Gearing a power function motor

[edsmith0075]

Hey everyone,

I have built a baggage car fo my EN and placed 2 small/medium PF motors inside.

My question is, how would different sized gears affect the movement of this car? I am currently using all small gears the same ones that are used in the custom built bogie. How would using larger gears in the baggage car affect the train or would it at all?

[Alasdair Ryan]

Well it all depends on how realistic you baggage car to be.

I am guessing you would what it quite slow and powerful, so maybe a 1:3 ratio.

Sariel's gear calculator may help you more,and also his gear's tutorial.

[Duq]

Sounds like you're new to the world of gears. In short: If you go from a bigger to a smaller gear then the next axle will spin faster but have less power.

So if you put a 20t gear on your motor and a 12t gear on the bogie, then the train wheels would go 20:12 or 1.66 times faster than the motor. However they would also have 1.66 times less power, so the motor would struggle to get a heavy train moving. Small gear on the motor and bigger gear on the bogie would slow the train down but make it stronger, so it could pull more cars or get up an incline.

[edsmith0075]

Thank you for the info Duq. I plan to regear my EN car to accomidate speed because the XL motor in the Engine is more then powerful enough. Right now it is geared with the same size gears all around. Its the size we use for the bogies. How would having the same all the way around affect speed and torque. I read that it is impossible to get a 1:1 ratio, would this be close to that?

[Duq]

Ah... I didn't realise you had a motor in the engine already. That changes things completely. When you say you read that it's impossible to get a 1:1 ratio I think what that means is that with an XL motor and large wheels in the engine and M motors and small wheels in the baggage car you can't get them both to run the same speed. I've never done the maths on that, I don't know how close you could get them. Would the motors be controlled by the same output on the receiver? The receivers have a limited amount of power they can supply. I think an XL and two M motors would be more than the receiver can handle. If you put them on different outputs then you have to somehow keep the outputs on the same level.

My main question though is: why? How many cars do you have behind your EN that you need extra motors?

[edsmith0075]

Great feedback...

So the M motors are running off the same reciever as the XL. There is enough power for all 3, although I never thought about that when I designed this. The primary motivation for this "spare" powered train car is because of the EN ridgid frame and that it often gets stuck on slight ups and downs with the track. Right now the trains run throughout my whole house when we set them up and due to differences in flooring textures the EN gets stuck on switches and other spots that none of the other trains seem to have issues with.

After testing this Baggage car design I found that having an extra car that pushes the engine just a little bit allows for the engine to smoothly ride over areas that it previously got stuck on. I hope this all makes sense. Oh and I was reffering to the baggage car gearing alone being 1:1. I never even thought of trying to match the car to the engine gear wise. Thanks again for the help.

[zephyr1934]

If your problem is the rigid frame of the EN, you might do fine depowering the EN and only using the power car. If so, you would also want to pull out the gears and remove the drive bands (or all but one drive band) from the EN to reduce drag. Another possibility that you could try is to rebuild your EN so that the front and rear trucks can pivot up when the engine hits a low spot. I did that on my EN but I don't have any photos handy.

[kieran]

If you really want lots of motors you should take a look at the v2 receiver currently shipping with the rock crawler set. This has newer motor controller chips in side that can deliver more current to your motors

[edsmith0075]

Below are the pics of the EN powered Baggage Car I built for this project. Any suggestion on better gearing or design? I have considered removing the drive gears in the locomotive but would really like to keep them and the XL motor. Thanks in advance to everyone for their help...

[Duq]

First tip: use the 'Share' button in Flickr, 'Grab the BBCode', 'Medium'. Then copy that code and paste in your post. Result:

IMG_0481[1] by Edsmith0075, on Flickr

Secondly your gearing. According to Philo's motor comparison the XL motor turns at 146rpm at 9V, while the M motor turns at 275rpm at 9V.

The EN is geared at 20:12 or 1.667:1 while your baggage car has 1:1 gearing. The wheels on the EN have a diameter of 30.4mm, the small wheels on the baggage have a diameter of 17.6mm (source).

This gives relative speeds of 146x1.667x30.4 vs 275x1x17.6 or 7397 vs 4840.

In other words, with your current gearing the baggage car would run at 2/3 of the speed of the engine. If you change the gearing of the baggage car to 20:12 like the engine then it would run at 10% faster than the engine.

It'll probably be hard to get the speeds closer than that without many more gears...

[edsmith0075]

WOW!!!! Thank you for that response! I have been wondering how to post the pics correctly, now I can so thank you!

Thank you for the math, I have a basic understanding of gearing bu t you clearly know you stuff and I have a lot to learn.

Based on that info Im getting a bit discouraged with this setup as Im realizing that the loco and car will not match in power and speed.

Any suggestions on getting them close atleast. Ive been considering now that you have pointed all this out to just remove the XL motor and resort to the pf train bogies perhaps one on the tender only or two on the baggage car to drive this train.

[edsmith0075]

Update, Last night I rebuilt the tender to accomidate the PF Train bogie and removed the gearing from the locomotive. The bogie struggled through turns. It is strong enough, perhaps too strong. It slid and failed to get good traction. Any suggestions? I really liked how smooth the train ran with this setup on the straight sections and how the train did not get hung up on uneven spots.

The XL motor is a powerful motor but noisy and slow. I love the PF bogie but it slips and fails to get enough traction to push the loco through turns and pull the cars.

[Alasdair Ryan]

Try the new L motor,It is becoming one of the most favored Lego motors for moc builders.

Edited May 30, 2013 by Alasdair Ryan

[edsmith0075]

To follow up on this topic. I was able to leave the XL motor in the engine. Instead of using the baggage car as an additional driving force I was able to fit a PF Bogie under the tender. I ended up using the old style bogie, the one that does not come with a cable already attached and with a red marking on it. This bogie was removed from another engine because it lacked the power needed for the newer train models. This motor did however pair up perfect with the XL motor and gearing on the engine.

I have resolved the problem with the EN getting stuck on uneven track! Use the XL motor on the engine and use the old PF bogie on the tender. This combo will ensure a smoother ride with less noise and amazing pulling power. Oh and you can use the directions for retro fitting the old 9V motor to the EN tender to apply the PF bogie just the same. Hmmmmm.... Now I have these extra PF M motors left over, What to build what to build ;-)