# Hybrid/Electric Car Drivetrains - Are There Any Without Axels? **URL:** \ **Category:** Factual Questions\ **Created:** [May 7, 2009, 2:43am UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624 "2009-05-07T02:43:47Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Omniscient](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/omniscient/32/3290_2.png) [@Omniscient](https://boards.straightdope.com/u/Omniscient)\ **Post date:** [May 7, 2009, 6:22pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/21 "2009-05-07T18:22:40Z")
> [@justrob](#): > > If the electric motors are inside the body and not hub mounted you would still need the drive shafts and associated CV joints. So at least part of the weight you are trying to save would still be there. CV Joints seem unavoidable in that scenario, but the axles would be on the order of 2-3 inches instead of 1-2 feet. ---
**Author:** ![Omniscient](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/omniscient/32/3290_2.png) [@Omniscient](https://boards.straightdope.com/u/Omniscient)\ **Post date:** [May 7, 2009, 6:28pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/22 "2009-05-07T18:28:00Z")
> [@BMalion](#): > > Well the Myers Motors NmG has only a front axle for steering and a drive belt for the rear wheel. > > Have I completely missed the point? Yes, I think you have. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [May 7, 2009, 6:28pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/23 "2009-05-07T18:28:35Z")
> [@Omniscient](#): > > CV Joints seem unavoidable in that scenario, but the axles would be on the order of 2-3 inches instead of 1-2 feet. The axle needs to remain connected during the full vertical travel of the wheel. A 2" axle connecting the wheel to a chassis-mounted motor won’t allow for enough travel. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [May 7, 2009, 6:30pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/24 "2009-05-07T18:30:04Z")
> [@zut](#): > > As well, motors tend to be more expensive than fairly simple mechanical parts like axles, so I’d wager that four wheel motors would cost more than a single larger motor and the associated shafts. I’m willing to be wrong about this, as production volume costing is not my area of expertise, but I don’t think I am. In the system as proposed by the OP, you’d still have to have a motor/generator connected to the combustion engine. It would be generating the electricity that’s being used by the wheel motors. So, compared to a hybrid like the Prius, it’s really just a case of replacing the mechanical drive shafts with wheel motors and associated cabling. However, when you completely decouple the combustion engine from the wheels, that changes a few things. That engine could be completely computer controlled; running only when needed and always at its most efficient rpm for turning the generator. The engine could be designed for that specific operation, which eliminates the need for things like variable valve timing. I’m sure there are efficiencies to be found there, but it would take time to develop and require some serious bank. I think there’s also a lesson to learn from aircraft design. Two engines are better than one, right? Well, it depends. If your plane can fly on one engine, hooray; now either engine can fail (and it happens) and you’ll be okay. But if you require both engines running to stay in the air, double the engines means double the chance of an unplanned landing. So, does our hypothetical electric car need all four of its wheel motors working? That’s a lot that can go wrong and leave you stranded on the shoulder. Three powered wheels would probably push to one side or the other. We could make the motors larger, so either the fronts or the rears could take over, but the point of this design was to save weight. There is one question about hybrids that I haven’t found an answer to, yet. They capture energy from braking to charge a battery, and resue it. What happens when there’s too much energy? If I’m coming down out of the mountains, I don’t want to trash my batteries by overcharging them, but I’d still like to be able to stop. It seems to me that you’ll always need some means of disipating energy, likely conventional brakes, unless there’s a lighter means of bleeding off unwanted electric current. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [May 7, 2009, 7:04pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/25 "2009-05-07T19:04:49Z")
> [@Robot\_Arm](#): > > In the system as proposed by the OP, you’d still have to have a motor/generator connected to the combustion engine. It would be generating the electricity that’s being used by the wheel motors. So, compared to a hybrid like the Prius, it’s really just a case of replacing the mechanical drive shafts with wheel motors and associated cabling. > > However, when you completely decouple the combustion engine from the wheels, that changes a few things. That engine could be completely computer controlled; running only when needed and always at its most efficient rpm for turning the generator. The engine could be designed for that specific operation, which eliminates the need for things like variable valve timing. I’m sure there are efficiencies to be found there, but it would take time to develop and require some serious bank. You’re describing the difference between a parallel and series hybrid, which is something different than the OP is asking. There are absolutely efficiency differences between parallel and series hybrids, but those differences (and the _reasons_ for them) aren’t affected much by choosing one or four drive motors. > [@Robot\_Arm](#): > > There is one question about hybrids that I haven’t found an answer to, yet. They capture energy from braking to charge a battery, and resue it. What happens when there’s too much energy? If I’m coming down out of the mountains, I don’t want to trash my batteries by overcharging them, but I’d still like to be able to stop. It seems to me that you’ll always need some means of disipating energy, likely conventional brakes, unless there’s a lighter means of bleeding off unwanted electric current. Ayep. It takes a metric assload of power absorption to stop your vehicle. Regenerative braking systems are unlikely to be designed to absorb that much power. It’s important to remember that brakes are a safety item. Even _if_ your system is designed to absorb _all_ the braking energy (unlikely), you’d want conventional mechanical brakes large enough to stop the vehicle as a backup system in case the regenerative system failed. ---
