Another gearbox discussion

[power]

I think its great they are getting away with only one gear for simplicity sake and reduced costs and weight. If you look at their power curve for the Roadster, it starts to fall off at 6000rpm. It doesnt end up with lot of power at 14000rpm, so all your accelleration potential is down at 60mph and falls from there. A CVT/IVT is not so much for a gas motor, as it is for any kind of power system WITHOUT constant power. since there is a power peak at 6000rpm, a CVT would allow the full 280HP to be available for acceleration all the way to the max speed potential. (Which is probably in the 170mph range). Part of the confusion I speak of, is that regarding the "Flat" torque curve. This, by definition, means that HP is rising proportional with RPM, it means that even in the lower rpm, accelerative forces are left on the table, not fully utilized. Just think how fast the Tesla Roaster would be if it was constant power, not constant torque! (via use of a CVT, or some sequential, close ratio, auto transmission). I can show you several high performance combusion engine torque curves that look very similar to the electric motor, right up to the point where it redlines. Then, the eletric motor performs its magic.

If Tesla decided to race one of these little gems, It would do very well in the club ranks as is. Picture how light it could be with all the interior gutted. A modification of a second gear would help it with accelerations in areas where it would most be mostly used . (i.e. after 60mph, more like 70 to 120mph). Even if the car only had a 120mph top speed, it would be fine for tracks here in northern california. I bet it would surprise a bunch of racer mainstream.

MK

I think Tesla should just stick with "direct drive" single ratio gear boxes for all models. The eMotor is so flexible that you can get away with that and it helps efficiency, and reduces cost and complexity. Also it eliminates one more thing to think about while driving.

If they need a bit more top speed they could work on better cooling and perhaps even a bit more high RPM capability without having to resort to the complexity of a shifting mechanism.

CVT/IVT is great/useful when you have a gas motor with peaky torque characteristics, but the eMotor is so flat that it doesn't seem needed.

[just-an-allusion]

Part of the confusion of the gear box discussion is a basic misunderstanding of what really accelerates a vehicle. Tesla has designed a single speed gear reduction that uses a near 8:1 ratio. Coincidentally, this is a very common final ratio for most high performance piston engine cars in 1st gear and usually reach a speed of 50-60mph. Because of its near flat motor torque curve, (which is no different than many piston engine's torque curves at near the same power levels), both a piston engine in 1st gear vs a Tesla Roadster with similar peak HP power plants will accelerate at near the same rate up. (If we are talking about comparable weights). The Tesla Roadster then still is able to accelerate up to 120mph still in the same single gear.
What's more amazing about the Tesla Roasters power plant, is not so much the flat torque curve to 4500rpm, but the slow decay of power to 14,000rpm. As we know, this limits the top speed and acceleration of the vehicle to 120mph. If the Tesla Roadster was able to have a second gear that was selected somewhere well past its peak HP was reached, its top speed would be extended as well as increased acceleration to that top speed.

Acceleration is proportional to power at any same vehicle speed as seen by this simple Newtonian identify:
Acceleration=Power/(mass x velocity)

Yes, everyone understands/remembers simple physics (doug), my primary problem is everyone's efforts in trying to correlate a motor's performance and functionality to that of an engine's, or vice-versa, when it's such a clear case of apples to oranges/they are two distinct, separate entities unto themselves with their own individual methodologies of operation and performance characteristics, i.e., while a "gear shift" may be a perfectly appreciable method of operating an engine at various speeds, the same doesn't hold true for a motor and any efforts on any car makers behalf to equate/integrate the actuating mechanisms of the one into that of the other earns them a lesson in futility, often had at quite considerable expense.

So, the idea is to maximize power at any vehicle speed. In the end, the way it will probably be done, will be to use a IVT (Infinitely variable transmisson). This way, max power would always be used when max acceleration was required, and some other rpm could be used that was in the motor's peak efficiency range for a given cruise speed.

Here is where I begin to see signs of a deeper intellect, i.e., if any form of a "transmission" is a requisite for an electric powered vehicle at all...it's a new form of powering our vehicles and as such should have the metaphorical table cleared/the chaulk board wiped clean of any vestiges of information relative to the "old school" method of powering our vehicles and an effort to begin anew should be the guiding philosophy of the day...but I like where your heads at.

[TEG]

I have driven a few EVs which had retained the old transmission from their post conversion days. The wide/early torque of the electric motor generally means you can just leave it in one gear and not bother with shifting. Sure, you could probably get a little bit better performance if you put in a CVT that could handle the torque, but does the Roadster really need it? I think it has sufficient performance to out accelerate just about any road car at street legal speeds.

