# Ditching transmissions (brute force direct drive)?



## Tremelune (Dec 8, 2009)

I'm (once again) contemplating an MGB conversion. The MGB gearbox is not worth keeping, and with Miata or T5 gearboxes being not much cheaper than the 2:1 TorqueBox (and also probably requiring chassis mods and a custom driveshaft anyway), I don't think swapping in a stronger gearbox is worth it.

The stock MGB rear differential can handle about 400 ft-lb of torque (and I've heard 600 ft-lb argued as well), so that's what I'd like to get to the driveshaft. I see three prominent paths:

1) Use a Lexus GH450H hybrid transmission. If it fits reasonably well in the transmission tunnel (I fear it would not), it would be a slam dunk: 280lb, 205ft-lb, 100hp, built-in 1.9 and 2.9 reduction gear and output yolk, and people have them working with open source inverters. I have plans to measure the tunnel and engine bay more precisely, but I suspect it'll stick out a foot or more into the engine bay, which would be a bummer for battery space up front.

2) Mate a Leaf (hard) or Hyper9 (easy) to a TorqueBox and be done. This is promising, though it means costs range from $5-10k for the motor and gearbox alone. If this fits such that I could clear the engine bay for batteries, it might be worth it (though I don't think that's possible with the boxy Leaf motor).

3) Brute force direct drive. Find a Warp9 or forklift motor and put enough energy into it to make 400 ft-lb at the output shaft, and ditch gearboxes entirely. If it's 1:1, it doesn't matter if they only spin to 6k RPM, because that would take me over 100mph.

I'm mainly asking about the last one. How much power can these "fork lift" motors really put out? Is this a viable option for highway cruising (which would be more like 50hp continuous)? I don't need regen (though it's nice), and if I melt a cheap motor every 10k miles, that's maybe okay (assuming it's easy to swap out)...Maybe two motors end-to-end...?

I expect I'll be using fairly large, fairly recent set of batteries that could put out a lot of amps for a while. From what I've read, it might just come down to how cool I can keep the motor, which is probably tricky for the ones without built-in water jackets...Are there any 300-400 ft-lb motors that cost less than $10k...? I know some have removed the gearbox from Tesla drive units, but that seems to involve quite a bit of fabrication that is beyond me.

I guess my basic question is: *Is it cost-effective to use a motor with twice the torque of a Leaf/Hyper9 in lieu of a $4k 2:1 reduction gearbox?*


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## brian_ (Feb 7, 2017)

You're going through a similar analysis process as I have, for our Spitfire. 



Tremelune said:


> 1) Use a Lexus GH450H hybrid transmission. If it fits reasonably well in the transmission tunnel (I fear it would not), it would be a slam dunk: 280lb, 205ft-lb, 100hp, built-in 1.9 and 2.9 reduction gear and output yolk, and people have them working with open source inverters. I have plans to measure the tunnel and engine bay more precisely, but I suspect it'll stick out a foot or more into the engine bay, which would be a bummer for battery space up front.


That's the L110 transmission, also used in L110F form in the Lexus LS 600h (with the addition of a transfer case for AWD which of course you wouldn't want). This is a relatively large unit, but might fit. The L210 transmission which was used in the (much less common) Lexus IS 300h is the same design, but with only a fixed-ratio single-stage planetary gearbox in the tail versus the two-ratio Ravigneaux double planetary gearbox in the tail of the L110 - half the gearing and leaving out the two hydraulic clutches needed for shifting makes the L210 substantially shorter and lighter; it also means that shifting doesn't need to be controlled. Since the IS is a shorter and lighter model on the same platform as the GS and LS, I suspect Toyota made this transmission variant both to save space and weight, and because the single reduction ratio is adequate.

The L110 has far more than 100 hp output: 145 kW has been reported. The L210 is rated at 105 kW (it may or may not use the same MG2), and about the same torque. It reportedly has a 3.33:1 reduction ratio in the gearbox.

The output fitting appears to be a three-armed spider for a flex disk (or giubo) joint, rather than a U-joint yoke. That's okay, as you can have a propeller shaft made (or modify the stock MGB shaft) with that at the front - it's a commonly-used design, not specific to the Lexus hybrid transmissions.

A possible route, which I have not confirmed is viable, is to split the L110 or L210 transmission between the front and middle sections, leaving the front section of MG1 and power splitter gearbox off, leaving only MG2 and the reduction gearbox. A custom splined shaft would be needed to couple the remaining parts together, or the shaft attached to the power splitter ring gear would need to be cut off and used without the ring gear; a custom plate would finish off the front of the remaining unit. In addition to losing much of the length and weight, the front section is the largest-diameter part. This would mean driving on only MG2, but that's what the Lexus does in electric-only mode. this stripped-down version would need only the same control of MG2 as used in the stock Lexus in EV mode, and if the L210 is used no shift control (which is done by electronic control of solenoid valves in L110) would be required.


