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Author Topic: Hand held clip in transfer system! drill powered  (Read 2062 times)

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Offline CradboardTopic starter

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Hand held clip in transfer system! drill powered
« on: March 05, 2010, 05:18:46 AM »
Ok guys i have been searching but cannot seem to find specific equations to determine which motor to spec.

i want to do the calculations myself.  i know the
mass
driven wheel diameter
desired velocity
desired acceleration
battery voltage

can anyone point me in the right direction for equations that will allow me to establish what motor to purchase etc.

do i need any more info?

thanks
« Last Edit: March 23, 2010, 02:36:02 PM by Cradboard »

Offline waltr

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Re: equations to determine the best motor
« Reply #1 on: March 05, 2010, 08:25:43 AM »
Look in the SoR tutorials (click on 'Robot Tutorials' below the above title on this page ). Beside the motor RMF calculator there is a tutorial on how to do the calculations.

Offline CradboardTopic starter

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Re: equations to determine the best motor
« Reply #2 on: March 05, 2010, 09:07:13 AM »
ive done this but it doesnt seem to make sense!

Mass = 1600kg
acceleration or the robot = 0.25m/s^2
velocity of the robot = 0.5 m/s

Force = 1600*9.81*0.25
F=3,924N

Robot Motor Factor
Torque * rps > = Mass * Acceleration * Velocity / (2 * pi)

Torque * rps > = 1600*0.25*0.5/(2*pi)
Torque * rps > ==31.85

using
velocity = diameter * pi * rps

rpm= 32, rps = 0.531

Torque = 31.85/0.531
Torque = 60Nm

i dont think this looks right tho? how to i establish the required gearing?

also if i know that only 80Kg of force is required to start the unit moving then can i not just calculate the torque by doing 80 times the radius of the driven wheel?

Offline waltr

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Re: checking motor calculations and necessity!
« Reply #3 on: March 05, 2010, 12:57:22 PM »
Quote
Mass = 1600kg
Are you sure this is correct as this is what a small truck would weight? That's 3520 Pounds or 1.76 tons(US short) in Imperial measure.
Maybe you mean the robot's mass = 1600g or 1.6kg (about 3.5 lbs).

Quote
how to i establish the required gearing?

That the motor RPM and divide by the required Wheel RPM to get a gear ratio.Say a motor turns at 5000 RPM and you need to wheel to turn at 32 RPM, the gear ratio is 156.25:1 but doesn't normally need to be that exact.

Quote
also if i know that only 80Kg of force is required to start the unit moving then can i not just calculate the torque by doing 80 times the radius of the driven wheel?

Yes, that is the definition of Torque.
« Last Edit: March 05, 2010, 07:29:56 PM by waltr »

Offline hopslink

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Re: checking motor calculations and necessity!
« Reply #4 on: March 06, 2010, 04:15:38 AM »
It looks right, to make it seem more 'real' calculate through to get the Force supplied. Here
Quote
Torque * rps > ==31.85

using
velocity = diameter * pi * rps

rpm= 32, rps = 0.531

Torque = 31.85/0.531
Torque = 60Nm
velocity = diameter * pi * rps

substituting:
0.5 m/s = diameter * pi * 0.531

diameter * pi = velocity / rps = 0.5 / 0.531 = 0.94m

diameter = 0.94/pi = 30cm or a radius of 15cm.

Calculating through for Force supplied:

Force = Torque/radius = 60Nm / 0.15m = 400N ~ 40kg

This seems ok since these calculations do not take account of friction in the system, which will be significant for 1600kg on dolly type wheels on a shop floor. When you measure you get a Force requirement of 80kg or ~800N and it is this figure you should use when specifying your motor/gearing as you correctly suggest above, and confirmed by waltr.   

Offline CradboardTopic starter

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Re: checking motor calculations and necessity!
« Reply #5 on: March 06, 2010, 05:20:26 AM »
Thanks guys yeah it does weigh 1600Kg!! its essentially a car on a trolley! my robot will drag the trolley!

so for torque just multiplying 80kg x 9.81 x 0.15m = 120Nm. i assume this is twice yours hopslink due to friction alone.

so now i decide on a motor and then on the required gearing to get it down to about 32 rpm! IDEAL

Offline waltr

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Re: checking motor calculations and necessity!
« Reply #6 on: March 06, 2010, 08:13:47 AM »
Quote
Thanks guys yeah it does weigh 1600Kg!! its essentially a car on a trolley! my robot will drag the trolley!
Ah, that makes sense.

