Wednesday, November 25, 2009

Re: [Electric Boats] Bearings and power transmission

 

David,
 
The gearbox solution will deliver more power, more efficiently than any other solution.   Helical gears are 97% efficient and seals account for losses of another percent.   Gearboxes have an integral thrust bearing.    The cast iron of the gearbox acts as a heat sink for the motor so the motor is capable of  running longer at higher loads.   There is no possibility of catching fingers or clothing like belts or chains can.    Gear noise is minimal with slower turning motors and big slow turning propellors.  Gearboxes can be mounted to a stainless plate and put back on the original motor mounts for accurate alignment.   Split / Flex couplings offer alignment and make it easy to install.    
 
The greatest advantage of the industrial gearbox is the many different gear ratios.   They are essential to be able to balance the system for optimum efficiency and power.
 
James Lambden
 
 
 
 
----- Original Message -----
Sent: Wednesday, November 25, 2009 7:06 PM
Subject: Re: [Electric Boats] Bearings and power transmission

 

David,
 
The flange mounted ball bearing has plenty of capacity to take the small thrust loads 6hp can generate and it has a spherical OD so will align itself with the prop shaft.  The timing belt does not need a tensioner, just mill slots in the plate to slide the motor to create tension in the belt.  The belt and pulley solution is lighter, cheaper and quieter than the gear solutions, plus you can change the ratio by substituting a new pulley and belt.
 
You could use your existing gear box from the ICE too, if you can devise a way to couple the motor to its input shaft plus mount the gearbox to the boat.  Not so simple.
 
I think the al plate is a better mounting system - it is more rigid than plywood w/fiberglass, easier to make and won't crush under the bolt heads.  You can machine 6061 aluminum with wood working tools, even cut it on a table saw with a carbide blade.
 
Denny Wolfe
 
 
Message -----
Sent: Wednesday, November 25, 2009 8:54 PM
Subject: [Electric Boats] Bearings and power transmission

 

Hello group, I'm putting together an electric system for an Islander 32' using the MARS brushless set-up. I'm puzzling out the power transmission and motor mounts. First question is about the motor mounting. Looks like most people are using 1/2" AL to mount the motor and shaft bearings. Could heavily glassed ply be used in its place or does the AL acting as a heat sink make it a better choice?

Second question is about power transmission. Seems there are three choices: use an existing marine transmission, use an industrial gear box, or set up something with belts and pulleys.

I have the gear box from the diesel we pulled, I just worry about it being inefficient and not allowing the prop to spin the motor for regen. Anyone know how efficient small marine transmissions are whether it would be a good way to go? It would certainly be the easiest solution and the MARS motor runs at about the same RPM as the Yanmar did so the ratios should match up well.

Second option is an industrial gear box like Propulsion Marine offers, this also looks like a good solution with a minimum of engineering involved.

Third option, which I'm leaning toward is setting up a board with the motor and some pulleys to bring the speed down for the shaft. V-belt, chain, or timing belt? One thing I haven't seen anyone address is idlers or tensioners on the belts, there has to be some method of tensioning the belts. Are people just using a slot and leverage before bolting down like an alternator? I've seen spring loaded tensioners for timing belts that looked like a good solution.

The other question I have is about thrust, a pulley and belt set up needs some sort of thrust bearing, do the flange bearings I see being used provide that function or is an additional bearing needed in the system? I'm new to the mechanics of power transmission, so I've got these questions.

Thanks, I'm looking forward to some discussion on the mechanics of setting up such a system. I've got a good grasp on the electrics, charging, and battery systems, its just the mechanical part I still need some help with.

Thanks,
David

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