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## brian_ (Feb 7, 2017)

Tremelune said:


> 3) Brute force direct drive. Find a Warp9 or forklift motor and put enough energy into it to make 400 ft-lb at the output shaft, and ditch gearboxes entirely. If it's 1:1, it doesn't matter if they only spin to 6k RPM, because that would take me over 100mph.


I like that idea for mechanical simplicity. In AC motors, if the Chevrolet Spark motor can be separated from its transaxle and if it fits in the tunnel (it's large in diameter) it has stupidly high torque (meeting your requirement in stock form), as it is designed to work with an overall gear ratio of about 3.5:1, like the MGB with only the final drive for reduction.


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## brian_ (Feb 7, 2017)

Tremelune said:


> ... From what I've read, it might just come down to how cool I can keep the motor, which is probably tricky for the ones without built-in water jackets...Are there any 300-400 ft-lb motors that cost less than $10k...? I know some have removed the gearbox from Tesla drive units, but that seems to involve quite a bit of fabrication that is beyond me.


The Tesla induction motors (Model S/X drive units) can only handle high current briefly before overheating. They have a liquid cooling jacket, but the heat is generated largely in the rotor - especially at high torque - and only the stator is cooled. Using them with only the MGB's final drive reduction, and thus at a small fraction of their speed capability, seems like a recipe for heat problems even with such a light car... but that's only my guess.


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## brian_ (Feb 7, 2017)

I looked at the Parker GVM motor series because someone mentioned them a while ago, and they seem to offer a range of motors with full specifications, and it may actually be possible to buy them (unlike most motors which are available to OEMs only). They come in two diameters, various lengths, and two voltage ranges, so you can pick what meets your needs. A 210-150-DPW (that's 210 mm diameter case, 150 mm long working section) could produce enough torque for my Spitfire (direct to the final drive) even at 120 V, but the high voltage version (320 V) would be needed for sustained highway speed (and similar torque capability). At 337 mm long overall and only 215 mm overall body diameter it would fit nicely. Unfortunately, if one can actually buy one I'm sure it's stupidly expensive, and would need a similarly expensive inverter.


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## Tremelune (Dec 8, 2009)

Very interesting, thanks! I shall look into the Spark motor...

I did not know about the L210...That seems even better for my car...The low gear only seems useful for burnouts in such a light car, so ditching that weight and clutches sounds divine (as long as it can be controlled in much the same way as the L110—meaning there's a board for it that actually works). Tricky bit is that the Lexus GS300H was never sold in the states, and shipping from Germany is $1,500...

From images I'm seeing, it looks like I could shave a few inches off the bellhousing of these transmissions such that the largest diameter would shrink, as well as the overall length. L210 wiki:






Toyota/Lexus GS300h CVT - openinverter.org wiki







openinverter.org


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## Duncan (Dec 8, 2008)

I'm using the large DC forklift motor route

You won't use very much power cruising on the highway - with my appalling aerodynamics I use less than 26 kW at 100 kph 
I did melt one motor but I am abusing my machine and I think it actually failed from where I had put a nick in one of the coils 

Cheap cheerful - and dare I say it entirely appropriate for an MGB


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## electro wrks (Mar 5, 2012)

brian_ said:


> They have a liquid cooling jacket, but the heat is generated largely in the rotor - especially at high torque - and only the stator is cooled.


These motors typically have a liquid cooled rotor as well, at least in the rear main motor versions: 




and: US7489057B2 - Liquid cooled rotor assembly - Google Patents

Overheating, apparently from the rotor, still is a limiting factor with these motors.


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## brian_ (Feb 7, 2017)

Tremelune said:


> From images I'm seeing, it looks like I could shave a few inches off the bellhousing of these transmissions such that the largest diameter would shrink, as well as the overall length. L210 wiki:
> 
> 
> 
> ...


I think that perspective is deceptive, and the potential length reduction wouldn't be as much as a few inches, although there may be more opportunity for case trimming of the L210 than the L110, due to internal component sizes. These transmissions are designed to mount to an engine like a normal transmission, so they have a bell housing size and shape that is needed for a clutch or torque converter which isn't in these transmissions, and a flywheel which isn't needed with an electric motor (any spare space would be clearance for the flywheel and dampening coupler).

