|Jon Lawes||14/08/2018 09:05:58|
370 forum posts
Just thinking outside the box, what about using brushless motors and lipo batteries? There are a lot of good speed controllers in the model car world, places like HobbyKing have a huge variety. I used one in my boat that worked out as almost 4hp powered by two 6S lipo batteries, good battery life and power. Only downside was the motor and speed controller both needed water cooling (which I achieved using a small pump).
|Ron Laden||14/08/2018 09:42:42|
1844 forum posts
I have quite a bit of experience with brushless motors, I used them in my RC aircraft days. I know of one 5 inch loco that is powered by one of the RC truck brushless motors. I have thought about it in the past but for now with the class 22 I will stick with brushed motors.
Edited By Ron Laden on 14/08/2018 09:43:23
|Ron Laden||15/08/2018 09:53:40|
1844 forum posts
If you read up on the characteristics and technical spec on the different battery types then the obvious choice for an electric loco would be a deep cycle (traction) battery.
What about in practice though..? there are lots of examples of things that work with no problems when theory tells you it shouldnt or wont perform so well.
The majority of electric locos I have seen are running on leisure batteries and I think I am right in saying that there now seems to be leisure batteries that are listed as "deep cycle", whether they are actually any different or not I dont know.
As I understand it, it seems to be how much capacity you take from the battery that is key. If you take a leisure or car battery down to 25% on a regular basis then it will start to have problems. So I wonder, are users of leisure batteries not taking them down any further than say 50% and that is why they have no problems.
I spoke to someone yesterday and he uses leisure batteries in quite a large loco and he said that the batteries are 3 years old and never been a problem. He doesnt measures how much they use but an afternoon at the track is probably no more than a total of one and a half hours running on and off. I am guessing that he probably doesnt take them down any further than 50-60%.
So could it be a case of "theory says.... but in practice...."
Edited By Ron Laden on 15/08/2018 09:55:47
|Ron Laden||09/05/2019 09:32:13|
1844 forum posts
Excuse my rough sketch but it shows another option for the loco bogies which would have sprung axle boxes and toothed belt drive against the gear driven trailing arm type bogie I posted previously.
I think this is a neater option housing the motors within the axles and the overall bogie length is 100mm shorter than the trailing arm type. Also the sprung axle boxes are more in keeping with railway practice plus the track to chassis top plate dimension is 100mm so it wouldnt look too leggy. Still not 100% decided on which bogie type to go with but it probably will be as below.
|Joseph Noci 1||09/05/2019 10:37:31|
|628 forum posts|
The typical brushless motors used on aircraft etc are not very good in this application Jon. They tend to have very little starting torque and if they do not get going, the controller and motor end up out of sync and the motor stalls. Some of the RC cars/buggies use sensored brushless motors for this very reason - to get low speed control and good launch without stalling or wheelspin. Problem is that the sensored motors are much more costly, and are not easily available in larger sizes. However, prudent choice of motor kv rating (RPM per Volt), motor size and gearing between motor and drive mechanisim may give a good result. We built a 'sand-buggy' - a one man go-kart, using a 80kv, 5KW outrunner, fed with 80volts. Tyres on the kart are 300mm diameter pneumatics ( from wheelbarrows..) . The kart reached speeds of 100km/h ( OHS...Don't ask..) and we could spin the tyres on tarmac. We could cruise at 20km/h for 1 hour with battery pack of 86volts/40A/H.
In the quest for the fastest 1/4 mile time, we blew the motor up at around 13KW input..
|duncan webster||09/05/2019 11:11:50|
2525 forum posts
Axle hung motors have the great advantage that the distance between axle and motor doesn't change with suspension travel and so you don't have to worry about gear meshing, belt tightness etc.
Having watched your rate of progress on the first loco, I expect to see this one running before the end of the year.
|Ron Laden||09/05/2019 14:05:55|
1844 forum posts
It is probably not clear from my sketch but the motors on this version of the bogie are not axle mounted they are fixed to the side plate. I am hoping that the belt tension will be ok, my maths and geometry is not up to it so I resorted to using a pair of dividers to check the upper and lower belt length against the axle travel. As far as I could see the dimensions cancelled each other out but I could be wrong of course. Should any of you clever chaps want to check, the motor pulley is 14.6mm dia and the axle pulley 68.75mm dia. The pulley centres are 73.0mm and the vertical travel of the axle is 6.0mm max. As per the sketch the axle is at its lowest point sitting on the horizontal centre line with the 6.0mm of travel being upwards.
|Ron Laden||15/05/2019 08:47:10|
1844 forum posts
The motors I have decided on have arrived, they are Chinese and available from UK electric scooter suppliers. It was a no brainer really, a set of 4 motors for quite a bit less than the cost of a single UK manufactured motor of equivalent spec. They are listed as 24 volt, 150 watt, 6.25 amp with a no load speed of 2750 rpm and come fitted with a 3mm - 16T belt pulley. They have twin ball races and having taken one apart look to be well made.
