Rooting around in the fascinating stuff at the bottom of a draw labelled 'Engineering - Junk Miscellaneous'. Delving amongst the delightful...
An Engineer in Wonderland – Wonderful generators in Freeplay radios
The generators in Freeplay radios have moved on a great deal from the original Trevor Bayliss design, and look quite superb. I noticed this when squinting through the blue tinted plastic of a Freeplay EyeMax (pictured). [Recently featured in a Gadget Master competition, btw - Ed.] Bayliss’ original leap of imagination was that a modern wind-up radio was possible, and he followed this up by developing one – coming up with a design that stored power in a spring. The spring unwound through a set of gears that spun a small DC motor operating as a generator. Effectively a Mark II, the next version was a better shape to grip when winding, and added a rather neat power-saving touch – a transistor shorted out the motor when its reservoir capacitor was full – which almost stopped the motor and effectively froze the spring until power was next needed.
I have had two of these. Reception is superb. With the exception of the Summit, all Freeplay radios I have tried pull out a clear sound in reception areas that leave other radios crackling – and the Summit is no worse than a ‘normal’ radio. The great advantage of the spring system is that you can get energy into the system very fast. Provided you count handle revolutions so you don’t smack the winder into its end-stop, less than 10s of winding gives almost an hour’s play. Really, the only issue with the power train is brush drag in the generator. This is multiplied many times by the gears between spring and armature. A nice brushless three-phase motor would have been a better choice – but very expensive, and I imagine Baylis had enough on his plate just getting the spring part right without trying to design a generator from scratch. Moving on, the springs have disappeared in new designs – when spring-types have seen a lot of use, something inside can let go and all that pent-up steel unwinds in a second or so. This happened to me and the radio leaped out of my hands and jumped around on the floor. Thankfully, as it was surely designed to do, the spring stayed safely in its internal strong-box, but the mechanism never worked properly again. Instead, it is the generator that is hand cranked in modern Freeplay radios, and this charges a battery. The latest ones have a proper little AC alternator with six or so axial coils and magnets rotating around the outside. The alternator in my Summit is single phase, but I was delighted to see than the EyeMax has neat little three-phase generator – just the sort of thing an engineer would come up with if given a pull-out-all-the-stops design brief. While the handle-alternator-battery approach saves the weight and expense of that magnificent spring, it does mean the 1:360 wind-to-play ratio is a thing of the past. This is probably due to the low maximum output current of the generator, but what ever it is, charging for an hour’s play is a slow process. That said, as I understand it, the generator in the firm’s massive and wonderful Lifeline radio is a 30W three-phase monster which could probably stuff an hour’s play into a couple of AA cells in a few seconds. However, I will probably never know how fast this generator can be charged by hand as the Freeplay’s worthy aid and development wing will not sell Lifeline to individuals because it is intended to be distributed only by aid organisations. At one time there were buy-two-get-one deals that meant you automatically gave a Lifeline to a worthy cause when you bought one for yourself, but these seem a thing of the past. Anyway, given an infinite amount of spare time, I would convert my defunct clockwork Freeplay to handle-alternator-battery using an ancient Sturmey Archer Dynohub I have lying around. This puts out 300mA with little effort, and with the existing solar cell would match well to two or three NiMH cells. Next time you are in a shop selling Freeplay EyeMax radios, peer through the case and feast your eyes on that almost jewel-like three-phase generator. ‘Alice’Tags: freeplay eyemax, master competition, phase motor, spring system, transistor