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Planetary gearbox for an Amsterdam environmental friendly cargo moped

How does a gearbox ensure that a classic cargo moped is allowed to access the city center? Environmental requirements ensure that old mopeds and motorbikes are no longer allowed to enter the center in many cities. Time for something new? Jop from Amsterdam didn’t want to give up his moped and approached Apex Dynamics for help with the conversion of his classic cargo moped. The result is a handsome 140Nm torque and a future-proof transport possibility!

Due to the new environmental zones in Amsterdam, Jop has to convert his antique Gazelle Apollo cargo moped into an electric moped. But, in order not to end with a ridiculously large gear or small rear wheel, a planetary gearbox is required. But which one? As an expert in the field of mechanical drive technology, Apex Dynamics regularly receives such questions and is happy to answer them. There is always a challenge in such unusual questions, also in the question of Jop.

Technical challenge for the electric drive

A 5kw BLDC motor from Golden Motor is the motor in the environmentally friendly cargo moped. This motor gets the moped after a push start up to approx. 14 km/h ahead, but then the motor protection is activated. Adjusting the swing arm and incorporating a right-angle gearbox was not an option here, but how do we ensure that the torque is sufficient?

Jop wrote to APEX Dynamics:

“can you prepare a quotation for me? Are there any issues that you need to know or that I should be aware of? Calculating the requested mass inertia is a step too difficult for me, maybe I will work it out together with someone’s help. But maybe it is easier for you to come to a ‘close’ proposal if I give you some basic information?”

Calculate a planetary gearbox

The ideal total ratio is above 10, this is the calculation-technical optimum between torque at the rear wheel and the top speed of 45 km/h. In the first test (without gearbox) a 428 pitch chain was used with a distribution of 11 teeth in front and 70 teeth at the rear, so a ratio of 6.36. If a gearbox with ratio 4: 1 is placed in between, there is enough possibilities to choose the right gear wheels. The drive train can therefore be optimized by changing the gears for different loads, for example for driving through the city or on country roads, with full or empty cargo, a flat road or even climbing hills, and so on.

Gearbox advice

Apex Dynamics recommended an AE090 with a gear ratio of 4 for the following reasons:

  • Helical gears, which means quiet
  • Reversible, so partial braking on the engine is possible
  • T2nom = 140Nm, sufficient for a bike!

Driving mass inertia “reversed”

Half a year after the gearbox was delivered, Jop later called that the gearbox was broken. After research, a mass-inertia mismatch in reversed driving proved to be the problem:

“Well, of course I mainly drive in the city, which means unfortunately a lot of acceleration and braking. Of course I can decide to brake much more on my mechanical brake, I did that as little as possible so that I regained as much power as possible. In the future when I live outside of Amsterdam, hopefully that will be less, but the problem will remain. Maybe my moped is just too heavy to brake on the engine so much that the momentum gives too much force on it when you try to brake it on the engine? ”

Changing driving behavior

The newly supplied gearbox functions just like the first, but for now Jop has simply removed the engine brake: “As long as I don’t travel huge distances I can easily manage it with my battery power. So putting a disc brake on my rear wheel is, I think, more easy and cheaper than building a freewheel.”

Jop is satisfied, Amsterdam is satisfied and we are satisfied, what more do you want.

And if you get this response back, that’s is very nice: “Thanks again for all the help! With kind regards, Jop ”