Two issues with trimming: 

You still need to bolt a bracket on the front to support the unit and take all of the output torque; the bolts to the engine normally do that, so when you cut off the front of the case you cut off the places to bolt to it.
The input shaft may stick out even further than the front of the housing: according to OpenInverter, "The input shaft pokes out 29mm from the general highest point of the back of the bell housing?". It could be just 29 mm past the front face recessed in the bellhousing, with the shaft end roughly flush with the bell housing face. Either way, it no longer needs to be connected to an engine, but if you want to use the front motor (MG1) by the straightforward method you need to lock it stationary with a coupler mounted to a fixed bracket. If you cut it shorter, you lose the splines to couple to.
I listed some information sources in another thread.


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## brian_ (Feb 7, 2017)

Tremelune said:


> I did not know about the L210...That seems even better for my car...The low gear only seems useful for burnouts in such a light car, so ditching that weight and clutches sounds divine (as long as it can be controlled in much the same way as the L110—meaning there's a board for it that actually works). Tricky bit is that the Lexus GS300H was never sold in the states, and shipping from Germany is $1,500...


That's unfortunate. Since the hybrids look the same as the non-hybrids of the same model, it's hard to tell how many are on the road. With some models being available in the U.S. but not Canada, I'm used to not seeing stuff that is readily available elsewhere in North America, so I didn't notice whether the IS (not GS) hybrid was available in the U.S. According to Wikipedia, "The hybrid IS 300h model is sold in Europe, Japan, and select international markets", although that was based on references from when the model was introduced.


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## mgbgte (Jun 10, 2018)

Tremelune said:


> I'm (once again) contemplating an MGB conversion. The MGB gearbox is not worth keeping, and with Miata or T5 gearboxes being not much cheaper than the 2:1 TorqueBox (and also probably requiring chassis mods and a custom driveshaft anyway), I don't think swapping in a stronger gearbox is worth it.
> 
> The stock MGB rear differential can handle about 400 ft-lb of torque (and I've heard 600 ft-lb argued as well), so that's what I'd like to get to the driveshaft. I see three prominent paths:
> 
> ...


Hi, I converted my 1968 MGB/GT to electric drive 8 years ago. I used an HPVES AC-50 motor and a 67 3 synchro tranny (the 68 4 synchro would have been more difficult to fit. I bough a restored 3 synchro for about $1100. I drive around in 4th gear MOST OF THE TIME!; can easily get up to 70 mph, keep up with freeway traffic. The acceleration in 4th is not very good; so I shift into 2nd at time; drive around in 2nd on hills. I get around 60-80 miles of range per charge. I use 36 lithium ion cells, divided into three 40 volt sub-packs for a total of 120 volts. I replaced the gas tank with a custom battery box built using carbon fiber, kevlar and fiberglass layers wrapped around an aluminum frame. There are 18 cells in the rear battery box, 6 in the original battery boxes constructed similarly to the rear box; the remaining 12 cells are split in two groups of six in front of and behind the motor. The battery packs are segmented into three 12 cells groups using contractors. The contractors are de-activated by an inertia relay in case of an accident, so the highest voltage in the car its a safe 40 volts when the ignition is not on. This is a safety feature that I thin all home conversions should have. 

Bottom line: the car runs about as well as the original ICE version when driven conservatively. I also used to drive a 57 MG ZB varitone that I have given to my son. I am trying to convince him to convert it to an EV. For a more detailed description check out: MGB GT Reborn Electric – Moss Motoringhttps://mossmotoring.com › mgb-gt-reborn-electric


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## Sagecrumpton23 (May 28, 2021)

Tremelune said:


> Very interesting, thanks! I shall look into the Spark motor...
> 
> I did not know about the L210...That seems even better for my car...The low gear only seems useful for burnouts in such a light car, so ditching that weight and clutches sounds divine (as long as it can be controlled in much the same way as the L110—meaning there's a board for it that actually works). Tricky bit is that the Lexus GS300H was never sold in the states, and shipping from Germany is $1,500...
> 
> ...


That looks A lot like the 1916 Owen magnetic


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## Sagecrumpton23 (May 28, 2021)

Tremelune said:


> I'm (once again) contemplating an MGB conversion. The MGB gearbox is not worth keeping, and with Miata or T5 gearboxes being not much cheaper than the 2:1 TorqueBox (and also probably requiring chassis mods and a custom driveshaft anyway), I don't think swapping in a stronger gearbox is worth it.
> 
> The stock MGB rear differential can handle about 400 ft-lb of torque (and I've heard 600 ft-lb argued as well), so that's what I'd like to get to the driveshaft. I see three prominent paths:
> 
> ...


I am doing a similar conversion on my 76 mgb and planing to put a electronic overdrive between the output of the motor and the final drive I am going to be doing it in steps starting out with 144v of lead then moving to a Tesla style lithium ion battery pack down the line do you by any chance have the output chart for the warp 9 showing the torque and horsepower output curve up to its maximum voltage


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## brian_ (Feb 7, 2017)

Sagecrumpton23 said:


> That looks A lot like the 1916 Owen magnetic


I suppose it does, and so does the longitudinal version of the GM Two-Mode hybrid transmission, but the power splitter and resulting mechanical transmission path are a critical difference. Of course the power-splitter design doesn't help using this as just an electric motor, and the Owens Magnetic would be even worse.


