ICE vs Electric Motor Transmissions

[speedyebikenoob]

Would people actually buy electric cars with transmissions though? Even if dumping more power into a direct drive is cheaper and more practical? I could imagine a stickshift electric car being pretty fun, I know a lot of people probably aren't going to agree, I drove a Tesla the other day, and yes it was pretty damn quick, but honestly it wasn't very fun. It just felt like it was missing something. If someone designed a tiny small miata like electric car with a manual transmission, I think I would totally buy it. It doesn't even need to be fast or anything.

 

[spinningmagnets]

Some of the early car EV conversions used the stock manual transmission, and most users reported only using second gear and the top gear.

Chevy is famous for their simple and robust 2-speed "Powerglide" automatic transmission. That might be an option.

I agree with Luke that these are most useful in a system that simply doesn't have enough volts, amps, and copper mass to do the job. Once you add a two or three speed...the motor, controller and battery can be smaller and more affordable. Although, it will still never have the performance of a big single-speed motor with high watts.

 

[Hillhater]

I agree with Luke that these are most useful in a system that simply doesn't have enough volts, amps, and copper mass to do the job. Once you add a two or three speed...the motor, controller and battery can be smaller and more affordable. Although, it will still never have the performance of a big single-speed motor with high watts.

Again...i refer you to the EV drag race records.

Rimacs new supercar dropped having a 2spd to having direct drive.

It does 1.9sec 0-60mph and does 258mph as a single speed.

The Rimac C2 retains a pair of 2 speed gearbox's to enable high torque at low speed, together with high speed on open roads/ closed tracks.

Rimac Automobili C_Two hypercar — A car alive with technology.
www.rimac-automobili.com › hypercars
rimac concept 2 from www.rimac-automobili.com
While a pair of single-speed gearboxes apply drive to the front wheels, a pair of two-speed gearboxes - again, one for each rear wheel - allow the C_Two to make use of its prodigious torque to produce both mind-blowing ...

 

[classicalgas]

Simply adding power to avoid a multi speed trany isn't a real life option for production ebikes...legal power limits, battery amps/cost, etc.

Evidently ebike manufacturers see a use for gearboxes, I've seen hub drives with two speed tranys, and a rear hub gearmotor with a three speed IGH built in.

 

[spinningmagnets]

The point of EV drag racers gaining exceptional performance from a 2-speed transmission is well taken.

However, there is not much else to the drag race battery system that is affordable, or long-lasting.

 

[Hillhater]

Agreed,.. there is not much about a record breaking drag race vehicle that is affordable or long lasting !
The batterys are chosen to give the best power to weight performance , but even if you restricted them to low power batteries...hence limiting the motor power... then the advantage of a multi speed gearbox would become more apparent.

 

[liveforphysics]

Simply adding power to avoid a multi speed trany isn't a real life option for production ebikes...legal power limits, battery amps/cost, etc.

Evidently ebike manufacturers see a use for gearboxes, I've seen hub drives with two speed tranys, and a rear hub gearmotor with a three speed IGH built in.

Anyone who doesn't understand how motors work could easily be confused into thinking it's a good idea, but it doesn't make it a good idea.

 

[classicalgas]

"Anyone who doesn't understand how motors work could easily be confused into thinking it's a good idea, but it doesn't make it a good idea."

So all the companies making and selling mid drives (kits and complete bikes) are "confused" ?

 

[classicalgas]

And these guys, who's business is converting ICE vehicles to electric?

https://quantumworks.com/multi-speed-gearboxes-can-offer-many-benefits-for-ev-powertrains-depending-on-application/

 

[Grantmac]

Bicycle sized vehicles can work well as a single speed provided they have +3kw of sustained power geared for <40mph.

With only 250-1000w they need gears.

 

[Chalo]

Bicycle sized vehicles can work well as a single speed provided they have +3kw of sustained power geared for <40mph.

With only 250-1000w they need gears.

Or, like, legal speeds.

The bike I built for my last girlfriend (a normal sized person) uses a 36V 18A nominally 350W controller and a Q128 geared front hub motor. It gets along just fine with only one speed for the motor and only one speed for the pedals. She is happy with the speed of it, and it conforms to local laws limiting the speed of an electric bike to not more than 20mph under motor power.

 

[Hillhater]

Just as well she is not living/riding around SanFrancisco or Sydney !
..she would be doing a lot of walking and pushing up hills .

 

[Grantmac]

I'd melt that motor without leaving my yard.
2kw barely gets it done geared to 20mph and gets plenty hot.
5kw geared to 40mph would be about right since I rarely run above 35mph anyways.

