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Chris

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Joined: 12/09/2005
Location: Australia
Posts: 146

Posted: 08:12am 11 Oct 2005

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Gday all.

Im planning on making a hybrid electric go kart at the end of this year. Now i was thinking of using a couple of 450w oatley motors to power it.

However, i changed my mind! I really want to use a F&P smart drive motor.

Now what i need to know is, what sort of RPM and power i can expect from 24v with the stock windings, mines a 60 series F&P motor.

I want about 500w or higher.

Would i have use a metal magnetic hub (get one made of course) or could i stick with the plastic one?

I dont really want to spend much on this conversion, probably my budget for the motor is about 150 dollars, give or take a bit. I know i'd be pushing it with that budge, but i already have all the bearings, and everything needed to mount the motor.

Glenn, i know you have done this before, could you give me some help? Do you still have the plans or file for the metal magnetic hub you got made?

Cheers guys
Your helps appreciated,
Chris

Gizmo

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Joined: 05/06/2004
Location: Australia
Posts: 5078

Posted: 11:08pm 12 Oct 2005

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Hi Chris.

I wouldn't go there. When we tried to use the F&P as a motor on our solar car I remember we had lots of problems, and gave up after several months of trying. It was easy enough to get it to spin, but speed control and back emf were the killers.

But if you were to use one, I think the plastic hub would be fine for strength. Remember it can spin a full load of wet cloths up to 1000rpm in a few seconds.

I would go for the Oatley 450watt motors and their speed controllers. A couple of these motors on a little go kart would go like the clappers! Oatley also sell chains and sprockets to suit.

You know what would be cool. 4 motors, one on each wheel. The 300 watt motors are a lot cheaper, give you 1200 watts total, and 4 controllers, all tied to one hand throttle. The kart would have some serious acceleration.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

Storm

Regular Member

Joined: 12/09/2005
Location: Australia
Posts: 43

Posted: 03:40am 13 Oct 2005

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Wouldnt the front steer wheels and motors be difficult to engineer especially if you were using gears and chains?

I would be more inclined to spend a bit extra and try to get the E-TEK motor by briggs&stratton from America, it has approx 15hp at 48v or around 12kw

Heres a link to some that sell them http://www.robotcombat.com/marketplace_etek.html

Although not so good for solar cars due to lower efficiencies compared to brushless, far more powerfull for size and it doesn't require the complex brushless controllers (a controller is still nessesary but not as complex or expensive)

Here's a machine that uses one

http://www.thunderstruck-ev.com/jackal_home.htm

Chris

Senior Member

Joined: 12/09/2005
Location: Australia
Posts: 146

Posted: 07:23am 13 Oct 2005

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Gizmo, the 4 motors one for each wheel would be very cool. However i want to run a CVT (constantly variable transmission) so its just simpler to run a couple of motors to the CVT.

Ill take your advice Gizmo and go with the oatley motors.

Storm, Ive looked into the E-teks and i think they would be overkill for my go kart, and the power requirements are huge, not to mention the size of the speed controller needed!

The E-teks are pretty expensive as well. Maybe 3 or 4 300w motors would give more then enough power to satisfy my needs. Especially with a CVT attached.

Chris

Senior Member

Joined: 12/09/2005
Location: Australia
Posts: 146

Posted: 07:31am 14 Oct 2005

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I was actaully thinking for the F&P motor, i could buy a controller off ebay, a brushless one designed for RC cars. They are about 50. Then pretty much just run some flying wires out to a external H-bridge circuit, it would give me perfect control and wold be pretty easy to construct.

MrBungle
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Joined: 07/10/2005
Location: Australia
Posts: 34

Posted: 08:14am 20 Oct 2005

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Hi Chris, I like your idea, would be great fun!
Your plan to use model BLDC controllers might be a problem though.
I used to race RC cars and currently build and fly BLDC powered RC aircraft and know that a basic model BLDC controller will not handle the power's your thinking of using. They mightl for short bursts, but not continuously.
The model controllers are very very very optimistic in their claimed power ratings.
There is however, a sensorless BLDC controller that one company(I think it was Schulze? I can't find the magazine I saw it in) was prototyping a few years ago, it handles model aircraft BLDC motors up to 5kW. Should be in production by now.
These controllers all need a servo signal for control, which is a 1.0ms to 2.0ms PWM signal.

