8 Seater Buggy Conversion

[Enemzack]

Hi Guys,

I purchased a custom made 48v 15kw bldc air cooling motor with vec600 controller (rated at 250A, max 600A).

The estimate weight approximately 1300kg.

On a normal flat road, the 8 seater buggy works perfectly on a full load.

Problem:
On a slope, it failed to climb.

the setting that golden ask to change is to change the battery drawn current limit to 235.

any ideas for improvement? or the motor power is not enough?


Nik

[Bikemad]

Hi Nik,

Unfortunately, I think the power is simply too low for that amount of weight.

Just as an example, my Vectrix electric scooter weighs 210kg, but the 120V pack allows the 7kW continuous motor to deliver over 20kW peak (27HP).
And the five seater Nissan leaf weighs ~1,500kg and uses a 80kW motor and a 365V battery pack.

Even with your battery drawn current set to 235A, that's only going to provide just over 10kW of usable power output at the wheels with a 48V pack (after electrical and mechanical inefficiency losses).

If you cannot increase the power, the only alternative I can see would be to lower the gearing sufficiently so that steep hills could be climbed with just 10kW of power (albeit at a very slow speed). 

Alan
 

[StadsImker]

I think the problem is that you need to realize is that an engine should rotate to generate power and it even doesn't matter what kind of engine or motor you use. Benzine, electric or what ever.

If it isn't rotating, there is no power or torque at all. It's simply stalled. If you try to force it.... it will damage it self somewhere. In a combustion engine it will burn you clutch or stops running. In an electrical engine... It will send a high current and... "notting happens" but a lot happens, but we don't hear it. But it screams HELP... On a electric bike you need to pedale to start on a hill... With a buggy you need to "create better conditions". Stop trying hills with no speed. Take a longer run and than go up the hill.

[Bikemad]

If it isn't rotating, there is no power or torque at all.

Actually, plenty of torque is available at zero rpm with an electric motor.

I once carried out a very simple stall test using a set of digital luggage scales attached by a piece of rope tied to the outer diameter of my tyre as shown here:



My modified Pie was drawing 65.94 Amps @ 25.6V (1,694 Watts) and although the controller cut the power before the luggage scales had time to lock the reading, I was able to read a reading of at least 28kgs/61Lbs of force on a couple of the tests, which I worked out to be around 93Nm of torque!

For a vehicle to pull away on a slope from a standing start, the stall torque needs to be greater than the torque required to drive the vehicle up the slope. If this minimum required amount of torque is not available, then it will not pull away.

Alan
 

[Enemzack]

Hi Alan,

If I can upgrade the motor, would the highest available motor golden motor have sufficient?

20kw 96v system.

[Bikemad]

Hi Nik,

I seem to recall an axle was also available from GM with a much lower 12.5:1 gear reduction, if this is still available, it would produce almost 65% more torque at the axle from your existing motor, but I still feel it would be underpowered.

According to the GM website, the 20kW motor has a rated torque output of 80Nm with a peak torque of 160Nm:


Model: HPM-20KW -- High Power BLDC Motor
Voltage:72V/96V/120V
1. Voltages: 72V-120Vdc
2. Rated power: 20-25KW
3. Peak power: 50KW
4. Speed: 3200-6000rpm
5. Rated torque: 80 Nm
6. Peak torque: 160 Nm
7. Efficiency: >90%
8. Dimensions: 30x30x25cm
9. Weight: 39kgs
10: Cooling: liquid cooling

If my calculations are correct, your vehicle should just about be able to climb a 7.8° slope (13.4%) with 80Nm of torque, and with the maximum peak torque of 160Nm it should even be able to climb a 17° slope (30.6%).

I have assumed your differential incorporates the 7.6:1 gear reduction as indicated on the current drawing.

I used a tyre diameter of 600mm in my calculations, so the slope angles will be slightly higher if your wheels are smaller (or less if your wheels are bigger).

Unfortunately, the performance data figures for the dynamometer test are not shown below 2560 rpm, so I don't know how many Amps will be required to achieve the peak 160Nm of torque at very low rpm.

Alan
 

[Enemzack]

Hi Nik,

I seem to recall an axle was also available from GM with a much lower 12.5:1 gear reduction, if this is still available, it would produce almost 65% more torque at the axle from your existing motor, but I still feel it would be underpowered.

According to the GM website, the 20kW motor has a rated torque output of 80Nm with a peak torque of 160Nm:


Model: HPM-20KW -- High Power BLDC Motor
Voltage:72V/96V/120V
1. Voltages: 72V-120Vdc
2. Rated power: 20-25KW
3. Peak power: 50KW
4. Speed: 3200-6000rpm
5. Rated torque: 80 Nm
6. Peak torque: 160 Nm
7. Efficiency: >90%
8. Dimensions: 30x30x25cm
9. Weight: 39kgs
10: Cooling: liquid cooling

If my calculations are correct, your vehicle should just about be able to climb a 7.8° slope (13.4%) with 80Nm of torque, and with the maximum peak torque of 160Nm it should even be able to climb a 17° slope (30.6%).

I have assumed your differential incorporates the 7.6:1 gear reduction as indicated on the current drawing.

I used a tyre diameter of 600mm in my calculations, so the slope angles will be slightly higher if your wheels are smaller (or less if your wheels are bigger).

Unfortunately, the performance data figures for the dynamometer test are not shown below 2560 rpm, so I don't know how many Amps will be required to achieve the peak 160Nm of torque at very low rpm.

Alan
 

Hi Alan,

we managed to disassemble the differential gear and attached is the number of teeth in the gear. now is in the process to design and fabricate the bracket for the massive motor 

any advise? might need to add few gear for the motor

[Bikemad]

Hi Nik,

According to the tooth count, your final drive has a total gear reduction of 10.27245:1 which is good for hill climbing but not so good for top speed. 

The stated 160Nm of peak motor torque should produce ~1643Nm of torque at the wheel, which would provide a forward force of around 5370N (547kg) with 600mm diameter tyres. That's enough force to climb a slope of over 23° (43%). 

The top speed will be limited by the motor maximum rpm (which is probably going to be ~4800rpm @ 96V) and at 4800rpm it would only achieve a maximum of 32.85mph (52.87km/h) with 600mm diameter tyres.

Alan