Help Me Choose a Motor -- I Found Some Great Ones

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Beagle123   10 kW

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Help Me Choose a Motor -- I Found Some Great Ones

Post by Beagle123 » May 26 2007 5:18pm

Here's my problem:

I building a electric scooter using a CVT transmission (pictured below).



If you aren't familiar with CVT's look at this animation:

http://auto.howstuffworks.com/cvt2.htm

So I bought this CVT from ebay, and I tested it by using an electric drill to spin the drive wheel. I wanted to spin the drive shaft fast enough to activate the pulleys, making it "shift gears." However, my drill wasn't fast enough. The CVT works by centrifugal force, so when the RPMs get high enough, it will start adjusting its gears. My drill says, "2700" RPMs on it, and it was probibly working at about 2400 RPMs, which wasn't sufficient.

You can see a video of this test attached below. ALLOW SEVERAL MINUTES TO DOWNLOAD.



This transmission was made to fit a x8 pocket bike. So, I researched the x8 on the internet. I found out that the engine can go up to 8000 RPMs (really more like 7000 with load)

So, I need to get a motor with very high RPMs.

Most scooter motors run at about 2800-3000 RPMs, and gearing them down is usually the problem. But I need more RPMS.

Then I found these Mag Motors:

http://www.battlekits.com/robot_motors.htm

The stats are truly unbelievable: Aparently they have a motor that's 83% efficient and puts out 3hp and weighs 4lbs. Another is 4.5hp, 84% efficient, and 7lbs. And both at 24V!!

Does anyone know anythiing about these motors?

Here's what I want to do:

I want to use 4 lead acid batteries at 17ah each to make a 48v system. I want to use a 50amp controller like thiis:

http://www.tncscooters.com/LB37.php

So, I need a motor that will operate at 6000-7000 rpms under maximized conditions. When its running that speed, it should be producing perhaps 1.5hp.

My question is: will I be able to achieve these types of RPMs without pumping 100+ amps into the motor? Do I want to use the smaller motor, so I get less torque and more RPMs? Do you think the samller motor will fry? (4lbs). Does anyone know of a better solution?

The way I see it, motors are pretty simple: If you pump 20 amps @ 48v into a motor, you're providing 960 Watts of power. Since the motor is 80% efficient, you should get 768 watts out of it. But those 768 watts can take many forms-- it could be a slow moving shaft with lots of torque, or a fast moving shaft with less torque. In my situation, I need the faster one.

Right now, I'm leaning toward the idea of getting the larger, S28-400 motor, then increasing the volts and amps until I get the needed RPMs. I'm afraid I'll be going 80mph before I'm done! I really don't want that. I want a 30+ mph scooter that just humms along, and takes the hills at about 20mph (but easily!)

Thanks, you guys rule.
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CVT transmission
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fechter   100 GW

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Post by fechter » May 27 2007 9:42am

If you go from 24v to 36v, the rpm will increase by 36/24, or 1.5 times.
The no-load current will go up as well, along with heating.

7,000 is really screaming for most electric motors. The small Perm motor (I forget the number, something 80) would be a good choice here.

The Magmotors are nice for robots, but won't last long in a scooter. I think Maytag burned up one. They can't take running for an extended time. (intermittent vs. continuous rating). I've heard of several Magmotors that failed in scooter use.

If you increase the voltage on a brushed motor, there is incresed arcing on the brushes, which can cause the commutator and brushes to overheat or wear out prematurely. I ran my brushed 24v Vego motor at 48v and it was fun while it lasted. Eventually the commutator failed, turning it into a paperweight.

With a brushless motor, you can get away with over volting a bit easier, but things can get expensive.

Most CVT's use centrifugal weights to activate the mechanism. If you can increase the weights or make the springs weaker, it will shift at a lower RPM. This might be a better solution if you can figure out a way to do it.
Then you could use a more commonly available 3000 rpm motor.
"One test is worth a thousand opinions"

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Post by Drunkskunk » May 27 2007 10:13am

I don't know what you're budget is like, but you might want to check some of the big electric RC aircraft motors.

They need cooling, but I get 400 watts out of a 4 ounce motor at 8000 RPM loaded. And thats at 12 volts.
You should be able to get your 1.5 to 2 HP for under a pound of weight.

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Beagle123   10 kW

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Post by Beagle123 » May 27 2007 8:11pm


Thanks for the tips.

I'm not so concerned with the weight of the motor. I'm more concerned with getting a reliable motor that doesn't smell like smoke.

I'm starting to get the feeling that it may be unrealistic to find a motor that goes 6000 rpm using 30 amps or so @48v.

I'd be interested to know the setups that others were using that blew-up their MagMotors. It seems like if they're capable of handling 200+ amps, then 30 apms should be easily done without blowing it up. However, I suspect that I won't be getting the 6000 rpms at 30 amps.

I may have to try fetcher's advise of using a weaker spring. I could solve the problem by using heavier weights, but that seems very hard to do.

Do you guys know anything about that?

The downside of the weaker spring could be that the belt might loose traction on the pulley, but I guess I have to try it.

