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Author Topic: HELP!  (Read 4919 times)

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Offline Matthew HoltTopic starter

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HELP!
« on: February 18, 2006, 11:42:58 AM »
Dear All,

I'm a university student studying computer aided design. I am designing an electrically assisted light aircraft tug as part of my final year. My design is to carry a large weight remotely using differential drive and I have no idea where to start!

I have nearly decided on what electrical motors I will be using, but I will need help deciding on everything else required to build it including how to wire etc.

Somebody please help!

Kind regards,

Matthew

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Re: HELP!
« Reply #1 on: February 18, 2006, 12:41:52 PM »
hmmmm what is an "electrically assisted light aircraft tug"? got a diagram perhaps?

diff drive is very simple . . .

and remotely? allowed to use a simple RC remote control, right?

you might want to consider going out and buying servos and a RC remote/receiver

someone asked me to write a tutorial on using remote controls but still finishing up another tutorial first . . . probably take me another 2 weeks to do it . . .

Offline Matthew HoltTopic starter

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Re: HELP!
« Reply #2 on: February 18, 2006, 01:46:02 PM »
Thankyou for the reply. Well the tug is currently under construction using CAD, so no images available at the moment. I don't have to build the tug, just use CAD to prove it.

Basically, it is a simple 3 axis vehicle using two parallel drive wheels and a free moving 360 degree wheel at the front (Very much like a castor). I am currently in the process of selecting my motors which will need to be both rated at 2HP in order to maneuver 7500 lbs at 5 MPH.

I understand I will require a speed controller, radio, radio receiver with separate battery not forgetting the two motors and their power supply.

If this list is correct what particular parts would you suggest for this application considering it's heavy duty?

Matthew

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Re: HELP!
« Reply #3 on: February 18, 2006, 03:00:24 PM »
sounds a lot like a battlebot actually . . . ok so you cant use what i described in my last post . . .

your list is all the main components you would need, plus wheels and chassis frame material (obviously)

this site sells battlebot stuff, worth looking into
http://www.npcrobotics.com/products/index.asp

so you asked for help choosing motors . . . you can easily choose your motor specs by choosing your wheels appropriately and knowing the rpm's/torque of your selected motor.

obvious equations, but here they are anyway:
velocity = wheel circumference * rpm
pulling force = motor torque for both motors combined / wheel radius

but you also need to calculate one more thing, and thats acceleration. a robot with really poor acceleration really sucks.

F = m * a
acceleration = pulling force / (weight to pull + robot weight)

lastly, pulling a really heavy load also requires wheels with really good friction.
to account for friction:
force of friction = weight * u.rubber-asphalt
Ff = robot_weight * .7

as for wiring, its actually almost plug and play. the motor driver accepts wires from the battery, reciever, and your motors. your reciever also accepts a seperate battery power.

Offline Matthew HoltTopic starter

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Re: HELP!
« Reply #4 on: February 18, 2006, 04:07:44 PM »
Thankyou once again for your reply and your link which is very useful. I have already made the necessary calculations for my motor and i'm due to see an electrical motor company on Monday.

Having looked at NPC Robotics I have discovered I will need a two channel speed controller since I have two motors, as long as this covers the voltage rating of my motors I guess i'm ok?

What receiver do you recommend? Do the remote and remote receiver come together as a package? I would expect them to be calibrated with one another.

Further more to my question. I need to operate a device to release my wheel cradle. Could I wire this device into my receiver as an alternative channel? How would this effect my decision when choosing a remote and receiver?

Kind regards,

Matthew


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Re: HELP!
« Reply #5 on: February 18, 2006, 04:40:36 PM »
yea it would need to handle two motors . . . i find it strange most only handle one!!!

it should be able to handle a few percent higher than your motor voltage, but also handle the current too. some just overheat if your motors start drawing a lot of current. badness.

as for remote and reciever, you can still use any typical hobby RC package. your motor controller just needs to be able to accept a typical RC servo control signal. fairly universal i think.

www.servocity.com has some good Hitec remote controls and recievers.
you just need to be sure they are both using the same frequency crystal. make sure it is a land based and not aircraft based frequency!!!

recievers have multiple channels. you will need one for each motor, and another for each device you which to operate. most recievers have at least 3 channels. some have 7+

a servo plugs right into a reciever channel, easy for operating other functions

side comment: servocity customer service sucks. if they dont have the crystal you want, they wont tell you. instead they will special order it and mail it to you 2 months later without telling you. they also ignore ALL emails to them. and dont rely on the servo dimensional data, its often wrong  :(

 


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