# Electric Car



## piotrsko (Dec 9, 2007)

for starters: at 18 volts, your motor isn't going 8000 rpm. From your data, you are making about 6 something HP ({275a X 18}/746) and what rpm you do make goes into a 40 divisor reduction unit. Even if the tires are 40 (1.101 meter) inches in diameter you will still get only 5 mph (10ish KPH) at 8000 rpm. OTOH, with the reduction unit, and traction, it will climb up the side of a wall.

On the ranger overall reduction is on the order of 3.73:1


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## major (Apr 4, 2008)

thesisshit said:


> We made this car generally from scratch and some pieces of metal, in a weight of around 200+ kilos, have a reducer attached on a 24V 4 HP 8000 revolution motor series-wounded 45 AMPS NO LOAD, 140 AMPS FULL LOAD, 8000 RPM FULL LOAD, as said in the specifications. But when i actually placed it in my system, with 3 6V (18V) 220Ah batteries it gave a current reading (meter on series connected batteries) of 275 +/- 10% Amperes. Attached to the motor is a reducer with a ratio 1:40, and its all connected using a chain and sprocket connection. Now i just dont understand, why is it running on a maximum of 6-8kph, is there something wrong?
> 
> *All of this is running without a controller so all values are of maximum*


Hi the,

First off the motor specification sounds real flakey. Post up a photo of it. While you're at it, let us see your vehicle as well. Now, the motor, if it is series wound, then it would not carry a no load specification of any type. You just don't run series motors at no load. The RPM tends to increase with decreasing load and go to infinity at true no load. The RPM is also proportional to applied motor voltage. So one can run a series motor at no load with a reduced voltage and that is in fact recommended to break-in the motor. But I've never seen a no load specification on a series motor at rated voltage.

Next, 4 hp at 24V and 140A is a stretch. But let's go with it. And 8000 RPM? That is really high for a series DC motor at rated load. It is more like a permissible maximum RPM. But again, let's use it. So if it would turn at 8000 RPM at 140 Amps at the rated 24 Volts, then you could expect 6000 RPM at 140A with 18V applied. 

Conversely to the RPM increasing with decreasing load, RPM decreases with increasing load. So you measure 275 Amps. That is twice rated load of 140A. Expect the motor to operate at reduced RPM at that increased load. You would need the speed-torque curve to figure the RPM at 275A. But I'd guess it would be down another 30-40%. 

So if your motor was actually designed to deliver 8000 RPM at 140A with 24V applied to it, it would not be unexpected to see about half of that at 275A with 18V. But I doubt the 8000 at rated load, so you could actually be seeing as little as 2000 RPM on your test.

This is all SWAGing on my part. What you need to do is instrument it better. Get a tach to read actual RPM and a voltmeter for actual motor voltage. 

And on top of all that, why is the motor loaded so heavily with a huge ratio? I would have thought it would see much less load on the motor shaft. It sounds like you may have a mechanical drag of some sort. Can the vehicle be pushed by hand easily? You might want to measure the force and back calculate the motor torque required to motivate it. 

Regards,

major


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## Rational (Nov 26, 2011)

thesisshit said:


> is there something wrong?


Back to hp = torque x rpm/5252, from what you've posted we don't know the torque but at 6 kph and a reasonable wheel radius we can figure the RPM and if you climb a steep incline we can fill in the torque.
Then you mess with the gearing and/or the hp to get what you want in accel, hill climbing capability, and top speed.

The principle should be is 'top down design'. 
You start at the highest level of abstraction by specifying desired torque and speed and work down to more and more detail until you can come up with the parts list. 
You don't buy a single part until the design is fully fleshed out on paper.
Since budget is always in the background or foreground, this is an iterative process, from abstract to concrete/literal, and back again. 
When you price out the parts list, you will probably go back to what you can reasonably afford in speed and torque.
Desire is constantly being traded off against what physics and budget will allow. And nobody wants an ugly vehicle.


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## bjfreeman (Dec 7, 2011)

also a trade off about high upfront cost for a longer term solution against a lower cost that will cost again in less time than if you went the high cost route.


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## Rational (Nov 26, 2011)

bjfreeman said:


> also a trade off about high upfront cost for a longer term solution against a lower cost that will cost again in less time than if you went the high cost route.


Sounds maybe like
http://en.wikipedia.org/wiki/Denomination_effect
no wonder it's so hard to avoid.

