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Post by Deleted on Oct 8, 2012 10:57:33 GMT
I'm having some trouble getting a cycle speedometer to work properly on my Modelworks Britannia. The first one I tried was a wireless type with the magnet positioned on a middle tender wheel. This worked for a time but was sensitive to the positioning of the receiver - it wouldn't transmit up through the body of the tender, but worked with the receiver low on the back of the tender. However, the transmitter battery only lasts a couple of months and it's fiddly to get at it to replace it. This week I bought a wired speedometer from ebay: www.ebay.co.uk/itm/ws/eBayISAPI.dll?ViewItem&item=270919953713 . This works OK - the wheel circumference can be set right down to 10cm, 27cm in the case of my tender, but the speed reading seems to max out at exactly 7.4mph on the back straight each lap, even though I continued accelerating beyond this point. It looks as though the electronics may be limiting the frequency of the pulses from the magnet - this number of rpm would be equivalent to an enormous speed for a bicycle. I can't really complain because the product obviously isn't designed for such small wheels, but I wondered if anyone had noticed this problem or can point me to a cycle computer that does work on a wheel of this size? Regards, John
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springbok
Statesman
Building a Thompson Class B1 in 5"g Plus restoring a 3" Fowler steam road Engine "The Wanderer".
Posts: 570
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Post by springbok on Oct 9, 2012 5:10:17 GMT
Why would you want a speedo on your loco!!!
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Post by flyingfox on Oct 9, 2012 6:59:31 GMT
Greetings John, to confirm your theory re max number of pulses that can be counted, why not alter, say halve the "wheel Diameter factor", and see if that reduces the top speed shown. Alternatively, 7.4 mph is your max speed. regards Brian B
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Post by alanstepney on Oct 9, 2012 7:04:17 GMT
Why would you want a speedo on your loco!!! To see how fast you are going?
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Post by peterseager on Oct 9, 2012 7:43:10 GMT
Certainly to see how fast you are going and its also interesting to log each run and record the total mileage.
Personally I believe they should be mandatory for passenger hauling. Some people don't seem to realize just how fast they are going.
My computer is fitted on the driving trolley. It is a Sigma BC800 and certainly works up to 10mph but is, I believe, no longer available.
Peter
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Post by englishlivesteam on Oct 9, 2012 7:52:57 GMT
I personally use a Garmin Etrex GPS. I had it for other uses but works well as a locomotive speedometer. Two AA batteries last 2 full days and you get other information like time moving, distance travelled, max speed, average speed, etc.
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Post by Deleted on Oct 9, 2012 8:58:30 GMT
Thanks for the comments. Our NLSME track has a mandatory speed limit of 10mph on the back straight and an advisory 6-7 mph on the rest of the track, and it seems sensible to be able to check the speed against these limits. It's also interesting to have a log of distance driven. Further research reveals that I have bought a SunDing model SD-536A - see www.sunding.com/en/product.asp?bigclassname=Bicycle%20Computer - and the manufacturer's spec says that it works only down to a wheel circumference of 60cm, despite the instructions on the box saying that it can be set to a minimum of 10cm. This probably explains the problem. I've now ordered the later model SD-536B, which has no lower limit. It only cost £2.18 on ebay, including postage from mainland China, so worth a try! I'll report back in due course, but may not get another chance to run this season after it arrives. I think it would be useful to have a recommendation on this board of a cheap speedometer that definitely works on wheels of this sort of size. Regards, John
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Post by peterseager on Oct 9, 2012 15:54:16 GMT
I use the same GPS on my bike along with a cycle computer. Comparing the two, I find the GPS under records because it cuts the corners ie takes a plot just before a corner and the next just after and calculates the straight line between these points. Not a big difference on the roads but could be large on a circular track. I'll have to try it sometime.
If you buy the right cycle computer all the parameters mentioned in the quote - and more - are available.
Peter
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Post by dickdastardly40 on Oct 9, 2012 16:19:39 GMT
Do you have a smart phone?
I have one starting with an 'i', and have 2 apps both of which work by GPS, both free one, called bikebrain, which gives you speed, average speed trip distance and total distance and even gives you a map of where you've been plus loads of other features (I do use it extensively for cycling) As it doesn't pick up on roads it doesn't cut corners as mentioned by Peter (I don't believe anyway) and another called dashboard which is a car speedo and good for checking the accuracy of your car so you know you're doing 30 or less.
I would imagine both could be used for the loco purposes you mention.
How are the club checking your speed? Gatso cameras or just a club member noticing that he thought a particular loco was going a bit quick.
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Post by Deleted on Oct 9, 2012 16:49:21 GMT
I do have a smartphone with GPS, but I'd only end up dropping it in the long grass if I tried to use it while driving.
