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Comment by SloopJon | Hacker News Reader

The first thing I notice is the chain. Ars Technica had a story earlier this week about the Sondors Metacycle: similar power, similar weight, but no chain. Also, $25,000 cheaper.

https://arstechnica.com/cars/2021/01/this-electric-bicycle-c...

Granted, that the Metacycle isn't an off-road bike, but I wonder which is better for reliability in an area so remote that you need solar charging: a chain, or a hub-mounted motor?

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Direct drive hub mounted motors are constrained by low rpm operation and power delivery is limited to how much brute amperage you can force through them. They're often designed with a large diameter to compensate for the low rpm issues, which increases weight.

Some bicycle-scale hub motors have built-in gear reduction, which reduces the available motor size and adds a barrier between the motor and air cooling. They're more efficient and lighter than direct drive motors, but heat retention limits constant power output.

Watt-for-watt of power output, frame mounted motors can be much smaller and lighter. They can have excellent cooling (including liquid coolant circulated to a front mounted radiator), gear reduction allows them to operate at efficient speeds, they can be designed to target only efficiency rather than compromising to match hub size, and can be scaled fairly arbitrarily.

I don't know about bikes, but in electric bicycles engine in the back wheel is much worse for offroad because of weight distribution. The huge, heavy battery these bikes have might change this.

And unsprung weight is a much bigger deal when your vehicle actually has to use its suspension, weighs practically nothing, has 2" of sidewall, no contact patch to speak of, rims made out of toothpick, etc, etc. Hub motors just suck for bikes and motorcycles. You can kind of get away with them for driving on really nice surfaces but that all goes out the window for anything even mildly off road.

While there are definitely challenges to in-wheel motors, I do wonder if we’ll see more innovation over time on in-wheel suspension systems to compensate for the unsprung weight.

Here’s a neat example for one in a bike wheel [video]: https://youtu.be/DSKDH2NNmcA

Here’s a write-up: https://www.karmanhealthcare.com/acrobat-soft-wheels-shock-a...

I’m sure putting a motor in there will be problematic due to stresses on the shock absorbers, but it does seem like sock absorbing spokes in wheels could help gain space in vehicles by moving the motors to the wheel.

Edit: just to be clear I know little about the company and tech behind that wheel i linked to, I just find it to be an interesting area, and recently came across that.

Neat! But looks like maybe an inch or two of travel? Hard to imagine it would fare well in serious offroad conditions.

Every little bit helps but that "wind up" action is going to really suck under acceleration/braking.

That hub motor weighs probably 40+ lbs to be able to do a fairly measly 8kW though, low RPM motors by nature are very large and heavy compare to a small motor running through a chain or gears.

A chain should last a very long time, as long as it's not overloaded and lubrication is used every now and then.

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