And if he knew ahead of time how much money how often [an annuity to the parts makers] he would reasonably be paying in the future to fix/upgrade this machine he could use the formula for the Present Value of an Annuity and see if this amount exceeds what he has already paid. 
'Look ahead and reason backwards'.

You can also use this formula to debunk offers of mortgage refinancing. My own insurance company's offer to me had a fat little five kilobucks hidden in the monthly payments.


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## major (Apr 4, 2008)

Rational said:


> Sounds maybe like
> http://en.wikipedia.org/wiki/Denomination_effect
> no wonder it's so hard to avoid.
> 
> ...


Hey Rational,

How is this relevant to the OP's question? You seem to make a habit of irrelevant posts and highjacking threads. If you want to discuss annuity, mortgage or insurance, you should start your own thread. I find your behavior impolite to say the least.

I apologize to thesisshit as this post is off topic. Hopefully we can get back to analyzing his electric car performance problem

Regards,

major


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## thesisshit (Dec 7, 2011)

Hi major, very thank you for your reply

This is the specification of our motor










This is a brand new 4 HP 24 Volt DC Reversible Electric Motor. Peak HP is 9 HP for short of power for short burst of power. This motor will produce 2 HP at 12 VDC with 4,000 RPM approximately. This motor is believed to be manufactured by Ramsey . The photos with the wire in it illustrate how to connect and reverse rotation of the motor shaft. The two alligator clips represent where power cables should be attached for power input (motor is case grounded). The green cable allows current to be redirected. This would be a great motor for scooters, go-karts and other projects requiring lots of power in a small package. This motor shaft is not designed for radial loads. It was designed for torque (turning power) only, such as driving a transaxle on a go-kart.

SPECIFICATIONS:

4 HP 24 VDC ELECTRIC MOTOR

45 AMPS NO LOAD

140 AMPS FULL LOAD

8000 RPM FULL LOAD

32 INCH POUND OF TORQUE

¾” DIAM. X 1 ¾” SHAFT WITH KEYWAY

MOTOR DIMENSION 4” DIAM. X 7 ¾”

SHPG 24 LB (ESTIMATED)

This is our vehicle in the picture. The motor (black) which is 30kg near the reducer is not the motor that we are going to use, but the motor on top (green) which is 10kgs. 1:40 (green) is our test ratio for rpm reduction, but we can choose to change it. Our motor seemed to overheat quickly and we concluded that it is because of the maximum performance it is currently showing without controller. We are just surprised that the current shown is 300A with 18V 220Ah voltage input.


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## major (Apr 4, 2008)

thesisshit said:


> This is the specification of our motor
> 
> 
> 
> ...


Hello thes,

I was afraid this would happen. I have been warning people about that motor for years. It is a winch drive motor made for reeling in a cable and pulling a load for a short time powered from a truck's starting battery. While the specifications listed may not be an outright lie, they are certainly misleading. 

This is a 4 inch diameter motor and the armature and comm diameters are less than about 2 inches. So it can in fact spin up to high RPM. It uses bushing type bearings instead of ball bearings. This will provide enough internal friction as to limit no load speed. At no load, 24V * 45A = 1080 Watts. That is lost power converted to heat in the motor.

The claimed 4 hp is at best achievable in ideal conditions. Even then this motor could only run at that load (140A) for a short time before overheating, a manner of minutes. It is totally enclosed with no ventilation. I do not believe it can run for long at any load without overheating. It is strictly an intermittent duty motor.

People are intrigued by this motor and a friend bought one even after my warning. I work with this guy so got to see the motor inside and out. It is a nice robust motor for its intended application. He wanted to use it on a go kart. So he installed ball bearings....not an easy job. And he milled slots in the end caps for ventilation. And he put a fan on the rear. He was able to run a kart with it but was never pleased. I think he gave up on it.

This is not the motor to use to propel you car 

Now, about that gear reducer. It appears to be of industrial nature, not automotive. And appears to have at least one right angle mesh. Having a 40 : 1 ratio I suspect it uses a worm gear. As such it will be inefficient. I suspect that gearbox alone is a large drag (load) on the motor. In other words, the gearbox robs a large portion of motor torque before power gets to the wheels. To verify this, remove the chain or belt from the gearbox output and observe the motor current. Multiply that current times the voltage and you see the watts loss before power ever gets to the axle.

