Multiple motor & controller approach?

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bobc
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Postby bobc » Tue Nov 04, 2008 1:30 pm

Problem with these things from a greenpower perspective is that they're too good; anything over 400W output will end up at lethal speeds with the little darlings in.....
Present greenpower motor is 240W but gets run up to twice that, & we hit max speed of 42mph at the final. You really don't want kids goin any faster than that. (note, winning car max speed was 34mph - it's an efficiency contest, not a speed contest!)

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qdos
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Postby qdos » Tue Nov 04, 2008 2:43 pm

bobc wrote:Problem with these things from a greenpower perspective is that they're too good; anything over 400W output will end up at lethal speeds with the little darlings in.....
Present greenpower motor is 240W but gets run up to twice that, & we hit max speed of 42mph at the final. You really don't want kids goin any faster than that. (note, winning car max speed was 34mph - it's an efficiency contest, not a speed contest!)


I do tend to agree and I know what you mean but I'm thinking of something for 16+ ages. Greenpower I think is superb for the youngsters but what I'd like to do is introduce something which could be put on the road too as currently the Greenpower machines would not be allowed on roads and consequently I feel reinforce youngsters impressions that if you want a road vehicle you have to use an ICE

What I'm hoping to do is get people interested in small efficient fun electric vehicles that can be used on the road. At the moment there's nothing between an electric assist pedal bike and the Gwizz. Something akin to what Cedrick runs makes so much sense. And I can see this might be a route to get more of this type of machine built and developed

Wilfried
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Postby Wilfried » Tue Nov 04, 2008 6:19 pm

qdos wrote: but what I'd like to do is introduce something which could be put on the road too

A road legal MEV Etrike XL ?

Wilfried

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qdos
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Postby qdos » Tue Nov 04, 2008 8:46 pm

Actually the Etrike is kind of sorted but I'm looking at something different to that for this. The small multi motors wouldn't be big enough for the Etrike I don't think.

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Jeremy
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Postby Jeremy » Tue Nov 04, 2008 9:29 pm

Thanks for those clips, Malcolm, very impressive!

Those Plettenberg Predator motors on the twin motor cart are fairly pricy (see here: http://www.plettenberg-motoren.com/UK/Motoren/aussen/Predator/Motor.htm if anyone wants more info) but are certainly phenomenally powerful.

The last clip is a cart using motors similar to the ones I have, from the same supplier. I'm pretty sure that the two purple HXT motors are these: http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142, but I can't positively identify the yellow Turnigy motor. The HXT motors are reasonable value at around $150 for 6500 watts.

[edited to add: Those HXT motors are the same as the Turnigy motors, I've just discovered. ]

Controllers are the problem though, as model controllers all operate at very low voltages, typically less than 30V. Two controllers arrived in the post today from China. They are rated at 30 volts, 130 amps maximum, 120 amps continuous. Total cost, including postage to the UK was £50 for the pair, which seems reasonable value. They have nice little heatsinks on the FET array and generally seem fairly well made. The amazing thing is the size, each is about the size of a matchbox!

Jeremy

MalcolmB
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Postby MalcolmB » Wed Nov 05, 2008 12:17 am

Imagination is running away with me now :lol:

Put 10 of those Turnigy/XT motors on a common shaft and you get a peak output of 65 kW from an assembly weighing around 20 kg, allowing for shaft weight and mid-shaft bearings. Mount the assembly in a transmission tunnel in a lightweight car (such as a mini, or a quadricycle Kelvin 8)), driving front or rear wheels through a 5:1 differential and you have an ultra-lightweight 100 mph capable drive system that leaves boot and engine bay free for batteries or luggage.

Who's going to be first?

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qdos
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Postby qdos » Wed Nov 05, 2008 10:18 am

Shame we're all spread around the country really though me and Jeremy are at least at opposite ends of the same road (the A354) LOL

I'd definitely like to try this in a vehicle I've got the machine in mind and it just so happens that we're all thinking along similar lines. I'm sure we can all do something. You're both very welcome to give me a call and we can have a chat about it.

bobc
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Postby bobc » Thu Nov 06, 2008 11:51 pm

I've bought a couple of these motors & will be trying to make a power converter for a string of 5.
that's 400A (!)
I'll let you know how I get on... plan at the moment is to make a front end current controlled buck converter followed by a fundamental frequency current source inverter (MOSFETs) controlled by optos on the shaft.
So rather than have a high power PWM inverter I'll split the job into 2 much simpler ones (at the expense of an extra FET & some extra losses. The extra losses are mitigated by reduced (0) switching losses).
So I should be able to make it pretty compact I hope ('cos I'll need quite a few for my project)
Note I will not be working to any EC regs, EMC standards, low voltage directive etc as my project is a 1 off & not marketed. Also BIG amps and low volts is a combination where parasitic inductance will make yours behave very differently from mine... layout is key! But I'll try to keep circuit & development saga up to date on here in a new thread.
If it starts to look impractical, e.g. magnets falling off the motors or paralleling looking impossible I'll try to say why I give up!

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Jeremy
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Postby Jeremy » Fri Nov 07, 2008 7:32 am

I'll be really interested to see how you get on with this, Bob. Although these motors are relatively cheap and fairly well made, there is a dearth of controllers suitable for EVs.

The cheap 120/130A BLDC controllers that I've just bought are only good for around 28 - 30V, which seems to be the case for the majority. I've found a controller that can take up to about 50V, but the cost rises to several hundred dollars each for a 120A version.

If you manage to get something working well, then I would certainly be interested in building one (having noted your sensible health warnings!).

Jeremy

bobc
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Postby bobc » Wed Nov 12, 2008 11:30 pm

2 motors arrived today.
I note that the prop connection is at the turning end of the outrunner & I'm a little concerned about the practicalities of keeping 4 motors in synch on a single 8mm shaft if they're just attached by grubscrews. Basically I'm thinking that a keyed driving collar will have to be made to take the torque from outrunner to shaft via the 4 screws provided for the prop adapter.
Suggestions & links to suitable hardware gratefully recieved....
They don't feel like 2500W when you pick 'em up do they ;^)


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