There is a question mark over the quoted figures though and I had a "technical conversation" with the supplier. He said: great motor, loads of power. Me: is the 150 watts input or output..? Him: silence, then "input" Me: it would have been better if the 150 watts was output. Him, silence again then, erm, no it must be output, loads of power......LOL
Anyway I read all the user reviews I could find and they all said the motor gives good power and is reliable. One guy thought the 150 watts was about right, based on what though I dont know. Another said probably a bit lower at 100-125. One guy uses one to power a watch makers lathe and he thought at least 150 watts but without proper testing who knows..?
Not knowing the actual figures leads to a bit of guesstimation and gut feeling when making calculations, gear ratio,s for instance. The quoted no load speed is 2750 but the motors I have are within 150 rpm of each other (which is good) averaging out at 4050 rpm.
Now 4050 rpm is quite a bit faster than 2750 so I have estimated a loaded speed and geared at 4.25/1 to achieve a loco speed of 6mph. Will have to see how it comes out in the wash but should I need to change the ratio I can easily change the motor pulley size up or down, hopefully I wont need to.
I was also thinking that one of these motors could be a good candidate for building a power drive for the mill table, doubt I will ever get around to it though.
Edited By Ron Laden on 15/05/2019 08:50:37
|5592 forum posts|
Batteries, automotive, leisure, and deep cycle differ in their internal construction. They all have the same construction, but:
Best battery depends on the purpose. You could borrow your car's battery to briefly test a loco was working without damaging it. An expensive mistake to use the same battery for a few hours on a track. Pricey deep cycle batteries are exactly right for a busy fork-lift truck, but probably over the top for chaps running a hobby engine at weekends. For hobby use, leisure batteries are a good compromise. A club might be better off investing in deep cycle batteries if they pull large numbers paying public around the track every weekend.
Motor ratings need close looking at. On it's own 100W or 150W written on the label is only indicative - the specification is incomplete. Is it input or output, and is it continuously rated or not? What limits the power of an electric motor is how hot it gets, and how much torque it can deliver, not what it says on the label. Many electric motors are not designed for continuous running, for example a petrol pump can expect to be used in short bursts, with time to cool-off between customers. This saves money, but can end in tears when a motor designed for a 20% duty cycle is fitted to a project requiring 100%. It's the quality of the insulation on the magnet wire that limits how hot before magic smoke. Older motors absolute max below 120°C, modern ones 150°C to 180°C, I've seen a motor spec quoting 220°C but that might have been a typo!
Motor input-output power, torgue and rpm specifications are best expressed as graphs. However, I found enough to reveal all in a table:
I'd interpret that to mean the motors are designed to run at a 'normal' 100W out, but that can be exceeded in short bursts (as in when fat bloke races his scooter uphill!) 78% of 144W in is 112W out. With four of them fitted to a 24V loco, the driver should avoid exceeding 4x6=24A, or 47.6A if wired for 12V. The spec doesn't give a duty cycle; scooters being short-range it's unlikely to be 100%, but it's probably more than good enough for a hobby loco. When the shunter is run for real keep an eye on the temperature of the motors; if they get hot, reduce the amount of work the loco is being asked to do. The good news is that your motors are designed for traction, and should do the job with no trouble. 400W is powerful on a track and you might not ever use all of it, but as a precaution, the closer your driving matches that of a scooter rider the better. And it probably will quite naturally!
Edited By SillyOldDuffer on 15/05/2019 10:44:00
|Ron Laden||15/05/2019 14:01:10|
1844 forum posts
I did base my decision to go with these motors on the fact that the labelled 150 watts is probably input with something like 100 watt output and I would be happy with 400 watts total. Dont ask me why but bench running the motors has led me to think that they may be a bit more than that though. It may be wishful thinking but I suspect I could have a total of 500 watts plus, the running of the loco will of course prove that or otherwise.
|5592 forum posts|
Yes Ron you will, but you can't tell how much without making the motor do real work. Watts are a measure of the rate of doing work, so you have to make the motor do something serious to measure them.
