OpenErg Based Erg Rower Generator

This pandemic has given all of us an opportunity to try something new or explore an idea that we would have otherwise not had time to do. Thanks to being stuck at home, here’s what I decided to do with my newfound time. For many years I’ve had an interest in human powered electricity, and my first adventures pursuing those interests resulted in my pedal generator designs (exercise bike, bike trainer and spin bike versions). I thought it might be a fun challenge to build a rowing machine generator.

Building a rowing machine generator has some unique challenges, mostly due to the 2 cycle nature of the rowing machine. Cycle one where the chain is pulled and power is created, and cycle two is the return stroke where no power is generated. In this design I do a couple of things to solve the challenge of smoothing out this cyclic power:

1. Use a heavy flywheel
2. Incorporate some ultracapacitors into the charging circuit

To make the story short: these two things did the trick and I’m able to generate 100-120 watts steadily and get in a great full body workout.

e-bike motor: https://amzn.to/3w4j1Wr
ultra capacitors (3 or more): https://amzn.to/39hm5EB
charge controller: https://amzn.to/3flnmhR
diodes: https://amzn.to/3flnmhR
3 phase bridge rectifier(alternate option): https://amzn.to/3flnmhR
wago connectors: https://amzn.to/3flnmhR
wire: https://amzn.to/3flnmhR
banana connectors: https://amzn.to/3flnmhR
banana plugs: https://amzn.to/3flnmhR
heat shrink tubing: https://amzn.to/3flnmhR
project box: https://amzn.to/3flnmhR
meter: https://amzn.to/3flnmhR
sockets(2+): https://amzn.to/3flnmhR
laptop charger: https://amzn.to/3flnmhR
inverter: https://amzn.to/3flnmhR
USB charger: https://amzn.to/3flnmhR https://amzn.to/3flnmhR
automotive splitter: https://amzn.to/3flnmhR
jockey pulley: https://amzn.to/3flnmhR
wall mount pulley: https://amzn.to/3flnmhR
nite-ize carbiner(2): https://amzn.to/3flnmhR
chain(order 2): https://amzn.to/3flnmhR
exercise band set: https://amzn.to/3flnmhR
fixed casters: https://amzn.to/3flnmhR
freewheel: https://amzn.to/3flnmhR
hook: https://amzn.to/3flnmhR
velcro: https://amzn.to/3flnmhR
seat cushion: https://amzn.to/3flnmhR
oak dowel: https://amzn.to/3flnmhR
slotted flat bar: https://amzn.to/3flnmhR
duct tape: https://amzn.to/3flnmhR

Tools:

miter saw: https://amzn.to/31oQ6OF
router table: https://amzn.to/31oQ6OF
router: https://amzn.to/31oQ6OF
round router bit: https://amzn.to/31oQ6OF or https://amzn.to/31oQ6OF
drill press: https://amzn.to/31oQ6OF
forsner bit: https://amzn.to/31oQ6OF
cordless drill: https://amzn.to/31oQ6OF
flip drive: https://amzn.to/31oQ6OF
dremel multi-max: https://amzn.to/31oQ6OF
dremel knock off: https://amzn.to/31oQ6OF
soldering iron kit: https://amzn.to/31oQ6OF
helping hands: https://amzn.to/31oQ6OF
speed square: https://amzn.to/31oQ6OF
clamps: https://amzn.to/31oQ6OF

Let’s get into how I built it. A great big shout out goes to Jim Flood for coming up with and sharing his rowing machine plans that can be built with common lumber and wood tools and a few other parts. Check out his website at https://openergo.webs.com/
The first challenge I ran into, Jim's plans are in metric, and US lumber is in "imperial" dimensions. I did some quick conversion and was on my way.

I deviated from Jim's plans in a a number of ways.

1. Put grooves using a 1" round router bit in the top of the two main rails for the seat.

2. Added a cross brace to the front of the rower as I noticed when rowing the frame was twisting a bit.

3. I used a bicycle jockey pulley to route the chain.

4. I used an e-bike motor for resistance rather than a bicycle wheel with fins.

Once I had the frame built, I measured the distance between the two main rails to determine the spacing needed for the fixed caster wheels. I translated those measurements to a couple of 3/4" pine boards I put together as the seat. Find the center line of the boards, then split the distance to determine where to center the casters. Measure the distance between the caster mounting holes and split the distance again, mark, drill and mount. I was worried I might tip front to back or side to side with this seat, but in use I have not found this to be a problem. Adding a nice cushy pad to the seat was a much appreciated addition.

