Weight of a 100-Mile Range Electric Unicycle with structural pack

[Yook]

Marty mentioned in 

... that he desired to see an EUC with a 100-mile (approximately 160km) range within their lifetime. This got me thinking about the practicality and what it would entail in terms of battery technology and design innovations.

To achieve a 160km range at an efficiency rate of 20Wh/km (a common figure for high-speed EUC travel around 40km/h), the total energy required would be around 3200Wh. Considering the use of 2170-type lithium-ion cells, which are common in electric vehicles and have a capacity of approximately 15Wh per cell (weighing around 70g each), we'd need about 213 of these cells to reach our target range. This would bring the total weight of the battery cells to approximately 15kg.

Tesla has innovated in battery pack construction by filling the battery enclosure with a fire-retardant foam. This not only enhances safety by mitigating the risk of fire in case of a cell failure but also adds structural integrity to the battery pack. The foam allows the battery box to serve as a load-bearing element of the vehicle's structure, which can reduce the overall weight of the vehicle since the battery pack itself contributes to the chassis's rigidity.

Wonder how many kg that would shave off the weight of a typical 3200wh EUC. 

 

[Panzer04]

The motor on a big EUC is going to weigh around 10kg, which gets you to ~25kg immediately. Add structural members for suspension etc, optimistically 10kg and you're looking at around 35kg.

The lightest EUC near that class currently is the S22 with 2200wh. I suspect the difference comes from motor + tyre being heavier than I expect and suspension frames being heavier than they could be (almost certainly true - lightweight frames are not exactly high priority on big wheels). Manufacturers tend to just throw more material at the problem to make sure nothing breaks. This is not like the bicycle market, where they will optimise to the nth degree to shave weight off a bike frame.

I think most heavy 40kg EUCs could optimistically shave about 5kg off their current weights with good design, but there's going to be big diminishing returns as you go lower, and a lot of expensive work getting custom hub motors that weigh less, reducing and eliminating unnecessary material, etc. All this will inevitably make them a bit more fragile as well, probably.

[alcatraz]

To get a ridiculous long range wheel I propose the S18 with a custom pack. It's the lightest suspension wheel 18x3in. 

The stock pack (60cells) weighs 4.2kg. (60x70gr) and is 1100Wh.

You can choose 160 cells 2960Wh = 11.2kg or 200 cells, 3700Wh = 14kg.

It means that the finished product minus larger battery cases comes out to ~31kg @2960Wh or 34kg @3700Wh.

That's a bit embarassing because it puts basically all current long range production wheels to shame in the weight department.

[Panzer04]

On 3/12/2024 at 5:47 PM, alcatraz said:

To get a ridiculous long range wheel I propose the S18 with a custom pack. It's the lightest suspension wheel 18x3in. 

The stock pack (60cells) weighs 4.2kg. (60x70gr) and is 1100Wh.

You can choose 160 cells 2960Wh = 11.2kg or 200 cells, 3700Wh = 14kg.

It means that the finished product minus larger battery cases comes out to ~31kg @2960Wh or 34kg @3700Wh.

That's a bit embarassing because it puts basically all current long range production wheels to shame in the weight department.

It depends if the S18 motor has enough copper to avoid overheating in more intense usage (mostly offroad stuff/hill climbing). I'd hazard a guess that's a sacrifice some people wouldn't mind making though. I'm assuming the S18 uses a lighter/thinner motor than is common in the 40kg class, so it'll heat up more to generate the same amounts of torque.

I think this also shows how the marginal weight of adding more battery to an EUC isn't actually that much. You can see that with the 3600wh EUCs which are only 4-5kg (the weight of 1200wh) heavier than all the 40kg 2400wh EUCs but with 50% more battery.

[alcatraz]

I think the weight is half in the motor and half in the frame. All newer wheels have porky frames and massive motors.

You'll have to weigh the pro/con. Do you value cruising at 60km/h more than carrying 10kg more weight?

Crusing at 50+ could be a matter of minutes, but the weight is every second of the journey.

Also without having owned an S18, some of its power/torque shortcoming is mitigated by the larger pack. The stock battery is quite laughable.

[Panzer04]

3 hours ago, alcatraz said:

I think the weight is half in the motor and half in the frame. All newer wheels have porky frames and massive motors.

You'll have to weigh the pro/con. Do you value cruising at 60km/h more than carrying 10kg more weight?

Crusing at 50+ could be a matter of minutes, but the weight is every second of the journey.

Also without having owned an S18, some of its power/torque shortcoming is mitigated by the larger pack. The stock battery is quite laughable.

The only hard limitation on power and torque is the controller, and to some extent the battery. You can put as much power as you like through a motor, so long as you don't let it overheat all is well. In 99% of usage an overheating motor is not a problem, so it might be a sacrifice worth taking for, say, 5kg of motor weight reduction.

Yeah, 1kwh of 50e cells or whatever is not great.

There's no reason a light euc can't go fast, mfgs just don't configure the right batteries/motor/voltage setup to permit high speeds.

[alcatraz]

1 minute ago, Panzer04 said:

The only hard limitation on power and torque is the controller, and to some extent the battery. You can put as much power as you like through a motor, so long as you don't let it overheat all is well. In 99% of usage an overheating motor is not a problem, so it might be a sacrifice worth taking for, say, 5kg of motor weight reduction.

Yeah, 1kwh of 50e cells or whatever is not great.

There's no reason a light euc can't go fast, mfgs just don't configure the right batteries/motor/voltage setup to permit high speeds.

The stock pack is 1100Wh and high capacity cells. Imagine the voltage sag it has.

I'd agree with your reasoning if we had 4-6 cells in parallel like in 1800-2700wh packs but we're talking about 3 cells 1100. The voltage drops like a stone when you try to pull current (torque the wheel).

I'm not saying the motor and controller aren't weak but with a long range pack the weakest link (battery) is fixed. Maybe that's good enough? I don't know. Apparently there are some S18 with 50S out there. It would perform similarly. How easy are they to over-torque?

[Panzer04]

39 minutes ago, alcatraz said:

The stock pack is 1100Wh and high capacity cells. Imagine the voltage sag it has.

I'd agree with your reasoning if we had 4-6 cells in parallel like in 1800-2700wh packs but we're talking about 3 cells 1100. The voltage drops like a stone when you try to pull current (torque the wheel).

I'm not saying the motor and controller aren't weak but with a long range pack the weakest link (battery) is fixed. Maybe that's good enough? I don't know. Apparently there are some S18 with 50S out there. It would perform similarly. How easy are they to over-torque?

At low speeds, I don't believe any EUC sans tiny things like mten mini should be power limited (ie battery limited). Not much voltage is required to drive current at zero speed, so the controller turns 100v 20A from the battery into 10V 200A at the motor. Instead they are controller limited, and upgrading the controller is what would prevent low-speed overlean.

The issue is primarily at high speeds where you are power limited, as getting that same 200A at 50kph might need 150A from the battery (since the motor now needs say 80V), which is clearly not happening without a bigger, higher current battery.

Edited March 14 by Panzer04

[alcatraz]

Yep. I'm not arguing low speed current inadequacy.

At 40-50km/h cruising, I would.