3DP Gears with Keyway

This is are some gears printed out of HIPS mounted to a PG-71 Gearmotor

And yes It will hold the key all the way to stalling the motor
printed on an anycubic Chiron out of $10/kg HIPS at 255 C Nozzle 105 Bed with a .8 nozzle .4 mm layer height


Do you have the size and weight for those? They look cool!

Yes I do

Weight for both gears in HIPS 48.24 gram including brim. I will add a link to the grab cad here once it uploads its a prototype

Pinion 16 tooth with 13.4mm hex The gear is 31 tooth with a 10.8mm hole and a 4.4mm cutout with the center tangential to the hole. So clearance for the PG71 shaft and key and for a hex shaft (churro etc 1/2 in) for the pinion
Modulus 1.5mm Pressure angle 14.5 deg double helix at 30 deg involute profile 20 mm gear width the gear has a 6mm spacer to allow for mounting plate for the motor. The holes are to guide the slicer and control the direction the filament is laid down for extra strength. Its printed with enough perimeters so each gear is a solid piece of plastic - as close as you can get to a molded one by using FDM, you probably can print it in PLA too but that will under load grind quite a bit and grind the gears down over time - HIPS will last in excess of a season (IDK how long we used hips gears the first time last season - they made it through the season and still look like new. We have used HIPS so far up to about 400rpm the next level up 3000+ we have used Nylon so at this time IDK if hips might make rpm over 400 we have not tried. But we ground 2 PLA gears to nothing running a few hours at about 200 rpm under load

Oh and the pinion is about an inch in diameter and the Gear about 2 in.


This is, as usual, pretty darn cool. My question becomes this; you tested it to stall, at what point does it fail when being backdriven, and with how much force?

IDK we used them last your on the lift to lift up the robot with a double rack and none failed. One in front and one in back with a setup similar to this (only thinner)

The problem we had with last years option was too much flex and a churro bending when we got hit by an alliance member crashing into us while the lift was deployed. So this is a little tougher. we added .2 to the modulus and use a 1/2in square tube that is much less likely to bend in the support and made the rack from 14mm wide to 22mm wide. each individual rack piece has been confirmed to reliably lift 100lb on the bench. Now the above gear is for driving the robot forward. That worked fine last season. So based on that I cannot tell you at what point the gear would fail as currently the point of failure is beyond our capability of testing it. The closest we can come from small break tests and multiplying by the gear size accounting that more than 1 gear engage at a time is a guess of a static load of somewhere between 400 and 500lb

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And the stall test we did was clamp the motor in a vice and put a C clamp and the predecessor to that gear that jammed against the vice and then hooked the motor up to a battery and disconeccted it when it got pretty hot.

Grab Cad Link is this

Oh and the naming of gears
1st letter is type
P=Pinion or planet in a planetary
then you got a number and T which is the teeth
then the modulus in in 1/1000 mm
If they are Helical you got H HH for double helical nothing else for the default of 30deg otherwise followed by the helix angle . Combo gears are separated by an _ if there is a unit corection in 1/1000 it follows with a U after it
Would be a gear with 31 Teeth 1.5mm pitch double Helical with a 0.125 unit correction Right now we use the same addendum project wide so don’t include it into the name we might at a future point

@mpirringer why did you choose to print double helical gears, over a standard 20dp?

What was your source for $10/kg HIPS?

P. Ry

First double helical cause its self aligning and does not need a thrust bearing. 30 degrees cause I read a quite extensive paper (can’t find it right now) that it was the best helix angle for plastic gears when using on plastic double helical gears. did not test it myself but relied on the tests the author did when writing his doctoral thesis on it. Its not that with 3DP we have to adhere to metal standard. I also read some research that stated that under load plastic on plastic lasts longer than plastic on metal. The steel seems to chew up the plastic especially at higher RPM. So when you can use plastic on plastic so as we do that we kinda “live” in a plastic environment where plastic rules take precedence. And until I see some research that for plastic 10,20 or 40 deg. is superior to 30 I go with 30. The advantage according to that paper was much less vibration and more teeth being involved taking the torque. The 14.5 pressure angle - we try to keep that angle as low as possible to reduce axial load and to decrease the load on the motor mound which is plastic too and 16T is about the minimum where the undercut is still acceptable when it comes to tooth strength It produces about a 2.74mm thick tooth at the thinnest point now we know a 3mm thick 10mm wide piece of HIPS will break at about 140lb average so we got 20mm so each tooth should be able to hold the torque needed to move the robot and they do as we know from last year. hence 16 tooth and the 1.5mm modulus which comes out to close to a 5mm pitch was determined to be the smallest modulus which will allow enough “meat” left on a 16 tooth gear to put a hex shaft through it. and it produces a tooth at the pitch circle an below (undercut) with a min thickness stated above. Due to space constraints the gear was kept as small as possible. The holes in the big gear are on the same circle (i have been told) that the mounting holes on the PG71 are at and of a diameter big enough to pass a phillips screw driver through to access the screws holding the motor to the mounting plate that will be printed probably (hopefully) Monday

How things work at 1989 is I teach the kids that stuff then we have a meeting to discuss that, then they hit the inventor - give me the ipt and stls, I inspect them for grave errors like they are not printable or something plainly obvious. If they pass that - I will print what they designed. Then (on monday in this case) they get the parts and take it from there. Now it is quite possible that this is not the final version. I see some potential places for problems. Like it might take 2 collars to hold the pinion in place and there is nothing but friction at this point to prevent the key from potentially slipping out. And then there is still the question can it actually be assembled the way it was intended or assembled at all. It would not be the first time that at cad time the room needed for human fingers to put the parts in place was misjudged. Just cause it fits on the screen does not mean it fits in RL.


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