[Richard500]

Hi all,

I'm a serious newbie, and am embarking on my first ev conversion (of a very tired old Triumph Spitfire) here in the UK. Can anyone explain to me in simple terms why most conversions keep the gearbox and use an adapter plate to bolt on the electric motor ?
I get that it's probably simpler for alignment etc., but also extra weight and a bit redundant given the torque of an electric motor ? ... my gearbox is pretty shot & I would prefer to do without it altogether and just connect the electric motor to the propshaft ... is this a really dumb thing to do, or is it a sensible proposition ?

P.S. Apologies if this has been answered many times before, but I couldn't find an answer through the search.
Many thanks,
R

 

[dedlast]

I don't think anyone is ignoring you, it just feels that way sometimes. The short answer is it depends on what motor you are going to use. Usually, the motor needs more reduction than the final drive can provide. For example, the Nissan Leaf has a final drive ratio (actually, the only ratio) of 8.19:1, depending on the model year. Meanwhile the Spitfire has anywhere from 3.27:1 to 4.11:1. So, slower RPM, less efficiency, and less torque at the wheels. That's just one variable that goes into that decision. And, unfortunately, all I have time for today.

B

 

[Electric Land Cruiser]

The reason is because of RPM like dedlast has said. I also want to direct drive my vehicle and ditch the transmission, but I need a 2:1 or 3:1 reduction in between to make it work. Think of it like this: the average internal combustion engine revs to 5000 or 6000 rpm, the average electric motor revs to 8000 or 100000rpm. That means to get the same wheel speed, the electric motor needs to reduce the output RPM by half, or have a Triumph Spitfire that has the potential to go 200mph (but never will).

If I were you I would look into changing the rear differential ratio to a taller ratio or to use a nissan leaf type transaxle in the rear of the Spitfire to maintain good RPM/MPH ratio.

 

[brian_]

The reason is because of RPM like dedlast has said. I also want to direct drive my vehicle and ditch the transmission, but I need a 2:1 or 3:1 reduction in between to make it work. Think of it like this: the average internal combustion engine revs to 5000 or 6000 rpm, the average electric motor revs to 8000 or 100000rpm. That means to get the same wheel speed, the electric motor needs to reduce the output RPM by half, or have a Triumph Spitfire that has the potential to go 200mph (but never will).

Right... and that's why using the original transmission and leaving it in second gear would work for a motor with that speed range.

If I were you I would look into changing the rear differential ratio to a taller ratio or to use a nissan leaf type transaxle in the rear of the Spitfire to maintain good RPM/MPH ratio.

Extreme final drive ratios are not readily available for the Spitfire.
Unfortunately, the Leaf drive unit (motor and transaxle) almost certainly won't fit in the space the Spitfire has in the back.

While keeping the original transmission (or a similar transmission) is one solution to this speed mismatch, another is to use a fixed-ratio (single-speed) gearbox instead. The ev-TorqueBox is an example of this.

For some conversions, the speed range over which the motor can produce enough power is not wide enough, and a multi-speed transmission serves the same purpose as it does with an engine: it is shift to change ratios to keep the motor speed in a suitable range.

 

[brian_]

Usually, the motor needs more reduction than the final drive can provide. For example, the Nissan Leaf has a final drive ratio (actually, the only ratio) of 8.19:1, depending on the model year. Meanwhile the Spitfire has anywhere from 3.27:1 to 4.11:1.

That 8.19:1 is the overall drive ratio. The Leaf - like most EVs - uses a two-stage gear drive, and while only the last stage is literally the "final drive", the ratios for the two stages are generally not provided... only of the overall ratio (of motor speed to axle speed). The final drive ratio of a Leaf is not much different from the Spitfire, but the motor needs the whole 8:1, not just the final drive portion.

