Electrifying a Honda NC50 Express

[Quasse] bought a 1978 Honda NC50 Express moped with the intention of fixing it up and riding it, only to find that the engine was beyond repair. So, they did what any self-respecting hacker would do: tear out the motor and replace it with an electric one. It’s still a work in progress, but they have got it up and running by replacing the engine with a Turnigy SK3 6374 motor, a 192KV motor that [Quasse] calculated should be able to drive the moped at just over 30 miles per hour. Given that this was the top speed that the NC50 could manage on gas power, that’s plenty fast.

The final result runs pretty well and is certainly an interesting build. [Quasse] goes into some detail on how they converted the moped, including milling out the motor parts to fit the electric motor into the existing space, 3D printing a holder for the sensors that monitor the motor speed, and laser cutting a case for the battery. There are also a lot of zip ties holding the cables in place, but as we noted, it’s a work in progress. Street legal? Perhaps not, but it is certainly a fun project for something that was otherwise destined for the scrap heap.

We’ve seen plenty of other electric conversions here, from a 1940’s gangster car to the Teslonda, a Frankenstein build of a Tesla and Honda.

[Thanks for the tip, Rusty!]

27 thoughts on “Electrifying a Honda NC50 Express

  1. just need to paint the motor controler and battery box in either the same orange or the grey of the drive cover suitable weathered and know one would have any idea it was modded.

    1. In Europe at least it is not that simple – there are rules it has to adhere to in order to count as a bicycle. IIRC max 15mph powered, max 500W motor, must have pedals and pedals must be going round to go above about 3mph. Otherwise it is a motorbike and you need to take a driving test, pay an annual road tax, have insurance and your bike has to pass an annual MOT roadworthy test.

      1. It’s 250W nominal for it to count as a basic bicycle although even the big names like bosch will happily put out 500+ watts peak. There are also speed pedelecs which are bicycles that are closer to motorbikes requiring motorbike helmets, moped licenses, plates and such. Speed pedelecs go up to 28mph and can have a 500W nominal motor.

        So Eric’s both wrong and right. If you ride a moped you need a license. If you ride a bike that’s as fast as a moped you need a license. If you ride a bike that’s half the speed of a moped and therefore not equivalent you don’t need a license. Seems fairly sensible.

        1. If you take the pedals off and install a throttle mechanism, regardless of the type of the motor or speed, it becomes a moped and you’re charged for driving without a moped license, proper helmet, and/or insurance fraud for not having any. That in turn, at least for a young person, carries the additional penalty of delaying their admission to have a proper drivers’ license by a year from the date of the crime in some jurisdictions.

          Should you make that modification, you’d have to register the bike as a moped, which requires the installation of lights, signals, and type-inspecting the vehicle (at your expense) for structural integrity, brakes, and control systems. The last part is impossible, as bicycles as how they’re usually built cannot pass the requirements for a moped.

          Getting type-specified is important from the standpoint of the police, who may have to verify that the vehicle continues to adhere to the specifications. Otherwise they’d have to trust YOU to say that it still adheres to the law. This is also technically true for DIY pedelecs that would pass as bicycles IF you could prove that they do. The police have no official means or procedures of verifying that, so unless you an whip out paperwork that says you built the thing out of a an already existing and approved kit, to show that you have not altered the design, you’re up the creek without a paddle should they decide to take on your case.

          In other words, DIY electric bikes in the EU are a legal gray area. While you might be able to show that the vehicle works as per law, no paperwork to that end exists and therefore your efforts are in vain. The police are not the vehicle authority, so they cannot write you a paper that says your vehicle is road-legal – so they cannot use their own judgement for a basis of telling whether it is.

          1. Being type-specified as a moped also carries the issue that you’re no longer allowed on the pedestrian lanes or cycling paths – you have to travel on the roadway whether or not you can keep up. Doing that on a bicyle-cum-moped is suicidal, and so you’re practically cut off from leaving the sub-urbs because while regular bicycles can use the bike lanes, you’d have to go with the cars at 50-60 kph.

          2. Don’t be silly, Luke – that would imply that anyone riding a regular bicycle would be unable to ride anywhere that doesn’t have dedicated cycle lanes. It’s not like the bizarre and murderous cyclists-vs-motorists situation that seems to exist in the US. I have no issues with riding a bicycle on any of the regular roads around my city (in fact most of the cycle lanes are oddly less convenient and often *less* safe than doing that), and an electrically boosted cycle would merely make that easier and reduce your speed differential with the motor traffic, not make things worse. And, in any case, petrol powered (50cc) mopeds have been legally limited to 50km/h since the 80s, and 45km/h for nearly the last ten years already (and in the UK never more than 35mph) and it doesn’t seem to have harmed their popularity or caused massive deaths from their riders being run down by faster vehicles. We actually have some kind of respect for human life round here.

