[stevesmithworks]

Hi! I'm new here but I've been casually looking into EV conversions for a few years. New cars just have zero appeal.

I'm considering converting a 1960s or 1970s Beetle. The idea of a single gear is very appealing. Simpler design, fewer parts, lower weight. Also easier driving especially when combined with single pedal regen driving. My question is can I convert without a transmission and if so then what would performance be like?

Info I've gathered.

Classic Beetles were very low power by modern car standards. They were in the range of 22 kW (30 hp) in the 1950s up to 45 kW (60 hp) in the 1970s. Reports on line say 0-60 mph times of 17-18 seconds and top speed of 130 km/h (80 mph).

Curb weights were in the range of 800–840 kg (1760–1850 lb). Getting the transmission out and changing some sheet metal to fiberglass or carbon fiber would drop the weight more. Change to lighter wheels, etc.

I don't need long range. This will be an "around town" car. I think that 160 km (100 miles) is more than enough.

I do need to drive up to 110 km/h (70 mph) but I don't need to drive over the speed limit.

Beetle tire size is 165/80R15 which has a diameter of 64.5 cm (25.4")

What I see online is the Beetle differential had a ring to pinion ratio of 4.375 (early to mid 1960s), 4.125 (late 1960s to early 1970s), 3.875 (mid to late 1970s.)

The AC-50 and AC-51 motors seem popular. The EV West website lists the AC-51 motor with the following specs.

• Weight: 52 Kg (115 lbs)
• Rated Torque: 108 Lb Ft
• Rated Power: 88 HP
• Continuos RPM: 5,000
• Max RPM: 10,000

Using this calculator with 5000 RPM, 25.4" tires, I see the following top speeds for each differential ratio

4.375 ratio -> top speed of 86.4 mph (139 km/h).

4.125 ratio -> top speed of 91.6 mph (147 km/h). I've never even driven any car that fast.

3.875 ratio -> top speed of 97.5 mph (157 km/h). I never want to drive a car this fast!

So I could choose the 4.375 ratio as it has plenty of top end speed for me and would provide the zippiest performance (of the above options) from a stop. At 56 mph (90 km/h), our local highway speed limit, the motor would only run at only 2871 rpm.

Would the single 4.375 ratio be too hard on the motor? Degrade its performance over time or limit its life?

Is there a way to estimate 0-60 mph time? Is the following correct? Given 800 kg (1763 lbs) curb weight, 146.4 Nm (108 lb ft) torque at the motor shaft, 4.375 ratio, and 64.5 cm (25.4") tires. The torque is increased by the differential ratio to 146.4 Nm * 4.375 = 640.5 Nm torque on the axle. The force at tire's ground contact patch is 640.5 Nm / 0.645 m = 993 N. The acceration would be 993 N / 800 kg = 1.24 m/s^2. Assuming that acceleration is constant up to 60 mph, to accelerate to 26.8224 m/s (60 mph) it would take (26.8 m/s) / (1.24 m/s^2) = 21.6 s. Ouch. That's slow! I see many people complaining about 9.0 s times. Is it reasonable to assume acceleration is constant given torque is constant on electric motors for the first few thousand RPM?

Hmm. Perhaps 108 lb ft is too little torque for a single speed car?

Thanks for any advice!!!

 

[brian_]

That's an excellent analysis, with one small (but significant) math error and a significant faulty assumption:

Beetle tire size is 165/80R15 which has a diameter of 64.5 cm (25.4")

... The torque is increased by the differential ratio to 146.4 Nm * 4.375 = 640.5 Nm torque on the axle. The force at tire's ground contact patch is 640.5 Nm / 0.645 m = 993 N...

You need to use the radius, not the diameter, of the tires to convert axle torque to force at the road surface. So, your force will be twice what you calculated.

The calculation looks otherwise sound, except that it assumes that all of the drive force goes to acceleration, because there is no drag. For the first little bit that's not bad, but there is rolling drag (roughly constant with speed), and aerodynamic drag which becomes important as speed increases.

Is it reasonable to assume acceleration is constant given torque is constant on electric motors for the first few thousand RPM?

Torque will be roughly constant - limited by a set current limit - up to some motor speed, either where the supply voltage becomes limiting or the controller is programmed to limit power. HPEVS's published performance charts show the transition. It would be "a few thousand RPM" with a production EV motor that is supplied with 360 volts, controlled to limit power, and capable of 10,000 rpm or more... but it will be lower with one of these low-voltage setups.

