Hi again, The Etek motor & the scooter - School Project

Uh...motors don't have AH (Amp Hour) ratings. Could you clear that up?

If lead is out of the question and you're trying to keep cost down, NiMH is really the only viable option. NiCD just isn't as good and any form of lithium is just way too expensive.

You're in luck. jstept is working on an almost identical project. He's even using the brushless version of the motor you chose. Here's the start of his blog.

The Etek is one of the best motors you can get for this sort of thing. Power isn't going to be optimal, but should still be enough.

Is there any particular reason you want to run it at 24 volts? With the amount of battery you're going to need to run it for a half hour there doesn't seem to be a reason not to run it at 36 or 48.

hi, sounds like a fun project. The E-tek motor is a great choice for this type of vehicle, I know a few people here in P.T. that use them on home-built scooters that are capable of speeds of 100kph or more, but I would check availability before commiting to this particular motor. From what I understand they are no longer being made. check on the perm pmg 132 also. these are very similar to the e-tek in capability, weight and price(maybe a little more expensive). keep in mind, however that any permanent magnet or series wound motor can be used with the same wiring, provided the motor is rated for both the volts applied to it and the amps it will draw.

For a controller, an alltrax axe is probably ideal, if only because it can be programmed to limit amp output and protect your expensive motor and batteries. also it can be monitored with a laptop for real-time measurements of current draw, temperature, etc.the alltrax website has complete wiring diagrams for their controllers.

I own an ego2 cycle that I have modified and re-configured a few times. I was able to reach 39 mph at 24 volts and 100 amps limited by the controller, which is 2400 watts (<4hp) , but it took forever to get there, and with 34ah of lead batteries, I would only have been able to keep it up for about 10 mins(if my motor lasted that long at nearly twice the continuous current rating). I would recommend 36 or 48 volts provided the motor you select will take it.

You say that your group is in charge of the electrical, implying that there is another group doing mechanical mods. if so, let them work out the gearing, just tell them how fast the motor will be turning(like I said, the E-tek will have plenty of torque).

Good luck,... maybe you could post some pictures of your progress as it comes together.

About availability of parts, there is http://www.electricmotorsport.com/PARTS/parts.htm. I haven't dealt with them so I can't recommend them but they have been around for quite a while. If nothing else, you can look at the pictures and get some indications on pricing and specs.

And you shouldn't rule out a brushless solution. Controller and motor might be a bit more expensive, but it lets you do away with (sometimes complex and expensive) safety circuitry needed in a DC setup. And even compared to a DC setup with those circuits, brushless will always be safer, which might be important in a school project.

Motors are (most commonly) rated by their continuous output power.

For example: If you have a 1000 watt (rated) motor, but it is only 85% efficient, then your going to need to put about 1177 watts of power into it.

Mind also, there is something called the Peukert Effect. This basically means that the faster you take out energy from the battery, the less capacity the battery has. This is why you hear a lot of talk around here about a batteries "actual capacity".

It is the most pronounced in the lead-acid type of battery. In other chemistries, the main issue is internal resistance. Actually, I don't know if the Peukert Effect is even present in other chemistries. Tracy? Care to clarify ;)?

Peukert effect is present in all chemistries. It's usually expressed as an exponent that plugs into a formula used to calculate the available Ah at a given amp draw.

Flooded lead acids are worse at around 1.3

AGM's are next at around 1.1

Lithiums are best at around 1.05

Check out this page: http://www.evconvert.com/tools/evcalc/?s=b (and that site in general is a great resource).

Hope this helps.

usatracy - no one's flaming and you're the one who normally turns up the heat with blanket statements, spend a little more time on presenting your message and reduce the hyperbole and you'll see less of what you consider "flames".

My comments were mostly overlooked and I believe they still stand:

1) A hub motor is a good choice, however, there are less available to the DIY converter.
2) The hub motors available to the DIYer are less powerful than the readily available alternatives
3) Chain and sprocket drive are less efficient than a hub motor - however, you can expect an efficiency of more than 90% (certainly better than the Mustang quoted at 85%)

All those points are relevant to your decision making on converting a Vespa. Your choice.

mike,

Earlier in your post you asked the question "does the voltage directly dictate the speed of the motor?" (or something like that). The answer is yes (assuming the load remains constant then increasing or decreasing the voltage changes the motor speed).

However... my understanding of how things work is that your controller does NOT alter the voltage it supplies to the motor. Instead it controls the duty cycle of a square wave that switches between max available volts and zero - known as pulse width modulation (PWM). This (approximately) square wave is at a high frequency (my Kelly controller is around 16kHz I think) - i.e. it ticks at over 16,000 times a second. The duty cycle is a way of stating how often the signal is at full power - so at 10% the controller 1 out of every 10 ticks is at the high voltage while the other 9 are all at zero. At 90% duty cycle we have 9 ticks at high voltage and 1 tick at low. This all happens so fast that the inertia of the motor keeps things spinning when there is no power. The effect of this is to control the power of the motor without altering the voltage - and this is an easier and more efficient electronic design to produce in a small robust package.

Now, the voltage coming out of the controller does vary - but that's a function of the voltage sag and the discharging of the batteries which affects the volts going in and also some voltage drop in the components in the controller.

I don't know if this helps your understanding (hey, you might get extra credit!) - but it sounded like you were wrestling with the problem of varying voltage between 0 and max volts.

(I also thought I read somewhere on this thread someone describing the controller controlling between 0 and max volts - but it must have been another thread).

Hope this helps.

Actually, some (maybe most, I don't know) do vary the voltage to the motor. Apparently they use a set of capacitors to smooth out the waveform to near a flat one, thereby altering voltage. I know my cheap $18.00 chinese controller does. At least, that's what my multimeter says. But it's digital so it could be averaging out the duty cycle. Wish I hadn't fried my good one. Had a 40MHz oscilliscope built in :(.