A few build challenges ago I put together this really cool MAC rail truck and powered it with the guts from a cheap RC car. It works but I haven’t been really happy with it.
Where can I get a decent motor for it that will give me scale speeds and power without breaking the budget? Also it uses 4 AA batteries and I would like to use the existing RC control.
Thanks.
Is there a source for small motors and gear boxes for custom builds?
Todd,
I have purchased several gear motors from Pololu for a variety of projects. Take a look at their web site at:
http://www.pololu.com/category/22/motors-and-gearboxes
(http://freightsheds.largescalecentral.com/users//bob_hyman/misc_photos/41FEh0bN5JL.SX425.jpg)
(http://freightsheds.largescalecentral.com/users//bob_hyman/misc_photos/51RtGMGldZL.SX425.jpg)
Todd,
You can also look at Pittman Motors http://www.ametektip.com/index.php?option=com_content&task=view&id=168&Itemid=99 or Micro-Mo http://www.micromo.com/.
Another option might be to do a general Google (or your favorite search engine) for Instrument Motors.
Bob C.
Good websites and just what I was looking for but which motor to use for my application? Another big question is which gear ratio to look for? If we look on the link that Bob Hyman supplied there are some nice loooking motor gear boxes with interchangeble gears to create different ratios. When I used the RC car motor I was able to pull the tires off and press fit train wheels on. It was pretty simple. Can the same process be used with one of these motors such as this one? http://www.pololu.com/product/118
Has anyone used one of these gear boxes and which one was it? There are so many to chose from.
So which one, which ratio and what size are these things?
Todd,
I guess the first question I need to ask is 'What size are the rail wheels you pressed on?". And what scale are you assuming this rail truck to be? (I know most are not scale specific, but I need a place to start the calculations from.)
Lets assume for our example that the scale is 1:24 and the wheel is 31mm (a standard Bachmann). 31mm divided by 25.4 (mm to the inch) and the wheel is 1.2204" (truncated to 4 decimal places). 1.2204 times 24 equals 29.2896 inches in diameter in scale. Pi times 29.2896 inches equals 92.0160 inches rolling circumference. Now we know how far your wheel travels in one revolution.
Now lets assume you want your rail truck to travel at a maximum speed of 20 miles per hour. In order to get to some common units of speed, lets break that down to miles per minute. Divide 20 MPH by 60 Minutes per hour and you get .3334 miles per minute. To get how many times the wheel rotates in that distance we need to first determine how many inches per minute we are traveling. so, .3334 times 5280 (feet per mile) times 12 (inches per foot) and we get 10,322.064 inches. If we now divide the distance traveled (10322.064) by the distance traveled per revolution of the wheel (92.0160) and we get 112.1768. Now for a 31mm wheel to travel at 20 scale miles per hour our maximum wheel rotation is 112.1768 PRM.
I appears that the motor/gearbox you have chosen has four different ratios. Lets see if any are close to what we are attempting to obtain. The first and second ration are definitely not low enough, but I will do the math to demonstrate. the motor (no load) RPM is given as 12,300. 12,300 divided by 12.7 is 968.5039 final output RPM. MUCH TOO HIGH. The next ratio is 38. 12,300 divided by38 equals 323 RPM. Much closer but still too high. Next ratio is 115. 12,300 divided by 115 is 106.9565. This is very close, and in my world would be quite acceptable in terms of speed. The final ratio would yield 36.8263, way too low.
Being as I don’t read Kanji, I cannot be sure, but I believe the output shafts to be a 6mm hexagon. If this is the case, you might check with an R/C hobby shop locally and see what they have that might be adaptable.
Also note that this is a 3V motor. Not very much, only 2 double A batteries will run this for a good bit.
I hope I have given clear enough directions on how to work backwards from what you know to what you want/need.
This links to the OEM site for Tamiya and gives some overall dimensions http://www.tamiya.com/english/products/70167gearbox/
PM me if you need any additional help.
Bob C.
I have had similar problems with small quarry locos .
One solution which has given no trouble so far is to use the motor/gearbox from a radio control servo . These are quite small (to fit into model aircraft) and are produced in sufficient quantities to make them cheap .