 

[classicalgas]

"5kw geared to 40mph would be about right since I rarely run above 35mph anyways." That's a motor vehicle by any reasonable definition, not an ebike. Once you hit moped power, you'd better plan on meeting motor vehicle licensing, lighting and brake standards. If not today, soon.

Gasbikes stayed under the radar until there were enough of them running past 40mph, and killing people, that politicians started noticing. A lot of cites have banned them in the last few years.

In fact, I'd say that as soon as you have so much power that a average person can contribute less than 25% to the power used in moving the vehicle, the pedals are extraneous, and it's motorcycle. I'd put that point at about 750W.

The Euro standard of three classes of ebike, with increasing requirements for safety equipment and licensing as power climbs past 250 W, makes a lot of sense.

 

[Grantmac]

Are we talking physics or law?

 

[Chalo]

Are we talking physics or law?

My point was that when you use an electric bicycle that complies with requirements for street use, you don't usually need multi-speed transmission as you asserted. You might find that you want multiple gears if you use a sub-1000W bike to ride at illegal speeds.

I lived in Seattle with a nominally 36V 750W front hub kit, and it worked fine in that steep city. Both hill climbing and cruising speed were entirely satisfactory, and I weighed close to 400 pounds at that time. Of course I had to use the pedals to get the best of it. It was an electric bicycle, not a feeble motorcycle.

 

[billvon]

I'd melt that motor without leaving my yard.
2kw barely gets it done geared to 20mph and gets plenty hot.
5kw geared to 40mph would be about right since I rarely run above 35mph anyways.

You're doing something wrong.

I cruise at 28-30mph with a 1500 watt motor.

 

[Grantmac]

You're doing something wrong.

I cruise at 28-30mph with a 1500 watt motor.

I think you misunderstand what's involved in riding around my yard. I could host a competitive trials motorcycle event.

For just cruising that motor is fine even when run at a human cadence and 25-30mph. Although it's definitely more efficient when spinning faster which is why I'm doing a build with independent chain lines and approximately twice the motor.

 

[billvon]

I think you misunderstand what's involved in riding around my yard. I could host a competitive trials motorcycle event.

Ah, my mistake. Yes, with the right terrain you can overheat almost any motor.

 

[classicalgas]

"Are we talking physics or law?"

Both. Good law ( fair, realistic, defensible) is reality based.

Double your vehicle speed( to 40 mph) and your kinetic energy (impact damage) is four times what it was at 20 mph "bike" speeds. That means four times the danger to pedestrians, four times the braking power needed...on top of half the obstacle avoidance time, plus whatever extra weight (also added to the kinetic energy of the bike) of that big battery pack and motor.

Moped level legal requirements aren't onerous, you don't get a free pass on the physics just for being green.

Back to the multi speed transmission. ICE dragsters have been successful with single speed transmissions. Does that mean street cars should be built that way? Throwing more power at the wheels isn't inherently the"best" solution, even if it works under certain conditions.

 

[Hillhater]

.....ICE dragsters have been successful with single speed transmissions. ......

Not really !...whilst they may have only one “gear”....the ratio between motor rpm and wheel rpm changes dramatically during a run.....thanks to a sacrificial clutch system.
Just a different form of variable transmission.

 

[classicalgas]

"Not really !...whilst they may have only one “gear”....the ratio between motor rpm and wheel rpm changes dramatically during a run.....thanks to a sacrificial clutch system.
Just a different form of variable transmission."

That's evading the question. Just because that strategy "works" (some single speed dragsters just use a combination of tire slip and diameter change with speed to do the same thing) doesn't make it a good solution for street vehicles.

 

[Hillhater]

What question is it avoiding ?
PS:..Name any competitive top dragster that uses only tire slip and dia change successfully without a progressive engagement clutch system ?
Progressive engagement clutches have proven very successful in road vehicles ..think “Torque converter”

 

[liveforphysics]

It's not a torque converter, its pure loss like a linear voltage regulator.

A torque converter uses acceleration of mass of fluid changing the radius of the fins its pushing against as its slung out. This lets it actually trade constant speed engine RPM for increased torque output.

A top fuel car has to just hold the engine RPM at 8-10,000rpm fixed so the engine makes useful torque, and then slips the clutch wasting the power, and not converting speed into more torque, just bleeding speed so they don't bog (until the vehicle is around the 1,000ft mark then they hookup 1:1).

 

[Hillhater]

You miss the point LFP..
I simply made two statements ..
1) dragsters use “Progressive engagement “ clutches.... to enable rpm difference between engine and wheels.
2) many road cars also successfully use “progressive engagement clutches”...in the form of a torque converter.
I did not say they were both the same or worked in a like manner..... just the purpose is the same.