Axle Hung Motor Gearbox (AHMG)

[John Candy]

A bit concerned about the 43C with no load.
Perhaps (when the battery has recharged) you could measure the current being drawn?
I had envisaged a C0-C0 with 2 motors per bogie for LMS 10000 but if the the 4 motors draw too many Amps under load (including climbing the 1 in 40 from LL to HL routes on my line) the cell pack will not last long and the motors may even produce unwanted smoke effects (or the cutouts will trip)!

Regards,
John.

[cabbage]

Ok -it is very nearly sunset... But I do have a couple of figures for you.

6.09 Volts @ 0.49 Amperes

12.3 Volts @ 2.17 Amperes

Resistance of windings COLD 2.6 Ohms

Resistance of windings HOT 3.12 Ohms

Sunday I will have a go at building and testing a simple brake dynamometer -using exactly the same techniques as used by Bulawayo Shed....

regards

ralph

[John Candy]

Thanks Ralph.

So 4 motors under heavy load could draw 15 to 20+A?
That would soon drain the battery.

John.

[cabbage]

"No!  What you have forgotten is series and parallel wiring systems.  If I wire all the four motors in SERIES then the same 0.49 amps travel through the chain of motors but I would have to use 24 volts -thus each motor thinks it has only 6volts across it.

If I wire all the motors in PARALLEL then each motor has 6 volts across but each motor pulls 0.49 amps.

The SERIES wiring is more efficient for this operation but there will be the problem of finding a good 24 volt ESC .  Your best bet is probably to wire two pairs of motors in SERIES and then connect them in PARALLEL. This will give you a 12 volt system pulling 1 amp. There are LOADS of ESCs that could deal with that!

regards

ralph

[John Candy]

I had been assuming that the 4 motors would be in parallel and supplied with 15V (the maximum quoted for the motors). If they get that hot on 6V and 0.49A with no load, I just wonder what would happen with 6+ coaches on, climbing 1 in 40 at full throttle and drawing God knows how many Amps. at 15V. Pairing the motors in series and connecting in parallel as you have suggested may be the answer but will the reduced (distributed) voltage provide enough top speed? A 30V ESC and 30V cell pack is probably not impossible in a large diesel body!

Regards,
John.

[cabbage]

John,

I have to go over to BOT and write 4 letters for the happy couples, but I will be back home before sunset. Judging on the amount of torque available at the Gear 4 running on only 6 Volts -then I would say that just running 2 serial pairs in parallel at 12 Volts across them would provide more than enough torque to climb your gradient. To increase your "effective" traction I would take a balance chain/belt drive from each of the outer wheels to the centre axle.

But I would advise against running your motors at full voltage as this is the LIMIT of their insulation rating and design for 12 Volts -always give yourself a slight margin.... If they are fitted with std insulation varnish then this is good to a working temperature of 180C. However the motors should be moving through cooling air and painting them matte black will help with the thermal losses!

I will design a "grunt" power supply for 12 Volts for you -but be advised that these things are not toys and errant fingers with conductive tools -should be careful...

Please remember the simple rule:

AC is AGH! Current
DC is Dead Currant

regards

ralph

[Peaky 556]

Ok -it is very nearly sunset... But I do have a couple of figures for you.

6.09 Volts @ 0.49 Amperes

12.3 Volts @ 2.17 Amperes

Resistance of windings COLD 2.6 Ohms

Resistance of windings HOT 3.12 Ohms

Sunday I will have a go at building and testing a simple brake dynamometer -using exactly the same techniques as used by Bulawayo Shed....

regards

ralph

Are those drawn currents under some kind of load Ralph, ie more than just rattling a few gears around, as the "official" figures quoted by John were something like 0.25 A free running at 12V?

Also do you have a means of measuring speed when you set up your dyno, or can you make use of mine?

Regards, Tim

[John Candy]

I wonder, if to provide the wide spectrum of power options of max. torque v. max speed to cater for hill-climbing with heavy loads, a form of control box (perhaps operated via a r/c servo) might be incorporated to switch the power supply to the motors between parallel and series modes?

In the days before electronic circuitry, I seem to recall the DC controllers on the SR emus had a "weak field" setting which was used when higher speeds with lower TE were required. Would switching between parallel and series produce the same effect in a model? What are risks of "flashover" and could there be a (?diode) arrangement to overcome such problems?

Regards,
John.

[cabbage]

I am taking a break from my duties. Cheese and Onion sandwich in hand as I thumb type...

Tim,

I have no form of  rotational measurement. The figures are simply "no load" just spinning the gears. The dynamometer will be made, (as was the original!), by sticking two wagon wheels together and wrapping a length of "rope" and applying weights. I will then measure the Amperage at each increase in weight on the "rope" from a 6 Volt source.

John,

Field Weakening would only work if your magnets were electrically energised, (i.e. series wound motors), this was done by shunting a HUGE rheostat into the field windings. These are permanent magnets, and thus this technique is not possible.

