative Cars in the 21st Century, with a Forward by Dr. Paul MacCready, was published in 2003.


In the News

  • The XR3 Do-it-yourself Hybrid - Robert Riley’s XR3 is an incredible machine that is able to achieve over 125mpg on biodiesel and a whoping 225mpg in hybrid mode. With its sleek composite shell and ultra-efficient engine we were expecting to see a stratospheric price tag, however we were stunned to hear that the you can build it yourself for around $25,000! (assembly and parts not included). (Inhabitat; Sept. 9, 2008)
  • 225 mpg DIY diesel hybrid on the road, kit version coming - Yes, with a few simple tools and plans purchased from Mr. Riley, you too can (eventually) cruise the highways in your very own XR3. Engineered to travel 40 miles with lithium ion batteries powering the back wheel before switching on the Kubota diesel engine that power the fronts, the XR3 is said by its maker to get 225 mpg. (AutoBlog Green; Aug. 16, 2008)
  • Plug-in Hybrid from Robert Q. Riley Enterprises to Debut on June 16 - The XR-3 uses the latest hybrid power system technologies in the most simplified way possible. While the front wheels are powered by a three-cylinder diesel engine, a single rear wheel uses an electric motor run by a lithium-ion battery. The ground provides the connection between the two systems, eliminating the need for a complex electronic and mechanical interface. (The Auto Channel; March 20, 2007)

Other Coverage

list here


See Discussion page


Robert Q. Riley Enterprises, LLC
P.O. Box 14465
Phoenix, AZ 85063-4465
24-Hour Secured Fax Order Line: 623-872-3476
Toll-Free Order-Line: 1-800-230-2855
Technical Questions: 623-872-8010


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