Perhaps 108 lb ft is too little torque for a single speed car?

That's probably marginal with the low torque multiplication provided by the assumed gearing. The Chevrolet Spark EV has similar gearing, but four times as much motor torque.

 

[stevesmithworks]

Brian!

What a silly mistake on my part. Thank you for catching it!!

Let me try again for the AC-51. I looked at the performance curves and 100 lb ft seems more accurate across the 0-5000 rpm range.

Again given 800 kg (1763 lbs) curb weight, 136 Nm (100 lb ft) torque at the motor shaft, 4.375 ratio, and 64.5 cm (25.4") tires.

136 Nm * 4.375 differential ratio = 595 Nm torque at axle.

595 Nm / (0.645 m / 2) = 1845 N at ground

1845 N / 800 kg = 2.31 m/s^2 acceleration

(26.8 m/s) / (2.31 m/s^2) = 11.6 s for 0-60 mph disregarding resistance. That's much better. It's still no sports car but it is better than with the original gasoline engines.

At 60 mph the motor will only be going 3472 rpm.

The AC-50 produces 110 lb ft of torque up to the mid 3000 rpm. That would get the time down to 10.5 s.

With the AC-76 ~150 lb ft of torque it could be down to ~7.7 seconds. Now that's getting respectable. At least it can beat a 2019 Toyota Yaris' 9 seconds time and match a base 2019 VW Golf's 7.7 seconds.

With the dual AC-35 ~180 lb ft it could be down to 6.4 s. The dual AC-35 has very nice performance curves with 180 lb ft all the way to 5000 rpm. I imagine the clutch and tires both slip with so much torque.

Now if I could find a way to get the car's weight down to scant 500 kg the time would be 0.625 of the times calculated above. It might be getting close to compete with the Golf R's 4.5 second time. It's fun to think about but not necessary.

So even with the AC-50 or AC-51, it does look like a single speed would work just fine. I saw a video from EV West showing driving around only in 3rd gear eventhough he just explained that they like having a transmission.

So why do folks actually keep the transmission in a Beetle conversion? Higher top speed? Overdrive for lower current and highway efficiency? Big hills? Towing heavy loads like a trailer carrying the next donor car?

With all the torque available, it seems like the original Beetle transmission isn't the best match for an electric motor. Perhaps better to have one under drive just in case, direct drive for most use, and one over drive for highway driving.

 

[stevesmithworks]

Brian!

What a silly mistake on my part. Thank you for catching it!!

Let me try again for the AC-51. I looked at the performance curves and 100 lb ft seems more accurate across the 0-5000 rpm range.

Again given 800 kg (1763 lbs) curb weight, 136 Nm (100 lb ft) torque at the motor shaft, 4.375 ratio, and 64.5 cm (25.4") tires.

136 Nm * 4.375 differential ratio = 595 Nm torque at axle.

595 Nm / (0.645 m / 2) = 1845 N at ground

1845 N / 800 kg = 2.31 m/s^2 acceleration

(26.8 m/s) / (2.31 m/s^2) = 11.6 s for 0-60 mph disregarding resistance. That's much better. It's still no sports car but it is better than with the original gasoline engines.

At 60 mph the motor will only be going 3472 rpm.

The AC-50 produces 110 lb ft of torque up to the mid 3000 rpm. That would get the time down to 10.5 s.

With the AC-76 ~150 lb ft of torque it could be down to ~7.7 seconds. Now that's getting respectable. At least it can beat a 2019 Toyota Yaris' 9 seconds time and match a base 2019 VW Golf's 7.7 seconds.

With the dual AC-35 ~180 lb ft it could be down to 6.4 s. The dual AC-35 has very nice performance curves with 180 lb ft all the way to 5000 rpm. I imagine the clutch and tires both slip with so much torque.

Now if I could find a way to get the car's weight down to scant 500 kg the time would be 0.625 of the times calculated above. It might be getting close to compete with the Golf R's 4.5 second time. It's fun to think about but not necessary.

So even with the AC-50 or AC-51, it does look like a single speed would work just fine. I saw a video from EV West showing driving around only in 3rd gear eventhough he just explained that they like having a transmission.