Prehaps, I could try taking apart the drive side of the unit. It may also have a spring that I can change. THen the back spring would still have its gripping power. In fact, I think that's the best move because the weights will cause it to grip.



Thanks again for your help

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Post by maytag » May 27 2007 9:27pm

Yup, I burned up a Magmotor C40-300 trying to pump 48v to it during a gas vs electric scooter dragrace. I won my leg of the 1/4 mile race but paid the price in the end. The Magmotor brushes are very soft, almost soft as lead. The commutator showed clear signs of major arcing and all of the brush holders were deformed and melted. Before boosting it up to 48v it ran great for many miles at 36v with a 36v/175A Curtis controller with a top speed of 30mph and awesome hill climbing ability. At 48v the scooter reached 38-39mph but I believe the same performance can probably be had using an E36 motor at 48v with forced air cooling.

And if you want to know about the smaller (but more powerful) S28-400 Magmotors you can ask my brother Joystix, he was using one of these in the same dragrace. It was sweet, wish we had it on video. 2 modified electric scooters vs 2 modified gas scooter. Ric was the front runner taking out the topdog gasser. I wasnt far behind them making the other gasser smell my burning brushes. Ric's S28-400 motor reached 42mph at only 36v, didnt melt anything but the soft Magmotor brushes were toast. His commutator also had some pitting. I ordered new brushes and repaired the brush holders of my C40-300 also lathed smooth the commutator pitting but it never ran the same after that day. Same goes for Ric's S28-400. Magmotors arent suited for EV use, just my opinion. Have you seen Fechter's Vego brushless motor setup? If I were to build another super scooter that would be my motor of choice now. Hope this helps.

Dave
Last edited by maytag on May 27 2007 9:29pm, edited 1 time in total.

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eP   10 kW

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Post by eP » May 27 2007 9:28pm

Beagle123 wrote:
Thanks for the tips.

I'm not so concerned with the weight of the motor. I'm more concerned with getting a reliable motor that doesn't smell like smoke.

I'm starting to get the feeling that it may be unrealistic to find a motor that goes 6000 rpm using 30 amps or so @48v.
Look at this

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Beagle123   10 kW

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Post by Beagle123 » May 28 2007 2:19am


That's a very interesting motor Ep, but I smell smoke. Somthing tells me that a tiny little motor will overheat when I make it drag me up a long hill.

But good news: I took apart the CVT transmission in the hopes that I could figure out a way to make the shifting operate at lower RPMs. And guess what I found?

I found that there are six little weights that cause the transmission to change gears, and luckily they were hollow little ceramic tubes. So, I made tiny little cylinders by cutting up a lag bolt, and inserted one into each tube and reassembled the CVT.

I figure that I more than doubled the mass of each weight. That HAS to have an effect.

I still can't get it to change gears with the drill, but I looked more closely at how it was spinning, and I think its only spinning at about 1100 RMPs. I want it to activate at about 2000 RPMs. So its time to get a motor and try it.

I'm thinking of getting this one:

<a href="http://tncscooters.com/product.php?sku=106170">Cheap unite motor</a>

What do yall think of that?

I"m not sure I trust that any of their numbers are right, but how much better motor can I get? Any other suggestions? What would you do?

Thanks

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eP   10 kW

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Post by eP » May 28 2007 3:03am

Beagle123 wrote:
That's a very interesting motor Ep, but I smell smoke. Somthing tells me that a tiny little motor will overheat when I make it drag me up a long hill.
It is depend on what the highest ratio at bottom gear you will have.

You can get 6000 rpm, so you need very high ratio.

It is not a tiny motor as its weigt over 3 pounds.
And is relatively quiet(brushless) and very efficient.

Have low winding resistance, so it is very efficient at wide voltage/rpms span. So you dont need ultra wide gearbox span for big torque at low speed and for high speed at the other end.

You can simply lower the speed at long hill at bottom gear and still get the high efficiency.

So if you apply right gearbox and right current limit
it is unlikely to easy burn this motor.

At flight it is able give out a few kW of power for a few minutes when is strongly cooled.

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Beagle123   10 kW

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Post by Beagle123 » May 28 2007 3:15am


Here are a couple of brushless ones:

<a href="http://www.cyclone-tw.com/dc48.htm">1050W ebike motor</a>

<a href="http://www.thesuperkids.com/600wahspsuto.html">1000W scooter motor</a>

Opinions?

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Miles   100 GW

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Post by Miles » May 28 2007 3:32am

Beagle,

That's a very inefficient transmission that you're intending to put your motor through....... as long as you're aware of that....

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Post by eP » May 28 2007 3:34am

Beagle123 wrote:
Here are a couple of brushless ones:

<a href="http://www.cyclone-tw.com/dc48.htm">1050W ebike motor</a>

<a href="http://www.thesuperkids.com/600wahspsuto.html">1000W scooter motor</a>

Opinions?
Check the prices and buy the cheaper one - the risk is low and you could learn a lot.
If your hour is worth $80 you lose more for posting than for real motors :wink:

Regards

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eP   10 kW

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Post by eP » May 28 2007 3:37am

Miles wrote:Beagle,

That's a very inefficient transmission that you're intending to put your motor through....... as long as you're aware of that....
Motor's inefficiences could be much bigger.

