# Help with motor selection



## osirislod (Sep 24, 2008)

Several friends and myself are planning a custom build tadpole. We are shooting for 1500lbs max weight including batteries. Trying to get a top speed of 45-50 mph with a 40 mile range. How much motor do you think would be neded for this weight?


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## major (Apr 4, 2008)

osirislod said:


> How much motor do you think would be neded for this weight?


Hi osirislod,

A lot depends on the details. Using a transmission? Aero drag? Hill climbing? I suggest you examine what others have done. Check out 

http://www.evalbum.com/ 

Regards,

major


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## osirislod (Sep 24, 2008)

Aero isnt going to be much. We are fabbing a body similar to the xr3 but with a lower profile and better front end design. Transmission is still an option we are using the rear swing arm and wheel from a motorcycle which gives us the option to hook the chain direct to the motor or route it through the transmission. Hills are not a factor in this area. It is fairly flat geography.


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## john818 (Aug 1, 2008)

osirislod said:


> Aero isnt going to be much. We are fabbing a body similar to the xr3 but with a lower profile and better front end design. Transmission is still an option we are using the rear swing arm and wheel from a motorcycle which gives us the option to hook the chain direct to the motor or route it through the transmission. Hills are not a factor in this area. It is fairly flat geography.


I've been thinking about a tadpole myself and would be interested in hearing everyone's thoughts on this as well. Seems to me that a lot more people are looking into trikes lately.

Osirislod, the research I've done has led me to believe that hooking up an electric motor to a motorcycle transmission isn't easy. Have you looked into this? I'd imagine your goals wouldn't be too difficult to meet without one, especially since you didn't indicate that acceleration is a big consideration and you have flat roads. Also, I'm not sure how well a motorcycle transmission would hold up under the strain of pushing a 1500 lb vehicle. But I'm no expert on any of this, so it might work fine, especially if you're using a heavy donor, like a Goldwing or something. Just go easy on the burnouts!


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## osirislod (Sep 24, 2008)

Acceleration isnt of great importance. We are building it as an in town only vehicle for comuting to and from work. As long as it accerates fast enough to not impede traffic, and can maintain the speed limit (which is 45 max around here) with a single speed then we wont go with the transmission. Its just available from the bike that was kind enough to donate the rear suspension assembly.

The major question now is the motor. We have a 36volt golfcart motor and speed controller donated to the cause also but I have doubts as to whether it will pull a car up to the speed we need. On the other hand i think one of the larger motors I have seen used in alot of ice conversions will be alot of overkill for this vehicle.


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## order99 (Sep 8, 2008)

Since you bring up Transmissions-

With 1500 lbs, how many seats are you going for? Is the Tadpole going to be four wheels or three? Given the weight...i'm no engineer, but I know a few Websites you might be able to ask:

http://www.nevco-ev.com/

The designer of the Bug-E designed this heavier version, the Gizmo-top speed=45MPH in newest stock configuration. I'm guessing the Gizmo is somewhere in the 1100 lb range once batteries are added...

http://www.zapworld.com/

These EVs average 40MPH, up to 50 with a 72V to 84V upgrade, and are much heavier than what you want in your own EV by at least 400+lbs...the tranny would certainly be robust enough if they sell it as a seperate component.

http://www.rqriley.com/

A site full of DIY kits and plans-an Email to the site might point the way to a light, rugged Tranny. 

Hope it helps.


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## Tesla (Jun 27, 2008)

For a small vehicle with a drag coefficient of 0.195 (gm ev1), a frontal area of 1.869m^2 ((width(m) x height(m))0.85 = frontal area m^2) that frontal area would be for a short two seater side by side (a bit larger frontal area than a '93 geo metro). a mass of 1500lbs(680kg) with 13" tall wheels with very little deformation (high pressure) at sea level (air density = 1.293kg/m^3) requires 2301watts or 2.3kw to maintain 45mph on a level smooth surface. 2.3kw includes aerodynamic and rolling resistance. You'll want a tad more than that for any acceleration. how much does this donated motor produce? if it doesn't say on it then try throwing the model number at google.


