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Im torn between these motors:
AmpFlow A28-400 - http://www.robotmarketplace.com/products/0-A28-400.html

AmpFlow A40-300 - http://www.robotmarketplace.com/products/0-A40-300.html

AmpFlow E30-400 - http://www.robotmarketplace.com/products/0-E30-400.html

AmpFlow A28-150 - http://www.robotmarketplace.com/products/0-A28-150.html

The motor will drive a 80 pound go kart + 140 pound driver and I would like high acceleration rate.
Along with this I need advice on a controller without breaking the bank. Any advice is appreciated! smiley
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Grand Rapids, MI, USA
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Of those 4 the A40-300 is probably your best bet.  You sacrifice a little in the way of horsepower, but you get more torque, and the all important thermal resistance is lower.  The Kv is also lower, so you won't have to gear it as much.   

The thermal resistance tells you how hot your motor will get when running.  The most powerful motor by my calculations would reach almost 1000 degrees C on the inside at peak power even with optimum heat sinking!  This motor can still easily overheat, but not as easily as the other one.  I would try hard to heat sink whatever motor I could to the frame or something else that can get rid of the heat in a hurry. 

To do this calculation yourself take the power you expect to run in watts multiply it by  (1 - efficiency) and multiply that by the thermal resistance to get the internal temperature at steady state.  Note that you would have to run the motor continually at that power to get that temperature, so quick bursts will not end your day, but heat sinking is going to be an issue.

For a controller you should find a controller that can take the 24V you will likely use, give you bidirectional control if you want it, and handle both the constant current draw and the stall peak when you slam on the gas.  The stall peak for this motor is at 340A, while constant run current will likely end up somewhere in the 20A to 100A range.
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Alright any idea where I can find such a controller??? Robot marketplace recommends a IFI Victor 885 but they don't make those anymore...

also since I have a 10 inch wheel diameter and a 5.06:1 gear reduction what will my top speed be??
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I'd suggest looking at http://www.dimensionengineering.com/ for a motor driver, notably because they're regenerative drivers (they recharge the batteries when you hit the brake).

Lead acid batteries come out to around 1Ah per pound, or two deep cycle batteries (for 24V) at 35lbs each would give you 35A for an hour. You mentioned your kart weighing 80lbs so you'll want to come down to earth a bit if you're expecting to push the 120A continuous that the IFI Victor 885 is spec'd at. Or perhaps you're creating some kind of drag race vehicle?
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Nope, this thing is gonna be made purely for fun, but on gravel/dirt. Dimension Engineering's top controller Sabertooth 2x60, with a peak 120A output and 60 continuous. Is that enough for my motor?
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80 punds? Come on? How much weight do you plan on for your batteries. If you use SLA your looking at around 60lbs if you want any kind of run time!

And if you look at your motor it could pull up to 300 amps so I would go for a better motor controller!
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The website says the sabertooth has over current protection and can move a 1,000 pound machine. And its 80 pounds dry excluding batteries and driver. Total is probably pushing 300 since I'm 140. Batteries and controller suggestions anyone???
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How long do you want to drive? & How much cash do you want to spend?

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Any amount of time above 15 minutes ideally, and I'd like to spend as little as possible smiley-razz
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Lets say your typical current draw is 60 amps. So for about 15min of run time you would need a 15,000mah(15AH) battery at 24v or two at 12v. 

I would go with two of these…
 http://www.robotmarketplace.com/products/0-CTN12-18NB.html

Or for longer runtime two of these…
http://www.robotmarketplace.com/products/0-CTN12-35C.html
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I have 2 12v 20Ah batteries right now. Will that work?? plus I noticed the controller has 2 outputs with 120A surge current on each output, the motor needs two sets of terminals... so I just need this sabertooth (http://www.robotmarketplace.com/products/0-SABERTOOTH2X60.html) and the motor and I'm golden for a decent power kart???
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Grand Rapids, MI, USA
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How Fast? ... 

Its hard to say as there are a lot of variables, but here are my rough calculations copied in from excel.

Volts: 24
KV:   168
Gearbox Ratio: 0.1976
RPM: 796.83 (Multiply above three togather)
Realistic RPM   557.78  (Multiplied by 0.7 for gearbox, drag, and many other losses)  Your number may be higher or lower.
   
Wheel Circumference    37.70"
   
inches per minute   21028.
inches per hour   1261683.
feet per hour   105140.
miles per hour   19.9

What I am saying is that with the perfect cart this motor would cap out at 19.9 mph.  Whether your cart can ever get there is another matter, but at first glance this would seem to suggest the gearing is about right.
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So that excel spread sheet says with a 5.06:1 ratio (chain drive) and 10 inch wheels i can do near 20 miles an hour?
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With all of the many caveats I mentioned above, yes. 

It does not say how fast you will get there, or if you have the power to do so, but those numbers seemed to be reasonable.  The 5.06:1 ratio chain drive seems about right.  I would try that first and go from there if you have issues.
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I have 2 12v 20Ah batteries right now. Will that work?? plus I noticed the controller has 2 outputs with 120A surge current on each output...

You can't get 120A surge out of a 20Ah SLA battery, or not without wrecking the battery. 60A is a more sensible limit.

24V * 60A = 1440 watts. To put that into perspective, if you were pedaling your kart you could max out an equivalent of 250W for a minute or so, or that 1440W of power would be the equivalent of six cyclists pulling it. Any hill you could pedal a bike up you could drive your kart up six times more quickly (ignoring the weight of the kart).
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