# Sliding gate motor selection

1. Mar 9, 2009

### ewomach

hi everyone,

i have slidig gate that i need to install a drive motor. the gate weight is 1500 kg and has 5 v-grove wheels. the dia. of the wheels are 160 mm. We already bought a motor for it but i am concerned about if that motor will be sufficient for this gate. i am trying to calculate the force required to accelarte the gate.
please see my calculations below and let me know if i am on the right track.

Rolling friction (fr) = C rr x Nf = 0.0005 x 15000 N = 7.5N
F - fr = m x a = 1500kg x 0.196m/s^2
F = 294N + 7.5N = 301.5 required to accelerate the gate

Motor Properties
Torque force = 1300N
Output revolution = 52 rpm
Pinion = Z18
Rated Power = 650W

I will be glad if someone can help me.

2. Mar 9, 2009

### Dr.D

You calcs are more than a little bit sketchy.

Your rolling friction calc shows three factors, C, rr, Nf, but then you only provided 2 numbers. Did you do this right?

Where did the acceleration of 0.196 m/s^2 come from?

Where did the 294N come from?

What on earth is a "Torque force"?

The short answer is, yes, any motor will do, if you are willing to move the gate slowly enough, and provided it is sufficient to overcome the system friction.

3. Mar 9, 2009

### ewomach

Crr is the dimensionless rolling resistance coefficient ,

i exactly dont know what the speed of the gate should be so i just used the motor speed = 52 rpm. pinion pitch diameter = 0.072m

v = 3.14 x D x w =3.14 x 0.072 x 52 = 11.76 m/minute = 0.196m/s

so i just assumed to reached this velocity in 1 second.

since i am not so familiar with with this. Is there any other loads than rolling friction.

i will be glad if you direct me how i should size the motor correctly

4. Mar 9, 2009

### Dr.D

Your assumption that it must reach this velocity in one second then is rather arbitrary. Since your group has (unwisely?) already purchased a motor already, perhaps you should approach this problem the other way around, namely, ask how quickly can this motor get the gate up to speed?

You have talked about rolling friction, and that will definitely be present. You have not talked about how the motor will drive the gate, what sort of mechanism will be used. Whatever drive you use will have some friction and associated losses in it as well, so you need to take those into account.

Is this gate hinged, or does it simply roll in a track? If it is hinged, there is friction there also.

Look at the whole system and try to estimate all of the possible losses. Then you can estimate the load on the motor and see how much power is available to accelerate the gate. From that, you can find out how long it will take to get the gate up to speed.

5. Mar 9, 2009

### ewomach

Torque force is what i didn't understand. in the product cataloque it is given as 1300N. so i assumed with Z18 Pinion (Pitch Dia. 0.072m) force applied to the rack. Torque= F x r = 1300N x 0.072 = 46.8Nm.

Other than the rolling friction. There are friction on the Bearings and as you mentioned there will be losses on the pinion rack mechanism. I dont expect those losses to be big.

if i check how quickly my motor can get the gate up to speed:
F - fr = m x a
1300N - 7.5N = 1500kg x a
a = 0.861 m/s^2
This accelaration does not sound so logical to me.
Can the Losses that i neglected (Friction on the bearings, dirt on the track, Friction on the guide rollers, Losses on the drive Mechaism) be so big?

6. Mar 9, 2009

### Dr.D

A rock in front of a wheel can cause the "wheel friction" to go up amazingly!

Nice of you to mention that there is a rack involved here.
What else have you not mentioned that really ought to be told at this point?
Perhaps a list (with full descriptions) of the parts you have already acquired would be a start.

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