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## EVMAN (Jul 26, 2007)

Why not build your 3-wheeler, that's the correct name for these things, openended? If U are going FWD, allow room for a large motor, but put in the one U can afford or have access to now. If doing single RWD, canibilizing a motorcycle can be a timesaver for design considerations. Escentailly, build your 3wheeler where U can substitute different motor/battery combinations.
I've noticed that most of the RWD 3wheeler "designs" do NOT show the rear 
drivetrain. Why's that?? I have been "designing" a 3wheeler since 2001. I still have not come up with a practical, simple to repair, easy to get parts for, transmission/drivetrain for a RWD 3wheeler. FWD like the Doran is the simplist.
Just get a subaru, or any FWD and cut and splice!! IMO, the X3 is too complex with the two complete drivetrains. The TriMagnum has poor seating. The Vortex, with modifications, to me is the most practical if U go to electric or watercooled ICE. Good luck.


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## Tesla (Jun 27, 2008)

that reminds me. in michigan three wheeled enclosed motorcycles are reffered to as "Autocycles" by our local government. knowing that makes it possible to actually find information about the legal requirements to get them on the road through their website. I wasted a good hour trying to find just that out. he's right about using the two front tires for the drive wheels. it'll simplify the process.


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## pquang (Oct 17, 2008)

Tesla said:


> For a small vehicle with a drag coefficient of 0.195 (gm ev1), a frontal area of 1.869m^2 ((width(m) x height(m))0.85 = frontal area m^2) that frontal area would be for a short two seater side by side (a bit larger frontal area than a '93 geo metro). a mass of 1500lbs(680kg) with 13" tall wheels with very little deformation (high pressure) at sea level (air density = 1.293kg/m^3) requires 2301watts or 2.3kw to maintain 45mph on a level smooth surface. 2.3kw includes aerodynamic and rolling resistance. You'll want a tad more than that for any acceleration. how much does this donated motor produce? if it doesn't say on it then try throwing the model number at google.


I think that the accelerator is very important, I resume that your car with mass of 680Kg , you want to reach the velocity of 45mph (75Km/h) for 1 minute , you have to caculate the power thru this solution as follows.
In this time , I eliminate the RR, the gravity force of the car mass.
1/
∆v = v - vi 
?km/hr * 1000m/1km * 1hr/3600s = ?m/s 
a = ∆v/∆t ( accelerator)
F = m * a (force)
2/
s = Vi * t + (1/2) * a * t^2 (distance )
W = F * d (work)
3/
P = W / t (power)

We have
The accelarator 
a= (75000-0) /3600)/60 =0.35m/s^2 
a=0,35m/s^2 
The force is : 
F=Ma= 680x0.35= 238 N 
The car run with the distance after reaching the velocity of 75km/h
S = ViT - (1/2)aT^2 =-1/2(0.35)T^2 =|1/2(0.35(60)^2|=630 m 
Work is :
W=F*S= 238*630=149940Joules 
Power is
P=W/T= 149940/60= 2500 Watt 
736W=1HP 
P= 3.4HP 
If you like to increase the accelerator as double , it means for 30sec you can reach the velocity of 75km/h , you must need the power which is higher than double.
As for the RR, the power must be higher than about 20-30% of the caculated value.
The result is P = 4.42HP or 3.2KW
And after you have the power , how to choose the motor? AC motor or DC motor?
If you choose the AC motor , It means you must loss the energy transfering from DC to AC about 25%, I think that you should choose the DC motor, but you use the used AC motor for changing into the DC motor as so as you can make the PWM for controling the speed of your car.
I will show my solution for change the AC motor into the DC motor and the block diagram for PWM for speed control within a next week


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## pquang (Oct 17, 2008)

Yesterday, I said that I would show my solution for changing the AC Motor into the DC motor.

*Analyzation*

I can find one used AC motor, or one AC motor which is defective by the burned windings, I choose one AC motor using the variable reluctance and 6 poles of the stator, I don’t need the rotor but I need the steel axle of the rotor , I make the rotor with 4 teeth for placing the permanent magnets at the tops.