I assume you want this vehicle to run for more than a few minutes. To prove to yourself it will not do so, just jack up the wheels and power it and let it run. I suspect it won't be long before you start smelling the motor 

For kicks I would remove the gearbox and drive the axle from the motor with the largest reduction you can get with a chain or belt. You might be able to get a 5 or 10 minute ride 

Regards,

major


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## thesisshit (Dec 7, 2011)

We also have an older motor which the one connected here... since it came from a Junk shop. its power is 1.6KW rated at 9600 RPM with a nominal voltage of 24V... is that enough and what type of gearbox should we use? Back then we also don't have a controller for that... However the controller what we have right now is a Kelly 48500 with all the shit connected to it ( i know most people here are saying it's shit but we don't pretty much have a choice now since it's already here) but the problem with that one is the contactors installed to it are for 48V and we just have 24V. if we changed the contactors will it work? (with the correct settings in the program presumably)


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## major (Apr 4, 2008)

Gearboxes with parallel shafts are better. But consider using 2 chains and sprocket sets. Make a jackshaft (intermediate shaft). The two ratios multiply.


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## Rational (Nov 26, 2011)

major said:


> Hey Rational,
> 
> How is this relevant to the OP's question? You seem to make a habit of irrelevant posts and highjacking threads. If you want to discuss annuity, mortgage or insurance, you should start your own thread. I find your behavior impolite to say the least.
> 
> ...


"Hey", Major. . .

Generally, I try to structure my posts to go from specific to general. That puts the problem in a wider context.
If you'd like I can reference the post in the Chit-Chat room and do my philosophy stuff over there. I'm only a lieutenant so it's your call.


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## major (Apr 4, 2008)

Rational said:


> If you'd like I can reference the post in the Chit-Chat room and do my philosophy stuff over there.


Yes, please do that.


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## Rational (Nov 26, 2011)

major said:


> Yes, please do that.


I've since had a much better idea, one that addresses the root cause of the problem rather than just the symptoms.

Find a tech bookstore and read up on the basics of electric vehicles. That way you'll have much more confidence in yourself and be less inclined to view things as a Turf War.
But. . .don't expect miracles.


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## poprock (Apr 29, 2010)

Hey Irrational, please stop denigrating Major and others. If you want an argument get married! We need to keep bitterness and vitriolic comments out of our forum and stick to our common goal of promoting ev use.


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## rochesterricer (Jan 5, 2011)

Rational said:


> I've since had a much better idea, one that addresses the root cause of the problem rather than just the symptoms.
> 
> Find a tech bookstore and read up on the basics of electric vehicles. That way you'll have much more confidence in yourself and be less inclined to view things as a Turf War.
> But. . .don't expect miracles.


Are you just trolling with this comment? Considering Major is one of the members of Team Lightning of the TTXGP, I doubt he would find much value in such basic reading material. He probably has more hands-on EV experience than anyone on this board.


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## thesisshit (Dec 7, 2011)

guys stop the feuding in this thread, as i am expecting reply from experts, like major.

Dear major, 
thank you for all your help. We are trying to solve the problem and consider to change the ratio, and use the old black motor. I feared the new one is not that good for our purpose.


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## DavidDymaxion (Dec 1, 2008)

Uh, isn't Major the guy that designed the controller that just ran a motorcycle 215 mph on the Salt Flats?  BTW I was there, saw the bike run, and met Major in person. If you have a problem with Major it certainly isn't something that'll be rectified by reading "basics of electric vehicles!"


Rational said:


> ... Find a tech bookstore and read up on the basics of electric vehicles. That way you'll have much more confidence in yourself and be less inclined to view things as a Turf War.
> But. . .don't expect miracles.


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## piotrsko (Dec 9, 2007)

I don't know that major does controllers, I thought he was a darned good (one of the best?) motor and go kart guru. BTW thesis your vehicle looks pretty interesting from here in reno. What are your requirements / goals?


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## thesisshit (Dec 7, 2011)

http://kellycontroller.com/simplified-5v-throttle-pedal-p-1028.html

I'm considering to take this as the pedal to be used is this ok? and What is the difference between a 5k and a 5V Throttle Control?


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## thesisshit (Dec 7, 2011)

We are now trying to get a gear box with a ratio of 1:15 and the input and output must be perpendicular to each other since that is the design layout... according to what i have read that bevel gears are not recommended to be used in high ratio applications so we are opting for a worm gear box instead (brand name Makishinko), any tips on what gearbox to get(better if the gearbox is for automotive applications rather than industrial)?


