Thought you guys might like to see the "Engine Room" of my Glasgow before it gets buried under the deck. 2 x MFA 919D (100:1) motors all joined up with MFA timing pulleys, toothed belts and bearing blocks. Belt tension is adjustable via a tilting motor mount.

Greebo,

If I could make a suggestion before you go too far.

With the gearing you have, if something gets into the paddles, you will just end up with a load of broken pieces.

What is needed is some sort of slippage. The easy way is to have a very lightly loaded idler wheel pressing on the belt, and if something does get jammed, the belt will slip. Another way is to put in slip couplings, so again the paddles will stop without being forced over by the motors.

John

Hi PD's & thank's Greebo...these new snaps will inspire new members to see a very tidy paddle shaft installation. between ball bearings in clamps & outborad to bronze bushings .......etc ..but is that 12 V ...7 amp Gel cell removable?........ ...regards

Mmmmm... I hadn't thought about getting stuff jammed in the paddlewheels John, thanks for making the point. What exactly are slip couplings? 
And yes, the battery slides out the back 

I didn't want to worry you unduly, with luck it would never happen, but I have seen a glasgow paddle wheel with a twig stuck in it and the same sort of drive system, it wasn't a very nice sight, half the bits ended up at the bottom of the lake.

These are the expensive type that I use for big jobs occasionally.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0748617

All they are, is a coupling that slips when a certain loading (you set it yourself) is reached. I usually have a few knocking about the shop and I would let you have a couple, but I think that they would be too big for your application.

You can make the same sort of slip coupling very easily by utilising your original toothed pulley on the shaft with a couple of spacers and light springs, and a few small fibre washers.

If you want a rough sketch, just ask.


The toothed belt system you are using is very efficient at transferring all that power, but it will not slip like say a small o-ring type belt, it just keeps on transmitting the power to the paddle, with dire consequences if it ever happens. You might get away with having very slack belts, and hope it jumps a tooth or two when something happens, but it is a bit hit and miss.

Just to prove the power output, have you tried to stop the motor output shaft from turning? Because of the gearbox, it would either be a very high torque loading before it stopped, or you just couldn't stop it.


John

One method I've used in the past is to flip the belts inside out - ie. the teeth are on the outside, and then they will slip on the pulleys if anything jambs in the wheel.....

As John rightly says, with a geared motor you have a massive amount of torque, and it will tear the plastic wheels apart if you don't design something to give before damage occurs.

Regards
Eddy