**Author:** ![Omniscient](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/omniscient/32/3290_2.png) [@Omniscient](https://boards.straightdope.com/u/Omniscient)\ **Post date:** [May 7, 2009, 7:31pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/26 "2009-05-07T19:31:08Z")
> [@Robot\_Arm](#): > > There is one question about hybrids that I haven’t found an answer to, yet. They capture energy from braking to charge a battery, and resue it. What happens when there’s too much energy? If I’m coming down out of the mountains, I don’t want to trash my batteries by overcharging them, but I’d still like to be able to stop. It seems to me that you’ll always need some means of disipating energy, likely conventional brakes, unless there’s a lighter means of bleeding off unwanted electric current. All current regenerative braking designs also have traditional friction brakes for the reasons you mention. Also, regenerative braking loses it’s effectiveness at slow speeds so for the final stopping friction would be required. New technology might change this one day making regenerative braking more powerful and able to capture power at a wide range of speeds, but chances are that traditional friction brakes will need to be available as a emergency backup system. Those systems could be much less complex than current robust ABS systems, but it’s unlikely they’ll be done away with completely any time soon. ---
**Author:** ![BMalion](https://avatars.discourse-cdn.com/v4/letter/b/e274bd/32.png) [@BMalion](https://boards.straightdope.com/u/BMalion)\ **Post date:** [May 7, 2009, 10:05pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/27 "2009-05-07T22:05:59Z")
> [@Omniscient](#): > > Yes, I think you have. Story of my life. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [May 7, 2009, 10:19pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/28 "2009-05-07T22:19:38Z")
> [@Robot\_Arm](#): > > So, does our hypothetical electric car need all four of its wheel motors working? That’s a lot that can go wrong and leave you stranded on the shoulder. Three powered wheels would probably push to one side or the other. We could make the motors larger, so either the fronts or the rears could take over, but the point of this design was to save weight. Electric motors don’t lock up when they fail. (Unless it’s the bearing that fails, but that can happen on an unpowered wheel as well.) And even if 3 out of 4 motors fail, I imagine you can limp to the repair shop (or home) on one motor. Unlike airplanes, cars don’t stall and crash if you have insufficient power, they just move slower. And while I have never driven a 1-wheel drive car, I’ve ridden many 1-wheel drive adult tricycles and they move perfectly straight. You can’t even tell which side the drive wheel is. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [May 7, 2009, 10:24pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/29 "2009-05-07T22:24:25Z")
Two wheel drive cars can provide traction to just one tire, and they move fine. ---
**Author:** ![gaffa](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@gaffa](https://boards.straightdope.com/u/gaffa)\ **Post date:** [May 7, 2009, 10:33pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/30 "2009-05-07T22:33:03Z")
The [Eliica](http://en.wikipedia.org/wiki/Eliica) is a proof of concept electric car with motors in each of it’s 8 wheels. It can do zero to 62 in 4 seconds and went 230 mph in 2004, beating a Porche 911 in a head-to-head race. Not needing to shift gains a significant advantage. The motors are custom built 60 kw and (if I recall the documentary I saw) capable from 0 to 12,000 RPM. They had to do a lot of engineering to get the motors to spin that fast, as normal designs started shaking themselves to pieces at that speed. While looking for videos of the Eliica, I ran across the Kilocycle, an electric motorcycle that can do [0-60 in less than a second](http://www.youtube.com/watch?v=a2JkMCzjTVE&feature=related). ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [May 7, 2009, 10:49pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/31 "2009-05-07T22:49:59Z")
> [@Rick](#): > > Since Mr. Rose can only be in one car at a time, . Nonsense. There are double and triple Axels. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [May 9, 2009, 10:26am UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/32 "2009-05-09T10:26:12Z")
> [@Alex\_Dubinsky](#): > > To the OP: Biggest problem is that you actually need a transmission no matter what. You need to cut the motor’s high speed down to what’s the best rpm (and torque) for the wheels. So now instead of zero or one transmissions, you have four. (You could technically do it with no transmissions, like on the moon buggy, but it’s inefficient… like a 1-speed bike.) False. > [@](#): > > A gearless or single gear design in some EVs eliminates the need for gear shifting, giving such vehicles both smoother acceleration and smoother braking. Because the torque of an electric motor is a function of current, not rotational speed, electric vehicles have a high torque over a larger range of speeds during acceleration, as compared to an internal combustion engine. [Wikipedia](http://en.wikipedia.org/wiki/Electric_car#Acceleration_and_drivetrain_design) And a one speed bicycle isn’t inefficient, it’s impractical for a human who can’t change mass. ---
**Author:** ![gaffa](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@gaffa](https://boards.straightdope.com/u/gaffa)\ **Post date:** [May 9, 2009, 4:01pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/33 "2009-05-09T16:01:39Z")
> [@naita](#): > > False. [Wikipedia](http://en.wikipedia.org/wiki/Electric_car#Acceleration_and_drivetrain_design) Correct. The Eliica I posted about above goes from 0 RPM smoothly to 12,000 RPM with none of those pathetic hacks like a “transmission”. ---
