Drive motor options

[Daniel]

Well my reason for switching to brushless was a bit more unusual. I took Huntsman to RoboGames 2012 and during it's second fight agaist Last Rites it had all 4 motors fail due to popped out brushes and shattered magnets. Then at our Nationals in 2012 my Vendetta failed in the finals for simalar reasons. So I chucked a wobbly at the world of complex brushed motors and went brought the brushless setup. I wanted cheaper motors that are made with less parts and smaller magnets, and therefore less likely to have mechanical failures from shock.

I chose the because NTM 42-30 750kv because on 4-cell they should hit 10800rpm. With a 10:1 reduction and 100mm wheels that is a calculated 5.65m/s. Under load it's probably half that and would therefore take 1.7 seconds to drive across our 4.8m wide arena which was simalar to my previous robot. I do all my calculations in m/s because we only drive a few meters before hiting the other side of the arena, in a few seconds, so miles or kilometers per hour isn't relatable. So 10mph sounds slow, but 2 seconds across an arena sounds decent, and it's actually the same thing.

[Liftoff]

If I had to build my own gearbox, would it be ok to use helical gears? Main reason I'd consider them is space, I could use narrower helical gears having the same contact area a wider spur gear would. But not too sure about the extra forces generated by those gears..... any one who built their own boxes used helicals, or knows of some reasons not to use them?

[shakesc]

Have a look at the toughbox gearbox options on http://www.andymark.com/Gearbox-Transmission-s/55.htm

[Liftoff]

Thanks for the link Chris, that's what I had in mind, something down that line. The problem with their boxes is they are quite large for the space I have. But still, got some ideas from their assembly drawings. I could build mine much smaller and probably lighter without the need for helical gears...

[maddox10]

Helical gears have an inherent disadvantage , because these load the bearing also longitudal, not only axial. That can be solved by using 2 next to each other in the herringbone setup.

But for our application just straight gears will do nicely.

[Liftoff]

Helical gears have an inherent disadvantage , because these load the bearing also longitudal, not only axial. That can be solved by using 2 next to each other in the herringbone setup.

Hmm, that will defeat the purpose of a light and compact setup if I had to use herringbone gears. I could maybe use helical gears and thrust bearings...but probably its better to keep it simple and do as you said...go with straight gears, any recommendations on who sells loose gears at a reasonable price, preferably within the EU not the States?

[maddox10]

Technobots has a suitable range of gears, and are very dependable.

[Liftoff]

Christmas shopping time!
Just need some advice before I start ordering stuff... I'm about to order gears for the gearboxes, motors and escs.
The motors I'm going for are these:
http://www.hobbyking.com/hobbyking/s...dproduct=16231
These spin at around 13500rpm on 4s. The diameter of the wheel/track is 80mm, I'm thinking of gearing it down with a 12:1 ratio.
Did some research of available gears and I'm looking at two stages of 6:1 using 5mm wide 0.7mod gears with 10 and 60 teeth.
Any suggestions if this is suitable and strong enough for the above motor?

[maddox10]

The NTM motors have a lot of torque, I would opt for mod 1 gears. Z12 to Z 36/Z12 to Z48.

The 12/36 double gear is one you can buy at www.Conrad.com , order number 240320 - 62
, making life easier.

[Ellis]

Two 6:1 stages makes for 36:1, not 12:1. Stage ratios are multiplied to get the overall reduction. That setup would get you a bit over 3mph!

Mod .7 sounds a bit small to me (roughly the same as what's in a drill gearbox), and I'd be even more cautious at just 5mm wide. I'd expect to use mod 1, 10mm wide, or similar.

[Liftoff]

Two 6:1 stages makes for 36:1, not 12:1. Stage ratios are multiplied to get the overall reduction. That setup would get you a bit over 3mph!

Mod .7 sounds a bit small to me (roughly the same as what's in a drill gearbox), and I'd be even more cautious at just 5mm wide. I'd expect to use mod 1, 10mm wide, or similar.

How silly of me! You're right! This will make my life much easier as I can select smaller gears with a larger modulus making the whole gearbox smaller.
Thanks to both of you, spared me a log of grief
Will have a look at Conrad tomorrow Mario, hope they have decent prices as the gears I found aren't exactly cheap!

[Liftoff]

Had a good look at Conrad and found the same items for a lower price from the UK http://www.rapidonline.com
Going for 10 and 35 teeth gears with two stages of 3.5:1 for a final drive of 12.25...that will fit in the space I got, the 48T gears will be too large and will require quite a lot of work to fit in.
I estimate the weight of the motor and gearbox to be around 340 gr each, that's a weight saving of 110 gr over my current setup...I desperately need to shed off weight!

[Liftoff]

Christmas presents finally arrived, slightly belated but that doesn't matter now!
Been doing some sketches for the gearbox in the meantime, I'll upload them and as this is my first attempt to building one please feel free to point out any flaws etc which can be noticed


20140102_142608[1].jpg

[Liftoff]

Gearbox details:

2 stages with 10t and 35t mod1 gears.
Gears interference fit on shaft.
Shaft material: chrom-vanadium (a 1/4" drive extension turned down to size)
Bearings: MR126 ZZ 6 X 12 X 4Mm, 6700 ZZ 10 X 15 X 4Mm
Side plates 7075t6 Aluminium 64x41x4mm
Grease : Rocol Aerospec100

The gearbox output shaft will bear no side loads as the drive wheel is supported by its own bearings.


Gearbox.jpg
gearbox1.jpg

[Max]

I'm confused as to where all the gears are mounted, presumably the first gear is attached to the output shaft of the motor, the second 2 gears are on a separate shaft both attached to te shaft with a grub screw so they rotate at the same speed. Then I don't get where the last gear is connected? Is it on a separate shaft inline with the motor's shaft but only supported on one end?