OFMG Guitar

The OFMG - our new custom guitar project

We made our first custom guitar about a dozen years ago, but at the time things like 3D printing and low-cost, powerful multi-core microprocessors were not available and to make the guitar into a real product was not feasible. Things have changed a lot in the years since and we can now take advantage of the advances in technology to make something I couldn’t have even dreamed of all those years ago!

The OFMG (Open Frame Modular Guitar) is our take on a what the ideal Rock Band/Guitar Hero/Clone Hero guitar should be. The primary goals are:

• Make it reliable - using long-life components and making it easy to replace parts (especially switches). Strum switches can be replaced without any soldering.

• Make it fun - incorporate active LED lighting on every button to provide feedback and excitement.

• Make it customizable and expandable - with open source firmware anyone can modify features. The included expansion port allows for connecting all kinds of peripherals for future capabilities we haven’t even thought of yet. The guitar body is separate from the “core” of the guitar (the neck and strummer) so almost any style of body can be accommodated. Custom bodies can be 3D-printed, or made from wood.

Roadmap

Note that we are not putting exact dates on the milestones to allow plenty of time for testing and feedback before we move to the next step. We are currently finishing up the 1st step (mechanical tests).

1. Mechanical Test Units - not electrically functional, using 3D-printed PCBs to check mechanical fit and operation of parts. We use these to both test the mechanical fit of the parts, and to test the “feel” of playing. This is perhaps the most time-consuming step, but is critical since most of the major design decisions will be made at this step.

2. Engineering Prototypes - incorporates functional electronics, but may use some “breadboard” or off-the-shelf circuitry. Used for software/firmware development, and a few are sent to key testers for feedback.

3. Pre-production Prototypes - uses 1st run of production PCBs, but firmware/software may not be feature complete. These will be sent to beta testers for play testing and feedback.

4. Initial Production Run - uses revised PCBs (if necessary) and incorporates all the changes from previous versions. These will be sent to early adopters.

Latest Updates

Latest updates at top

[Dec 2, 2024] The design of the frets and strummer are now “frozen” and I’m quite happy with how they are working. We’re still sending test units out to get feedback and so may tweak the designs a bit, but the mechanical layout of the PCBs is set, which means we can go ahead and finish the PCB layouts and get some prototypes made. This week I’m working out some of the details for how the body attaches to the “core” of the guitar. We want to keep the design of the body as simple as possible and make it easy to attach different bodies. We already have a few solid-wood bodies left over from a previous project that we are using for testing. In the final product a solid-wood body would probably be too heavy for most people, so the default option will probably be a laser-cut plywood body “sandwich” with either plastic or wood spacers between the top and bottom panels.

[Nov 16, 2024] We’re continuing to make a lot of progress and have even sent some mechanical prototypes to a few key testers to get feedback. A big change was recently made to the strummer and the results have been fantastic. We did away with the old axle arrangement and are now using sealed steel cartridge ball bearings instead. There is now no play in strum bar, but it also moves more freely than ever. It’s been designed such that even if things are out of alignment a bit, the strummer still moves freely without any slop or binding!

Here’s a rough CAD rendering of the current design — the yellow button is for activating “overdrive”; the small blue rectangle is the OLED display (for accessing setup menus and diagnostics); and the white rectangles on the fret buttons are “backlit” by the LEDs underneath. There are also LEDs under the strummer area which light up the “pick guard” area around the strummer. You will be able to control the brightness and color scheme of all the LEDs. The “core” of the guitar sits in the body, but there are no electronics in the body itself and it’s purely cosmetic, so the core can easily be used in other body styles.

I still can’t say for sure when the guitar will be done and don’t want to put any arbitrary deadlines on this project since we don’t want to cut any corners just to save time and end up compromising the design, but we are working on it every day now and I think we’ll have the mechanical design “frozen” very soon, which means we can get PCBs made and start building some fully functional prototypes.

[Nov 7, 2024] Lot of progress in the last few weeks, so many things are happening it’s hard to keep up, much less keep this page updated! We’re printing lots of parts and building prototypes, testing and revising the design almost daily, so anything I’d post here would be out-of-date quickly. Nonetheless things are starting to coalesce and the design is coming together and we are mostly working on the nitty-gritty details now. I’ll post some pictures of the prototypes and share more information in the next few days.

[Oct 12, 2024] We’re continuing to print mechanical prototypes and evaluate the feel of the control layout and the fit of parts. The placement of parts on the “core” modules (the strummer and control boards) is almost finalized. The neck design is finalized. In the next couple weeks we’ll continue to refine the mechanical design while also finishing the PCB layouts. There’s still a lot of work to do but things are starting to come together!

[Oct 2, 2024] The neck design and PCB layouts are pretty much done and now we are iterating the strummer and control panel designs and finalizing the electrical parts selection. Picking parts is non-trivial these days, as not only do you have to check all the electrical and mechanical specifications, but also check the supply chain history to make sure you can actually get the parts you need from a reliable supplier.

One thing that will be quite different on this guitar compared to the standard Rock Band or Guitar Hero guitar is the OLED display and menu interface. We’ll still have the standard D-pad and start/select buttons, but there will also be an additional knob for navigating the menus on the OLED. The menus are where you will set options like LED light color schemes, fret button behavior, over-strum rejection settings etc…

This week I hope to have the strummer and control panel design finished and print out a few mechanical prototypes. We also have the parts we need to start building an electrical breadboard to double-check our electrical designs before we commit to getting the PCBs made.

[Sept 19, 2024] For the last couple weeks I’ve been concentrating on getting the neck design finalized. We’ve printed out a few prototypes, did some testing, made revisions, and now have a design that we can move forward with.

Below are some pictures of the neck assembly — the design is modular and the guitar can be built with either one or two sets of fret buttons (using just one set of frets makes the guitar more compact for those with limited space). The firmware can be programmed to operate either set of frets as “solo” buttons. (In some games the solo buttons allow you to play notes without strumming).

The neck structure is built on a set of aluminum rods with rigid PCBs attached via brackets. Covers are then installed over the assembly, and it’s then bolted on to the main core of the guitar.

Each button has a programmable LED underneath it which shines through a specially printed keycap. The switches are low-profile mechanical keyboard switches.