Open to discussion- Hub motors for race car!

[turbineracer]

Hi all,

Hope you are all having a good time with your e-bikes!  I am new here and from reading through the forum some of you have had good experience with the motors sold by GM.  I am posting to ask for your ideas. 

Basically, to cut a long story short, I have this 'race car', weight about 200 kg including the driver.  I am thinking of buying two of the 1000 W HBS36F hub motor to power the rear two wheels of the 4-wheeled car.  I am most definetly going to need two controllers but is there anyway I can use just one throttle?  Any ideas?  Do you think that two motors of 1000 W each are enough to power the 200 kg car without getting fried?

ANY kind of help would be greately appreciated.

Thank you very much!   

[muzza.au]

It can be done, I think you just wire up the throttle in parallel to the two controllers. Check out this thread on Endless-sphere for more info: http://endless-sphere.com/forums/viewtopic.php?f=2&t=8487

Muzza

[turbineracer]

It can be done, I think you just wire up the throttle in parallel to the two controllers. Check out this thread on Endless-sphere for more info: http://endless-sphere.com/forums/viewtopic.php?f=2&t=8487

Muzza

Hey Muzza, thanks a lot for that, that is very helpful.  Just got another question!  So the throttle I am guessing is just a potentiometer, is that right? What if I remove the throttle and the throttle input in the controller is connected to the output of a power supply which gives a constant dc voltage, would it work?  Does my question make any sense?  Or am I talking jibbrish here?!

Thanks in advance

[Bikemad]

Do you think that two motors of 1000 W each are enough to power the 200 kg car without getting fried?

This is not a simple question to answer, as it obviously depends on many factors.

Perhaps you would like to give us some more information and some pictures if possible;

• What sort of terrain are you racing on? (dirt, tarmac, level or slopes etc.)

• What maximum speed are you hoping to achieve?

• Does the car have an aerodynamic body or is it open?

• What batteries are you planning to use? (Voltage, Ah rating, quantity and type)

• What size wheels and tyres are you planning to use?

• Roughly how long do you expect a typical race to last?

• What power trains are other entrants using in their race cars?

• Any other information you think might be useful

Alan
 

[muzza.au]

So the throttle I am guessing is just a potentiometer, is that right?

No, they actually have a hall sensor in them and a magnet that goes past it as you turn the throttle and the controller sensors this and varies the speed of the motor according to the position. Potentiometers are not as reliable as its a physical connection that can wear out over time. Have you ever had an old radio where the speaker crackles alot when you adjust the volume? Thats a potentiometer.

As far as any other method to simulate a throttle without a throttle, I don't know, that is beyond my current knowledge.

If your building an electric car, then this is what you need:


Muzza.

[turbineracer]

Hey Alan & Muzza,

hmmm, hall effect sensors, might be difficult to replace it with what I have in my mind.  Anyway, I did a bad job in explaining exactly what I was trying to achieve.  Let me set it out for you. 

We are making a wind powered vehicle (similar to the one here: http://en.wikipedia.org/wiki/File:AeolusRace2008-2.png), it has two turbines instead of one (1 at the front & one at the back) and each generates power through generators.  We have two hub motors (1000 kW ones) to power the aft 2 wheels.  So in short (forgetting about the important little details), I want to connect the generator output to the hub motors through the controller etc.  As this is an experimental project there are a lot of things that I don't know:

The track is straight line asphalt (tarmac) with no elevation,
max speed 20 km/hours,
yes it 'will' have an aerodynamic body but the turbine at the top gives a lot of drag!
want to use the regulated generator output to power the motors, no battery for the motors (is this possible?)
wheel 20", race will last 10 minutes max depending on wind speed, in last year's race mechanical drive trains were used by most entrants.  The max power available for each motor will be around 600 Watts. 

Does this make it a bit clearer.  Really appreciate your help guys.

Thanks

[e-lmer]

The big difficulty is going to be power regulation.  The turbines, with no battery, are going to have
variable power output.  With no buffer (battery) you will need to supply as many watts as you want
to use at as many volts as the motor needs (45v for 1kW gm motors)

The bigger problem you have is that generator-motor combinations are very good at heating up
the environment, but not very good for power transfer.  I suspect that is why the competition is
leaning towards mechanical solutions.

