Discussion in 'HO Scale Model Trains' started by Freelancer, Sep 1, 2008.
Have you tried Backwoods Minuatures
I think an n-scale motor is bigger than the one you are using, but not by a lot. I would put the motor inside the bed of the truck rather than trying to hang it under the frame between the axles. If your high rail vehicle is going to be a flat bed, you might be able to put the motor under the hood. You may need to raise the floor of the cab interior a bit to get clearance, but lpb's work as well without legs as they do with them!
If you put the motor in the cab/under the hood (still can't believe that little silver dot is the motor...!), then why not make it front wheel drive?
And for the record, I don't think it looks funny... I think it looks like this:
It's a 1947 Caddie converted to a track inspection car. Similar era to your truck, so not out of line that they would have switched the wheels and dedicated it to rail travel only...
I think if you make it front wheel drive, you will still end up with the motor in the cab with the gearbox under the hood.
Probably a stupid idea, but if the main problem with a resistor to drop the voltage is heat, perhaps you could mount the resistor in front of the vehicles grill, like a pneumatic cylinder. Or represent an air tank?
The resistor will not get hot if it has the correct power rating, or like you said, use multiple resistors. Will you be able to control the speed somehow? What is the current draw (amps) of the motor at 1.2 volts?
If you are really going to run this on DCC (I just read that in your post, duh) you need a decoder, no??
I have never heard of them so until now, I have not. However since you mentioned it I checked them out, but it does not look like they have anything in the size I am looking for. Thanks for the suggestion though.
If I have to go with the larger motor, then I will probably leave it as a box truck, but I was hoping to go with the smaller motor between the frame because it fits so nicely. However I am not opposed to disguising the motor as some type of cargo. I was really hoping to go for the effect of "how'd he do that?" by using such a small motor making it seem impossible to power it elsewhere. Putting the motor under the hood might not be a bad idea, it might get messy but it is very much a possibility.
Not in this case as they will need their feet to push on the gas. I am actually still debating on putting any lpb's inside as it would be a pretty tight fit. If I go the route of putting the motor in the hood then I will add lpb's, but if not, I am not sure I want to tear into the cab.
Front wheel drive is now out of the question as I have JB welded the gear to the rear axle and would prefer not to have to tear that apart. I suppose I could run a drive shaft from the motor in the cab area, then it would look pretty prototypical, although I do not know what kind of problems a shaft like that might create.
Hmm...I will have to think about this one. Umm...nope it still looks funny.:mrgreen: However that Caddie sure has class! Maybe that will be the next project.:twisted:
The heat is one of the main concerns but I like your idea, right in front of the grill mounted above the bumper. Disguised as an air tank or maybe a winch, great idea!
Is it possible to find a proper resistor that will cut 12v down to 1.2v? Everything that I have read so far suggests that it is not possible. That is why I was hoping the Zener diode would help. I am not sure of how many amps the motor pulls as I cannot seem to find the car and battery that this originally operated in. I will have to see if I can find something to test this with. However, I might have found a similar sized motor that can handle up to 3v. I have yet to find the exact dimensions, but if it is close then that would help keep the down step a little less drastic.
Yes I will need one, I was planning on using a Z scale decoder and either hiding it somewhere in, under, or on the truck by placing it on the bed and covering it with a "tarp". However, I am concerned about how the voltage reduction will effect the operation with the decoder. Obvioulsy the reduction would go between the decoder and the motor, but I do not know how things will behave.
All of your input is great! Keep it comin'.
I think a decoder will create an additional complication. Decoders are designed to take 12-14 volts in and then turn on the voltage as needed to run the locomotive at the speed that you want to run. Trying to get a decoder to operate a 1-3 volt motor with speed changes may be difficult. If you just "crack" a little voltage to the motor, it might work, but at that small a voltage your controller will be more like an on/off switch.
Can I suggest a linear voltage regulator?
It will depend on how much current you need but I know there are many that drop 12V to 1.2. I do this all the time to power FPGAs in our electronic designs. The issue will be the size in relation to the current.
I am just taking a guess with the specs here; but here is a LDO from STmicroelectronics.
Part number is LD1117S12TR. It comes in a SOT-223 package. That means it is about 6mm x 7 mm or .256"x.275".
Edit: You will also need 2 small capacitors for this as well. These do not need to be very large as you signal does not need to be filtered too much.
