Michael Edge's workbench

[cctransuk]

1 hour ago, SR71 said:

 

Hi John,

 

I wrote the attached excel to work just that out. From experience I found I wanted more than the scale top speed so that you aren't flat out if you get a chance to run on a big layout and also because somehow the speed visually didn't scale and looks too slow.

 

It should be self explanatory, fill in the boxes that don't have formulae in and it spits out a speed. I've had to do several transfers on my phone etc. to upload this so if it doesn't work let me know and I'll try on the PC.

 

Motor wheel speed.xlsx 5.01 kB · 10 downloads

 

Thanks - I'm not exactly sure what I should see - no formulae visible.

 

I see an example for a 63000 rpm. motor and a ratio 42:1, giving a top speed just over 100mph.

 

CJI.

 

 

[BMS]

Simples - Just type on top of the existing figure(s) with your requirements and the speed drops out.

[Camperdown]

2 hours ago, SR71 said:

 

Hi John,

 

I wrote the attached excel to work just that out. From experience I found I wanted more than the scale top speed so that you aren't flat out if you get a chance to run on a big layout and also because somehow the speed visually didn't scale and looks too slow.

 

It should be self explanatory, fill in the boxes that don't have formulae in and it spits out a speed. I've had to do several transfers on my phone etc. to upload this so if it doesn't work let me know and I'll try on the PC.

 

Motor wheel speed.xlsx 5.01 kB · 22 downloads

Not too sure what you're done, but it doesn't seem right.

 

The example shown in the spreadseet is for a wheel diameter of 22mm, i.e. 5.5 ft.

 

With a 16000 rpm motor, and gear ratio of 42:1, the wheel rotates at 16000/42 or 381 rpm, i.e. 6.35 rev/s (381/60).

 

This represents a speed of 5.5 * pi * 6.35 = 110 ft/s.  60 mph is equal to 88 ft/s, so this speed is 110 *60 / 88 or 75 mph.

 

Your spreadsheet gives an answer of 120 mph.  Suggest you check your working.

 

Incidentally, I usually aim for about half to two thirds of quoted no load speed for maximum model speed.

[Camperdown]

 

2 hours ago, Michael Edge said:

Not sure what went wrong there Dave, the one I've just fitted is as unstoppable as the ones with all spur gears - at least in this small 4mm loco. When I first tried to knock the final shaft out I managed to lock it all up solid, which is why I carried on to dismantle the gearbox so maybe you managed to jam some of the spur gears?

Going back to crown wheels, a vast quantity of them turned up from Aliexpress last week - I thought I had ordered 10 and got ten packs of ten.... They still weren't very expensive though.

 

So which version of the N20 gear motor do you prefer, all spur gear with bevel or crown/pinion final drive, or worm/spur with output regauged to 1/8in ?

[Ruston]

2 hours ago, Michael Edge said:

Not sure what went wrong there Dave, the one I've just fitted is as unstoppable as the ones with all spur gears - at least in this small 4mm loco. When I first tried to knock the final shaft out I managed to lock it all up solid, which is why I carried on to dismantle the gearbox so maybe you managed to jam some of the spur gears?

I don't think anything was jammed. It was in the scratchbuilt Hudswell Clarke frames that I built and ran just fine light engine, or with a light trains, but was gutless with a load. Where anything else meets a load that it can't move it breaks traction and spins its wheels, but this thing didn't have enough go in it to turn the motor. The anti scuff paste seemed to bring down the amount of friction on the worm and it became a good enough runner, and could pull a decent amount but it put me off using those units again. It was no Hercules for sure.

 

This was it newly installed in the frames, with temporary rods.

 

Completed loco. It was able to spin its wheels after the anti scuff paste was applied but the motor was straining under the load.

 

[SR71]

Hi @cctransuk @Camperdown

 

Not sure what happened to the file there but I've just changed it on the original post and added some instructions to the file on my PC. The speed it was giving was indeed incorrect, one of the variables had gone a bit odd when I was swapping formats I think. Hopefully it works now.