But as far as the speed controllers, there are basically two options, the hall sensor controllers
like golden motor uses, or the pulse width (duty cycle) controllers like those from Castle Creations
(hobby controllers) 

A resistor would not be suitable for control because it is a power sink (just turns current into heat)

[turbineracer]

The big difficulty is going to be power regulation.  The turbines, with no battery, are going to have
variable power output.  With no buffer (battery) you will need to supply as many watts as you want
to use at as many volts as the motor needs (45v for 1kW gm motors)

The bigger problem you have is that generator-motor combinations are very good at heating up
the environment, but not very good for power transfer.  I suspect that is why the competition is
leaning towards mechanical solutions.

Hey e-lmer, you are right about power regulation.  We have a power supply (connected after the generator) that outputs a regulated 48 V DC to the whole circuit.  We do have super capacitors to ensure that at times when the voltage is low the capacitors make up for the missing volts. 

I do understand that this system can heat up the environment but according to my (hopefully reasonable) calculations we have enough power available for the motors.

Do you are anyone by any chance knows the starting torque of the 1000 W motor and the weight limit on it?  Also, how does the braking working in the hub motor? What kind of brakes are used?

Thanks.

[Bikemad]

In last year's race mechanical drive trains were used by most entrants. 

Did any of the non-mechanical drives achieve a forward speed comparable with the mechanically driven ones?

The max power available for each motor will be around 600 Watts. 

• An input of 600W (12.5 Amps @ 48v) would give an output of approx 500W at 80% efficiency.

• At this power, each motor would develop approx. 11.5Nm of torque @ around 420rpm.

In order to maximise propulsion using this torque, you would need to use a very small wheel.

I estimate a tyre size of 10" outside diameter would give a maximum speed of 20.7Km/h at 420rpm.

Perhaps you can find some solid tyres suitable to fit directly onto the hubs (without the need for a rim to be fitted) in order to get a small enough diameter to produce the required force.

My biggest concern is whether 184N (41.25lbs) is enough force to overcome the 200kg overall weight and the amount of drag on the vehicle (especially with two turbines working at full load) and still propel the vehicle anywhere near this speed!

Alan

[turbineracer]

Did any of the non-mechanical drives achieve a forward speed comparable with the mechanically driven ones?

It's funny you ask, there was only one team with electrical drive and they broke down half way through the race!!

My biggest concern is whether 184N (41.25lbs) is enough force to overcome the 200kg overall weight and the amount of drag on the vehicle (especially with two turbines working at full load) and still propel the vehicle anywhere near this speed!

Yeah that is right, I have the same doubt but we have about 5kW of power available from the output of the generator.  According to some rough calculations the drag on the car is about 250 N, a lot more than the propulsive force!!  Hvae to re-do the calulations I think!!

Do you by any chance know the starting torque of the 1000 W motor?

Thanks

[Bikemad]

Do you by any chance know the starting torque of the 1000 W motor?

Sorry, I don't have any figures for the starting torque.
The highest torque figures I have on the dynomometer results are 37.42Nm @ 313rpm (1792.61 Watts input @ 48v = 37.46Amps.)

The torque and Current figures are very similar from 25.38-37.42Amps (25.87-37.46Nm.)

Hopefully someone else on here can at least give you an indication of the stall current on this motor!

Alan

[turbineracer]

The highest torque figures I have on the dynomometer results are 37.42Nm @ 313rpm (1792.61 Watts input @ 48v = 37.46Amps.)

The torque and Current figures are very similar from 25.38-37.42Amps (25.87-37.46Nm.)
 

Hey Alan, thanks for the info.  Did you measure the torque yourself?  Does it match according to the torque and RPM values given on the Golden Motors website? What happens to the torque if you put in more power?  Stall current would be very useful, anyone??

Cheers!

[Bikemad]

In answer to your questions:

"Did I measure the torque myself?"
No, I obtained these figures from a pdf document.

"Does it match according to the torque and RPM values given on the Golden Motors website?"
I don't think links to the 48V 1000W figures are currently shown on the Golden Motor site, so I've added them here:

Dynomometer results and performance curve.

"What happens to the torque if you put in more power?"
I would expect the torque to increase, relative to the power, until something fails!

"Stall current would be very useful, anyone??"

Alan

[Bikemad]

How does the braking working in the hub motor? What kind of brakes are used?

These generally use "V" brakes (or older style caliper brakes) acting on the wheel rim.

If your motor has a threaded boss on each side, you can fit a disc brake (or a compact drum brake if you can locate one) to one side.

You could also fit a simple freewheel (working in reverse) on the other side of the hub to stop it from being blown backwards!  

Alan