L vs XL Motor and Servo Motor for RC Car Model?

[ARXD]

I have the Motorized Bulldozer (8275), so I got two XL motors, two M Motors and remote.

I wish to build RC car (I got all the right parts from other sets), but I don't have L motors or a Servo motor.

I plan to build 2 speed transmission: first gear for crawling (high torque - low speed) , second gear for fun speed around the house (low torque - High speed)

1. Should I buy a servo motor, or one of the M motor that I already have can do the Job?

2. L motor (that I don't have) vs XL Motor to power the wheels?

what is the advantage that L motor has over XL motor beside size? (if any)

Don't want to spend a ton of money on unnecessary parts.

Thanks.

Edited January 8, 2016 by ARXD

[JJ2]

In my experience an XL motor is best for larger builds that need high torque and slow speed but L motors are good for smaller vehicles that need more speed that torque. M-motors are great for steering for slow vehicles e.g. a crawler, but are not the best with fast vehicles.

Hope this helped!

Edited January 8, 2016 by JJ2

[ARXD]

Anyone else?

[aminnich]

I think JJ2 hit the nail right on the head. Unless your doing a speed gear box then you might want an XL and L motor, but it doesn't sound like that's what you want

Edited January 11, 2016 by aminnich

[PunkTacoNYC]

Hey, you can definitely use what you already have. Depending on the size, an XL or two XLs will do the job (note that XL motors, as powerful as they may be, are somewhat underpowered when it comes to speed). You can use one of your M motors as if it were a servo with one of these systems: http://www.eurobricks.com/forum/index.php?showtopic=54104. And finally, for the gearbox, you can use your other M motor for the gear shift via a worm gear, linear actuator, or pneumatic pump. I suggest the worm gear with - if possible - a white 24 tooth safety clutch gear. Good luck on your build!

P.S. about the XL motors, if you want your creation to have good speed without using a buggy motor, you are going to want your car to be rather small with preferably two XLs. Yup, two. Here are two points for reference in terms of the relationship between size of the model and propulsion needed: http://www.sheepo.es/2011/10/xr7-mini-rally-car.html and http://www.sheepo.es/2014/03/axr-400-crossbone.html.

[xyz]

See why You shouldn't buy LEGO Servo Motor CLICK

Edited January 12, 2016 by Alasdair Ryan
Removed link

[dalswede]

See why You shouldn't buy LEGO Servo Motor *****

You might want to check your link out, as when clicked, it opens up some ad site first which just showed some naked girl. Click a second time and it's something else.

So not friendly for the younger members on here maybe. (Obviously you will now get a million clicks )

Edited January 12, 2016 by Bob De Quatre
Removed link

[ARXD]

See why You shouldn't buy LEGO Servo Motor CLICK

Sorry, I can't see that link, It was removed.

Hey, you can definitely use what you already have. Depending on the size, an XL or two XLs will do the job (note that XL motors, as powerful as they may be, are somewhat underpowered when it comes to speed). You can use one of your M motors as if it were a servo with one of these systems: http://www.eurobrick...showtopic=54104. And finally, for the gearbox, you can use your other M motor for the gear shift via a worm gear, linear actuator, or pneumatic pump. I suggest the worm gear with - if possible - a white 24 tooth safety clutch gear. Good luck on your build!

P.S. about the XL motors, if you want your creation to have good speed without using a buggy motor, you are going to want your car to be rather small with preferably two XLs. Yup, two. Here are two points for reference in terms of the relationship between size of the model and propulsion needed: http://www.sheepo.es...-rally-car.html and http://www.sheepo.es...-crossbone.html.

Thank you very much for your post, it was VERY helpful.

[andythenorth]

L Motor

- great form factor, many connection points

- can make a very compact axle with one motor per wheel, almost direct drive, with optional gear ratios

- quite fast, and adequate torque, but not super efficient: http://www.philohome...s/motorcomp.htm

- relatively expensive

See album + video here for direct drive with L motors: https://www.flickr.c...157649987860696

XL motor

- large form factor: suits larger models. Needs placing away from wheels in smaller vehicles: means longer transmission, more parts, more to break, more power lost to friction.