So why do folks actually keep the transmission in a Beetle conversion? Higher top speed? Overdrive for lower current and highway efficiency? Big hills? Towing heavy loads like a trailer carrying the next donor car?

With all the torque available, it seems like the original Beetle transmission isn't the best match for an electric motor. Perhaps better to have one under drive just in case, direct drive for most use, and one over drive for highway driving.

 

[olegil]

Hmm. Perhaps 108 lb ft is too little torque for a single speed car?

Thanks for any advice!!!

I wouldn't want to drive a WV Beetle above 100 km/h unless it's been quite heavily modified, the car body simply doesn't give enough down force to handle high speed safely. So maybe you shouldn't limit yourself to the ratios used by WV?

Besides, the diff is integrated in the gearbox anyway, so how would you use the diff without using the gearbox in the first place?

Also, given the error pointed out by brian_, you're looking at 11 seconds before taking wind and tire resistance into account. That's gonna be more zippy than any original Beetle, and you've limited yourself to rated and continuous values rather than max, so I don't see why that would be hard on the motor. I would say that car is pretty much the perfect candidate for that motor, but either with the original gearbox, or with an un-original diff. If you keep the gearbox, you could probably stick it in third for 95% of driving (1:1.26 or so ratio), and occasionally use 4th on the highway (1:0.89). If you don't need 1st, 2nd or reverse, that's a simple HI/LO shifter hooked up to one fork. I found some really nice pictures of the inside of the transmission at https://www.thesamba.com/vw/forum/viewtopic.php?t=498142, which shows what I'm talking about.

 

[brian_]

I wouldn't want to drive a WV Beetle above 100 km/h unless it's been quite heavily modified, the car body simply doesn't give enough down force to handle high speed safely.

Few road cars produce any downforce - the best one can usually hope for is that the lift is reasonably evenly distributed between front and rear, or at least that it isn't so excessive at the rear that it causes loss of control.

I'll agree that the old Beetle is aerodynamically poor by current standards, and isn't much of a high-speed car.

Besides, the diff is integrated in the gearbox anyway, so how would you use the diff without using the gearbox in the first place?

I wondered the same thing. There are some options...

1. The stock transaxle could just be left in one gear (single-gear driving in a multi-gear car) to avoid shifting, but that wouldn't bring the benefits of fewer parts and less weight.
2. The transaxle could be replaced with a final drive (differential with ring and pinion gears from another vehicle, but then the available VW ratios wouldn't be relevant.
3. Parts could be removed from the stock transaxle, reducing weight (and mechanical drag) a bit, but is that really worthwhile?

 

[stevesmithworks]

Brian!

What a silly mistake on my part. Thank you for catching it!!

Let me try again for the AC-51. I looked at the performance curves and 100 lb ft seems more accurate across the 0-5000 rpm range.

Again given 800 kg (1763 lbs) curb weight, 136 Nm (100 lb ft) torque at the motor shaft, 4.375 ratio, and 64.5 cm (25.4") tires.

136 Nm * 4.375 differential ratio = 595 Nm torque at axle.

595 Nm / (0.645 m / 2) = 1845 N at ground

1845 N / 800 kg = 2.31 m/s^2 acceleration

(26.8 m/s) / (2.31 m/s^2) = 11.6 s for 0-60 mph disregarding resistance. That's much better. It's still no sports car but it is better than with the original gasoline engines.

At 60 mph the motor will only be going 3472 rpm.

The AC-50 produces 110 lb ft of torque up to the mid 3000 rpm. That would get the time down to 10.5 s.

With the AC-76 ~150 lb ft of torque it could be down to ~7.7 seconds. Now that's getting respectable. At least it can beat a 2019 Toyota Yaris' 9 seconds time and match a base 2019 VW Golf's 7.7 seconds.

With the dual AC-35 ~180 lb ft it could be down to 6.4 s. The dual AC-35 has very nice performance curves with 180 lb ft all the way to 5000 rpm. I imagine the clutch and tires both slip with so much torque.

Now if I could find a way to get the car's weight down to scant 500 kg the time would be 0.625 of the times calculated above. It might be getting close to compete with the Golf R's 4.5 second time. It's fun to think about but not necessary.

So even with the AC-50 or AC-51, it does look like a single speed would work just fine. I saw a video from EV West showing driving around only in 3rd gear event hough he just explained that they like having a transmission.

