High torque planetary gear with low ratio

[magnusrm]

Hi, im designing a motor which needs a planetary gear with low ratio, 1:2 is ideal, but due to the principle of ( ratio ) = (sun teeth + ring teeth)/(sun teeth) thats not possible.
The motor has an output torque of 85Nm and max speed of 4000 rpm. I havent found any solutions or manufacturers who delivers this kind of gearhead with lower ratio than 1:4.
Any tips?

 

[drawoh]

magnusrm,

Why does the gearbox have to be planetary?

A 2:1 ratio can be easily done with one set of gears. The only downside is that the output shaft does not line up with the motor shaft.

--
JHG

 

[BrianPetersen]

A 2:1 ratio can be done with a planetary set if the planetary carrier is held, the sun gear is driven, and the ring gear (with twice as many teeth as the sun gear) is output. The output will be in the reverse direction of the input.

 

[Tmoose]

How close to 2:1 can you accept ?

I bet you are looking for a purchased solution. But A bunch of US automatic transmissions have ratios in the ballpark.

http://www.oldengine.org/unfaq/leadfoot/trans.htm

Some aftermarket companies supply ratios real close to 2:1.

http://www.tciauto.com/tc/gear-ratios/

Adapting those gear sets would be quite an engineering exercise.

 

[magnusrm]

Thanks for your replies, guys.
Well, it doesnt need to be planetary, but it will ease the design and manufacturing process if the output shaft is coaxial to the motor shaft.
Also, in my head, a planetary gearbox is more compact due to multiple gears transferring the torque. I would also prefer to have a off the shelf solution that I could add between the motor and the outputshaft.
I will however evaluate using standard gears.

Do you have any tips on suppliers who deliver gears and have a easy to use CAD-file database? Metric is preferred

http://khkgears.net/

seems promising, but other tips are welcome.

 

[drawoh]

magnusrm,

Modelling gears in CAD is easy, especially of you have some old drafting books around. My 1941 copy of French's Engineering Drawing comes in handy. This assumes that you are not not using the CAD model to manufacture your gears.

Off the shelf gears need to modified to attach to your shafts. This is especially true for high torque applications. Forget those set screws! If you get a gear cutter to fabricate your gears, they can cut the bore first, and use it to fixture the tooth cutting. I don't know how COTS gears are bored out.

--
JHG

 

[SwinnyGG]

I would call Boston Gear. They do planetary and inline helical drive reducers in ratios as low as 1.6.