 

[Duncan]

The rpm mismatch is a problem if using a modern high revs AC motor

If you use a second hand DC motor from a forklift that problem goes away

If you slightly modify the trans tunnel then you should be able to fit a 9 inch forklift motor where the gearbox normally lives - that will give more than adequate performance and give you the whole engine bay for batteries

I'm using an 11 inch motor - but that would probably tear a spitfire diff apart

 

[brian_]

The rpm mismatch is a problem if using a modern high revs AC motor

If you use a second hand DC motor from a forklift that problem goes away

If you slightly modify the trans tunnel then you should be able to fit a 9 inch forklift motor where the gearbox normally lives - that will give more than adequate performance and give you the whole engine bay for batteries

I'm using an 11 inch motor - but that would probably tear a spitfire diff apart

All valid... yet most traditional conversions use brushed DC series-wound motors, keep the transmission, and don't run it in the 1:1 gear at low speed. Only the builders who choose this approach could authoritatively explain why.

NetGain sells the "TransWarP" versions of its "WarP" motors with a transmission tail housing mounted on it to make it easy to use to connect to the driveshaft without a transmission, for people who want to take this approach of using the final drive gearing as the only reduction gearing. This is an easy way to go, but this specific hardware is not required; for instance, Duncan doesn't use this particular motor series.

To match the first-gear acceleration of a stock non-US-market late Spitfire, the motor without additional gearing would need to produce the 111 N-m (82 lbf-ft) of the stock engine multiplied by the 3.50:1 first gear ratio, or 389 N-m (287 lbf-ft). NetGain says that their 9" motor at 500 amps can produce at most 95 N-m (70 lbf-ft). What works for Duncan with an 11" motor and over 300 volts into a 1000 amp controller in a minimal car won't work as well with a 9" motor and typical brushed DC motor voltage into a 500 amp controller in a heavier car.

Among the many Spitfire conversions there are probably multiple cars with 9" brushed DC motors. Even if they have original style transmissions, the drivers of those cars could comment on the performance of the car if driven only in the 1:1 gear (typically the top gear of a 3-speed for 4-speed).

 

[Duncan]

When I was first making my car I intended to use a gearbox
but when I did the calculations I discovered that in top gear I would be able to spin the rear tyres
That made the gearbox a bit unnecessary

When it was first on the road I found that 500 amps was far more than enough to make it fly up the steepest hills
and lose traction on anything except clean tarmac
A spitfire is heavier than my car but has less weight on the rear wheels and the rear suspension is not as good

Currently I run 1200 amps - but this is excessively exciting when I have my cheap road tyres fitted - so for road use I have a resister switched into the throttle circuit
This drops me back to 40% - about 500 amps - which is more than enough to make it a fast road car

The voltage is needed to get highway speed - 150 volts and a 9 inch motor is more than enough to maintain 500 amps up to 80 mph

An 11 inch motor will give more torque - but I am not sure that is a good idea with a spitfire back end

 

[Richard500]

Gentlemen,
You are stars ! ... this are exactly the kind of issues I have been mulling for a couple of years now, ... but without anyone (who wasn't trying to flog me a £20,000 conversion) to bounce ideas off, I have been struggling a bit. The good thing is I'm now retired, so I have a bit more time to play and figure it all out.

So, if I understand you right, if I'm looking for an AC motor along the lines of a Leaf, I will probably need to keep the gearbox (set at 2nd gear) which gets the AC motor into the 8000 - 10000 rpm range ... in order to get the torque required, or is it just an efficiency thing ?. If I run the Spitfire gearbox in 2nd, then I get an overall ratio (gearbox & final drive) of ~ 8.4 (without gearbox it's 3.9) which gets me into the 10000 rpm range for 80mph that @Electric Land Cruiser , @dedlast and @brian_ mention. Can you guys tell me what voltages & current these motors generally require ?

However, I could opt for DC motor which can run on lower revs and do away with the gearbox as per @Duncan. You,re right, Duncan, that the Spitfire backend is a bit twitchy to say the least, so I am looking for something reasonably tame ... if it gets me to 80mph, get me about town and has a reasonable range then that's as good as it needs to be. I think what you're suggesting is that I need to be looking at running a 9" motor at about 150v and 500amps at top speed. If I have enough battery cells to get me to 40KWh, then am I wrong to think that gives me a range of ~ 45 miles (or is that overly simplistic) ?