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## jrab (Jul 26, 2007)

Direct drive “brut” would probably be fine, but I think you might be disappointed with performance. For my 914, i could stay in 3rd all day, but not exceed 60 without redlining. If I stayed in 5th to theoretically hit 100 at 6000 (never tried it), acceleration from 0-30 would really suffer, and you’d probably be overloading (overheating) the system constantly.


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## brian_ (Feb 7, 2017)

I think the approach of targeting a torque value is good, because that is what determines low-speed acceleration. 

The 400 lb-ft value was chosen for a motor without additional transmission as what the final drive can stand, but for comparison, an original MGB had roughly 100 lb-ft available at peak (depending on year and market) and first gear was between 3:1 and 3.7:1 (depending engine, etc), so there was something in the range of 300 to 400 lb-ft of torque to the final drive in first gear - match that, and you match performance, roughly. With second gear around 2.2:1, even 300 lb-ft would be more than enough to keep up with the original once the original shifts to second.

I'll note that with any motor torque will drop off with speed after some point. That's not a problem, as long as power at high speed is still sufficient.

The issue of overheating is valid, though... with no way to shift and thus change motor speed, the motor and controller need to be able to handle the required current for normal driving continuously, so that's a consideration. Liquid-cooled motors would be better in this respect.


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## John_G (Jun 6, 2020)

Tremelune said:


> I'm (once again) contemplating an MGB conversion. The MGB gearbox is not worth keeping, and with Miata or T5 gearboxes being not much cheaper than the 2:1 TorqueBox (and also probably requiring chassis mods and a custom driveshaft anyway), I don't think swapping in a stronger gearbox is worth it.
> 
> The stock MGB rear differential can handle about 400 ft-lb of torque (and I've heard 600 ft-lb argued as well), so that's what I'd like to get to the driveshaft. I see three prominent paths:


A gearbox is only needed with a DC motor, they (most) simply cannot handle the RPM needed for direct-drive at highway speeds.



> 1) Use a Lexus GH450H hybrid transmission. If it fits reasonably well in the transmission tunnel (I fear it would not), it would be a slam dunk: 280lb, 205ft-lb, 100hp, built-in 1.9 and 2.9 reduction gear and output yolk, and people have them working with open source inverters. I have plans to measure the tunnel and engine bay more precisely, but I suspect it'll stick out a foot or more into the engine bay, which would be a bummer for battery space up front.


These are a very good option, having an integrated parking mechanism and all. However, they REQUIRE an external hydraulic pump (factory ones are prone to failure) and locking of the input shaft to function as an EV drive system. Don't overlook the TWO motors, so a Toyota Inverter is almost a necessity and a way to control it.



> 2) Mate a Leaf (hard) or Hyper9 (easy) to a TorqueBox and be done. This is promising, though it means costs range from $5-10k for the motor and gearbox alone. If this fits such that I could clear the engine bay for batteries, it might be worth it (though I don't think that's possible with the boxy Leaf motor).


I doubt a gearbox would be needed for the Leaf motor, they make 250-320 Nm as-is and you can get one for under $1k, if not under $250.



> 3) Brute force direct drive. Find a Warp9 or forklift motor and put enough energy into it to make 400 ft-lb at the output shaft, and ditch gearboxes entirely. If it's 1:1, it doesn't matter if they only spin to 6k RPM, because that would take me over 100mph.


Again, a DC solution, which is fine, but what will take that 400 lb-ft from the motor to the driveshaft?

The Leaf drive train uses reduction of about 8:1, weighs over 1500kg and has respectable acceleration. If you can get the weight down by 50% to 750kg or so, a 4:1 differential that is directly driven would net similar acceleration to a Leaf. Certainly better than many small British cars from the 60's had when new.


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## Duncan (Dec 8, 2008)

John_G said:


> Again, a DC solution, which is fine, but what will take that 400 lb-ft from the motor to the driveshaft?
> 
> The Leaf drive train uses reduction of about 8:1, weighs over 1500kg and has respectable acceleration. If you can get the weight down by 50% to 750kg or so, a 4:1 differential that is directly driven would net similar acceleration to a Leaf. Certainly better than many small British cars from the 60's had when new.


I just use a short driveshaft - it has to take that torque anyway after the gearbox
"net similar acceleration to a Leaf"
I'm at 800 kg and I do the 1/8th mile in 7.8 seconds at 96 mph - couldn't get traction when I did the 1/4 mile so I took 13.4 seconds and 104 mph


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