What I didn't see mentioned is that where gears reduce the speed (RPM) of the motor, gear reduction increases the torque on the output shaft.  So if you have a gear reduction of 100:1 the motor turns 100 times the rate of the gear output, and the torque on the output is 100 times the the motor's torque (minus frictional losses).

Just didn't what you trying to find a motor with the calculated torque required at the wheels.

Offline CradboardTopic starter

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Re: checking motor calculations and necessity!
« Reply #7 on: March 07, 2010, 09:12:15 AM »
for those that are interested here is a basic mock up.

the latter two images show the hydraulics at the back of the system.  essentially the ram will lift the plate under the gold trolley and apply a force of up to 100kg vertically to ensure enough traction is generated over the driven wheel





Offline hopslink

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Re: checking motor calculations and necessity!
« Reply #8 on: March 07, 2010, 03:17:03 PM »
Be aware that around 75% of that weight will be on the rear wheels of your device and only 25% on the front since the base of your ram is closer to the back.

Offline nottoooily

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Re: checking motor calculations and necessity!
« Reply #9 on: March 09, 2010, 02:32:48 AM »
Much worse than 75%! In the position shown, none of the car/frame weight will be on the driven wheel.

That cantilever on the jack will apply a moment which transfers the entire load to directly under the golden leg.



Offline CradboardTopic starter

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Re: checking motor calculations and necessity!
« Reply #10 on: March 09, 2010, 06:40:12 AM »
Agreed, the rear castors have now been moved back to allow sufficient force over the driven wheel.  the unit shouldnt really need it if it weighs in excess of 120Kg but hmmmmm

Offline nottoooily

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Re: checking motor calculations and necessity!
« Reply #11 on: March 09, 2010, 08:29:10 AM »
120kg, haha so you need another trolley to move the trolley that moves the trolley :P

Offline CradboardTopic starter

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Re: checking motor calculations and necessity!
« Reply #12 on: March 09, 2010, 04:33:22 PM »
yes yes very funny lol!  in light of what was mentioned above and some more calculations i have adjusted the packaging!!



the absolute simplest way i can think of doing this is to replace the castors at the bottom of the gold trolley with a different driven wheel/system that has no batteries or motors, then using some sort of link up use a power drill to turn the wheel.  does that make sense? this is by far the simplest and most cost affective method of doing this but i cant get my head around it! lol

Offline Soeren

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Re: checking motor calculations and necessity!
« Reply #13 on: March 10, 2010, 01:55:09 PM »
Hi,

the absolute simplest way i can think of doing this is to replace the castors at the bottom of the gold trolley with a different driven wheel/system that has no batteries or motors, then using some sort of link up use a power drill to turn the wheel.
I'm not sure a power drill will do, if you want to move a real car (1600 kg sounds close to a real car to me ;D).
Another problem might be turning, if you only power the wheels of the bar in front (or back), so I'd recommend powering both.
If you change one wheel of each bar with one that has a cogwheel on the side (perhaps the wheel needs to be larger than in the drawing then) and you have some holes/pegs/whatever on the bar that a motor assembly can be hooked up to with a few clicks, you can link them with a small (bicycle) chain.
A Sharp distance sensor on each bar can be used to keep the car driven from crashing into the wall and/or you can make a simple RF remote control to start/stop the motors.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline nottoooily

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Re: checking motor calculations and necessity!
« Reply #14 on: March 11, 2010, 02:14:48 AM »
Detachable motor reminds me of what railway guys use to move wagons in a depot. They have a hand-held, probably air-powered motor that they clip onto the end of an axle and walk along driving it.

So how about the power comes from wires hanging on the ceiling? To avoid any gears on the trolley you can use a universal/CV shaft and resist the torque with either a lever handle or a rigid tube around the drive shaft.

Offline CradboardTopic starter

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Re: checking motor calculations and necessity!
« Reply #15 on: March 23, 2010, 02:35:22 PM »
Here is the proposed handheld option then!

basically i am looking to build the grey components of this, its a bolt on unit that will allow you to drag the gold legs around using a cordless drill. you plug a standard cordless drill in at the top, (the bracket is symbolic and not representative) this drives the long rod which in turn drives the wheels. the second rod which goes from the back of the drill to the edge of the unit steers it. i have tried to show you how this works in the pictures.

essentially i need to gear the thing down from 1000rpm from the drill to 60 rpm on the wheels but also transmit 120Nm of torque. i can either use the gearing system shown or a worm gear or potentially a CV joint as mentioned by nottoooily

or i also need to find a CV joint small enough but capable enough of coping with the torques.

does any of that make sense? lol? any ideas on this design thanks guys


 


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