All electric motors can deliver far more power output than it says on the label - for a while! Your motors aren't somehow limited to 100W maximum, the label only suggests that's the rate at which they can work comfortably. An electric motor can be pushed beyond its rating, but if it can't get rid of excess heat, the internal temperature will rise until the brushes burn or the insulation fails and shorts the motor out. If you run a heavily loaded 100W motor wired for 12V from a big 24V battery with thick wires, you should get at least 300W out.
Overloading motors is not recommended because it shortens their lives. As a general rule for a given weight the working life of a motor is inversely proportional to its power output.
I think your shunter has plenty of power in hand even if your motors can't maintain 100W continuous without overheating. Found the IMLEC results for 2010 here. The smallest engine measured had an average power output of 0.1 Drawbar HP (74W) and the largest 0.39 DBHP (291W). Most 5" gauge steam engines look to output less than 200 Watts.
And unlike electric motors which can be overloaded on demand, the power output of a steam engine is inherently throttled. Steam engines are held back by the rate at which steam can get into the cylinders and by the engine's ability to withstand violently reciprocating mechanical stresses.
Given decent batteries, I expect your shunter will perform like a sports car...
Edited By SillyOldDuffer on 15/05/2019 17:08:56
|Ron Laden||17/05/2019 16:46:12|
1844 forum posts
Assuming I am understanding the IMLEC 2010 results in your above link correctly I am amazed at the figures.
In first place a Brittania (4-6-2) which hauled 16 adults for 1/2 an hour using just 1.25 lbs of coal, surely that is high end efficiency. Also it is listed as having 0.35 drawbar HP (260 watts), I always thought of the larger model steam loco,s as having much more power than that.
Edited By Ron Laden on 17/05/2019 16:47:11
Edited By Ron Laden on 17/05/2019 16:49:21
Edited By Ron Laden on 17/05/2019 16:56:46
|5592 forum posts|
Yes, the numbers are a little surprising, but when you dig into the figures there's a lot of energy in coal. Wikipedia gives 6.7kW hour per kilogram for coal. If Britannia converted coal at 100% efficiency, she would have output 260W for nearly 13 hours at IMLEC. Actually steam engines are poor converters of energy to work, usually well under 5% efficient. Your electric motors are 80% efficient or better.
260W is a third of a horse and applied correctly as on rails it can do a lot of work. I count 13 men on the roof in this Wikipedia picture of the Mumbles Horse Tram, and there are at least 4 more inside. That tram must weigh a bit too! Railway lines are a very effective way of moving heavy weights even without an engine because they are are low friction and flat.
Assuming your shunter's wheels gripped the track (railway engines need to be heavy), it would be powerful enough to haul the full-size Mumbles tram. Power-wise it's a big boy compared with most steam engines of the same gauge. It's weakness is the limited time it can keep going before the battery goes flat.
In theory, a steam loco could keep going forever by simply picking up more coal and water. In practice locomotives need a lot of maintenance : someone will know for sure, but I think full-size steam locomotives rarely managed more than 400 miles a day and then needed a good few hours in the shed getting ready for the next run. Electric trains are much more reliable, and energy efficient, and they out accelerate steam, and don't hammer the track. With a pickup system, electric trains are the bees knees. The main reason they're not universal is the high initial cost of wiring up the line.
In a sense steam engines are sheep in wolves clothing. Flame, smoke, steam, whistles, puffing, blowing off and pounding pistons make them look really impressive, and they smell the part too. Steam is dead sexy. But totally boring little electric motors easily outperform big reciprocating steam engines of the same power output. If it wasn't for those pesky batteries...
Edited By SillyOldDuffer on 17/05/2019 17:55:05
|duncan webster||17/05/2019 18:01:03|
2525 forum posts
400 Watts from a loco doing 8 mph (3.7 m/sec) is a tractive effort of 108 kgf. The best coefficient of adhesion you can rely on is about 3 (less on ally rail) so best make your loco weigh at least 325 kg, which is a hell of a lot. 108 kgf is enough to pull a train weighing over 5 tonnes up a 1 in 100 slope even allowing for rolling resistance.
|An Other||17/05/2019 18:09:57|
|161 forum posts|
Just a thought: I know deep-discharge batteries are expensive, and will do the job, but it made me think a bit about what I would call the duty cycle of the loco. I would assume the batteries would be run down to the extent of needing a recharge every time they are used, but how often is the loco used?
