Brushless DC Motor size requirement

[HeatF15]

UNCLE! I’ve spent countless hours attempting a solution to this challenge without any real solid leads to go on. Instead of continuing to burn away the hours getting nowhere, I thought I’d make an attempt to ping the experts.

I need some help in determining the required motor size for a prototype project I'm developing (not a robot or an airplane). The mass is 100 lbs, initial velocity of 0ft/sec, with an average acceleration of 3.6ft/sec2 to reach a sustained speed of 7.3ft/sec (5 mph) in approx. 2 seconds, then maintain that speed.

I'm trying not to gear-reduce the motor, but since I'm looking at brushless dc motors that have high rpms, I'm concerned I’ll have too much speed without the torque required to achieve the initial acceleration requirements. The planned prototype motor is capable of running at approx. 6000rpm (245 rpm/volt X 12v = 5880rpm) but I plan on running it at 500-600rpm. I want ample power for the prototype and don’t mind spending a bit more to “over-motor” the p-type initially. However, my question is will this be bad for the motor in some way? Will it run hot (low rpm under a load) or is it being way underutilized?

How can I find the perfect balance between the initial acceleration torque required and the 500-600rpm top speed required at cruise? Is there a way I can look at the specs of a motor and tell if it has the torque I need to get the mass moving in the time I set?

Like I said, I don’t mind starting with a motor that’s too big for the application, but I would like to find out what the minimums are and then go from there (double or triple the mins to allow for excess loads, higher speeds, inclines, wear & tear, etc.).

Thanks in advance…. Paul

 

[HeatF15]

Hyperlink didn't show... here's the url for the brushless dc motor:

http://h1071307.hobbyshopnow.com/products/description.asp?prod=EFLM4160A

Paul

 

[TurbineGen]

Accelerating a 100lb object to 5 mph in 2 seconds shouldn't be too hard to achieve. Without a gearbox, the plot thickens.... That Power 160 is not what you want in this application. It will certainly work, but you are planning on running it at 10% pwm. Not very efficient and very hard on your controller. Are you opposed to buying a motor with integral gearbox? Why not buy a brushed motor with a built in planetary gearbox?

If you must use a brushless motor without a gearbox can you drop your voltage to 6V or maybe 7.4V (if going with a lithium battery)? This will put less strain on your controller. I would also go with a better motor. Try a Scorpion 55mm from innov8tive. They use N50 magnets and iron rich stators which will deliver the torque you need. I built one of their motor kits up and was duly impressed by material and workmanship. I'd go with either the 4025-16 or the 5525-170.

The "magical" torque number you are looking for is a quantity labeled kT (torque per Ampere). Figure out what torque you need, divide by the motor's kT, and you'll have the number of Amps the motor requires to deliver the torque you need.

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More information:

I found this post from Lucien Miller:

http://www.rcgroups.com/forums/showpost.php?p=11190082&postcount=4187

You'll get a lot more hits and information by posting your question here:

http://www.rcgroups.com/electric-motor-design-and-construction-361/

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[israelkk]

First of all you talk about mass and linear velocity. On the other hand the motor has a rotational velocity, Therefore, there should be a system that transfer rotational velocity to linear velocity and you didn't mentioned such arrangement. If you want more serious responses please give more detailed information.

If you have a motor you should give the motor complete data including motor torque constant, back emf constant, rotor inertia, Coil inductance, Ohmic resistance, etc. Your design case is a transient case therefore, without this information an accurate analysis can not be performed.

 

[israelkk]

Regarding the motor, some of the missing information I mentioned in y previous post appear on he link you posted but some is missing. This is a motor for airplane models. What is the nature of you application? If it is for military and aerospace use then the motor should fit for such demanding applications and environment which I doubt this motor can do.