Rather than use Jim's fixed mounted foot rests, I decided to use the other 16" left of the 1.25" oak handle to make some movable foot rests that rotate with each rowing stroke. The approach works better than I expected. I drilled a 1.25" hole through the frame with a Forsner bit, filed a bit to make the hole a little bigger, then put the dowel through the frame. I then used the same Forsner bit to drill out a couple 2x4 base plates with a hole right at the edge of the boards and mounted those to the dowel on each side. On top of those I put a 3/4" pine foot rest boards, along with a 2x4 heal stop. Adding a couple Velcro straps to each side with some screws and washers and the foot pedals are complete.

I used 2 full lengths of bicycle chain for this rower, and that seems to be just enough. I routed the chain using a bicycle jockey pulley from the e-bike motor to the underside of the rower. Connecting the end of the chain to an exercise band with a Nite-ize carabiner. The exercise band then routes through a wall mounted pulley and back to the front of the rower where I used a hook to secure the end of the exercise band.

The handle for the rower was made with 1.25" dowel, 20" long with an eye bolt through the center, also connected with a second Nite-ize carabiner to the bicycle chain. I put some duct tape on a couple wood screws and use those as a rest/stop for the handle.

To mount the e-bike motor, 2 flat iron slotted steel mounts were made. I measured the width of the flat sides of the e-bike drive shaft and used my Dremel Multi-Max, Dremel knock off, and metal file to create the proper size slot on each mount. I marked center line for these mounts. Drill and mount with a couple bolts and nuts on each. I used a Shimano freewheel instead of the 7 speed cassette that came on the e-bike motor. I went with a single speed freewheel to keep the chain line straight and limit chain derailment. I did go through a couple freewheels, though. The first one was really noisy, so I picked up a Shimano one, which is much quieter.

I used 2 steel flywheels together for my flywheel. They each weigh 28 pounds, total of 56 pounds. I had a local water jet cutting company make these. The dimensions I gave were:

1. Just inside of the e-bike side plate mounting bolts
2. A little less than 18" outside diameter

I had originally had these cut for a bicycle based pedal generator, but repurposing for this project, and they worked out very well!

Some alternatives:

1. You could make a wooden flywheel, check this out for how to make a circle:

With the extra cross brace, it looks like a 32" diameter flywheel will fit, but you could extend the length of the motor mount braces to go bigger on the flywheel if desired.

2. You could get a fully build e-bike wheel, and fill the tube with water using a garden hose and an adapter

The circuit is basically this:

E-bike motor->3 phase bridge rectifier->meter->ultracapacitors->charge controller

The charge controller is a 24v->12v step down controller that connects to a couple automotive sockets which can be used to charge phones, laptops or power a TV or other devices with a DC to AC inverter.

From my experience with building pedal generators, I found that the off the shelf 3 phase bridge rectifiers can get pretty hot and call for ventilation and/or a cooling fan. One of the guys that built my plans suggested I use Schottky diodes instead, as they are more efficient. I've made a couple bridge rectifiers with these diodes, and the do run much cooler, eliminating the need for added ventilation and cooling. I use some 4mm banana connectors and heat shrink tubing to make the rectifier.

Next, to add a buffer during the "return stroke" on the rower to keep the electricity flowing, I added three small ultracapacitors to the circuit. These make the rower generator possible, but are also the limiting factor to how many watts I can currently produce with this rower. Once I can afford it, I will be picking up some larger ultracapacitors to really see what the upper limit is of this design (and me!).

Next in line is the charge controller, which is a component typically used battery powered golf carts to run 12 volt devices. The one I'm using is a 24v to 12v step down controller. Input voltage range is 18-36 volts, right in line with what I'm seeing from the e-bike motor while rowing. If I really pull on the rower, it will go higher than that so I use the meter as my guide to stay under the high end. This Drok meter has a setting that will blink the screen when the voltage goes over (or under) a set limit. Besides current volts, it also displays current amps, total watt hours and current watts.

This was a fun project for me and now provides me a great full body workout alternative to my pedal generator. I am able to get a good workout in, while charging my phone, laptop, iPad and other devices - I can even power a TV to watch while I work out! Another plus of this - if the power goes out, I have an option to charge my phone or other devices until the grid comes back online. Those that live off grid, this could be used to supplement your off grid battery bank.

Thanks for checking out my project - I welcome any questions as you plan to build your own!