A few more follow-on questions spring to mind ...
1. I'm clearly going to have to brush up on my EM motor physics, but why does the AC motor need to rev so high ?
2. Am guessing ebay or gumtree are good places for 2nd hand 9" forklift engines ? ... or are there better places ?
3. Does a forklift engine controller have a CanBus type output to drive a digital speedo (& if not, how do I go about replacing my mechanical speedo currently connected to the gearbox) ?

Many thanks for your responses so far, they've already given me a lot of fuel for thought.
Cheers, R

 

[brian_]

Just picking out some small items to start...

1. I'm clearly going to have to brush up on my EM motor physics, but why does the AC motor need to rev so high ?

It doesn't. The power from any motor is the product of the torque and the speed (just multiplied together). The torque capability of a motor is very roughly dependent on the size (mass) of the motor, so it can make sense to use a smaller motor at higher speed (and less torque), to save weight and bulk compared to a heavier motor at lower speed (and higher torque). Since brushless motors can run faster (because they don't have brushes to fail or wear out), they provide the opportunity to go faster and therefore smaller.

2. Am guessing ebay or gumtree are good places for 2nd hand 9" forklift engines ? ... or are there better places ?

They're probably lousy sources; it's likely that the only such motors on eBay are being listed by people who got them for their own projects and are giving up. The frequently shared idea is that you can go to some place that uses electric forklifts, ask nicely, and strip a perfectly good motor out of an old forklift (that has been scrapped for some other reason than battery or motor failure) for next to nothing; while people have done this, it probably is not possible any more in many areas.

3. Does a forklift engine controller have a CanBus type output to drive a digital speedo (& if not, how do I go about replacing my mechanical speedo currently connected to the gearbox) ?

A DC motor controller doesn't even need to know the speed of the motor, let alone provide it to you on a communications port.
If you keep the gearbox you still have the speedometer drive; if you don't there are electronic speedometers of various designs.

 

[zepol_wube]

I did not see any any of these replies state an alternate option and our eventual plan. We are running a VW golf through the OEM tranny. We were not sure what gear we wanted. We have found 1st to be TOO much fun and now failed. 2nd is great in the city, 3rd for over 55mph. Someday we will drop it all out and either remove R,1,4,5 OR remove R-5 and put in a ~2.8nd single set. In 2nd 0-60 is 6.7 with the motor amps limited to 150 on a Nissan leaf 400V 24kWh pack.
You should be able to shuck out most of the tranny and save in the refit effort of a new solution.

 

[dougingraham]

One thing I haven't seen mentioned by the other posters is that the series wound DC motors have a preferred direction of rotation. You can make them run the other way but it takes at least three contactors to do so. And when running backwards the motor advance timing is not advanced, it is retarded. This causes really rapid brush erosion and wear on the edges of the commutator segments. I kept the transmission in my 85 RX-7 conversion primarily because of the issues with reverse and secondarily to get a closer match to the ideal reduction ratio.

In your spit conversion you will use 2nd gear to take off briskly and probably use third gear most of the time. I normally drive the RX-7 in third gear around town and only shift into 4th on the highway.

About range. My RX-7 has averaged 204 wh per mile over its life. With a 40 kwh pack this would mean a drop dead range of 196 miles. I have a 16 kwh pack which gives me a 78 mile range. This is with a Warp 9 motor and Soliton controller and the energy measured at the outlet the charger is plugged into. So it includes the losses in the charger.

I recommend buying a salvage Nissan Leaf or Tesla model 3 and taking the parts you need from it and selling the rest rather than buying a series DC motor and controller. You will probably end up with a better conversion this way and it is what I would do if I were going to convert another car.

Best wishes with your conversion!

 

[Duncan]

Gentlemen,
You are stars ! ... this are exactly the kind of issues I have been mulling for a couple of years now, ... but without anyone (who wasn't trying to flog me a £20,000 conversion) to bounce ideas off, I have been struggling a bit. The good thing is I'm now retired, so I have a bit more time to play and figure it all out.