 

File attached here also for anyone that wants to test it out.

 

SR71

Motor wheel speed 2.xls

[Michael Edge]

39 minutes ago, Ruston said:

I don't think anything was jammed. It was in the scratchbuilt Hudswell Clarke frames that I built and ran just fine light engine, or with a light trains, but was gutless with a load. Where anything else meets a load that it can't move it breaks traction and spins its wheels, but this thing didn't have enough go in it to turn the motor. The anti scuff paste seemed to bring down the amount of friction on the worm and it became a good enough runner, and could pull a decent amount but it put me off using those units again. It was no Hercules for sure.

 

 

The one I've just fitted can spin the wheels with me pressing down (quite hard but not enough to disturb the Gibson wheels) on the body, I think you might have just got a duff one there. The others without the worm drive can easily spin the wheels in my 7mm 05 which weighs about 700g.

[Michael Edge]

1 hour ago, Camperdown said:

Not too sure what you're done, but it doesn't seem right.

 

The example shown in the spreadseet is for a wheel diameter of 22mm, i.e. 5.5 ft.

 

With a 16000 rpm motor, and gear ratio of 42:1, the wheel rotates at 16000/42 or 381 rpm, i.e. 6.35 rev/s (381/60).

 

This represents a speed of 5.5 * pi * 6.35 = 110 ft/s.  60 mph is equal to 88 ft/s, so this speed is 110 *60 / 88 or 75 mph.

 

Your spreadsheet gives an answer of 120 mph.  Suggest you check your working.

 

Incidentally, I usually aim for about half to two thirds of quoted no load speed for maximum model speed.

It's still not much help if I don't know how fast the motor is running - how do I measure that?

[SR71]

Hi Michael,

 

All motors will have a noted speed at a rated voltage - although not all sellers will give it. If you look at the ebay listing I posted they give the N20 as having an unlaiden speed of 16000rpm for all the gearbox variants.  It was that listing I did the sheet for intially to decide what to puchase.

 

It won't help for salvage motors or sellers which don't give a speed for the motors they sell but then in all instances that will have to be suck it and see.

 

SR71

[Michael Edge]

That's theoretical, as I said earlier there's a big difference in speed between various control systems on my own layouts and many motors seem to run significantly slower on the NCE DCC system I have used on Carlisle and Herculaneum Dock.

In answer to an earlier question about which n20 type I prefer, this is the first one with a worm drive I've used.  Good results with many of the others but the difficulty is usually finding a good 1:1 final drive, the best I've had is with a set of skew gears but I've no idea where they came from. Bevels are good if properly fitted, crown wheel and pinion is much easier to fit, I'll be evaluating these next. In 7mm I've used the "folded back" type which can be fitted across and between the frames with a simple spur gear drive.

[Camperdown]

5 minutes ago, Michael Edge said:

That's theoretical, as I said earlier there's a big difference in speed between various control systems on my own layouts and many motors seem to run significantly slower on the NCE DCC system I have used on Carlisle and Herculaneum Dock.

In answer to an earlier question about which n20 type I prefer, this is the first one with a worm drive I've used.  Good results with many of the others but the difficulty is usually finding a good 1:1 final drive, the best I've had is with a set of skew gears but I've no idea where they came from. Bevels are good if properly fitted, crown wheel and pinion is much easier to fit, I'll be evaluating these next. In 7mm I've used the "folded back" type which can be fitted across and between the frames with a simple spur gear drive.

Thanks.  Crossed helicals would be the ideal to get the right angle drive, but I've never seen any, at least not for 4mm scale locos.

 

The quoted 12V no load speed is the speed at which the motor --- acting as a generator --- will produce exactly 12V back emf, to oppose the 12V supply.  So at the no load speed, there is no net voltage across the windings and no current is flowing.  Top speed with a load, i.e. driving a light engine through a gearbox, is maybe half that.

[Michael Edge]

12v DC is a guide but not necessarily what we actually put into the motors.

I have one more set of the skew gears, can't decide yet what to put them in though.

