Electric scooter (brushless or brushed motor)

[rascupanamuha]

Here i am again, with a new project ! Electro scooter
I want to do everything myself. I will connect and program electronic part with arduino

The problem is this:
I have wanted to use this motor: https://www.hobbyking.com/hobbyking...y_RotoMax_1_40_Brushless_Outrunner_Motor.html

And here is what i have calculated so far:
I want max speed of 10m/s
Diameter of wheel: 16cm (circumference=0.5m)
Motor has 228kv, and with 24V battery, that is 5472rmp=91.2 rotates per second
If i want max speed of 10m/s, i should use gear ratio 1:4.55
I dont know what current would it need, and the rest of this...

So what do you think? Is brushless motor goot for this? Or should i go for brushed one?
I am worried if this motor could start scooter with me on it...

Please give me your suggestions

 

[Mr RB]

I doubt that little motor equates to "2775 Watts" but at 80x80mm size with a 8mm output shaft it's probably good enough for a scooter. Although I think your goal of 10 metres/sec on a scooter is a bit much!

It's max RPM looks about 8400 RPM, so it should make some decent traction power at <4000 RPM. However i think your gearing needs to be thought through carefully, a scooter will spend a LOT of time at very low speeds stopping, starting, slowly going up ramps at high loads etc. Even if you could gear it for silly high speeds like 10m/s it would work very poorly at 0.5-1m/s which you will use all the time.

Maybe you should have a look at commercial scooters and see what their speeds are?

 

[alec_t]

I dont know what current would it need

According to the spec the speed controller (ESC) should be rated at 120A, although the motor max current (we don't know if that is the stall current or the current at maximum rated load) is 75A.
I agree with Mr RB re the gearing.

 

[rascupanamuha]

I dont know, their speeds aren't so low. I mean max speeds.
On the other forum they told me that this motor is not good enough, because it is meant to be installed on RC airplanes. And on them, torque is 0 at the beginig, because there is no air resistance then. And after it reaches high speed, torque is not 0 because air resistance is high.
In my case (electric scooter) it is completely different. I need highest torque at the start. And this motor is sensorless and it stator doesnt know rotors position, it works well only on speeds 10% to the max speed. So they started to puting hall sensors to solve that problem: http://www.linushelgesson.se/2011/12/modifying-the-turnigy-80-100-brushless-outrunner/

Also, speed isnt 8400 (it is on 36V), speed will be 5472 RPM

And you are saying that it will spend a lot time at low speeds, that is true, but then it should only pull higher amount of current, isnt that true?

 

[alec_t]

it is meant to be installed on RC airplanes. And on them, torque is 0 at the beginig, because there is no air resistance then. And after it reaches high speed, torque is not 0 because air resistance is high.

No. The motor neither knows nor cares whether it is on an R/C plane, a scooter or a moon buggy. At low speed the motor back-emf is low so the current, and hence the driving torque, is high. At low speeds the counter-torque produced by resistance (due to friction, air viscosity and lubricant viscosity) is low so the nett torque will accelerate the motor/prop. As the speed rises the back-emf and resistance both rise so the acceleration falls and eventually a steady-state arises where the driving torque balances the counter-torque.

 

[jpanhalt]

Here are a couple of useful links, since HobbyKing doesn't have much engineering information on it. The calculator application (second link) can also be reached from the Neu site directly.

**broken link removed**
**broken link removed**

Stall current is hard to find for these motors. I can tell you that if you put too much load on the motors, the battery or controller will probably go first. That is, within reason of course. I lost a couple of battery packs because I had a prop that was a little too big.

You may also want to find an operating sensorless motor to trial test, so you will know how they behave. That test motor does not have to be the same size as the one you are anticipating using. They can start from a dead stop a little differently. It is usually explained that they don't "know" which way to turn at the instant power is applied. On a scooter, that might not be a problem, as a very small push will get them going right away.

And finally, the open, outrunner motors do need cooling. At 10 m/s, that might not be a problem, but as has been pointed out, you won't be going that fast very much of the time.

