Author Topic: Sizing Motors  (Read 614 times)

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Offline MastermimeTopic starter

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Sizing Motors
« on: June 07, 2013, 03:52:21 PM »
Hello everyone,

I wanted to confirm some motor calculations with you guys.  The robot I am building uses treads and will operate on various surfaces that have a high coefficient of friction (mud, grass, carpet, concrete, dirt), which is why I inputted a low efficiency.  When I put these same specs in on the calculator at TheRobotShop, I got different results.  According to the calculator on TheRobotShop, I need insanely high wattage motors (talking thousands).

The robot itself is only 200 lbs, but it will be pulling 150 lb loads (250 lb max), which is why the weight is so high.  Also I will only need to pull these loads at about a 10 degree incline, but the robot itself will have to climb 30 degree inclines when its not pulling that load

That just didnt seem right which is why I'm double checking if 24v 900 watt motors will suffice for what I need.

Thanks

Offline waltr

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Re: Sizing Motors
« Reply #1 on: June 08, 2013, 06:57:50 AM »
875Watts sounds about right for the input values you used in the calculator.


Offline Pomacs

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Re: Sizing Motors
« Reply #2 on: June 08, 2013, 07:05:03 AM »

Offline MastermimeTopic starter

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Re: Sizing Motors
« Reply #3 on: June 08, 2013, 11:42:30 AM »
Thanks Waltr for the confirmation.

Pomacs, did you read my post...???

Offline jwatte

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Re: Sizing Motors
« Reply #4 on: June 08, 2013, 09:32:03 PM »
Note that the friction of the ground doesn't matter very much for rolling or treaded robots. The friction of the ground just keeps the tire or tread planted, so it can pivot around its axis. Although as the ground gets macro-level rougher than the tire/tread are designed for, that may start to add to the load of the robot.
Treads are inherently less efficient than tires, though, so using a low efficiency estimation is probably right because of that.
900 Watts is slightly above 1 HP, so if you think a 2 HP lawn mower motor could pull your 450 pound load up a 10 degree incline, then two of those motors would be enough. I think it'll work, but it's likely to be sluggish when encountering the max specifications. You typically want to over specify by up to 2x to get a system that actually performs well within the actual specification limits.

Offline MastermimeTopic starter

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Re: Sizing Motors
« Reply #5 on: June 09, 2013, 01:01:45 PM »
Jwatte,

Thanks for the reply.  That lawnmower analogy makes me feel a little more assured.

If I could, I probably would go more towards 1000 watts, but the size and availability of 24v motors of that wattage is whats restricting me to 900w.

 


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