If your motor has three pairs of windings for the 6 poles, typically connected as shown in the schematic diagram in Figure 1.1, with one terminal common to all windings, it is most likely a variable reluctance stepping motor. In use, the common wire typically goes to the positive supply and the windings are energized in sequence. 
The cross section shown in Figure 1.1 is of 30 degree per step variable reluctance motor. The rotor of this motor has 4 teeth and the stator has 6 poles, with each winding wrapped around two opposite poles. With winding number 1 energised, the rotor teeth marked X are attracted to this winding's poles. If the current through winding 1 is turned off and winding 2 is turned on, the rotor will rotate 30 degrees clockwise so that the poles marked Y line up with the poles marked 2
To rotate this motor continuously, we just apply power to the 3 windings in sequence. Assuming positive logic, where a 1 means turning on the current through a motor winding, the following control sequence will spin the motor illustrated in Figure 1.1 clockwise 24 steps or 2 revolutions: 
Winding 1 1001001001001001001001001
Winding 2 0100100100100100100100100
Winding 3 0010010010010010010010010
time --->
There are also variable reluctance stepping motors with 4 and 5 windings, requiring 5 or 6 wires. The principle for driving these motors is the same as that for the three winding variety, but it becomes important to work out the correct order to energise the windings to make the motor step nicely. The motor geometry illustrated in Figure 1.1, giving 30 degrees per step, uses the fewest number of rotor teeth and stator poles that performs satisfactorily. Using more motor poles and more rotor teeth allows construction of motors with smaller step angle. Toothed faces on each pole and a correspondingly finely toothed rotor allows for step angles as small as a few degrees. 

We can design the PWM for the speed variation of the motor The frequency is named the working frequency which is calculated by making up double from the AC frequency of the old motor.It means that if this motor frequency is 50 Hz sine wave, you must design the working frequency which is 100Hz but the square wave.I think that if this frequency is variable from 10Hz to 1Khz the power coefficicient and the effect of the motor which can be increased considerably.
Three RS Flip flops are made as the shift register or the ring counter with the initial number is “1” at the first time, after the clock of the working frequency from 0 to 1 , 1 is shifted thru FF1 to the next FF2 and then the next clock, 1 is shifted from FF2 to FF3 .It means that the windings 1 has the energy, after the clock of the working frequency, the windings 2 has the energy, and the next clock , the wingdings 3 has the energy….and then going back to the winding A.
However, the very important fact is the modification frequency . It is variable from 10Hz to 5Khz , the require power and the speed of the motor will be solved with the highest effect
I think that you will success your EV by this design

*Designing a PWM Circuit*

The concept of PWM inherently requires timing. Two 555 timer ICs and some potentiometers can be used to generate a PWM signal, and since PWM provides a digital, on/off signal, it is also easy to use a PC or micro-controller to create the signal; however this is beyond the scope of this article.


The circuit in figure 2 uses two 555 ICs and is actually a combination of two types of circuit. The first is a free running multivibrator (astable) with an adjustable frequency around 30Hz. The output of this circuit then triggers a pulse shaping (monostable) circuit which adjusts the width of the pulse. The circuit produces a duty cycle in the range of approximately 0.3% to 97%.

The speed of the motor is controlled with a single potentiometer (variable resistor). It is possible to run a highe power motor to test the circuit, and it will run from dead still to full speed using the potentiometer speed control and a 12V battery as the sole power source. 


*Designing a working frequency Circuit*

For the highest performance of the motor , I think that I can increase the effect of the power coeficient by the way of increasing the working frequency range which is variable from 10Hz to 1Khz continuously. At this time I haven’t thought yet that how much the advantage will be brought from this thing , Would you please evaluate my solution !
Thanks


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## pquang (Oct 17, 2008)

Hi Mr Tesla,
I think that you are the EV expert , Please try to evaluate my solutions in two replies on this topic.
Thanks
Best regard,
Pquang


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## Tesla (Jun 27, 2008)

lol sorry but I'm nowhere near being an expert but as far as I know you did very well to correctly educate in calculating the power required to accelerate in any given time span. When it comes to rewiring an AC motor to run on DC and then building the circuit to control it I'm still very ignorant. Hopefully someone else here could be of more help.


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