[Izzy]

35 minutes ago, Camperdown said:

.  Crossed helicals would be the ideal to get the right angle drive, but I've never seen any, at least not for 4mm scale locos.

Slaters do a 2.9-1crossed helical brass gearbox but it’s £27. I used them back in the late ‘80’s in S gauge coupled to 20 x 20 faulhaber motors with integral 59-1 gear heads. At 177-1 they weren’t capable of much more than around 30mph scale speed - some MR class 3 goods and a freelance industrial - but the running was quite good………..and once the wheels started turning nothing stopped them as you might expect. I’m sure the size of the Slaters boxes would fit most 4mm stuff. 
 

 

Edited December 4, 2022 by Izzy

[cctransuk]

1 hour ago, SR71 said:

Hi @cctransuk @Camperdown

 

Not sure what happened to the file there but I've just changed it on the original post and added some instructions to the file on my PC. The speed it was giving was indeed incorrect, one of the variables had gone a bit odd when I was swapping formats I think. Hopefully it works now.

 

File attached here also for anyone that wants to test it out.

 

SR71

Motor wheel speed 2.xls 7.5 kB · 2 downloads

 

All these 'hard sums' are not good for me at this hour on a Sunday !

 

However, I conclude that, with an N20 non-worm motor / gearbox having an output rating of 2000 rpm at 12V, combined with a 20:12 crown and pinion set and 5'-3" (21mm.) dia. wheels, the top speed would be a scale 70 mph.

 

Now that seems not unreasonable for my purposes - I will order some of the relevant N20 motor / gearboxes to go with the crown / pinion gears already on order.

 

This should be interesting ...... !

 

John Isherwood.

 

PS. Please do tell me if I have b@llsed-up the 'sums'.

[Dave John]

I used the 136 RPM double shaft n20 with a 20 mm wheel on a recent project ( 1/50 scale metre gauge ) though that isn't far removed from 4mm in terms of wheel size. I was surprised by the motors, as described unstoppable. 

 

I chose to leave the 3 mm n20 axle in place and form sleeved wheels. 

 

Some traction tests ;

 

 

[Michael Edge]

Not a very good photo but I got the latest C14 finished today.

Back to the 7mm N2 now, photos later this week.

[Tony Teague]

Excellent!

[gz3xzf]

On 06/12/2022 at 20:33, Michael Edge said:

Not a very good photo but I got the latest C14 finished today.

Back to the 7mm N2 now, photos later this week.

That is really nice Michael, it would work nicely on my little shunting layout. 😉

[Michael Edge]

Last job before Christmas finished now.

7mm N2 built from a Warren Shepherd kit - and the less said about that the better, suffice to say that Judith has been reminded recently of why she set up the kit business (You design better kits and I'll sell them, to also reduce the bad language from the workshop).

My former apprentice (David) has now nearly finished his 7mm Hunslet 67T 0-6-0DH (from our kit of course).

Just handrails, front heatshield and buffers to fit now.

[Michael Edge]

Better photo of the C14 now varnished and glazed.

Also finished this Hunslet 0-6-0DH

[Michael Edge]

This month's test track photo shows a bit less than usual but some new work.

The N2 is still here, waiting for the customer to collect it, the SR 0-6-0DE is substantially finished now but still waiting for sandbox patterns to be made. In between some kit development and the next job - no prizes but does anyone know what they are yet?

[t-b-g]

I am thinking that the 0-4-4T is something like a well tank, as it has sandboxes on the rear splashers. Or something with very short tanks.

 

A GNR Stirling well tank is a bit like that with sandboxes on both splashers, as is the L & Y 0-4-4T but I would need to see a bit more progress to be certain.

 

 

[Enterprisingwestern]

 

Dunno what's there, but can't see any wagons!

 

Mike.

[Michael Edge]

No wagons being worked on at the moment....

[ianmaccormac]

Is this a GNR Stirling 0-4-4T as described? I am a LB&SCR Modeller. Just came across some photos of photos at Kew I took in 2007! Rail 1014.35 if anyone interested. Cheers, Ian