I am working on a linear actuator and am searching for a tooth belt drive sprocket that offers a helical wrap of the belt around itself such that the tooth belt in and out paths are parallel but offset.
The sprocket axis will as a result be non-perpendicular to the belt but this is acceptable for my application.
Does such a design exist. Has anyone any comments on this scenario.
What is the reason for the helical wrap.. which does not work :-(
Can't you use a normal arrangement on it's side ?
And the reason it doesn't work, as Jonathan says, is that a helical belt joins a pulley at some helix angle, and departs it at some helix angle, so the divergence of the belt, coming to going is twice the helix angle. Parallel? No! Well, waddaya know!
Brian Whatcott
Hmm, yes, I realised this could not work a fraction of a second after hitting the 'send' key.
My application requires a linear actuator that will climb or descend a
5m vertical tooth belt but with only has space for the gear/motor/sprocket assembly on the tooth side and just 3mm free space on the flat side.The design is such that I cannot apply pressure into and perpendicular such that I could use a rack, hence the belt. So this is where erroneous helical wrap idea started.
The belt is tensioned by a load of 100kg which will limit any simple guide rollers to lay the belt around a proper proportion of the sprocket.
Oh, and it's a very low cost app. The motor/actuator/planetary gearbox (inside the sprocket) has to cost under USD40
wrap around a driven sprocket about 120 degrees, come back round an idler on the smooth side 180 and then a free wheeling sprocket 60 to put the belt on its original line...
You don't say what size the mechanism is, the force needed, or how many units you are building so it's hard to say if USD 40 is going to be enough.
I wouldn't dismiss guide rollers without a little research. 100kg isn't much radial load for a needle bearing cam follower.
Maybe a cam follower would be pricey, but you might look at the very cheapest radial ball bearings mounted on bolts. If it's a low speed application, you may find that a plain sleeve bearing would work.
Peter wrote in news: snipped-for-privacy@4ax.com:
Must the drive motor reside on the carriage? Would be easier to fix the belt to the carriage and put the drive at one end of the fixed mounting.
This is an option for me and would give me a pi radian wrap around the sprocket, which would be an advantage. It's just that I have very little space to fit the drive system in this manner.
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