I haven't done the figures, but could it not work out more economical to use standard batteries, despite the inability to handle continuous deep discharge, and have two, or even three sets? That would allow for a set in use, and a set charging, which may prevent deterioration occurring too early due to the discharge. I did a quick scan of batteries, and it seems to me that two sets of standard batteries could work out cheaper than one set of deep discharge batteries. This also could mean that early failure of one or more batteries is not so expensive.
I would assume also that during extended periods between the use of the batteries (winter?) then one would need to keep even the deep discharge batteries on some kind of trickle charge.
This thinking also does not take into account how difficult it may be to change a set of batteries 'at the trackside' - I guess if you need to dismantle the loco to do the job, then its a no-go.
I hope this makes sense - it was prompted by me thinking about the ever-increasing cost of items these days - in some ways these hobbies are becoming very expensive, and by the comments in the thread from people who seem happy with standard car batteries.
5125 forum posts
When I looked after the club electric loco 24v 40Ah class 08 shunter when used at the club running for an hour but not hauling passengers just the driver and maybe one extra it would recharge in half a hour or less. When used on the portable track at an event if the steamer had a problem it would be gasping after a couple of hours. So one of the things to consider is the attention span of your grandchildren.
|duncan webster||17/05/2019 20:58:11|
2525 forum posts
OOPS, sums wrong! Having a bad day, or at least that's my excuse
tractive effort is 108 Newtons, not kgf, so the weight only needs to be 33 kg, which is much more manageable. Max load up a 1 in 100 will then be 550 kg, about 7 people plus the loco
Edited By duncan webster on 17/05/2019 21:02:47
Edited By duncan webster on 17/05/2019 21:31:45
|Ron Laden||18/05/2019 08:51:56|
1844 forum posts
Well thats a relief Duncan but I did suspect something not quite right, if I had a 5 inch - 400 watt loco capable of hauling 5 tonnes up a 1 in 100 I think I would have built the most powerful model the world had ever seen...
|martin perman||18/05/2019 09:57:05|
1805 forum posts
As somebody else said theory and practice dont always match, I have just changed what I believe is the original car battery, the car was built in 2009 and the battery had a build date sticker of 2008. I changed it because if I left all the car doors opened, loading with camping gear etc or large loads, the interior lights drained it to a point where I couldn't turn the engine over but a jump start would sort it until the next time.
I have a five year old car battery which I use on my winch hauling my stationary engines in and out of my trailer from spring to summer and in between times and winter it sits on a trickle charger because I've found that the cold kills batteries unless they are constantly monitored and finally I have a leisure battery which gets used in my caravan, has started a car and generally anything else that I need 12volts for.
I also have two mobility scooters, my wifes and and mine, which sit connected to chargers all the time we dont need them.
Maybe the abuse I give them does them good.
|5592 forum posts|
It does make sense - exactly the sort of thinking an engineer should apply to a problem. What's the cheapest way of achieving the desired result? Preconceptions, beliefs, opinion and what grandad was told in 1928 not allowed.
In theory car batteries used for traction will have a short-life. They degrade by losing capacity, an 60Ah battery successively converting itself into a 40Ah, 20Ah, or 5Ah, battery and then a door stop. What's hard to answer is how long a mistreated battery will last when used intermittently in a particular engine with an unknown duty cycle. Chatting casually to owners at the track-side may not help. In the absence of proper data, it's hard to tell the difference between the chap who's just fitted a new battery, and the chap who has a battery going strong after 5 years experience. Only the second is worth talking to!
My practical experience of ruining car batteries comes from amateur radio. In my youth this took me up hill-tops with a radio transceiver to take part in competitions. I'd do it perhaps 3 weekends each summer. Car batteries were the obvious source of power - a 12V transceiver would draw about 100mA continuously on receive, and a peaky 6A on transmit, perhaps 20% of the time. In theory a car battery has more than enough storage to cope with 48 hours of busy radio fun. On return home, the car battery was trickle charged ready for the next outing.
Admittedly the radio pattern of discharge/recycle is even more abusive than traction, but radio competition killed a new car battery in about 3 months: expensive! It's the pattern of slow deep discharge coupled with slow recharging that seems to do most damage. The same transceiver fitted to a car, where the battery also does normal motoring duty, does not kill the battery.
I think a £100 car battery that lasted 3 years on the track would be a bargain. An expensive mistake if it only lasted 3 months. Theory is a helpful way of avoiding expensive mistakes, but it always needs to be validated in the real world. Be really good for owners to share their practical experiences, especially anyone who has successfully used the same car battery for more than 2 years.
Edit: I typed this before reading Martin's contribution. We agree about theory and practice!
Edited By SillyOldDuffer on 18/05/2019 10:42:50
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