**Author:** ![Hunter\_Hawk](https://avatars.discourse-cdn.com/v4/letter/h/50afbb/32.png) [@Hunter\_Hawk](https://boards.straightdope.com/u/Hunter_Hawk)\ **Post date:** [May 9, 2009, 4:53pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/34 "2009-05-09T16:53:08Z")
No cite, but ISTR that I saw an article in some pop-sci magazine several years ago that described a large truck-type vehicle designed for the military that had a setup like this. There were individual electric motors for each wheel, and a diesel engine to power the motors. Does this ring any bells? I don’t recall if the vehicle was in production or just a prototype. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [May 9, 2009, 6:35pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/35 "2009-05-09T18:35:59Z")
> [@naita](#): > > And a one speed bicycle isn’t inefficient, it’s impractical for a human who can’t change mass. What does shitting on the go have to do with transmissions? ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [May 10, 2009, 6:27pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/36 "2009-05-10T18:27:05Z")
> [@Alex\_Dubinsky](#): > > What does shitting on the go have to do with transmissions? Nothing. I’m puzzled as to how you managed to interpret my post that way. But humans, with their fixed mass, can only apply a limited range of torque to the bicycle pedals, which makes the single speed bicycle impractical in many settings. That doesn’t mean it’s inefficient. The internal combustion engine also has a limited range of torque, albeit not as limited, and is inefficient at the high end, so requires a transmission. Electric motors on the other hand can be designed with a range of torque way beyond an internal combustion engine, and with high efficiency at any point in that range, which makes a transmission unneccessary. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [May 11, 2009, 3:39am UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/37 "2009-05-11T03:39:56Z")
> [@naita](#): > > Nothing. I’m puzzled as to how you managed to interpret my post that way. But humans, with their fixed mass, can only apply a limited range of torque to the bicycle pedals, which makes the single speed bicycle impractical in many settings. That doesn’t mean it’s inefficient. > > The internal combustion engine also has a limited range of torque, albeit not as limited, and is inefficient at the high end, so requires a transmission. Electric motors on the other hand can be designed with a range of torque way beyond an internal combustion engine, and with high efficiency at any point in that range, which makes a transmission unneccessary. I think you’re missing the power component of the equation. Power is torque x RPM. Electric motors (and humans!) have great torque at even 0 RPM. (Is 160 pound-feet enough?) They can get their asses moving from a standstill, which is a big plus. But to expend their maximum power, they need to be running at a high RPM. You can feel the acceleration when switching to a low gear and pedaling fast. Humans can ride 1-speed bikes just fine, and electric motors don’t _need_ a transmission. But it always helps to have one. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [May 11, 2009, 1:15pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/38 "2009-05-11T13:15:43Z")
By the way, the “internal-combustion engine running a generator which powers electric motors to turn the wheels” system is already used for many vehicles: most locomotives use this (with a large diesel, and one motor per axle); I’m fairly sure some buses and large trucks do; and I believe it’s starting to be used in large ships. ---
**Author:** ![Hunter\_Hawk](https://avatars.discourse-cdn.com/v4/letter/h/50afbb/32.png) [@Hunter\_Hawk](https://boards.straightdope.com/u/Hunter_Hawk)\ **Post date:** [May 19, 2009, 5:21am UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/39 "2009-05-19T05:21:17Z")
> [@Hunter\_Hawk](#): > > No cite, but ISTR that I saw an article in some pop-sci magazine several years ago that described a large truck-type vehicle designed for the military that had a setup like this. There were individual electric motors for each wheel, and a diesel engine to power the motors. > > Does this ring any bells? I don’t recall if the vehicle was in production or just a prototype. OK, I think the [HEMTT A3 Hybrid Truck](http://www.hybrid-vehicle.org/hybrid-truck-hemtt.html) is what I was thinking of. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [May 19, 2009, 3:53pm UTC](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624/40 "2009-05-19T15:53:45Z")
[QUOTE=Quercus] By the way, the “internal-combustion engine running a generator which powers electric motors to turn the wheels” system is already used for many vehicles: most locomotives use this (with a large diesel, and one motor per axle); I’m fairly sure some buses and large trucks do; and I believe it’s starting to be used in large ships. [/QUOTE] It’s definitely catching on with cruise ships. Not sure about cargo ships, though. A ship I was on a couple of months ago runs something like three 16-cylinder and two 8-cylinder diesel engines. The engines drive AC generators, and they can freely cut engines on and off as needed to support propulsion and hotel loads (lighting, air conditioning, etc.). In port, they can run the hotel load on one 8-cylinder engine if the port isn’t equipped for “cold ironing” (an old maritime term for shutting off the engines completely and plugging the ship into shore power with a set of massive plugs and cables.) The ship’s propulsion is handled by two azipods and three bow thrusters, which enable the ship to maneuver in ways only dreamed of not long ago - they can crab the ship sideways for docking without needing assistance from tugs. [Previous page](https://boards.straightdope.com/t/hybrid-electric-car-drivetrains-are-there-any-without-axels/495624.md?page=1)