# How to define the best motor/ gear box

5325 Views 26 Replies 6 Participants Last post by  Boxster-warp
I'm new to conversions and try to prevent typical mistakes. Currently I try to get a feeling based on theoretical comparisons to find the best combo.
The chart represent a VW T2b with CP gearbox, Curtis AC50 (96V). This combo is possibel - not the best.
Note: Peak power, based on converted torque values of HPEVS diagrams, which are not consistent. Rated power is much lower.

Explanation:

• blue curve is the drive resistance (wind drag, loss of gear box, wheel resistance, load of the vehicle, incline/ slope (0%)).
• The other colors are the max power in the gears over speed.
• If the gear curve cross the blue line it defines the max. speed in this gear.
How did you figure out your matching setup?

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#### brian_

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I believe that you are already well above the level of sophistication of typical DIY project (electric or gasoline) in this analysis. Looks good to me.

I would add that in addition to illustrating the top speed, the available power in excess of the power required to overcome the calculated resistance is the power available to accelerate.

#### Duncan

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Hi

You want to have torque and not power on the axis

Then you will be able to instantly see the amount of "extra" torque above the "steady state" torque that you will have available with each gear

#### brian_

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You want to have torque and not power on the axis

Then you will be able to instantly see the amount of "extra" torque above the "steady state" torque that you will have available with each gear
Sure, that would be proportional to acceleration, rather than rate of kinetic energy gain... as long as you are doing torque at the wheels (or at least at the final drive input), not at the motor. And you really want it to be drive force (not torque), corresponding to what has already been calculated for "resistance".

It's the same information, just differently presented... but fortunately, it's an easy transformation.

#### aquabiologist

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Nice!

Finally, I can put my own spreadsheet from hell put to use.

The following shows:

Torque at the Motor for a vw t2ab with original gear ratio for the Hpevs 50, the netgain hyper 9, plus the original 1600cc ice.

The ‚drag torque‘ is based on car weight, coefficient of drag, stock tires, road friction plus some guesstimate losses for the gears.

With these numbers: the hpevs ac 50 seems a bit underpowered for a vw t2 if you want to be able to run on highways for longer trips.
The hyper 9 seems a nice replacement for the 1600cc engine.

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#### OliverH

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The 1600 (AS?) is the 50 HP engine? I had such a T2b many decades ago. This one was totally underpowered. I like to replace a Type 4 2.0 as a california edition (fuel injection, TSZ-H ignition, catalyst with lambda sensor). As we made a year ago the EV step with the family car the T2 should follow now.
The diagram below is the minimum witch is possible. It’s just for orientation and not the preferred path. I’ll post the same diagram with a 5% slope to show the “problem”:
The 4th gear is not usable. 3rd gear is limited at close to 80 km/h with not much power buffer.

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#### OliverH

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Netgain HyPer 9 (peak performance) flat road..

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#### OliverH

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Netgain HyPer 9 (peak performance) 5% slope..

It outperforms the Curtis AC50 with no doubt. But the torque could be to much for the 091 CP gear box. Rumors say it withstand round about 200 Nm and the HyPer 9 could distribute 235 Nm. Weddle gears could solve the problem.
The main question is to go with the original/ modified gearbox or a drive train with reduction gear box (Tesla, GKN, Getrag,..). That's the reason for this thread.

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#### Boxster-warp

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Hallo Oliver
Heiko fleck sell now the scottdrive controller with an watercoled Motor.
600 ampere and 350v.
Nice combi.
Greeitings boxster-warp

#### OliverH

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Hallo Oliver
Heiko fleck sell now the scottdrive controller with an watercoled Motor.
600 ampere and 350v.
Nice combi.
Greeitings boxster-warp

The question is to find an e-engine which fits to the original gear box or use a drive unit. Our beloved historical cars are worth to spend some more money with the right solution. But interesting to see his 210 KW (a gear box cruncher) engine which is not listed on his shop. That's a reason to talk with Heiko Fleck and Kreisel 1to1 in summer.

#### brian_

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The following shows:

Torque at the Motor for a vw t2ab with original gear ratio for the Hpevs 50, the netgain hyper 9, plus the original 1600cc ice.

The ‚drag torque‘ is based on car weight, coefficient of drag, stock tires, road friction plus some guesstimate losses for the gears....
Expressing this all as torque at the motor/engine output is a little strange, because
1. it makes it look like drag takes steps at the points where you have chosen gear shifts (25, 50, and 80 km/h)
2. it forces all power sources (engine, both motors) to follow the same shift points, whether they are appropriate or not.

It would make more sense to me to do force at the tires, torque at the axles, or torque at the transmission output (they would all work similarly), so the drag would be the continuous curve that Oliver shows, and each power source (engine and both motors) can step through the gears at the points suitable for the specific source.

If your spreadsheet is in some commonly consumable source form (Excel file, Google Sheet, etc) and you are willing to share it, I might try the alternate presentation.

