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View Full Version : Help Please: Gear and linear speed calculation

BigBrand
31-01-2021, 08:29 PM
Help!

What am i doing wrong here... I've just tried to work out the gearing speeds and thus linear speed of my rack and pinion on the X axis.

The set up looks like this:

29449

Its 2 speed reduction belts in series measuring roughly like this...

29452

The max operating speed of the motor is approx 4000rpm. Its giving a linear speed at the rack of 1.8m/s which cant be right its the slowest machine in the world.

Have i just slipped up on some units somewhere?? I cant spot where i am going wrong.

Muzzer
31-01-2021, 09:41 PM
You aren't far off. I agree with 720rpm. For a 2" pinion, that's 4523 in/min (multiply by pi x D). Divide by 39 (inches per meter) and 60 (seconds per minute) and I get 116 m/min and 1.93 m/s.

If it's moving slower than that, you should check the actual motor speed perhaps?

m_c
31-01-2021, 10:02 PM
Big thing that jumps out to me, is you're using pulley diameters, not number of teeth.
Although diameters will give you a rough calculation, it's not going to give you an exact one.

You also need to count the teeth on the pinion, and find out what pitch the rack is.

BigBrand
01-02-2021, 10:16 PM
You aren't far off. I agree with 720rpm. For a 2" pinion, that's 4523 in/min (multiply by pi x D). Divide by 39 (inches per meter) and 60 (seconds per minute) and I get 116 m/min and 1.93 m/s.

If it's moving slower than that, you should check the actual motor speed perhaps?

Its set to 4m/m for my rapids(?). However, i've spotted the max voltage of the motor is 140 according to an old pdf i found and i think the supply is only 100-110v approx. Also i can almost guarantee they are not set up correctly. I downloaded the settings from the drive when i bough it and this is what is still in place as i didnt want to touch it without a better understanding of what im doing.

I guess its also not just the hypothetical max speed but more the acceleration / deccel of the motor also that determines the real life performance.

Im not too concerned about the current motor setup as that will be getting binned off.. what im trying to work out is what speeds i could expect of some new motors in real terms if i kept the current belt pulley and pinion drive systems or maybe part of them.

The closed loop steppers im looking at claim 10nm and 1200rpm max speed. If i feed that back through the equation im getting 216rpm and 55nm at max stated speed which equates to 0.56m/s. However, what speed do you typically run steppers at knowing they lose their torque?

Anybody got any input on what is a happy medium. Do i need to bin off one of the sets of pulleys and maybe change to just 1 set of 1:3 for instance?

BigBrand
01-02-2021, 10:18 PM
Big thing that jumps out to me, is you're using pulley diameters, not number of teeth.
Although diameters will give you a rough calculation, it's not going to give you an exact one.

You also need to count the teeth on the pinion, and find out what pitch the rack is.

Ahhh i see. Rough calculations for now is fine but yes ill count the teeth. Also what difference does the amount of teeth on the pinion make? I thought it was just the outer diameter (circumference) of the pinion that sets the speed?

m_c
02-02-2021, 12:06 AM
Don't cripple a machine this size with steppers.
Servo's aren't that much more expensive, and will be far better than even closed loop steppers.
https://www.aliexpress.com/store/group/A4-series-AC-servo-motor-kit/1907567_513054652.html
I'd probably guess 1 or 1.2KW would be a reasonable match, but I'm sure Jazz will give you a better answer.

Ahhh i see. Rough calculations for now is fine but yes ill count the teeth. Also what difference does the amount of teeth on the pinion make? I thought it was just the outer diameter (circumference) of the pinion that sets the speed?
Technically the Pinion pitch diameter is the figure you need, however it's easier just to find out what pitch (it'll either be MOD or DP) the rack is, and the number of teeth on the pinion, then multiply the number of teeth by the pitch.