Timber crane/backhoe slew ring

[farlet]

I am about to start planning a timber crane which can double up as a light duty backhoe. I am wondering if anyone has ever tried to use the ring gear/flywheel off a large truck to do the slewing/turning. I was thinking to drive it with a slow hydraulic motor and use the gear from the starter motor. I have all the stuff to do this lying around so cost will be zero.

Any thoughts ? The other thought was to use a planetary hub off a loading shovel which I also have

 

[4570Man]

I’ve seen boom trucks that use a gear to turn them but it’s a much bigger gear. I don’t think it would be practical to get a drive motor with enough toque to do that with a small gear. I’d probably look for a junk boom truck to rob for parts.

 

[Stimw]

In the mid 70's I used to have a 21' boom truck and it used a large sprocket and chain to a small sprocket on hydraulic motor.
I think that would be more fail safe.
An advertiser on this site might have the parts you need- Surplus Center

 

[otlski]

What were you planning to do for a slewing bearing? That may be harder given the overturning load the bearing would see in operation.

I am guessing (wild guess) that a typical fractional horsepower starter might make 100 foot lbs of torque. At low speed the gears might be able to transfer ten times that operationally.

 

[GLyford]

Would you have several that match? I think the loading would be a little much for just one, but for a stack of two or three I'd feel more comfortable it would hold up. Also thinking about swing bearings, if either the pinion or ring gear had flanges, that would at least keep the gears from popping apart vertically when you had a good load on the rest of the structure. Might still want to run the pinion at 90 degrees from the boom so that it would be out of the plane of the most flex.

 

[4570Man]

What were you planning to do for a slewing bearing? That may be harder given the overturning load the bearing would see in operation.

I am guessing (wild guess) that a typical fractional horsepower starter might make 100 foot lbs of torque. At low speed the gears might be able to transfer ten times that operationally.

I don’t think the starter gear will work. It’s not meant for that much toque and it doesn’t match the ring gear. The boom trucks I’ve seen that do this have a small gear several inches in diameter.

 

[GLyford]

Not sure why a flywheel ring gear and starter gear would not work together...?

 

[4570Man]

Not sure why a flywheel ring gear and starter gear would not work together...?

I missed the flywheel in the first post. I thought he meant ring gear from the rear end. I still don’t think the starter gear will handle the toque. Finding a hydraulic motor to work by itself is also doubtful. The boom trucks I’ve seen have a gear box on the swing.

 

[farlet]

Thanks for the replies. So its not looking good for the flywheel idea - I can see that. I will use the hub from a 12t axle for the bearing, I think this will be plenty strong enough. I had also thought of using a triplex roller chain and 2 sprockets. I was worried about too much play if I did this, but maybe it would be OK after the initial stretch. I have the chain and one sprocket already, so I would only have to buy the large sprocket - this would fit into the low cost/no cost budget idea for this build ! Stimw ; did your boom truck do OK with the chain and sprocket or were you forever fiddling with it ? It looks like the Wallenstein cranes use this type of system

 

[4570Man]

I’ve also seen boom trucks that used a chain drive. I’ve seen boom trucks that used a worm drive against a big gear. I personally think the big gear driven by the little gear is the simplest way.