The powers-that-be know the distance between the signals, so can apparently detect speeding without even leaving the signal hut!
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Post by peterseager on Oct 9, 2012 16:53:13 GMT
My GPS does not pick up on roads either it simply plots and records the track of the GPS. The track is then downloaded to the PC using an application called Anquet Maps and displayed on a digital OS map. You can zoom in on the track and clearly see the corner cutting. Whether a more expensive GPS with built in maps would follow the road and be more accurate I don't know. I suspect not, turning into your drive would give it a problem.
Peter
Edit: I should qualify the accuracy of the Cycle Computer. If I download a track to Anquet it calculates a total mileage for the route, including inclines, and this closely tallies with the mileage given by the GPS. Anquet also gives you the option to plot your own route (and, if you wish, loading it into the GPS). In this case you are in charge and can plot carefully and follow the road exactly. In this case, when you cycle the route, the Cycle computer will be very close to the mileage calculated by Anquet at the planning stage.
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Post by Deleted on Oct 9, 2012 18:29:02 GMT
Thanks for the comments. Our NLSME track has a mandatory speed limit of 10mph on the back straight and an advisory 6-7 mph on the rest of the track, and it seems sensible to be able to check the speed against these limits. It's also interesting to have a log of distance driven. Regards, John Haha.. this made me laugh John, I can't remember the members names, the two guy's who own the nice B1, anyway they have a speedo fixed to their tender and have recorded a top speed of 12.5mph on our club track. I do recall some months back a young mother with her kids saying 'he was going very fast'... still no one fell off.... BTW your loco looked great on Sunday, it was great talking to you and seeing the Brit again. kind regards Pete
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Post by peterseager on Oct 9, 2012 19:37:11 GMT
I have seen an accident on a ground level track where a passenger leaned sideways on a reasonably fast train and derailed the train. Fortunately there were no injuries. If the accident had happened a few feet further down the track the derailed cars would have slewed into a fence post and the results might have been different. We all like to open a loco up given the opportunity but not when passengers are being hauled.
Peter
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Post by digger on Oct 9, 2012 22:53:08 GMT
12.5 mph pah! I have done 15mph with my GWR Manor, on the WDMES Daresbury track, this reading being obtained pulling the club dynamometer car, long downhill section after the pond, heavy braking applied to negotiate bottom curve leading to the station. I would not attempt that sort of speed now, older and wiser, 7 to 8mph quite fast enough now.
Digger
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Post by dickdastardly40 on Oct 10, 2012 17:34:38 GMT
What sort of scale speed would say 12 MPH equate to in the various guages please; Is there a simple calculation for working them out?
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Post by Deleted on Oct 10, 2012 18:04:47 GMT
IIRC scale speed is calculated by the square root of the scale of the model concerned multiplied by the actual speed measured. Example a 5" gauge steam loco would have a true scale of 11.33, the square root of this is 3.36. Therefore if you multiply 3.36x12 you get 40.32 So 12 mph in 5" gauge would be 40.32 mph. We used to do this a lot back in my model boating days to try and get our warships to look better while moving on the water. Hope that's correct... Pete
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Post by fostergp6nhp on Oct 10, 2012 18:06:28 GMT
For std gauge prototypes. 3.5" = 192mph 5" = 135mph 7.25" = 96mph Times the fraction that the model gauge is of full size by the actual model speed. Example 7.25" = 1/8 of full size so. 12mph x 0.125(1/8)scale = 96mph which the full size would do at the same wheel rotations per minute.
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pault
Elder Statesman
Posts: 1,497
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Post by pault on Oct 10, 2012 18:56:32 GMT
Hi All I would agree with Digger, even in 7 1/4 I would say 6 to 8 mph is fast enough and comfortable for all, young and old, small and large. As has been said it’s fun to open them up but when passenger hauling it’s not a white knuckle ride. Regards Paul
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Post by Deleted on Oct 10, 2012 19:16:37 GMT
For std gauge prototypes. 3.5" = 192mph 5" = 135mph 7.25" = 96mph Times the fraction that the model gauge is of full size by the actual model speed. Example 7.25" = 1/8 of full size so. 12mph x 0.125(1/8)scale = 96mph which the full size would do at the same wheel rotations per minute. Hmmm.. I beg to differ, I think my calculation is closer to the mark, there is another more involved calculation where you measure the distant covered over the time taken but in general by taking the square root of the scale which is then multiplied by the actual speed achieved you are very close to the true scale speed of the model. Regards Pete
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Post by RGR 60130 on Oct 10, 2012 20:01:45 GMT
Pete,
From towing tank experiments using scale ship models and subsequent calculations when I was studying Naval Architecture, I believe you are quite correct. I can't remember the calculation for sure, but using the square root rings a bell. I certainly remember it was not as simple as a linear ratio.
Reg
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