DIY Leslie Horns - still not "up to speed"

[theseacowexists]

Maybe some of you remember how a few months back, I added horns to my Leslie 130. The motors came from an internal Leslie unit, so it had the large pulley on it. For a tensioner, I used a screen door roller on a custom-made adjustable bracket. The motor was also installed like the lower motors, so that the tension can be adjusted by moving the motor further from or closer to the horn. The belt is a new horn belt from Tonewheel General. It took some tedious adjustments to get it working regularly, but it did.

...until I realized that the horns were not spinning nearly fast enough on tremolo. Through recording it, I determined that they were only going about 350RPM. 400RPM is the sound I want, and that you'd probably want too. It's noticeable enough to bother me while playing, although I'm probably the only one in the band who's noticing! So I replaced the large pulley with a three-tier one, and adjusted the motors to accommodate this. I can now get a 400RPM tremolo with the perfect ramp up/down times. The trade off is that the chorale is definitely way too slow, somewhere around 30RPM. Worse, the chorale seems to eventually lose its momentum and stop spinning altogether. I found the same thing would happen before switching pulleys. Tighter belt = good tremolo/bad chorale, looser belt = bad tremolo/good chorale.

Short of completely rebuilding the shelf so that the measurements are identical to a 122/147 horn shelf, what can be done with my current setup to achieve chorale/tremolo nirvana? Do I need to make adjustments for where the slow motor engages the O-ring? Or just trial and error with adjusting the belt tension?

Here's a video of it in action: https://youtu.be/KrbTjtGbfbM

[Tim_at_Jonas]

It you are using a standard Leslie motor stack:

De-glaze the o-ring (run it while holding 150 grit sandpaper against it)

Clean the o-ring and the slow motor armature (I use CRC QD electronic cleaner)

Adjust the tilt of the slow motor so its armature contacts the o-ring correctly.

[theseacowexists]

I've got a can of DeOxit, would that work? Or just some alcohol?

[Wes]

FWIW, I've never clocked a "real" Leslie as fast as 400 RPM on the middle pulley. You might be trying to achieve something that is not really achievable with stock motors. The maximum motor RPM will be just shy of synchronous speed with this motor design, you can never get it faster than synchronous.

[Wes]

Edit: looks like I'm wrong, I found my notes - here are some real horn speed measurements:

147 #1 (good condition): 430/48
147 #2 (no maintenance): 425/48
51C (good condition): 408

Normally I run the middle pulley, but I'm wondering now if the 51C was run on the big one for that test.

[theseacowexists]

Seems like I finally got it right. The slow motor armature was definitely too tight to the o-ring. It probably didn't hurt that I de-glazed and cleaned the the o-ring as well. Thanks for the tip! Another adjustment I made was raising the entire motor stack about 1/4" higher so that the large tier is in line with the tensioner and the horn (no angle on the belt).

While I was making these adjustments I found that the slow motor on the rotor was not disengaging right away, leaving a brief but noticeable "stop" going from chorale to tremolo. This slow motor was set too tight too, but in this case it did not affect either of the rotor speeds.

[Goff]

That sure is an unorthodox idler pulley. The belt is wanting to be stretched, not squeezed and the right tension of the stock idler pulley spring does not hamper the rotor's rotation and inertia, but works with it, not against it.

But yeah getting the balance of the slow motor's movements is key. The slow motor has adjustments for the drop position of the spindle. The adjustment of the tire on the fast motor figures into where the center of the rubber is so factoring that in as how the tire is set onto the fast motor's shaft has bearing on the slow motor's reaction.

Soaking the rubber tire in some dish soapy water brings rubber back to life (if it is "rubber") being an organic material coming from rubber trees. Water helps. The soap helps remove dust and oil.

If one uses non-Leslie parts, you will not get the same reactions. The more one veers from the tried and true, you get diminishing returns.

Not all rotary cabinets are created equal.

[tiredoldgeezer]

That sure is an unorthodox idler pulley. The belt is wanting to be stretched, not squeezed and the right tension of the stock idler pulley spring does not hamper the rotor's rotation and inertia, but works with it, not against it.

What I think he's saying, and I agree, is that your tensioner is on the wrong leg of the belt.

Look at a bicycle derailleur. The upper part of the chain is the 'power' side. It's straight from front to back. The lower loop of the chain is the 'return' side. This is where the tensioner resides. Do likewise with your belt tensioning. Even a car belt, V or serpentine, follows these same principles.

Now, at these forces, it'll hardy be noticed unless, as now, something else is amiss. So yes, once all the alignments and functionality is restored with your motors, then you might wanna check into putting the tensioner on the 'return' leg of the belt.

Then you'll have something better than stock.