Also the idea of trying to gear the Roadster differently to make it into a 170MPH vehicle seems misguided to me. I think the current eMotor would overheat, and the battery pack probably wouldn't be too happy trying to maintain the power required to achieve that sort of speed. At the moment I think heat build up of the eMotor is the most limiting factor, but the health of the Li-Ion cells probably aren't too far behind. They don't like to be discharged too quickly.

[power]

I think anything that Tesla can do to compete against the supercars is not misguided. Certainly, they need to work out a few other things first before they start looking at revolutionizing racing

I dont think overheating would be an issue if the car was to spend a little more time at its max power range. Its not uncommon for these type of motors to have some type of full power rating. There is also no difference in (to the motor and drive electronics) in accelerating from 40 to 80 mph , (operating in the peak HP range) than to operate from the 80 to 160mph. ( I just corrected an assumption by looking at the Tesla power/torque curves. peak hp happens at near 8000rpm not 4500rpm as I first stated.)

A simple 2 speed gear box wouldnt be that much of a challenge. Im sure some of the sequential, no accelerator lift, racing transmission technology could be used here!

Certainly there could be considerable performance gain potenatial for the roadster past 80mph where the power is falling off past its peak power pretty rapidly. In a racing environment, this is where the performance needs to be. The roadster would be anemic by losing near 100 hp compared to its piston engine competitors in this speed range. A simple gear box could drop the rpm back down to just below its peak HP range

MK

I have driven a few EVs which had retained the old transmission from their post conversion days. The wide/early torque of the electric motor generally means you can just leave it in one gear and not bother with shifting. Sure, you could probably get a little bit better performance if you put in a CVT that could handle the torque, but does the Roadster really need it? I think it has sufficient performance to out accelerate just about any road car at street legal speeds.

Also the idea of trying to gear the Roadster differently to make it into a 170MPH vehicle seems misguided to me. I think the current eMotor would overheat, and the battery pack probably wouldn't be too happy trying to maintain the power required to achieve that sort of speed. At the moment I think heat build up of the eMotor is the most limiting factor, but the health of the Li-Ion cells probably aren't too far behind. They don't like to be discharged too quickly.

[TEG]

There is also no difference in (to the motor and drive electronics) in accelerating from 40 to 80 mph , (operating in the peak HP range) than to operate from the 80 to 160mph.

Actually there is... At 80+ MPH you are using a lot more power to fight wind resistance, so the available acceleration power will be less. Therefore you would spend a LOT more time doing the 80 to 160mph acceleration thus causing a much longer period of full power being applied. I think the vehicle is designed for shorter bursts of acceleration, not prolonged full power as would be required by some racing and autobahn use.

I think Tesla basically proved their point with the roadster, and they would like to move on into more mass production vehicles, not into specialty racing. Certainly some Roadster customers have inquired about racing opportunities, but I don't think that is where the company has their focus right now.

[vfx]

A simple 2 speed gear box wouldnt be that much of a challenge

!!

[graham]

A simple 2 speed gear box wouldnt be that much of a challenge

!!

Hee! I have seen that movie before... it didn't end well...

[just-an-allusion]

I think Tesla basically proved their point with the roadster, and they would like to move on into more mass production vehicles, not into specialty racing. Certainly some Roadster customers have inquired about racing opportunities, but I don't think that is where the company has their focus right now.

"Racing" is never where Tesla had their focus.

The impetus behind the ideology of Tesla was/is to produce a real world, market viable alternative to the ICE, the next step, that would propel the World in to the future of vehicle powering...and perhaps even beyond the inherent limitations of the commuter arena.

Basically, to prove that it could be done, which they have, unlike GM who chose instead to (attempt) to prove that it couldn't (If only they had the benefit of hindsight, though they should have known better).

[Brent]

A simple 2 speed gear box wouldnt be that much of a challenge. Im sure some of the sequential, no accelerator lift, racing transmission technology could be used here!

Just to clarify what some other posters have alluded to...it turns out that it IS a challenge to make a two speed gearbox for an electric motor. TM nearly sunk itself financially over botched designs, and is still not out of the woods. A google search should turn up loads of info on the problem.

I believe the biggest challenge stemmed from the high RPMs at which the e-motor operates. Most regular (non-racing) autos' gearboxes don't deal with RPMs in the 13,000 range, so the Roadster's required new designs, none of which seemed to work out. Either the gearbox wasn't reliable long-term or it didn't shift quickly enough or it wasn't cheap enough. When TM announced that it was skirting the problem by using upgraded electronics, you could almost sense the sigh of relief.

[just-an-allusion]

Perhaps it is that the whole issue at the core of all of the engineering turmoil and financial expenditure that Tesla (as well as many other prospective EV manufacturers) has undergone is due to everyone's inability to think of the drive train as a motor (that it is) instead of as an engine (which it is not).