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## piotrsko (Dec 9, 2007)

A worm drive does not allow coasting the vehicle without turning the motor. there are belt and pulley systems that allow for a 90 degree turn in power. The problem with bevel gears is that it is difficult getting massive enough gear sets to deal with the power and loads developed. Automotive would be the better choice because massive gearboxes are rare in industrial applications.


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## thesisshit (Dec 7, 2011)

is there a gearbox set with the said ratio? that is for automotive applications...


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## DavidDymaxion (Dec 1, 2008)

What piotrsko said. With a worm drive the wheel would likely skid if the motor ever quit.


piotrsko said:


> A worm drive does not allow coasting the vehicle without turning the motor. ...


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## piotrsko (Dec 9, 2007)

there are appropriate bevel gears in the typical automotive differential, but they are generally in a much lower ratio, say 1:1.12. However I am generally familiar only with VW and most american brands.


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## thesisshit (Dec 7, 2011)

We have changed the ratio from 1:40 to 1:15, keeping the other parts the same, it seems that the vehicle runs in the same speed, running in 7.5kph (maximum using throttle knob). We measured the current - from 60A (using 1:40 gear reducer) to 30A (using 1:15 reducer) Is there an explanation to this? Our old and new reducer are of the same weight.


Our motor specifications:
22V to 1600KW

running in 24V battery (4 6V deep cycle battery)


Using the previous reducer,
running 22V x current reading of 60A = 1320W

When we used the new one,
running 21.7V x current reading of 30A = 651W

*current reading of motor armature attached to the controller.

Does this mean there is a huge power loss when we used the new reducer? What happened or where did it go? Are there other possible reasons or problems why results is so?

Thanks.


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## major (Apr 4, 2008)

thesisshit said:


> We have changed the ratio from 1:40 to 1:15, keeping the other parts the same, it seems that the vehicle runs in the same speed, running in 7.5kph (maximum using throttle knob). We measured the current - from 60A (using 1:40 gear reducer) to 30A (using 1:15 reducer) Is there an explanation to this? Our old and new reducer are of the same weight.
> 
> 
> Our motor specifications:
> ...


Hi the,

We need more details to figure out your problems. Is this the same motor used for both experiments, with the 40:1 and the 15:1 reducers?

Your 7.5kph relates to about 80 RPM on the wheel, IMMIC (If My Math Is Correct ). So that would be 3200 RPM from the motor using a 40:1 and 1200 RPM using the 15:1 reducer. These two numbers are inconsistent for the same motor at the same voltage and at 60A and 30A respectively.

The difference in power may well be explained by gearbox loss. But unless there is slippage (which doesn't happen with gears), loss does not affect the RPM ratio.

When you test, see if you can get the RPM measurements. Also measure the voltage at the motor terminals and the current into the motor. Please post a picture and spec for the motor. Include tests with the wheels spinning freely off the ground as well as actually propelling the vehicle. How did you determine speed? At 7.5kph it may be difficult to judge difference from one test to the other especially one day to the next. Use a GPS or time to travel a calibrated distance to get accurate kph.

The good news is that 30A (651W) is a vast improvement over your first attempt  A little less than 1 hp may be about what to expect for that vehicle at 7.5 kph. If you're still using a right angle gearbox it will be robbing a good bit of that power before it gets to the road.

Regards,

major


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## bjfreeman (Dec 7, 2011)

thesisshit said:


> We measured the current - from 60A (using 1:40 gear reducer) to 30A (using 1:15 reducer) Is there an explanation to this? Our old and new reducer are of the same weight.


so with the 1:40 you motor was turning 40 times for 1 turn of you wheel.
now with the 1:15 you turning 15 times or less than half for 1 turn of the wheels.
so your require torque to turn the wheel has increased.
also your RPM for you motor should be reduced for the same speed.
so the drop in current is correct I would say. The extra amps at 30 is the required power to over come due to torque.


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## major (Apr 4, 2008)

bjfreeman said:


> The extra amps at 30 is the required power to over come due to torque.


For the same conditions (vehicle speed and load), the torque required at the input to the gearbox is 2.7 times less for the 40:1 ratio than the 15:1, neglecting gearbox loss. So how does that explain twice the current when using the 40:1 box? It is just the opposite of your quoted statement. There is less torque on the motor with the 40:1 box, not more.