Excuse me -I have finished my sandwich and must return to my writings.

regards

ralph

[John Candy]

Ralph,

Field Weakening would only work if your magnets were electrically energised,

I realised that but what i was querying was can the same effect be simulated by switching between series/parallel combo to all parallel .... i.e.switching from 6V to 12V per motor to increase top speed?

Regards,
John.

[Peaky 556]

John
From Ralph's early impressions it sounds like running these motors at 12V will only be 'safe' (from the overheating of windings insulation point of view) when at zero load, ie spinning the wheels in fresh air.
To switch to 12V when at moderate train speed, which also implies a lot more load than spinning wheels in fresh air, sounds like a recipe for smoke effects!
Although a little disappointed in the motor prospects, that case temperature measured by Ralph was when dissipating about 25 W, so four or six of these motors will handsomely exceed the empirical needs of around 70/80 W in total for an express train.
This is Gauge 3 scenic, not people pulling....
I will carry on plotting to fit three into a Peak bogie!
Regards, Tim

[cabbage]

OK I am home!

John, It would be possible to use "sequential connection" but it would be extremely difficult given the confines of a G3 loco. What you would need would be a set of heavy duty reed relays connected back to a selector switch with "lock out" sectors... You could then "notch up" from Full Parallel, Series Parallel, to Full Series. Wether the inertia of a G3 loco is sufficient to carry on the train as the "Clunk, Bang, Thud" of the selector and interlocks making and breaking the contacts. Arcing occurs during "breaking", I have made "submerged" relays as a demonstration example for friends but I would only use commercial ones otherwise.

Rather than all the switching required above  -the "F" series ESC by Electronize uses variable PWM which would give you the same effect. My recommendation would be to use two pairs of motors in series and feed them in parallel from a 12V "grunt" supply.

Sunset in about an hour and I will back after some much needed food!

regards

ralph

[John Candy]

Ralph,

I thought it might be a bit too complicated to fit into a model and have used Electronize ESCs in several of my locos.
Whether the 7-pole motors are ideal for this application remains to be seen from outcome of your experiments.
Two motors per C0-C0 bogie (with chain drive to centre wheelset) will certainly provide plenty of TE to move a heavy train but whether top speed will be satisfactory and the question of possible overheating remain to be resolved.
In the Sentinel, the cell pack is 9.6V nominal (c.11V actual at full charge) and the loco is slow moving with plenty of "pull" but runs are of short duration. The motor is almost fully enclosed with little or no natural cooling.

Regards,
John.

[cabbage]

Piece of personal design philosophy!

I prefer each part of a piece of equipment to have its own independent power supply. Thus my locos have POWER batteries and RECEIVER batteries. This keeps power surges "off" same wiring feeding the Rx system. I will admit to being old fashioned but I still use it.

What you are looking at is the "grunt" part of the supply.



There are two relays -both heavy rated (30A). Both of them are DPDT. They draw power from the RX supply. Thus if the small RX fuse blows IT KILLS THE WHOLE LOCO. Relay One connects the main power to the ESC. Relay Two connects the capacitor bank to the main system. The capacitor bank provides amps as required -but is dangerous. Thus the capacitor bank discharges itself through the large multi watt high value resistance "R", (typically a 7W wire wound with a as big a KOhm resistance as you can find). The Capacitors are arranged so that two of them float between 12V + 6V and 6V + 0V, whilst the other floats across 12V + 0V. Their function is to "dump current" onto the main lines. A high "ripple rating" is normally used on such capacitors -look for something over 2 Amperes. These do not have to have a high Farad rating -10,000uF would be ample.

The fuse sits between the upper and lower banks of SLA. Should IT blow the loco will stop dead. The main problem is that the lower Capacitor will remain charged until the main switch is turned off. I personally do not like self resetting circuit breakers, once model has "died" -I prefer the model to continue to be "dead"!

The power system relies on the reduced impedance of the batteries to provide most of the Amperage required. It is a "fast" power supply -unlike a simple battery and some thought would have to be given to charging it in situ, if the SLAs can come out as bricks and are charged individually then that is actually a lot better. When re-assembling the system use a voltmeter to check the voltage on each battery. Pair up those of similar voltage on each "level".

This type of circuit has been around for decades. It was originally an amplifier, then computer, and now finally G3 model locomotive power supply!!!

regards

ralph

[cabbage]

Dynamometer  constructed! This is a classic brake dyno and I will run 16 weights on it. Despite this being a metric kid I do have a set of kitchen weights that go from 1 to 16 ounces, (thank you Grandma!).

I will display the table and give you a result at the end in Grammes per Centimetre of torque which I think given the small size of our wheels is more useful than one in Newton Metres.



I am using 1.5 wraps rather than 10 wraps as the friction is way above 1 oz weight loading. OK so it is not as accurate but we are dealing with small weights!!! The gearing is: 10:60 40:48  37.5:48 which is 9.2:1 thus I can tell you that HQ7P can generate 173g/cm from a 1oz weight. How much more it can go -we shall find out after lunch!!!

regards

ralph