So why do folks actually keep the transmission in a Beetle conversion? Higher top speed? Overdrive for lower current and highway efficiency? Big hills? Occasional heavy passengers? Towing heavy loads like a trailer carrying the next donor car?

With all the torque available, it seems like the original Beetle transmission isn't the best match for an electric motor. Perhaps better to have one under drive just in case, direct drive for most use, and one over drive for highway driving.

 

[MRMOPARMAN1]

Its probably not a cheap way to go, but the tesla small drive units fit in the rear of a beetle. Then all your gearing/torque etc calculations are already done for you. And they seem to be quite well supported in the aftermarket industry

 

[dtbaker]

couple things here caught my eye....

Here my opinion on this:

I just finished a 74’ beetle conversion for my father last summer. I got a 296V nominal pack, weighs in at about 330 lbs or so, and I got a zilla z1k-hv and a warp 9. As far as drive train goes, you can STILL drive around in one gear practically with the transmission. The tranny weighs literally like 60 lbs, and that’s not gonna reduce your range much by eliminating it to be honest. It’ll simply cost you a lot more time, money, and headache to drive it with a single gear reduction.

I just throw the car in second and leave it, performance is amazing! Running an aluminum flywheel too, and this thing will smoke a corvette at a stop light any day of the week. The warp 9 is putting out about 200HP and 350 ft lbs of torque. 0-60 time is approx 4 seconds!

1. I am amazed you can put 300v thru a warp9 and and haven't burned up the insulation yet?

2. I absolutely agree on leaving IN the transmission (for reverse if nothing else!), but you have to consider the design torque limitations. I am (this week) replacing the tranny in my eMiata after 20k electric miles because I have been doing plenty of hard starts off the line in 2nd and 3rd.... which are NOT designed for 200-250 ft# of torque from a stop and completely destroyed the teeth on 3rd gear. So, if you intend to drive hard, you might want to look at options to change the diff to the tallest gears possible, so you can use 1st gear to start. My plan is to swap out the Miata rear end for a modern Mustang with IRL having 2.73, 3.11, or maybe 3.15 depending what I can find.

 

[Tremelune]

I like the idea of ditching an old transmission to reduce weight, complexity, and maintenance...but it doesn't seem worth it to lose the versatile gear reduction and easy installation of the electric motor.

hyper 9 kits are VERY a reasonably priced, and cheapest motor and controller combo you can currently get.

Maybe. A Leaf motor/inverter is $500-1000 and a controller is $500-1000 for 210 ftlb of torque. The tricky bit is that you need a 360V nominal battery pack to get it to 10k RPM...but that wouldn't be needed in this car if the transmission stayed in place.

 

[Duncan]

Oh I should specify, I most certainly don’t put 300V through the warp 9 lol, I apologize. I have it set at 160 or 170v or something like that.

But yeah custom tranny work is needed if you wanna drive it hard, or don’t mind replacing a tranny down the line.

I don't see why not - I put 340v into my Hitachi 48v forklift motor - and I didn't bother with a gearbox

 

[dtbaker]

I don't see why not - I put 340v into my Hitachi 48v forklift motor - and I didn't bother with a gearbox

hhhhmmmm, so I'm curious how many volts, and how many amps, you typically put thru the motor? Most forklift windings have insulation rated only for 160v.... I'm surpised you haven't had problems if you are running the full 340v thru the motor?

Also curious how many miles you've driven your clutchless/transmissionless setup? Presumably using reversing contactors for reverse? How has that worked out for you?

I asking because MOST of the builds I followed on this forum that started 'direct drive' ended up re-building with a transmission... mostly because it ends up being easier than reversing contactors, and easier to have at least two gears for decent low end torque AND top end speed.

 

[Duncan]

Hi
Duncan's dubius device has been on the road for six years now - not a lot of miles as I'm retired and looking after my wife - about 6,000 km so far - no exact number as I'm on my forth speedo!

https://www.diyelectriccar.com/foru...dubious-device-44370p15.html?highlight=duncan

The motor only sees the full 340v (sagged to less than 300) and 1200 amps on the drag strip and then for a couple of seconds

I have a throttle resistor so I only use 40% (about 500 amps) on the road - and on the road it uses a max of about 160 volts

That gives spritely performance up to and over the speed limit

I did replace my original reversing contactor (off a 24v forklift) after four full power runs at this years drags it started sticking - so I now have a bigger one