It’s fairly simple to remove the travel stops so that it will continuously rotate , and they are quite quiet in operation , also having enough oomph for teeny trains .
Mike Brit
ps I used chain drive because of space constraints .
Bob Hyman said:
Todd,
I have purchased several gear motors from Pololu for a variety of projects. Take a look at their web site at:
http://www.pololu.com/category/22/motors-and-gearboxes
(http://freightsheds.largescalecentral.com/users//bob_hyman/misc_photos/41FEh0bN5JL.SX425.jpg)
(http://freightsheds.largescalecentral.com/users//bob_hyman/misc_photos/51RtGMGldZL.SX425.jpg)
Bought quite a few of these from a UK/Chinese firm and much cheaper with free postage as well! EBAY them… They seem to come from China initially and then posted on in the UK.
There are a couple on here…
20 rpm 60 rpm 80 rpm 100 rpm…there are possibly more…Silent…
http://stores.ebay.co.uk/Assisi-Electric-UK/_i.html?_kw=12V&_kw=MOTOR&_kw=GEARBOX&_sid=370969529
Specification:
SAMPLE SPEC OF motor as shown above - Drive shafts lengths vary so read the adverts)
Product Name DC Geared Motor Rated Voltage DC 12V Rated Current 65MA ( no load )
Shaft Diameter 3mm/ 0.118"
Gearbox Size 26 x 12 x 15mm/ 1" x 0.47" x 0.59" (LWH)
Overall Length 50mm/ 2"
Main Color Silver Tone Material Metal,
Electronic Parts Weight 23g Package 1 x DC Geared Motor
Wow Bob Cope are you an engineer or what? This sure is complicated for this simple guy that is why I was hoping someone could say “I used this one in my “—” and it worked great, here is the model number”
On my railtruck I used the standard plastic LGB/ Bachmann wheels. I would say the model is 1:24. A scale speed of 15-20 mph would be good. The simple controller is either on or off so the gearing needs ot control the speed. I used the battery box from the RC car and it has 4 AA batteries. I only picked that gearbox to show the type I’m looking at. I didn’t look at the details that closely. The one that Bob Hyman posted sure is small but it only has one shaft. Would the wheel be pressed onto that giving only one wheel for traction or am I missing something?
Just had another look at the pololu website and I don’t think they have what I need.
Too many choices. The trouble is too many choices is daunting and it leads to not making a choice and putting the project on the back burner for another day.
No makee mind up…makee shelf jobby!!
By the way there is a gear drive available on EBAY site above that will allow both wheels to be driven if mounted at the rear.
This site looks promising, but I haven’t yet tried it out, but the Fosmotor might be perfect for the speeder. It looks similar to a magic carpet
http://www.peterspoerermodelengineers.com/90275/info.php?p=7
Vic Smith said:
This site looks promising, but I haven’t yet tried it out, but the Fosmotor might be perfect for the speeder. It looks similar to a magic carpet
http://www.peterspoerermodelengineers.com/90275/info.php?p=7
He used to have a much larger photo of the FOSMOTOR than shown…
Bit ridiculous having it so small on a sales website.
Todd… I’ve used the motor and gearbox from the Hartland Woody… They work very well. Not sure it would be small enough for your application…
Todd Haskins said:
Wow Bob Cope are you an engineer or what?
To answer the direct question, yes, I am a mechanical designer. Todd, I spent the time to step through the ‘how to’ not just for you, but so anyone can get from square one to a finished product.
Generally speaking, “If you don’t know where you are going, you most likely will not like where you end up.” Asking what others have done is OK to use as a guide, but with out the rest of the story you may end up running way too fast or way to slow and you will not be happy in the end.
Consider all the hoopla over the gearing in the K27. For the prototype, it runs at warp speed. I was trying to assist you to not have a similar fauxpa.
Todd, I only ran through the numbers on that gearbox because that was the gearbox you presented. Not necessarily because it was the best choice. It did however prove out to be quite suitable speed wise, if not size wise.
Bob C
great question ! great info contained in thread !
Todd , be careful about the motor you choose , the control systems on the cheap r/c cars will possibly burn out when trying to drive a motor other than the one it came with .
Mike Brit