Hacksburg Wiki

The wiki for Blacksburg's Workshop

User Tools

Site Tools


2015 Summer Booth Project

The Idea

The idea (started by Mike Newsome and ran with by others) is to come up with a light/sound show or device, built by Hacksburg, to show off at gatherings like Solstice Fest, Steppin' Out, etc.

Mike came up with the idea of some kind of light and sound show, something that people could build and then see what came of it. This eventually morphed into an idea to do a light/sound-based project for Solstice Fest. We decided on some kind of large, interactive visual and/or auditory project.

What's happened so far

We did some brainstorming at the March 10th meeting about what to do. The following week, Ben knocked together a prototype of a capacitive sensor using a water-filled ping-pong ball, an LED, an Arduino, and various electronic components; his research is ongoing.

Bike Generator

One idea that was talked about was a bicycle powered generator. Both as supplemental power source to (partially) recharge batterie(s) and fitting in with the “Sustainability” theme of Summer Soltice fest. We have a 24V DC permenant magnet motor that could be run in reverse as a generator. Some research suggests that it needs to be turned at a faster speed than direct drive from a bicycle chain to a sprocket on the motor shaft could drive it. Three approaches I have found on the internet is to add a second level of gearing (shown link to be added if I can find it again). Another approach is to the tire to a roller on a bicycle trainer then use this roller via an attached pulley or cog to drive the motor .. Yet another approach is to use a Vbelt on the wheel (minus tire) to drive the generator, this requires a Vbelt pulley for the shaft of the motor, approximately 2“ diameter with a 5/16” bore ( the shaft on the motor should be 8mm (need to verify) and 8mm is slightly larger than 5/16“ so it would need to be drilled out to 8mm) Such a pulley is here External Link possibly we could find a vbelt pulley locally or salvage one that could be used.Lots of information on bicycle generators

Mike donated a bike towards the project and Carl loaned his bike trainer (which allows us to raise the rear wheel several inches above the ground and pedal). The trainer also has a friction roller that the rear tire can rest upon.

At the Hacksburg birthday party we did some voltage vs speed tests on the DC motor we are planning on using as a generator. Yeilding these results for voltage at different RPMs and electrical loads

* 2650 RPM no load 18.4 Volts

* 1900 RPM 20 Ohm load 17.57 V

* 1620 RPM no load 11.8 V

* 1620 RPM 20 Ohm Load 11.26 V

We need a voltage > 12.6 and < 15 V for battery charging the above data suggest we need greater than 1620 RPM minimum. Doing a linear interpolation yields about a 1760 RPM target for approx. 14.5 V output. (Each RPM change results in approx 23mV of change in output). We have some potential to vary the RPM both by changing the pedal rate and adjusting the gearing on the bicycle. Humans pedals somewhere between an easy 50 RPMs of the pedal to 100+ RPMs (someone in good shape sprinting flat out). The bike is a two chain ring and a think 6-7 gears on the rear cogset. This setup should give approximately a 3-5:1 ratio between the turns of the rear wheel in the slowest gear to the highest gear. (we need to count the teeth on the gears to figure out the exact gearing.) The average difference between gear ratios should be about 13%. In any case it looks like we need more gearing. As 1760 RPM / 50 is 35.2 and 1760 RPM /100 is 17.6. Because of the variation of the pedaling rate of humans we should aim for somewhere near the middle of the bike's gear range and allow for shifting gears to adjust RPMs. Once we know the exact gearing we can calculate the amount of gearing we are going to need.

summer_2015_booth.txt · Last modified: 2015/04/02 03:56 by evansl