### Author Topic: Up a 45 degree ramp...???  (Read 4166 times)

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#### jhonilson

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##### Up a 45 degree ramp...???
« on: August 31, 2008, 08:29:17 AM »
HI, My mobile robot need to up a 45 degree ramp. The ramp is make with wood and matte white paint.  My robot have 4 servomotors these have suficient torque for the ramp but.... the wheels have not suficient grip (or friction) for the ramp and the robot fall.

Anybody know some material or idea for climb this ramp??? I tried with a tank tread but not suficient friction anyway.

Thanks so much.

NOTE: sorry for my english, i am not from USA.

#### MadMax

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##### Re: Up a 45 degree ramp...???
« Reply #1 on: September 01, 2008, 12:29:12 PM »
rubber, that always does the trick, if normal, flat, rubber doesn't work, try using something with tracks

#### airman00

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##### Re: Up a 45 degree ramp...???
« Reply #2 on: September 01, 2008, 02:00:49 PM »
related question : How do you calculate how much torque you need to go up a 45 degree ramp. I looked online but I can't find an equation anywhere. Can someone please post it up and explain it a bit?

Thanks
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#### MadMax

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##### Re: Up a 45 degree ramp...???
« Reply #3 on: September 01, 2008, 03:21:17 PM »
I just whipped this up for you:

picture

block 1 explains the angles
block 3 explains the the different magnitudes of all the gravity forces (Fz is dissected into Fz perpendicular and Fz parallel)
block 4 explains how much torque 1 motor should have
block 5 explains all the symbols
block 2 explains how you should calculate the same for multiple engines

Keep in mind that the torque should also conquer air friction and friction between the tire and the plane the robot is driving on, so you might need it a little higher.
The final formula:

MotorForce > ((sin(angle) + (M * 9.81)) / WheelRadius) / NumMotors

Does that explain enough?

#### airman00

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##### Re: Up a 45 degree ramp...???
« Reply #4 on: September 01, 2008, 03:26:32 PM »
thank you MadMax
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#### jhonilson

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##### Re: Up a 45 degree ramp...???
« Reply #5 on: September 01, 2008, 04:20:52 PM »
Hi friends, Thanks for you replies.
But i am using 4 servomotor they have suficient torque and force for to climb the ramp. My problem is the tired have not suficient friction and these slide.
I did try TRacks but not work, at least that i need a special material??

Thanks

#### Iron Man

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##### Re: Up a 45 degree ramp...???
« Reply #6 on: September 02, 2008, 07:13:08 AM »
There are these mats that you stick in the bottom of drawers to keep things from sliding around, they look like they are made up of tons of tiny bubbles. This might help as far as a material.

you could also add weight to the front of your robot, as long as you still have sufficient torque to move up the ramp, the increased weight will give you added friction.

#### airman00

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##### Re: Up a 45 degree ramp...???
« Reply #7 on: September 02, 2008, 01:32:42 PM »
MotorForce > ((sin(angle) + (M * 9.81)) / WheelRadius) / NumMotors

Just want to make sure that M is the height of the ramp in meters . Is it?
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#### Rebelgium

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##### Re: Up a 45 degree ramp...???
« Reply #8 on: September 02, 2008, 05:31:40 PM »
Asumming your servo's are strong enogh (have enough torque) , you'll just need to increase your grip.

Try putting rubber patches on your tracks. Just something rubber you find, like pieces of an inner tube of a tyre.
Can you modify the ramp? if so, try putting sandpaper on it. that ought to do the trick...

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orgcrime.net

#### jhonilson

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##### Re: Up a 45 degree ramp...???
« Reply #9 on: September 02, 2008, 06:42:23 PM »

#### Ro-Bot-X

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##### Re: Up a 45 degree ramp...???
« Reply #10 on: September 02, 2008, 08:16:00 PM »
Try Lego wheels, their tires have verry good grip at a painted surface. The regular motorcycle wheels will go well on the servos. You still need to attach them to a servo horn with some screws...

BTW, if you click on the link in my signature you will see how those whells look like on my balancing robot.
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#### Iron Man

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##### Re: Up a 45 degree ramp...???
« Reply #11 on: September 04, 2008, 07:19:49 AM »
or you can add more weight....

it'll increase friction, as long as your servos are powerful enough to compensate for the added downward component.

#### MadMax

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##### Re: Up a 45 degree ramp...???
« Reply #12 on: September 04, 2008, 01:13:18 PM »
MotorForce > ((sin(angle) + (M * 9.81)) / WheelRadius) / NumMotors

Just want to make sure that M is the height of the ramp in meters . Is it?

No, M is mass, mass * 9.81 equals the force gravity exerts on an object

#### airman00

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##### Re: Up a 45 degree ramp...???
« Reply #13 on: September 04, 2008, 05:07:20 PM »

No, M is mass, mass * 9.81 equals the force gravity exerts on an object

Oh thanks , I understand it now
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#### Admin

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##### Re: Up a 45 degree ramp...???
« Reply #14 on: September 06, 2008, 09:18:37 PM »
jhonilson, scroll down to where I custom make my wheels and add tread:
http://www.societyofrobots.com/robot_ERP.shtml#upgrade

airman00, my RMF accounts for ramps:
http://www.societyofrobots.com/RMF_calculator.shtml

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