90 Degree VersaPlanatary Drive - Miter Gear Design

Last crawled date: 1 year, 10 months ago

A 90 Degree Drive for the Vexpro VersaPlanetary
4 flavors. Each use different Martin Miter Gear (each available from McMaster).

Light duty - 16T@16DP (conservative est 10:1 ratio with 775Pro input) 2X2 square tube

Medium duty 18T@12DP (conservative est 30:1 ratio with 775Pro input) 2.5X2.5 square tube (Two subflavors of this flavor THIN and THICK -- thick is stronger obviously)

Heavy duty 20T@10DP (conservative est 65:1 ratio with 775Pro input) 3X3 square tube

Note Conservative Estimates are probably 2/3 of true value (can probably use 1.5-2X safely).
Also, McMaster sells unhardened teeth, hardened teeth (which Martin makes) will give another 1.5-2X ratio

NOTE. Redesigned for Christmas! Based on building one of these, made some changes/improvements.

Fixes/updates in this re-release:
- fixed some dimensions and ticky tack problems
- simplified the housing (gave up some tilt control on the gears but based on the first sample, this is not going to be a problem) much rather have simple manufacture
- included drawings for the housing and the gear modifations (more like sketches but the info is there)
- made a thick and a thin middle version (18T12DP gear) -- That gear is a BEAST. I am surprised at how beefy it feels in your hand. I suspect that with the thick housing it will be pretty much unbreakable -- or rather it will not be the weakest link, the VP will fail first. Just a gut feel but...
- removed the covers for the largest gear version (20T10DP gear) and made the housing thicker. I am very confident that this gearbox will be stronger than the VP.

I hope you enjoy the design.

UPDATE: 2016-12-08a
Fixed a lot of ticky tacky problems. Primarily, modified length of 20T10DP gear was wrong.

Also, HARDENED TEETH, versions of Martin Gear available from Motion Industries. ~50% cost up but worth it.
-- 16T16DP 3/8" bore hardened teeth = HM1616 $37 each (vs McMaster 6529K11 $22)
-- 18T12DP 1/2" bore hardened teeth = HM1218 $48 each (vs McMaster 6529K17 $31)
-- 20T10DP 1/2" bore hardened teeth = HM1020A $61 each (vs McMaster 6529K23 $43)

Dr. Joe J.

ALSO. Native CAD files are in Solidworks -- use configurations to easily switch between design options. All the files are in a PackAndGo Zip file. JJ

UPDATE 2016-12-22:
Artur pointed me to this table from Martin.
http://www.martinsprocket.com/docs/default-source/catalog-gears/miter-gears.pdf?sfvrsn=14

They have HP ratings for each miter gear. Using that I can back out a max effective ratio (recommended by Martin -- which will be pretty conservative).

Here is what I get:
ONCE AGAIN, let me stress imho these numbers are conservative for a FIRST robot but it is a good point of references and it is easy. YMMV.

Using the 10RPM numbers (effectively stall) = ~1Rad/sec

Big gear HM1020 would be 0.05HP = 37Watts = 37N-m so the max effective ratio is at 50:1 (37N-m/0.71N-m stall torque).

I get similar numbers using the 50RPM
Big gear HM1020: 0.3HP@50RPM = 223W @ 5 Rad/sec => 43N-m => max effective ratio 60:1

Mid gear HM1218. 0.02HP@10RPM = 15W @ 1 Rad/sec => 15N-m => max effective ratio 20:1
Mid gear HM1218. 0.15HP@50RPM = 112W @ 5 Rad/sec => 21N-m => max effective ratio 30:1

Little gear HM1616 0.02HP@25RPM = 15W @ 2.5 Rad/sec => 6N-m => max effective ratio 6:1
Little gear HM1616 0.04HP@25RPM = 30W @ 5 Rad/sec => 6N-m => max effective ratio 8:1

Other notes.

*** These are for if you STALL the 775Pro, not always the case.

*** These numbers use EFFECTIVE ratio not actual ratio. I would use 80-90% per stage on the VP so for example if you used (3) 5:1 ratios, you would have an actual ratio of 125:1 but an EFFECTIVE ratio of something between 70:1 and 90:1 after efficiency is accounted for.

*** AND FINALLY, let me stress AGAIN imho these numbers are conservative for a FIRST robot application.

*** The Vex 15T 12DP gear that many FRC folk are familiar with, assuming that the teeth are hardened would be able is on that Martin table as well.
HM1215 0.1HP@50RPM = 75W @ 5 Rad/sec => 14N-m => max effective ratio 20:1