Hi again dear MOD users
Once again I am here reporting about the long awaited Expression Pedal, our longest-living soap opera.
For those not willing to read a long text here’s the short version:
Albeit slow, the process is moving forward.
Release candidate metallurgy samples are being shipped next Friday.
Plastic gears have been narrowed down to the optimum teeth size and tooling is happening. Samples are to be shipped still in April.
Firmware is already functional but still in beta.
And now the long version
Catching up from my previous update, I am glad to tell that I managed to move important steps.
The gear pair is selected. I tried multiple pairs, from modules ranging from 0.7mm to 2mm and finally settled with a 1.5mm module. From my tests this tooth size yielded the best compromise between:
- Possible variations for in-between gears distance due to tolerance adjustments;
- Minimum teeth count for the pinion
- Angular displacement multiplication factor.
The expression pedal is, mechanically speaking, an angular displacement amplifier. Foot movements bigger than 25 degrees are highly un-ergonomic. Since potentiometers have excursions of 270 or more degrees, it is desirable to use as much of this excursion as possible. With the selected pair we’re getting about 160 degrees of potentiometer rotation, which I find to be very good. The old expression from 2014 had a 45 degrees rotation on the pot and one could feel the noise from the pot influencing the action.
Here are two images to help you visualise:
On the top, the selected gear pair. On the bottom, my initial attempt with the very small module.
When using gears, the smaller the teeth, the smoother the rotation, hence my initial choice of the small module. But we’re dealing with a multi body system and the points of error generation are many:
1 - The flap that holds the pot is bent and can bring dimensional variations
2 - The U shaped articulation can be slightly misplaced
3 - The bolt that binds the pedal to the articulation has a minimum clearance that is not zero
4 - The attachment of the gear to the pedal can (and very probably will) bring a bit of misplacement to the big gear.
From the four items mentioned above, item 4 is the most problematic and I tried multiple ways to minimise the errors.
After trying side bolts, top bolts and even press-fitting bosses, I settled for male treaded studs welded directly to the aluminum pedal.
One very cool aspect of this arrangement is that it enables different gear pairs to fit the system in a interchangeable manner. That said, I will publish 3D files for matching gear pairs and those willing to change the mechanical responsiveness of their pedals will be able to easily 3D print their custom parts and attach themselves. Who says hacking is just for coding and electronics?
Details apart, the Expression is coming out beautifully. The final footprint of the unit is really appealing and I believe we managed to reach a great size X ergonomic relation. I do not know about you guys, but mammoths like the Ernie Ball and the Fender, albeit super comfortable, are a pain to carry. It feels like having one of those big old style american cars. On the other hand, all of the "mini" options - DOD, MXR and Zoom - feel to small for my sized 43 feet…
Last but not least, the firmware.
@jesse is doing a great job in providing a useful layout for the display info and also the arrangement of possible controls. The picture on the right side shows a rough sketch of what it will look like.
To close this long report, I’d like to reassure to you all that this is coming to life. I know the wait has been long and I personally feel even a bit ashamed of it. But that is life and unfortunately we cannot control all the aspects of it.
The MOD Expression is a product on its own and I now believe a company could be created only to design and sell it.
We keep pushing to offer you all the best we can. That’s the way we have acted till now and that is the way we will always do. I cannot allow myself to settle for less.
In the next weeks I’ll try to give you guys a proper - and realistic - shipping date.
Let’s all step onto the future!