Gizmo: I designed a BLDC controller a long time ago, but never finished it due to the Chinese imports being as cheap as they are. I never had any problems with back-emf popping the mosfets though, did you use Flyback diodes? The integral ones sometimes aren't very good.
Maybe I was just lucky with my choice of Mosfet?
Oh yeah, It's also very very important that a small pause is used between phase change switching. It's very easy to have a direct short between the two rails if the mosfet's are not switching off fast enough, then a high side and low side transistor for one phase could both be conducting and .... ffzzzzt!.
Anyway, Just a thought.

Chris

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Joined: 12/09/2005
Location: Australia
Posts: 146

Posted: 10:27am 20 Oct 2005

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MrBungle, thanks for your response.
I knew that the BLDC controllers would no way handle the F&P motor as themselves. Thats why i said i would build a external H bridge circuit powerful enough for the motor. The H-bridge circuit is controlled by the BLDC controller.

As for the 0.1ms to 0.2ms pulse thing, i can get around that too, just build a square wave generator. Wont be too hard.

I bet the schulze controller rated at 5kw would die if you connected it up to the F&P. You always see speed controllers with bs ratings, like 120A contious current flow. Thats the equivilant of 4awg wire and the controller has 14awg wire coming out of the case. Go figure. All the ratings that are given are simply theoretical values that are lifted off a data sheet.

I might try it one day, bit to busy atm though.

MrBungle
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Joined: 07/10/2005
Location: Australia
Posts: 34

Posted: 11:59am 20 Oct 2005

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Chris said <snip>...a external H bridge circuit powerful enough for the motor. The H-bridge circuit is controlled by the BLDC controller[/quote]

Opps, sorry, missed the external part!

[quote]<snip>...i can get around that too, just build a square wave generator. Wont be too hard.[/quote]

Yep, too easy, the framerate is 50hz BTW.

[quote]I bet the schulze controller rated at 5kw would die if you connected it up to the F&P...<snip>[/quote]

I dunno, the photo I saw was of a very impressive bit of kit. There were many many decent sized fets on that large board! The tracks were beefed up with copper bars too. I wish I could find the magazine, but from memory there were no wires to the motor, it had four paralleled bannana style sockets per phase, leaving wire selection to the customer. The battery wires(which are always short due to inductive problems at the high switching rates) I think were paralleled and looked bigger than 14guage, probably commonly available 12 or 10 guage.
Maybe the production version(I've not seen it) has been derated, which would be strange because they only decided to do it after customers asked for a many kW controller.

12guage wire will handle surprising currents in short lengths.
A single 4" length will only drop 0.6v at that current but generate almost 7W of heat, not sure if thats enough to fuse or not.

Simo

Chris

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Joined: 12/09/2005
Location: Australia
Posts: 146

Posted: 01:28pm 20 Oct 2005

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Hmm, how big is this actaul controller?

Do they use it in large scale RC planes?

MrBungle
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Joined: 07/10/2005
Location: Australia
Posts: 34

Posted: 07:24am 31 Oct 2005

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Yep, large scale RC planes.
I found the magazine, I was wrong about the bananna plug sockets, there's only two parralleled per phase.

Using my highly accurate method of using a ruler on the photo and measuring components I know the size of, I'd say the mainboard(power electronics) is about 120mm (5")long, by 75mm wide(3")-ish.
There are 24 large mosfets on this board, and two bussbars on the sides to carry the current, looks like the mosfet's are D2PAK's, definatelly bigger than DPAK's(approx same body size as a TO-220).
The daughterboard has all the control electronics(inc. an Atmel ATMEGA8) and is dwarfed by the mainboard.
I'd have a guess and say the mainboard is of 2oz copper, so the tracks can handle the current. The phase tracks look about 20mm wide.

Edit:
ahhh, I found some pictures of a slightly different one.
This is the Schulze Future-40.160WK which is a 40volt 160A controller
The photo I have in the magazine is of the 32.170, 32 volt x 170A.
The only difference seems to be that there are more mosfets on the 40volt version (higher voltage fets have higher resistance), and the daughterboard is covered.

top:

bottom:

Nice eh? Might be pricey tho!.

Simo.
Edited by MrBungle 2005-11-01

Chris

Senior Member

Joined: 12/09/2005
Location: Australia
Posts: 146

Posted: 12:42pm 31 Oct 2005

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Interesting.
Theres alot of power handling capabilities there. I really wanna make my own, just so i can say ive done it....

My guess is those arnt cheap!

Would be cheaper for me to make my own.

cloudelectric.com have some nice controllers and motors too, at pretty nice prices too!
Edited by Chris 2005-11-01

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