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Motor & gearbox

A project log for Solder paste and flux dispenser

DIY for hobby use

VitalyVitaly 08/10/2019 at 06:330 Comments

Many hand made dispensers use 28BYJ-48 motors. Those are very cheap, but not enough small and not convenient to mount. We need something better:

Let's estimate desired gearbox ratio.

All small 10-15mm steppers usually have 18° step (20 steps per turn). Gearbox can be:

Other data:

Desired portion size per single motor step is 0.006 mm³.

Let's calculate, what stepper with plastic gearbox 1:50 can give us:

(3.14 * 15² / 4) * 0.5 / 50 / 20 => 0.09

 0.09 mm³ is very bad. It's 1.5x more than portion size and 15x more than desired precision. What can we do?

1cc syringe has dia about 5mm. Portion per step will decrease in 9x. Better, but not perfect. Let's use metal gearbox 1:295.

Estimate for 3cc syringe (9mm inner dia):

(3.14 * 9² / 4) * 0.5 / 295 / 20 => 0.005

Estimate for 1cc syringe (5mm inner dia):

(3.14 * 5² / 4) * 0.5 / 295 / 20 => 0.001

In total:

Of cause, we could use dynamic model (quick step forward and back) and cheat with paste viscosity. But that's much more complicated and result will depend on paste temperature. Also, it's not good idea to use micro stepping, because it's not precise with cheap motors and consumes more power.

Conclusion

That's all with boring maths, next time I'll try to post some pictures :)

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