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Post by Miles » May 28 2007 3:37am


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eP   10 kW

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Post by eP » May 28 2007 3:43am

Miles wrote:I believe this is the range that the motor in eP's link above comes from: http://www.hackerbrushless.com/motors_a100.shtml
I suppose my link is for lower quality/performance substitute but it is 4 times cheaper, so it is worth of try i'm sure.

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Miles   100 GW

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Post by Miles » May 28 2007 3:45am

eP wrote:
Miles wrote:Beagle,

That's a very inefficient transmission that you're intending to put your motor through....... as long as you're aware of that....
Motor's inefficiences could be much bigger.
True, but the transmission inefficiency is always there (relative to power, of course...) The efficiency of those pulley CVTs is appalling...

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eP   10 kW

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Post by eP » May 28 2007 3:53am

Miles wrote:
eP wrote:
Miles wrote:Beagle,

That's a very inefficient transmission that you're intending to put your motor through....... as long as you're aware of that....
Motor's inefficiences could be much bigger.
True, but the transmission inefficiency is always there (relative to power, of course...) The efficiency of those pulley CVTs is appalling...
The best way to learn is to try yourself. The faster he try the more he save - it is better for him than posting and reading if he is able to earn a lot of money per hour.

I'm not jealous - it is my simple opinion (i'm sure i'm right).

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Miles   100 GW

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Post by Miles » May 28 2007 3:57am

eP wrote: The best way to learn is to try yourself. The faster he try the more he save - it is better for him than posting and reading if he is able to earn a lot of money per hour.

I'm not jealous - it is my simple opinion (i'm sure i'm right).
You have a point :)

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Miles   100 GW

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Post by Miles » May 28 2007 4:10am

eP wrote:
Miles wrote:I believe this is the range that the motor in eP's link above comes from: http://www.hackerbrushless.com/motors_a100.shtml
I suppose my link is for lower quality/performance substitute but it is 4 times cheaper, so it is worth of try i'm sure.
Yes, you're right, it's not a Hacker. Seems to be a Hextronic motor, imported from China. Very cheap, definitely worth investigating.....

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Post by TylerDurden » May 28 2007 6:31am

Miles wrote: Very cheap, definitely worth investigating.....
Yes.

Any tips on mounting a sprocket onto a 10mm shaft?

http://www.unitedhobbies.com/UNITEDHOBB ... oduct=5144

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Have a Nice Day,

TD

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Post by eP » May 28 2007 6:48am

TylerDurden wrote: Any tips on mounting a sprocket onto a 10mm shaft?
I think you need mount the teeth wheel onto the shaft , and after that at next axle next wheel and the sprocket.
One stage reduction is not enough at this case as you can get 6000 rpm at 48V.

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Post by fechter » May 28 2007 9:33am

TylerDurden wrote:
Any tips on mounting a sprocket onto a 10mm shaft?

http://www.unitedhobbies.com/UNITEDHOBB ... oduct=5144
The sprocket can be cross drilled and tapped for a pair of set screws. Put the pair at 90 degrees apart. Once the sprocket is on the shaft, tighten enough to make a mark on the shaft with the set screws. Remove the sprocket and use a Dremel grinder to make flats on the shaft where the set screws sit. Install sprocket and use loctite on the set screws.

This is how I mounted the sprocket on my BMC motor. It's never budged and it takes LOTS of torque.

I've also seen gear reduction units for some of them.

One thing about the RC motors is they usually don't have hall sensors, so you need to run them with a sensorless controller or install hall sensors. They also depend on lots of airflow to keep them cool. A blower might be necessary.
Last edited by fechter on May 28 2007 10:59am, edited 1 time in total.
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Post by TylerDurden » May 28 2007 10:13am

eP wrote:One stage reduction is not enough at this case as you can get 6000 rpm at 48V.
Thanks guys,

I will use 24v if I get this motor. :)
Have a Nice Day,

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eP   10 kW

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Post by eP » May 28 2007 1:16pm

TylerDurden wrote:
eP wrote:One stage reduction is not enough at this case as you can get 6000 rpm at 48V.
Thanks guys,

I will use 24v if I get this motor. :)
But this way you will lose a few % of efficiency at high load.
One stage reduction would be OK if you dont care about power out and don't care about efficient high slope climb ability.

You would like to use two of them for example: one with two stage reduction and freewheel at rear wheel and the other one with the sprocket and fixed gear at the front.

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Post by Miles » May 28 2007 2:47pm

eP wrote: You would like to use two of them for example: one with two stage reduction and freewheel at rear wheel and the other one with the sprocket and fixed gear at the front.
:roll: :)

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Post by eP » May 28 2007 2:57pm

Miles wrote:
eP wrote: You would like to use two of them for example: one with two stage reduction and freewheel at rear wheel and the other one with the sprocket and fixed gear at the front.
:roll: :)
I'm quite serious.
This way you could avoid wide span expensive gearbox needs. And you still will be able to climb at any high grade hills and be able to riding fast at flat at high efficiency.

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