John

 

[alec_t]

On the other forum they told me that this motor is not good enough, because it is meant to be installed on RC airplanes.

They may have told you that because of problems with cooling it in the absence of a good airflow. Without excellent heat-sinking such a small motor would get very hot if powering a scooter.

 

[rascupanamuha]

No. The motor neither knows nor cares whether it is on an R/C plane, a scooter or a moon buggy. At low speed the motor back-emf is low so the current, and hence the driving torque, is high. At low speeds the counter-torque produced by resistance (due to friction, air viscosity and lubricant viscosity) is low so the nett torque will accelerate the motor/prop. As the speed rises the back-emf and resistance both rise so the acceleration falls and eventually a steady-state arises where the driving torque balances the counter-torque.

Yep, you are right about that, but i know that motor doesnt cares and knows where it is put
The point was that on scooter first i need high torque, and then low torque, and these sensorless motors can provide high torque only at high speeds, and very very low torque on low speeds. Please look at these projects too. Bike seems to have 2x 7kW motors, i havent find where to buy that big hobbyking motors (any help?)
**broken link removed**

Here are a couple of useful links, since HobbyKing doesn't have much engineering information on it. The calculator application (second link) can also be reached from the Neu site directly.

**broken link removed**
**broken link removed**

Stall current is hard to find for these motors. I can tell you that if you put too much load on the motors, the battery or controller will probably go first. That is, within reason of course. I lost a couple of battery packs because I had a prop that was a little too big.

You may also want to find an operating sensorless motor to trial test, so you will know how they behave. That test motor does not have to be the same size as the one you are anticipating using. They can start from a dead stop a little differently. It is usually explained that they don't "know" which way to turn at the instant power is applied. On a scooter, that might not be a problem, as a very small push will get them going right away.

And finally, the open, outrunner motors do need cooling. At 10 m/s, that might not be a problem, but as has been pointed out, you won't be going that fast very much of the time.

John

I think cooling wouldnt be a problem, i could put hot sink, and some fans to deal with that..
That is true that these motors dont know where to go at the start (and low speed), i kave tons of small ones so i know. Adding a hall sensor seems to solve that and the problem with low torque at low speeds: https://diydrones.com/forum/topics/adding-a-hall-sensor-to-brushless-motors?xg_source=activity

 

[Mr RB]

Personally I think instead of using a tiny fussy high RPM low torque motor that costs close to $100, you should buy a low RPM high torque motor suitable for electric vehicle use. There are tons on ebay, from the same Chinese companies etc that make commercial electric bikes and scooters. Those motors are perfect.

Something in the 24v or 36v, 300W to 400W range will make a pretty nice electric scooter. AND you only need a cheap DC PWM driver to operate the motor, not a tiny fussy unreliable ESC designed for model aeroplanes.

 

[jpanhalt]

One additional problem with a geared, high-speed motor is what happens when you take your foot off the pedal while going 10 m/s. The scooter may stop almost instantly, depending on the type of gearing used, while you continue on at 10 m/s. You will need a clutch.

John

 

[rascupanamuha]

I was thinking of clutch, but i dont know..
Is motor with 5400RPM high speed compared to 2500RPM regular brushed e-bike motors? Speed is higher but that is max speed only. And my gear ratio would be 5:1, and i dont think when i turn the motor of that it would stop instalntly. I think it will just slow down. It would stop if i put 20:1 or so, maybe, but with this...i dont know, but i dont think it would be a problem. I was thinking to put one-way-bearing, but as i said, i dont think it is necessary..

And with hall sensors it seems that i can get really a high torque, and also a lot of power..

 

[tcmtech]

Given the points made so far its rather obvious to me why the small electric scooters and the like all use simple DC motors instead of PM brushless ones.

Simple to control, high torque at low RPM, substantial over load and peak power capacity, cheap to buy.

 

[jpanhalt]

Agreed. And, a simple DC (non-PM) motor won't require a clutch. I am not sure the OP understands that old technology may still be the best for his application.