So, if I understand you right, if I'm looking for an AC motor along the lines of a Leaf, I will probably need to keep the gearbox (set at 2nd gear) which gets the AC motor into the 8000 - 10000 rpm range ... in order to get the torque required, or is it just an efficiency thing ?. If I run the Spitfire gearbox in 2nd, then I get an overall ratio (gearbox & final drive) of ~ 8.4 (without gearbox it's 3.9) which gets me into the 10000 rpm range for 80mph that @Electric Land Cruiser , @dedlast and @brian_ mention. Can you guys tell me what voltages & current these motors generally require ?

However, I could opt for DC motor which can run on lower revs and do away with the gearbox as per @Duncan. You,re right, Duncan, that the Spitfire backend is a bit twitchy to say the least, so I am looking for something reasonably tame ... if it gets me to 80mph, get me about town and has a reasonable range then that's as good as it needs to be. I think what you're suggesting is that I need to be looking at running a 9" motor at about 150v and 500amps at top speed. If I have enough battery cells to get me to 40KWh, then am I wrong to think that gives me a range of ~ 45 miles (or is that overly simplistic) ?

A few more follow-on questions spring to mind ...
1. I'm clearly going to have to brush up on my EM motor physics, but why does the AC motor need to rev so high ?
2. Am guessing ebay or gumtree are good places for 2nd hand 9" forklift engines ? ... or are there better places ?
3. Does a forklift engine controller have a CanBus type output to drive a digital speedo (& if not, how do I go about replacing my mechanical speedo currently connected to the gearbox) ?

Many thanks for your responses so far, they've already given me a lot of fuel for thought.
Cheers, R

Re- Forklift motors
DC motors were used until about 2005 - then forklifts went AC - that means that controllers for car use became basically unobtainable
So you need a pre- 2005 motor
They are still about - but as Brian said getting rarer
You need to find the companies that repair forklifts in your area - and go scrounging

I have 14 kwh - and that gives me about 50 km range at 100 kph - with my awful aerodynamics
Speedo
You can buy a nice GPS speedo - if you look you can find a nice retro styled one that does NOT say GPS on the front (they are very accurate but not always "legal"

40 kwh is a lot of batteries - for a small car like a Spitfire you will have difficulty fitting them!

 

[macngee]

I did a lot of research before putting the standard transmission in our Chevy Metro. Most of the posts say there is no need for shifting or using a clutch. A few people say you need to be able to shift the car to make driving enjoyable. The car was originally built with a DC motor coupled to a gutted automatic transmission with around a 3:1 gear ratio. Acceleration from a stop was very uninspiring. I wanted to get the gear ratio down to 6:1 or 8:1. We are currently running an HPEVS AC-51 motor at 120 volts. It is nice to be able to test the car and see the effect of the different gear ratios with the standard transmission. I followed the common route and built the car without a clutch. I will NEVER build another electric car with a transmission without a clutch. To be fair, I race cars and like to drive fast and to shift through the gears. Shifting without a clutch is possible, but it is difficult and slow. The car is an absolute hoot to drive in first gear. When you punch the throttle, it spins the tires and accelerates great. It tops out at about 30MPH in first. Shifting into second gets you to about 55MPH, third tops out around 80MPH, and fourth is good for over 100MPH. Fifth gear is nice for cruising, the lower RPM's make the car quieter and it seems like it's just coasting along. Going up a hill, a lower gear makes the car draw less current so it's more efficient. It's fun just cruising down the road and shifting gears. Especially in an old sports car. I strongly recommend using the standard transmission and a clutch. If you just want to put around and save "fuel" you can get away without a transmission, but if you like torque you will appreciate all of the gears.