          3. Legally speaking, you’re supposed to drive a motor vehicle on the lane, not on the shoulder, and everyone already hates scooters and micro-cars going 45 kph in a 60 kph zone. You have the legal right to be there, and be as slow as you have to, but you’ll see a lot of overtaking and will risk your life.

            Driving on the shoulder is again a legal gray area, and the police can technically stop and fine you if they choose to.

          4. Besides, the 45 kph rule for mopeds is only nominal, because when the police check your speed they have to subtract 3 kph for “error margin”, and then depending on country/region you also have a minimum margin like 6 or 7 kph for a ticket, so actually your moped can very well go 55 kph and the police won’t bother to bother you. There’s nothing they can do about it except give you a stern talking to.

            Combined with most cars having their speedo adjusted to show 10% too much, leaving the traffic flow at around 54-57 kph in reality, the end result is that a moped in a 60 kph zone can well keep up with traffic. When I was young, the 45 kph rule was in place but nobody had a moped or scooter that really went under 60. The least thing you’d do is swap the rear sprocket to change the gear ratio.

            Two stroke engines are really easy to modify, especially since the law doesn’t state how much power you’re allowed to get out of it – only how fast it goes. Mine had a 50 cc racing cylinder with bigger ports and reeds on the intake to increase compression, and the stock 11 mm carb couldn’t give enough fuel for it except for the fact that I added a choke on the airbox, which altered the A/F ratio and made my little PV-50 go 85 kph on level road. Boy did it scream.

    2. At least in my part of the universe that’s a law on the books but not on the street. My friend has one of these exact bikes, same color! Engine still barely runs, though. His roommate uses it to commute to work every day with an empty license frame, just puttering down the shoulder of the highway. Police have definitely noticed, but I suppose they figure his life is already punishment enough.

    1. “KV” in this context doesn’t mean kilovolts, though the notation has mutated to look like “KV” is a unit because people don’t know how units work in math. Properly, that motor has Kᵥ = 192 RPM/V. Kᵥ is the ratio of rotation rate to back-emf, so this motor requires 192 RPM to produce a back-emf of 1 volt.

      1. Huh, interesting. What’s the significance of that measurement? Seems like an odd metric to use as a general measure of a motor. Does it basically determine the top RPM? Would that be advantagious to simply listing that RPM? I’m curious.

        1. Permanent magnet DC motors work as generators, where the output voltage depends on the speed. KV is the speed constant that relates the generated voltage.

          The generated voltage appears in series with the power source. If you have a battery as a power source, the motor appears as if a second battery was connected in parallel with the first, and the current going from one to the other, from the real battery to the motor, depends on the voltage difference between them. When the two are equal, no current can flow and the motor has reached its top speed.

          That’s why you can’t state a top RPM for the motor. It depends on the driving voltage. How much voltage the motor can handle depends on other things: power dissipation, insulation thickness, arcing of the brushes if any… temporarily you can “overspeed” the motor significantly, and many electric vehicles have undersized motors on the point that you won’t be going 160 mph for too long.

      1. Who came up with that stupid and clearly easily-confusable metric and shorthand? And in any case wouldn’t that only work for a motor with no load on it, because a motor with 48V applied to it probably isn’t going to be capable of reaching 9216rpm up a steep hill, but will decidedly exceed that going downhill. It’s kind of like rating a combustion engine for a certain RPM vs grammes of fuel consumed per minute, which is something no-one’s ever going to bother with because the actual speed depends on the load, gearing, and so-on, and it’s far more convenient to describe the torque and power output at particular rpms…

        1. It’s supposed to be written Kv so nobody confuses it with kV, but you make something idiot-proof and they invent a better idiot. Like people who mix kWh, kW/h and then kW all in a jumble.

          No, it doesn’t apply to just a motor without a load. It’s a constant that sets the slope of the torque-speed curve at a certain voltage. When you know that curve, you can plot it, then you take your air drag equation, plus your rolling resistance, plus your “gravity drag” (going uphill) and plot it on the same graph, and where the two curves intersect is how fast you will be going when you put so many Volts into the motor.

  2. Nice build. One possible solution would be to license it as the original “historical” moped. The driver still needs to meet the other regulations to drive on the street, but at least it would be legal to do so. It shouldn’t have any problem meeting emissions requirements:-)

  3. This is really well done – as an abstract exercise, I wonder if anyone’s tried running the motor with a flywheel that matches the one intended for the piston connecting rod, then simply linking the two with a connecting rod thus replacing the piston/cylinder with the motor to avoid all the machining/fabrication.

    1. …and where would the custom connecting rod come from, if we’re not machining anything? Seems it would be easier to put the motor in place of the flywheel itself (bolting it up to the transmission input) and welding up or otherwise permanently locking up the centrifugal clutch. Or even just bolting the motor output to the output gear of the clutch. Not exactly a huge job of work.

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