John

 

[rascupanamuha]

Ok, as you all are smarter than me, and i think you may be right after all. Brushless is newer, but it doesnt make it better for this kind of thing. And it is alot more expensive than the brushed one. ESC for brushed motor that has option for hall sensor costs 70$, simply too much.
As plan has changed, please answer me some questions i have now..

1) i am not an arduino expert, so question is can i easily make PWM modulation, to regulate speed with lets say petentiometer?
2) if i want really powerful scooter, that would be 500W? 1000W?
3) i have a broken scooter with 100W dc motor, and 4.5Ah 12V battery (2x). It had some electronically blocade not to turn on motor if you dont start scooter by foot. With 500 od 1000W motor would that be a problem (high current)?
4) if it has 2500RPM, and i want to go max 10m/s, that would be 1250RPM with wheel diameter 0.48m. So gear ratio would be 2:1. Would that be powerfull enough?

Btw, here it is how it looks like now

 

[audioguru]

Electric scooter?
Never in Canada except I saw a little kid on a battery powered tiny scooter. It was not fast, like my normal walking speed. The kid got no excercise so he got bigger and bigger and bigger and bigger and.... like all the other obese kids.

 

[Mr RB]

There's a lot of electric scooters AG, some are ok transport, some are just kids toys.

To the OP; 1000W is way too large unless you plan on racing and charging your battery every 10 minutes. A 300W or 400W size motor running <200W in normal use will give you plenty of power overhead when needed, but be cheaper/lighter/more energy efficient.

As for gearing you really can't tell from a calculation. Electric vehicles are notorious for people making them and always needing to change the gearing later once they can test it in the real world. The specs for the motor only tell you some of the info, they usually won't tell you how much the motor slows down under load vs the real world loads you will encounter, and of course the real world loads are not known because they depend on how and where you drive it AND on what gearing you chose!

As a general rule you could guess that the motor will slow down to half it's free running speed when it has a decent real world load. And generally you are better off gearing more, for the vehicle to be a bit slower than your goal, that will reduce motor load and motor current. The worst thing to do is to make up a high speed figure you want to reach then gear it to do that!

 

[audioguru]

I have seen many expensive electric motorcycles lately. They creep slowly along the street with very dim lighting at night. They always seem to have a dead battery. They are a hazzard on the road but might also be a hazzard if they drove on sidewalks.

The brushed motors on my electric RC model airplanes fail after running for only a few hours. The common failure is that they do not start running and need a push to get going. Then their power is low.
Two airplanes have very powerful brushless motors that do not fail after running for many hours.

 

[rascupanamuha]

So what you are saying? That i should rather buy brushless than brushed motor? I have an eye on 2 dc brushed motors (350 and 500W) with price arond 100$.
I have calculated that the torque needs to be over 1.9Nm on wheeles, so with 2:1 ration on those brushed motors 0.95Nm, and they have 1.6Nm torque.
With brushless motor i have mentioned earlier, with hear ratio 5.1 they should have torque over 0.38Nm

So... which one to buy now?

Motor 1: https://www.hobbyking.com/hobbyking...y_RotoMax_1_40_Brushless_Outrunner_Motor.html
Gear ratio for speed of 10m/s (max): 5:1

Motor 2: **broken link removed**
Gear ratio for speed of 10m/s (max): 2:1

 

[audioguru]

Brushed motors wear out soon. Brushless motors cost a little more but last "forever". YOUR CHOICE.

You forgot to say if you are a big f** sl** or if you are normal weight and size.

I am not allowed to say what is normal and what is morbidly obese because nearly everbody today (except me) is TOO FAT.
I have never seen an electric scooter propelling a huge obese person.

 

[rascupanamuha]

Hahahaha

No, im not fat at all. I weight 75kg. Scooter will be <15kg

I think i found the answer to all my questions: **broken link removed**

And on the page 2 or 3, someone made scooter with 20$ motor, and it goes 25km/h with 12V 6Ah battery for 10km