Hello,
I am designing a simple and inexpensive gearbox which will drive two parallel shafts. We have a current design which works, but due to various reasons we must make a new design. I would like to take this chance to improve where possible. costs, noise, efficiency ?
The current method uses 3 stages (1:27 reduction) with all gears made of POM injection moulded, except the motor gear which is brass and pressed onto the motor (50-75W DC motor) axle.
- I know my desired output speed and torque, and any combination of motor speed and gear ratio may achieve this. What are some things to keep in mind when finding the best combination? Space constraints, noise available motors...
-I was thinking about changing the brass gear to a POM gear and using a key or a flat spot on the axle, in order to save costs. Torque here is less than 0.3 Nm. Does anyone have experience with fastening techniques. Would it be hard to keep a pitch line runout within tolerance using these methods?
-As the output must be split to two shafts, the current design splits at the final stage. That is, both axles have a gear which pair to the same middle gear. Is this the best place to make the split? If I make the split directly off the motor pinion, I need the extra space and gear for seperate gear trains, but is there an advantage to doing this? Better to split at higher or lower speeds?
-Are there significant challenges to matching helical gears?
Sort of diverging...
-The two shafts will drive each a 37mm roller which is used to transport a wire. The rollers have a relatively large tolerance on diameter. This means that as rotational speed between the two rollers is fixed, but linear velocity of the wire can be different as diameter varies. Would a differential gearbox be something to think about? As I understand the power would take the path of least resistance, so my main concern is that one roll would carry all the load which therefore defeats the purpose having a second roll, which is to provide extra grip on the wire. After a certain amount of complexity the costs are unjustifiable. Any thoughts are more than welcome.
Thanks for the input,
Darrell
Hi Darrell,
First off, spur gears are about as noisy as a gear-train can get. Robust, but noisy. The ratio is not that great a stretch for a small worm-drive gearbox. Tons quieter and all done in a single gearbox with just two working components.
II would suggest driving one output shaft directly then chain coupling the other to it. Use a chain tensioner on the return side to maintain good load sharing and you are done.
Hi Pinkerton,
Thanks for the response. You are right the spur gearbox we have now is rather noisy. On the other hand it seems a good deal more efficient than the worm gear.
Not an Engineering term I am familiar with.Originally Posted by surfmase
A chain seems to be a rather expensive solution as well
Er, OK, just what kind of budget are you working with ??
http://www.grainger.com/Grainger/TSU...093?Pid=search
$4.56 per foot
http://www.grainger.com/Grainger/TSU...112?Pid=search
$18.85 each
4 plastic injection moulded gears + 1 brass pinion + 2 cylindrical pins < $3.00
1 plastic injection moulded worm-wheel + 2 sprockets + 1 chain + 1 tensioner assembly > $3.00 x 14
Maybe have a look at this and think about reconsidering the worm drive as Dave suggested?
http://en.wikipedia.org/wiki/Worm_drive
Not sure if you are talking about a one-up for in house use or if this is a product your company is selling... but either way you need to consider the life of the unit when looking at unit cost? Will the system you described hold up well? If the unit doesn't hold up then you don't save anything.
Also ought to be able to easily get your reduction with one worm and take up less space doing it? So now you have a big noise reduction and probably a smaller unit with less parts... and less parts is usually less $$ ?
Just tossing things out there...
Have fun...!
Bob
Hey there RWolfeJr,
The product is a wire feeder. The lifetime is over 10,000 Hrs. We achieve this with a current plastic spur gear design. I have thought of different gear systems such as planetary, harmonic, spur and even worm. The advantage of the spur is that the motor rotor is parallel to the output shafts, which is desireable for the geometry of everything. And it is certainly more efficient. The one thing is that its loud. If I can overcome the geometry problems you may have me convinced with the space and noise solution. On the other hand there is the option to use helical spur gears on the first one or two stages to try to reduce the noise. There is always something to think about, cost is usually toward the top of the list.
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