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### Author Topic: 120 lb battlebot  (Read 2583 times)

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#### UCkid

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##### 120 lb battlebot
« on: October 04, 2007, 10:39:53 PM »
Three fellow students and I are designing and making a 120 lb robot to compete in the BotsIQ competition next spring and my job is the drive train.  My plan is to use 2 3" S28-150 magmotors and power these using 2 24 V 3600 mAh battlepacks (one pack for each motor).  I am going to join the motors to a pair of team whyachi gearboxes.    The problem here is that we are doing this for a senior design project and given that i'm an ME (mechanical engineer) not an EE (electronics engineer) I was hoping that someone here could help me prove or disprove my system.  If need be I could wire the batteries in parallel to get more current out of them but thats what I need the calculations for.  What do you think about my setup?   I thank anyone in advance for your help.
« Last Edit: October 05, 2007, 12:03:31 PM by UCkid »

#### Admin

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##### Re: 120 lb battlebot
« Reply #1 on: October 05, 2007, 06:44:34 AM »
This just so happens to be my specialty . . .

So first, you need to calculate how effective your robot will be with these motors. Its nothing to be subjective about when your expensive robot is at risk

go here:
http://www.societyofrobots.com/mechanics_dynamics.shtml

For a battlebot, high acceleration is best.

Secondly, since a round is only a few minutes, who cares about battery life - just buy a few and charge them all. Swap them out after each round. Instead of getting high capacity batteries, use that weight for better armor.

Finally, you asked about current. Look up the datasheet on the motor. It will tell you required current draw vs output torque (which you calculated earlier). Knowing current draw and voltage of motors, you can calculate what batteries you need. For example, if a motor requires 10A of current but your NiCad batteries can only handle 6A, then that means you need two in parallel, etc. Knowing current draw, you can determine exactly how long your batteries will last, too.

Ive seen batteries fry during these competitions because people dont bother with these calculations . . .

let us know how you do!

#### UCkid

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##### Re: 120 lb battlebot
« Reply #2 on: October 05, 2007, 09:57:11 AM »
I have not been able to find current vs torque specs on these motors.  I know the peak draw but I doubt I will peak them out being that I will have enough torque to spin the wheels if i get stopped by something.

#### Admin

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##### Re: 120 lb battlebot
« Reply #3 on: October 05, 2007, 10:34:03 AM »
Do you already have the motors? If so you can just run an experiment on them.

Otherwise, its all guesswork . . .

#### UCkid

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##### Re: 120 lb battlebot
« Reply #4 on: October 05, 2007, 12:04:47 PM »
Yea we dont have the motors yet

#### Admin

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##### Re: 120 lb battlebot
« Reply #5 on: October 05, 2007, 12:52:52 PM »
Im not sure what your budget is, but the more expensive motors usually come with datasheets.

try here:
http://www.societyofrobots.com/robot_parts_list_motors_servos.shtml
http://www.npcrobotics.com/
http://www.robotstore.com/

You can also look for motors that have datasheets that are similar to yours and just assume they have comparable specs.

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