That is unless the 40:1 gearbox is terribly inefficient or otherwise has mechanical binds, drag or friction. The other factor which could account for the discrepancy the use of different motors for the two cases.


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## bjfreeman (Dec 7, 2011)

major said:


> For the same conditions (vehicle speed and load), the torque required at the input to the gearbox is 2.7 times less for the 40:1 ratio than the 15:1, neglecting gearbox loss. So how does that explain twice the current when using the 40:1 box? It is just the opposite of your quoted statement. There is less torque on the motor with the 40:1 box, not more.
> 
> That is unless the 40:1 gearbox is terribly inefficient or otherwise has mechanical binds, drag or friction. The other factor which could account for the discrepancy the use of different motors for the two cases.


we agree, that is what I intended to say, apologize if I was not clear.
you are saying from one reference I am saying from the other reference both are correct.


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## bjfreeman (Dec 7, 2011)

bjfreeman said:


> so with the 1:40 you motor was turning 40 times for 1 turn of you wheel.
> now with the 1:15 you turning 15 times or less than half for 1 turn of the wheels.
> so your require torque to turn the wheel has increased.
> also your RPM for you motor should be reduced for the same speed.
> so the drop in current is correct I would say. The extra amps at 30 is the required power to over come due to torque.


to clarify went from 1:40 @60A
to 1:15 @30amp
so the motor is turning slower @1:15 therefore drawing less current (30A)
however the ration of 1:40 to 1:15 is not the same as 60A to 30A.
the reason the 30Amps is not less is the extra Torgue to turn the motor with 1:15


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## major (Apr 4, 2008)

bjfreeman said:


> so the drop in current is correct I would say.


O.K. So let's look at it this way. Thesisshit says his vehicle speed is the same. He goes from the 40:1 gear to the 15:1. He cuts his power in half yet does the same rate of work with the vehicle. And you say that is correct?

Obviously there is more to this story. The numbers given do not make sense and is the reason I requested more information from thesisshit. If as you say the drop in current is correct, what accounts for the missing 669 watts?


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## bjfreeman (Dec 7, 2011)

major said:


> O.K. So let's look at it this way. Thesisshit says his vehicle speed is the same. He goes from the 40:1 gear to the 15:1. He cuts his power in half yet does the same rate of work with the vehicle. And you say that is correct?
> 
> Obviously there is more to this story. The numbers given do not make sense and is the reason I requested more information from thesisshit. If as you say the drop in current is correct, what accounts for the missing 669 watts?


lets not look at the speed of the vehicle but the speed of the motor.
you have the motor turning faster so requires more power.
then gear box translate that power to the wheels at the ratio of the gearbox.
Constant speed on wheels same that both are the same once it gets through the gearbox.


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## major (Apr 4, 2008)

bjfreeman said:


> lets not look at the speed of the vehicle but the speed of the motor.
> you have the motor turning faster so requires more power.
> then gear box translate that power to the wheels at the ratio of the gearbox.
> Constant speed on wheels same that both are the same once it gets through the gearbox.


Instead of looking at the speed of the motor, let's look at its torque.
You have less torque from the motor so requires less power.
Then the gearbox translates that power to the wheels at the inverse ratio of the gearbox.
The torque on the wheels is the same once it gets through the gearbox.

The above is using your logic except with torque instead of speed.

The correct way to view it is that the power into the gearbox is equal to the power out of the gearbox neglecting the torque loss due to inefficiency of the gearbox. The gear ratio alters the torque and speed but does not change the product of torque and speed (power). So this reply of yours does not address the 669 watts difference.


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## bjfreeman (Dec 7, 2011)

major said:


> Instead of looking at the speed of the motor, let's look at its torque.
> You have less torque from the motor so requires less power.
> Then the gearbox translates that power to the wheels at the inverse ratio of the gearbox.
> The torque on the wheels is the same once it gets through the gearbox.
> ...


Ok what is your explanation?


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## major (Apr 4, 2008)

bjfreeman said:


> Ok what is your explanation?





major said:


> Obviously there is more to this story. The numbers given do not make sense and is the reason I requested more information from thesisshit.


I am admitting that I cannot explain it with the available information.