I have no useful advice, but this is a very fascinating project. I am definately looking forward to the end result.
Best of luck.
I was affraid someone would say something along these lines. So you think it will still have that effect when the regulation is placed between the decoder and the motor? Theoretically the decoder would still function the same and put out the same amount of voltage, but the motor would only receive a fraction of that voltage. I was guessing that because the motor runs on such little voltage now, that it would still be sensitive to the decreased voltage from the decoder. Is my reasoning correct? Does anyone know what the smallest amount of voltage is that a decoder puts out when starting to accelerate?
You most certainly may. However I was looking into circuits that were along those lines and they all seemed to be way too involved requiring many components that would not easily fit within the space allowed. Either that or I was looking at example schematics of how they could be used. Can you elaborate more on the use of this device? In theory will the only components I need is this LDO and two resistors? Or will it take two LDO's, one on each wire to the motor to allow for the change of direction? Also, does this regulator work by limiting the voltage up to 1.2v or does it build up the voltage until it has 1.2v and acts like a constant voltage device?
You are not the only one, I am pretty anxious for the end results as well.sign1
The decoder output alternates polarity. I think the zener is the wrong device because it regulates when reverse biased. Just try a 50 ohm 2 watt resistor in series with the motor. Hook up the motor, decoder, resistor to the DCC unit on the bench. Run it a while and see if it gets hot!
This thread has gone way over my head, but it is fascinating! If the voltage regulator is linear, then a decoder sending an input to the voltage regulator should control the motor fine. If the voltage regulator is not linear, then you may have problems with control.
DCC works by DC pulse width modulation, not voltage levels. DCC pulses to the motor are typically 12-14 volts, with pulse duration controlling speed. Different decoders use different pulse frequencies, but all I know of use PWM because it is simple and efficient to implement in very tiny silicon.
Your low voltage motor is not going to like spikes of that voltage, no matter how short the duration. Even some 12 volt coreless motors struggle with overheating on DCC.
Looking at the options - how practical would fixed voltage operations be instead of controllable? If you could arrive at a reasonable speed at a given voltage, that fixed voltage reduced from track power would be more easily achieved with a simple circuit. I'd suggest battery power, but that would be even more space consuming, especially if a recharging circuit was added.
If you are still planning to go down the DCC road (lots of advantages), I would suggest the combination of a tiny 24 volt coreless motor with a Z decoder. The 24 volt motors have a reasonable RPM at 12 volts, and won't self-destruct on DCC PWM. I have friends who swear by them for remotoring projects. The downside is availability and high cost.
just my thoughts, your choices
The series dropping resistor has the effect of reducing the voltage on the motor to the required 1.2v. The value is a WAG and it will depend on the actual motor load current, which we don't know.I just called it 0.2 A. If the motor current draw is lower, the resistor will need to be a higher value. If it's 0.1A the resistor should be closer to 100 ohms. (and only 1 watt rating required). Like Fred implied, a higher voltage motor will require less series resistance. I suggested bread-boarding it on the bench to find the correct combination easily.
I was at my local hobby shop earlier today. They had an n-scale industrial switcher that looked remarkably like the Athearn Li'l Hustler. That thing was so small that the motor could not have been significantly bigger than the one you have pictured in your high rail truck. I don't model n-scale, but I'm sure you could find an n-scale motor that would fit and do the job nicely without needing to deal with dropping voltage to handle a 1.2v motor.
That is a good point. :cry:
Thanks for the clearification. It makes sense but does not seem practical, I am glad there are people around to figure this stuff out.:yep:
So basically just find a speed that I want it to run at and it would run at one speed and work as an on/off switch like Russ was refering too?
I debated on doing that and using the existing circuitry from the r/c car but figured it would be either too difficult to get it to recharge from track power, or it would be too inconvenient to have to take it off the layout to charge it every few minutes.
If you want to use DCC track power with no decoder, then you will need a diode to rectify the power, in addition to a resistor to lower the voltage. I really think the decoder is very slick way to go, if you can fit it in.
And I really don't think you need the resistor if you are using the decoder, because I think you can control the max output with CVs. Here's a link to a little DCC info.
Again, if you have a test track, a motor and a decoder, it an easy hook-up to test, just needs 4 wires...:mrgreen:
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