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HOME > No.23, Nov. 2020 > Starting development of a wireless charging system for amusement park Go-karts

Starting development of a wireless charging system for amusement park Go-karts

A future vehicle that will make children’s dreams come true By Takashi Ohira
Takashi Ohira

In response to a request from the city of Toyohashi, the Future Vehicle City Research Center at Toyohashi University of Technology has started to develop a wireless recharging system for the go-karts at Nonhoi Park , Toyohashi’s Zoo & Botanical Park. Nonhoi Park operates a go-kart track for children. Just as for cars on public roads, converting the go-karts on the premises from conventional gasoline-powered vehicles to electric ones would help reduce their impact on the environment. In addition, electric go-karts are also more child-friendly as they emit no exhaust gas or engine noise. Furthermore, the electric go-karts are motor-driven, meaning that they also have higher starting acceleration performance. This makes them the perfect machine for a go-kart track with many curves. Not only children, but adults too will be fascinated by the experience of exciting, real-life go-karting that cannot be found in any digital game.

A mechanism for transferring energy from the road surface to a go-kart battery
A mechanism for transferring energy from the road surface to a go-kart battery

Typical electric go-karts have a drawback specific to the electric type: namely, the battery problem. Currently, the heavy batteries are removed from the go-kart by an attendant and carried to an electrical facility for charging. This led the research team to consider the challenge, "When the go-kart returns to the boarding area after traveling on the track, might it be possible to charge the batteries quickly before the next departure without removing them?" One early thought was to attach and remove a charging cable to and from the go-kart. However, the cables for quick charging are thick and heavy, making them too cumbersome for easy regular use. Therefore, we came up with the idea of wireless charging. If we could lay electrode plates on the road surface of the go-kart stopping area and wirelessly transmit power to the go-kart from there, there would be no need to handle heavy cables.

The laboratory has since commenced this research on wirelessly charging the go-karts in Nonhoi Park. The key to successful quick charging is the efficient transfer of large amounts of power. Focusing on hyperbolic geometry, a special kind of plane geometry born in Europe in the 19th century, as the key to high efficiency, the design and prototyping of a wireless quick charging system that make full use of hyperbolic geometry is already underway. Such hi-tech go-karts could become a social implementation model for future electric vehicles. The future go-karts will make children’s dreams come true with them as they take flight.

"We faced a major hurdle when thinking about how to efficiently deliver energy from the power source to the go-kart batteries wirelessly. We found that the wireless electrodes and batteries which we were trying to mount on the go-kart had a completely different high-frequency impedance (ratio of voltage to current). We fumbled our way through various different methods at first, thinking that there had to be some way for us to overcome this barrier. Finally, we realized that this problem came down to planar geometry, which deals with how to bring two points that are far apart from each other on the plane closer together. At the same time, our laboratory proposed an attempt to utilize hyperbolic geometry, a 19th century European discovery, to solve contemporary problems. (References [1] to [9]).

The 19th century mathematician : Henri Poincaré  (Drawing by Marimo Matsumoto, TUT 1st year graduate student from the Electrical and Electronic Information Engineering department)
The 19th century mathematician : Henri Poincaré (Drawing by Marimo Matsumoto, TUT 1st year graduate student from the Electrical and Electronic Information Engineering department)

We call this attempt the ‘analog renaissance’. In hyperbolic geometry, if we try to connect two points on a plane by the shortest distance, the path is not always a straight line. The key to solving the problem was the hyperbolic distance metric concept, advocated by French mathematician Henri Poincaré. New solutions are created by incorporating counter-intuitive geometric ideas into system design. We will showcase this new solution at Toyohashi Nonhoi Park." said Research Team Leader, Project Research Associate Minoru Mizutani, the research team leader. We are grateful that he could share such fascinating insights about this research.

The goal of the research team members is to implement the world’s first future-vehicle technology in Toyohashi at Nonhoi Park. Their hope is that many people will be thrilled by the experience of this new go-kart, and that it will spread to amusement and theme parks not only in Japan but all around the world.


[1] T. Ohira, "A radio engineer’s voyage to double-century-old plane geometry," IEEE Microwave Magazine, .vol21, no.11, pp.60-67, Nov. 2020.

[2] M. Mizutani and T. Ohira, "Design theory of a standing wave mitigator for a moving load along a transmission line," IEEE International Conference Radio Frequency Integration Technology, pp.214-216, Hiroshima, Sept. 2020.

[3] A. Suzuki, S. Tsukamoto, and T. Ohira, "Diskwide spiral trajectory impedance matching network for frequency-diversity power transfer," IEEE International Conference Radio Frequency Integration Technology, pp.217-219, Hiroshima, Sept. 2020.

[4] T. Ohira, "Poincaré length," IEEE Microwave Magazine, vol.21, no.3, pp.120-121, March 2020.

[5] K. Yamada and T. Ohira, "Graphical representation of the power transfer efficiency of lumped-element circuits based on hyperbolic geometry," IEEE Transactions Circuits Systems II, vol. 64, no. 5, pp. 485 - 489, May 2017.

[6] 大平 孝, "スミスチャートの歩き方," 電子情報通信学会誌, vol.103, no.7, pp.709-712, July 2020.

[7] 大平 孝, "ポアンカレ視点で見るコイルとコンデンサ, " CQ出版 RFワールド, no.50, pp.113-115, April 2020.

[8] 大平 孝, "電界結合ワイヤレス電力伝送," CQ出版 MOTORエレクトロニクス, no.10, pp.93-102, April 2019.

[9] 山田恭平, 非ユークリッド幾何学を用いたリアクタンス回路の特性の表現, 豊橋技術科学大学博士 学位論文 13904甲第783号, March 2018.


By 大平 孝








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Researcher Profile

Yuu Hirose
Name Takashi Ohira
Affiliation Department of Electrical and Electronic Information Engineering
Title Professor
Fields of Research Wave Engineering, Wireless Power Transfer