#### aquabiologist

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Expressing this all as torque at the motor/engine output is a little strange, because
1. it makes it look like drag takes steps at the points where you have chosen gear shifts (25, 50, and 80 km/h)
2. it forces all power sources (engine, both motors) to follow the same shift points, whether they are appropriate or not.

It would make more sense to me to do force at the tires, torque at the axles, or torque at the transmission output (they would all work similarly), so the drag would be the continuous curve that Oliver shows, and each power source (engine and both motors) can step through the gears at the points suitable for the specific source.

If your spreadsheet is in some commonly consumable source form (Excel file, Google Sheet, etc) and you are willing to share it, I might try the alternate presentation.

It does look odd and is for my gearing, but torque at wheel would not compare to motor specifications. So thats why.

Thanks for your offer to do the other graphs. Did i mention its a spreadsheet from hell? I seriously need to clean it up first

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#### aquabiologist

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Netgain HyPer 9 5% slope..

It outperforms the Curtis AC50 with no doubt. But the torque could be to much for the 081 CP gear box. Rumors say it withstand round about 200 Nm and the HyPer 9 could distribute 235 Nm. Weddle gears could solve the problem.
The main question is to go with the original/ modified gearbox or a drive train with reduction gear box (Tesla, GKN, Getrag,..). That's the reason for this thread.

I always assumed that you could set max. torque in the controller software?

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#### OliverH

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Nice!

Finally, I can put my own spreadsheet from hell put to use.

The following shows:

Torque at the Motor for a vw t2ab with original gear ratio for the Hpevs 50, the netgain hyper 9, plus the original 1600cc ice.

The ‚drag torque‘ is based on car weight, coefficient of drag, stock tires, road friction plus some guesstimate losses for the gears.

View attachment 106370 View attachment 106378

With these numbers: the hpevs ac 50 seems a bit underpowered for a vw t2 if you want to be able to run on highways for longer trips.
The hyper 9 seems a nice replacement for the 1600cc engine.

Gesendet von iPhone mit Tapatalk

Why do you've steps in the drive resistance curve? The ideal curve should be smooth. My curve is also only a calculation and reality could vary (different resistance at different speeds of the gearbox, bearings axle shaft, bearings on the wheel hubs) but this should be a small different

#### aquabiologist

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Why do you've steps in the drive resistance curve? The ideal curve should be smooth. My curve is also only a calculation and reality could vary (different resistance at different speeds of the gearbox, bearings axle shaft, bearings on the wheel hubs) but this should be a small different

As i shift, rpm drops, the minimum torque at the motor to overcome ‚drag’ must increase. Power output would be a smooth curve.

This way I can limit my motor torque, so it won‘t kill my gearbox. And estimate the performance of my setup. At least thats what i think i am doing.

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#### brian_

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It does look odd and is for my gearing, but torque at wheel would not compare to motor specifications. So thats why.
Engine or motor, both can be compared at the same point in the drivetrain. You multiply the engine or motor torque by the transmission ratio (for transmission output) and by final drive drive ratio (for axle torque) and divide by tire radius (for driving force) in either case.

Thanks for your offer to do the other graphs. Did i mention its a spreadsheet from hell? I seriously need to clean it up first

Well, I'm still willing to at least have a look!
Don't clean it up just for me.

#### brian_

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Why do you've steps in the drive resistance curve? The ideal curve should be smooth.
The curve of torque at the wheel or at the transmission output is a smooth function of speed... but this graph shows torque at the motor/engine output or transmission input, so it is the torque at the transmission output (smooth like yours) divided by the gear ratio being used at that road speed.

#### brian_

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I always assumed that you could set max. torque in the controller software?
By limiting current, yes. That's what I was thinking, too.

#### brian_

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As i shift, rpm drops, the minimum torque at the motor to overcome ‚drag’ must increase. Power output would be a smooth curve.

This way I can limit my motor torque, so it won‘t kill my gearbox.
...
At least thats what i think i am doing.
On the other hand, transmissions are normally rated by torque input (rather than output), so for any given required power output, you can go easier on the transmission by using higher motor speed and lower transmission input torque, which means staying in a lower gear, within the maximum rated input speed of the transmission and the efficient speed range of the motor.

#### aquabiologist

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Engine or motor, both can be compared at the same point in the drivetrain. You multiply the engine or motor torque by the transmission ratio (for transmission output) and by final drive drive ratio (for axle torque) and divide by tire radius (for driving force) in either case.

Well, I'm still willing to at least have a look!

Don't clean it up just for me.

Ok, but you have been warned

First: I am a biologist so go easy on me with all the technicalities. Its aimed at predicting my conversion and i believe its as close as i can get. Tested it against commercial EVs and its good enough for me.

Btw: works only with excel

Here is my spreadsheet from hell for EV calculations