This blog made a guest appearance on the Kneeslider and suggested that it might be nice to test drive a Piaggio MP3 Scooter with a 48V brushless DC in-wheel motor and lithium polymer batteries.
Piaggio, which first built the iconic Vespa in 1946, states the belief that the MP3 represents a revolutionary concept. It has two front wheels. Piaggio claims that such innovation provides much greater stability and traction in wet and rough road conditions. Not only does the MP3 have two front wheels, but the two front wheels also can tilt as much as 40 degrees.
Tilting is an important element in safer design of a three-wheeler that has two wheels in front with a single drive wheel in back. Tilting Three-Wheelers are nothing new. Ernst Neumann seems to get the credit for such innovation, which occurred about the same time as when Piaggio first introduced the Vespa. Fast forward to now and we see that the Compact Low Emission Vehicle for Urban Transport also uses a novel, tilting chassis.
Recent mention of three-wheeled electric transportation and innovative design of a wheel hub motor was cause to re-think some recent criticism of the English, green mini-car designed at the University of Bath.
The criticism was that the design was backwards. Rather than two drive wheels at the rear, the two drive wheels should be in front for greater safety. Examples are the now defunct, NEVCO Gizmo or Corbin Sparrow (now revived as the Myers Motors NmG).
This design has a disadvantage: two drive wheels in the front add complexity and cost, whereas the MP3 has a single, rear drive wheel, reducing complexity and cost. Plus, the MP3 has the two tilting front wheels that overcome some of inherent instability in the design.
While a single rear drive wheel appears nifty, without tilting ability there is a tendency for the vehicle to rollover when accelerating while turning.
Nevertheless, while a tilting chassis may overcome a tendency to rollover when accelerating while turning, there still remain two other problems:
- The chassis must be designed to hold back the rear engine in case of a forward collision
- A powerful engine can cause the vehicle to spin around
Does the design of the Piaggio MP3 take such factors into account? The motor is centered beneath the rider and low powered, at least for the models with smaller engines. The 125 provides a maximum of 15 bhp (11 Kw) at 9,250 rpm with 12 Nm torque at 8,500 rpm. But, what happens if Piaggio engineers incorporate a clean, quiet, all-electric model?
Ferdinand Porsche is credited with thinking of the electric wheel hub motor. Hochschule Offenburg continues such innovation more than 100 years later.
The unified, or independent, rear swing arm, now holds an in-wheel motor. To the untrained eye, it would appear to be just a 12-inch wheel rim with standard motorcycle tire. Fit into the wheel is a removable wheel hub containing a lightweight, 48-volt motor with integrated electronics, which improves efficiency by 1) providing regenerative braking and 2) decreasing drive line drag.
WaveCrest has developed an electric propulsion system for one- or two-passenger and cargo scooter applications.
Furthermore, an electric drive train is intrinsically more efficient than an internal combustion engine. So, is that sufficient impetus for Piaggio to find reasonably priced, off the shelf, motor and power electronics? A quick search finds a 15 kW (20 hp) electric motor from UQM Technologies as an example. It operates at 42 VDC and 2800 rpm. It, however, was an incomplete match since there is a considerable difference, in the greater amount of torque, 710 N•m (524 lbf•ft). Another choice might be the eTraction 350SM/1. It is delivers 6kW at 48V and, on the average, 150-200 Nm torque with a peak of 600 Nm.
One might assume that Piaggio engineers can find suitable electric motors and power electronics since competitors, such as e-Max, Oxygen (Lepton), and EVT offer full size electric scooters made in China. Once there is a match between motor and controller, the other components are much easier to identify. For instance, a recent entry into the golf car market from China uses an Altrax controller and Lester on board charger. Now comes the fun part: testing.
Pictured above is the e-Max electric drive with 2kW hub motor, which accepts 40A, or 73A by engaging the Power Button. The battery pack consists of eight, 12V / 20AH silica gel, maintenance-free, SLA batteries.
The e-Max might be a good model for comparison with an MP3e. Texas eRider rode the e-Max Sport and pronounced it the finest electric scooter ridden to date. This was, in part, due to the robustness of the electric drive, plus a ‘real’ drum brake, not a ‘band brake’ in the rear combined with a front disc brake to allow for instant panic stops. The reviewer described the brakes as working as well as systems found in Honda, Vespa, or Yamaha scooters. It would appear that the integration of regenerative braking with the braking system still remains a challenge, however.
Suffice it to say, there is considerable development now underway, especially with more and more sophisticated power electronics and the impetus to produce them at lower cost for a wider market. There, perhaps, are some corollaries to the development of personal computers. There certainly is a correlation to the development of lightweight lithium polymer battery packs for light electric vehicles whether with two, three or four wheels.