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## bjfreeman (Dec 7, 2011)

Can you walk through you logic and put ? in the missing pieces.
that way he will know where to look


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## major (Apr 4, 2008)

bjfreeman said:


> Can you walk through you logic and put ? in the missing pieces.
> that way he will know where to look


I thought I was pretty clear with post #27. Here it is again. What am I missing?



major said:


> Hi the,
> 
> We need more details to figure out your problems. Is this the same motor used for both experiments, with the 40:1 and the 15:1 reducers?
> 
> ...


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## thesisshit (Dec 7, 2011)

Hi major, the motor we used is the same. How does the current work actually, I'm sorry, I somehow don't understand the relationship of the torque and current, besides it being directly proportional as well as completely oblivious to the fact of the power lost during our transfer. 

We, the proponents concluded, that there might be no more battery, having it run in 21.7V which is like the discharge voltage of four 6V (max 6.5V) batteries;
26V max in series. Can that be one of the reasons why our motor is performing poorly? The design of the reducer is the same with the previous reducer, still worm gear 90 degrees. We expected, that the speed will go faster, knowing that we reduced the ratio already, but it seems the speed is just the same?

Thank you for all your replies.


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## major (Apr 4, 2008)

thesisshit said:


> Hi major, the motor we used is the same.


O.K. Then this applies.


> So that would be 3200 RPM from the motor using a 40:1 and 1200 RPM using the 15:1 reducer. These two numbers are inconsistent for the same motor at the same voltage and at 60A and 30A respectively.


 We need to retake some data points. Make sure you measure voltage and current for the motor, not the battery. And take the data points at the same instant along with RPM.

It would help me to know more about the motor you are using. Is it series wound? Please post a photo and specs.

It is possible that something strange is happening, but the rule is more current, more torque. It is not always a linear proportionality, but I'd say the motor was developing about twice the torque at 60A compared to 30A. Again, inconsistent with the gear change for the same load.

The batteries certainly look to be in a poor state of charge. If your voltage and current readings had been made as outlined above you would have valid data, just at reduced voltage. But please charge the batteries before further testing. The voltage will hold more constant during the test.

The change from the 40:1 to 15:1 should increase the speed of the vehicle. But that will increase the motor load by at least a factor of 2.7, which should have been evident in the current, but was not. Please look again at my post #27 and do some more testing. 

Regards,

major


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## thesisshit (Dec 7, 2011)

Our motor is connected to the controller in a series manner, which is the armature (1 & 2) to the controller; the field (1 & 2) to the reversing contactor poles to activate the clockwise/counter-clockwise of the rotation of the armature 










So with that, the current is the same to and from the motor, stated on the previous post I made.


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## major (Apr 4, 2008)

thesisshit said:


> Our motor is connected to the controller in a series manner,...


O.K. Thanks. Are you sure the motor is series wound? Does the nameplate indicate series wound? If it doesn't specify, measure the resistance of the field, from field terminal 1 to field terminal 2. A series field will have very low resistance and register off-scale low on a DVM. A shunt field will measure maybe like 5 to 20 Ohms.


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## thesisshit (Dec 7, 2011)

I'm back! And yes, sir major, I'm sorry for replying so late. Our motor is series wounded. We are able to increase the speed by changing the ratio of our reducer.. and one thing bugs me...

Worm gears, should be irreversible right? I mean it self locks when you move it from the driven shaft (worm wheel)? 

We somehow revised our worm gear (particularly the driven shaft) in a way that we can disengage the sprocket in the driven shaft for our manual mode: a mode in which the user of our tricycle can move our vehicle by manual means (pedaling) so with that, we disengage the sprocket from the key slot of the worm driven shaft in order to make the sprocket free moving. But we never opened the worm gear itself... 

So now, our gear reducer has a mechanism of switching that can lock the sprocket (motor mode) or unlock the sprocket (manual mode)

Now, when locking the sprocket, the vehicle seems to be coasting!!?! which should not -_-, is it because the force is a lot stronger to move the worm wheel -> worm gear (reversibly)?

And now, after the revision, our vehicle is now coasting (which should not)


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## Woodsmith (Jun 5, 2008)

Whether or not your worm gear lock is dependent on the ratio.
The lower the ratio (high numbers) the more it will lock, the higher the ratio (low numbers) the less it will lock.

An example is the 1:1 skew helical gear.
Two helical cut gears of the same hand, or direction of cut, and same tooth count can engage on a skewed shaft and work both directions.
If the helix is cut at 45deg then the shafts will be at 90deg to each other but not in the same plane.


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