 

[Duncan]

I did a lot of research before putting the standard transmission in our Chevy Metro. Most of the posts say there is no need for shifting or using a clutch. A few people say you need to be able to shift the car to make driving enjoyable. The car was originally built with a DC motor coupled to a gutted automatic transmission with around a 3:1 gear ratio. Acceleration from a stop was very uninspiring. I wanted to get the gear ratio down to 6:1 or 8:1. We are currently running an HPEVS AC-51 motor at 120 volts. It is nice to be able to test the car and see the effect of the different gear ratios with the standard transmission. I followed the common route and built the car without a clutch. I will NEVER build another electric car with a transmission without a clutch. To be fair, I race cars and like to drive fast and to shift through the gears. Shifting without a clutch is possible, but it is difficult and slow. The car is an absolute hoot to drive in first gear. When you punch the throttle, it spins the tires and accelerates great. It tops out at about 30MPH in first. Shifting into second gets you to about 55MPH, third tops out around 80MPH, and fourth is good for over 100MPH. Fifth gear is nice for cruising, the lower RPM's make the car quieter and it seems like it's just coasting along. Going up a hill, a lower gear makes the car draw less current so it's more efficient. It's fun just cruising down the road and shifting gears. Especially in an old sports car. I strongly recommend using the standard transmission and a clutch. If you just want to put around and save "fuel" you can get away without a transmission, but if you like torque you will appreciate all of the gears.

If you use a wimpy motor....
But my Hitachi will spin the tyres and is till accelerating HARD at 96 mph
So no need for gears or a clutch

 

[macngee]

I hear you, I want to use a Tesla motor for my next conversion. The issue is most of the conversions people are doing would be more fun with a transmission and a clutch.

 

[Richard500]

They're probably lousy sources; it's likely that the only such motors on eBay are being listed by people who got them for their own projects and are giving up. The frequently shared idea is that you can go to some place that uses electric forklifts, ask nicely, and strip a perfectly good motor out of an old forklift (that has been scrapped for some other reason than battery or motor failure) for next to nothing; while people have done this, it probably is not possible any more in many areas.

Thanks Brian, I hadn't thought of that, will do some digging around the local area & see what turns up.

 

[Richard500]

I have 14 kwh - and that gives me about 50 km range at 100 kph - with my awful aerodynamics
...
40 kwh is a lot of batteries - for a small car like a Spitfire you will have difficulty fitting them!

Thanks, good to know you get 50km from 14kwh (& my aerodymanics probably aren't much better than yours, its actually a morgan-esque kit based on a Spitfire that I built about 35 years ago)
Re 40kwh - yes agreed, hence the desire to lose the gearbox, but I reckon that using the petrol tank space as well, if I need to, I should just about do it.

 

[macngee]

40kWh could probably get you a 100 mile range. I think 20kWh would be plenty, depending on how you are driving.

 

[brian_]

I followed the common route and built the car without a clutch. I will NEVER build another electric car with a transmission without a clutch. To be fair, I race cars and like to drive fast and to shift through the gears. Shifting without a clutch is possible, but it is difficult and slow.

It is difficult and slow because the huge rotational inertia of the motor makes the job of the synchronizers much more difficult, especially when shifting down (requiring the input shaft and motor to spin faster).

The obvious solution is the same as used with an engine and double-declutching: "blip" motor power to bring the input shaft up to the matching speed for the target gear when downshifting (and brake with it to bring the input shaft down for upshifts). Motor controllers don't do this, because production EVs don't shift and aftermarket controllers are not designed as part of a complete powertrain with a transmission. So no one does this, but someone could as a DIY project.

The other non-clutch solution is to use a dog-ring transmission instead of a synchronized transmission... but that would be pretty harsh in a street vehicle. Dog rings would work well in combination with motor control for speed matching, and perhaps a mechanical sequential shifter. I'm not holding my breath waiting for anyone to do this, because it's so much easier to just use a large motor and single-ratio transmission.

At least one electric drag racer used a Lenco transmission, which incorporates cone clutches as shift elements. Lencos are expensive.

The Rimac cars and the Porsche Taycan both have two-speed transmissions (in the rear only), which are shifted by clutches... like a dual-clutch automatic but with only two gear sets and thus no synchros or gear shift mechanism.