Winfried

Hello,

On their Radwagon longtail, Rad Power Bikes made the decision to use a 750W (manufacturer says 500W), direct drive rear hub motor with only 40Nm of torque, which doesn't seem much considering the bike itself already weighs a hefty 33 kgs.

Besides, using a > 250W motor means it's a major pain to use over here in Europe since it's considered in some countries as a moped… with all its consequences (license plate, insurance, moped-certified helmet, bike infras are off-limit, etc.)

A bit of googling indicates that Shengyi motor sells for a few tenner$.

So I was wondering if a 250W alternative were available with 50-90 Nm torque around the same price range… or there's simply no way to get that torque with a 250W hub motor. Are more watts simply required to get even that modest torque on a direct drive hub motor?

Thank you.

2old

FME, you'll have a difficult time locating a 250w hub motor that can be described as high-torque. The best possibility is a mid-drive OEM bike. Also, take a look at the simulator at ebikesca.

Winfried

That's what I feared :-/

https://www.ebikes.ca/tools/simulator.html

Thank you.

Rick

Affordable is a bad option for ebikes. If you need high torque than buy a high torque motor. If you set it up with a pedal assist instead of a throttle and don't speed then you will not be noticed. The GMAC motor at Grinn Tech/ebikes.ca is a high torque motor. This is Grinns version of the Bafang Mac motor. It is a geared motor with regenerative braking. The cable comes out the side instead of the center of the axle. The axle is 10mm so it fits in the frame without modification of the dropouts.

Winfried

The reason I asked, is that I was wondering if there were a 250W motor that could provide at least the 40Nm available on the Radwagon without 1. spending a lot more for a higher torque motor, and 2. the hassles of riding a > 250W motor over here.

I guess the reason why RadPowerBikes decided on that cheap 500/750W Shengyi motor is that the extra watts provide an acceptable torque for most people. But it doesn't look like the right bike for people living in hilly areas.

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Edit:

GMAC Rear Kit, Advanced PAS
Price as configured: US$906.00
https://www.ebikes.ca/shop/electric-...anced-pas.html

And then, we'll have to add ?$500 for a good battery.

Way more than what the ebike gear costs on the Radwagon :-/

2old

The closest you can get AFAICT is a Q128 motor (look at BMS Battery, but they're a so so vendor) which can be run @ 52V with a 15 amp or so controller. Obviously not 250w, but can "look like it".

Winfried

Thanks.

https://endless-sphere.com/forums/viewtopic.php?t=47042

It's no good if it's > 250W, as the insurance companies will love not paying a penny in case the rider hurts/kills a pedestrian.

Looks like there's just no way to get a longtail as cheap as the RadWagon that provides at least 40Nm of torque using a legit 250W.

morganw

Depends on whether you're talking Watts to the motor or Watts produced by the motor. Motors generate max torque at 0 RPM, but they're inefficient at low speed. Questioning that "high torque" claim for the GMAC, which is only 5:1 reduction, I tried it out on the Grin Tech motor simulator in my config. I have one with the torque arm defect, so I've limited my Phaserunner to 70A and it does 78Nm from 8% efficiency at 0.5MPH up to 64% at 10MPH. Efficiency peaks at 84% at 24 MPH.

At 90A, torque is 101 Nm up to 4.6 MPH.

The battery is delivering over 1kW at these low speeds, but mechanical power is only 250W at 1.8 MPH.

This heats up the motor like the dickens, though which is why I tend to pedal from stops.

When I was considering buying a turnkey, major manufacturer bike, I test rode the Trek Super Commuter and Riese & Müller Delite, both mid-drives and both only about 350Watts nominal. They were *fantastic* climbing hills (400 ft in 2 miles in Larkspur, Calif.) (and presumably pulling heavy cargo at lower speeds), but that's not enough power to push me sitting upright to the 28MPH limit. In fact, with a 750W limit on the GMAC, I can only get about 25MPH. I figure it takes 200-250Watts of human power (so 1kW total) to maintain 28MPH (motor simulator agrees).

The smaller DIY/kit mid-drives are cheaper than a fancier hub motor like the GMAC. Everyone in the US is on to the BBSHD, but the BBS02 is still available and you won't have all that gear melting problem that that over-voters have. They have gear reduction before the chainring, then you can get another 2x with a small ring up front & a wide-range cassette in the back. The way to higher torque is a longer lever.