- slow and very high torque: needs gearing up to achieve decent speeds

- so much torque that it will destroy technic gears trivially if blocked

- relatively cheap

For both L and XL, real-world power output is capped by current limitations on PF receivers (and probably battery box). This can be solved by using more receivers and battery boxes. e.g. I have

- truck with 3 XL motors for drive and an M for steering, with 2 battery boxes and 3 PF receivers.

- truck with 4 L motors for drive and a servo for steering, this has one battery box and 3 PF receivers.

- truck with 8 L motors for drive, this has 2 battery boxes and 4 PF receivers

The current limitations can be calculated by people who understand that stuff, I just test by trial and error to find what gives good performance.

Edited January 12, 2016 by andythenorth

[ARXD]

I am going to try to couple 2 XL together, that will give me twice the torque with the same RPM (using Adder differential)

For high speed, I will use the extra torque to gear it up to 2.7:1 = ~400 RPM at 10.5 N.cm

For low speed, I will use the extra torque to gear it down to :1:2.7 = ~52.5 RPM at 80.5 N.cm

Edited January 12, 2016 by ARXD

[zux]

From my experience with XL motors you would want to have as less gears as possible between motor and wheels. Otherwise expect damaged gears.

[andythenorth]

I am going to try to couple 2 XL together, that will give me twice the torque with the same RPM (using Adder differential)

I have tried this approach before. 2 XL motors on the inputs for the differential will quickly destroy the 12-tooth gears in the differential.

[oracid]

This interests me a lot !

Regardless of the differential problem, do you think it is not advisable to couple two motors XL, powered from the same battery?

[andythenorth]

Regardless of the differential problem, do you think it is not advisable to couple two motors XL, powered from the same battery?

Depends what your goal is.

Two XLs will work fine from one battery box / IR receiver. If you're adding any other motors (steering, other functions), you might want a second battery box / receiver. Three XLs won't perform well on one battery box / receiver.

Other factors:

- there are different versions of the IR receiver, there is a comparatively rare 'v2' receiver, which I think handles more current.

- battery type: I use rechargeable NiMH AA batteries at 1.2v, which gives 7.2v. You get more performance/longer run time from alkaline AA batteries at 1.5v, giving 9v. So I am using more battery boxes with NiMH than someone might need for alkaline.

- more batteries = more weight. More weight = more tractive effort (pulling power - good for trucks), but also higher battery drain, slower, and if you're building a crawler, worse crawling performance over obstacles (more weight to lift, more likely to topple over or slide due to battery weight).

There's no right answer for every situation, but it's fun to build and find what works well and what works badly

[ARXD]

Well, I was experimenting last night with the 2 XL Motors on a very basic experimental vehicle,

- Empty and with heavy wight on it.

and here is what I have found so far:

- Two XL Motors are always better the one XL motors, that extra torque is significant.

- Reduction Gear Box for two XL motors is NOT what I need for my next creation!

In 1:1.4 ratio test, Motor connected directly to rear differential (20T to 28T differential) the motors are VERY POWERFUL and VERY SLOW,

this is great for constructions models like my old Bulldozer or for a 4x4 Crawler, BUT not suited for my next RC FATH (Fun Around The House) model.

In 1.19:1 ratio test, Motor pass through 1.6 Multiplier gear box to rear differential (20T to 12T, 20T to 28T differential) The experimental vehicle drive in fair speed and still have a A LOT of torque to spare!

I will continue to experiment in the next few days, coming up:

1.985:1 Multiplier gear box, (20T to 12T, 20T to 12T, 20T to 28T differential)

2.143:1 Multiplier gear box, (36T to 12T, 20T to 28T differential)

And for the fun of it , I will also try:

6.429:1 Multiplier gear box, (36T to 12T, 36T to 12T, 20T to 28T differential) - I will video-tape this one :)

I really want a good gear box, possibly with "Gear Adder", witch will also open up others Multiplier gear box ratio like

1:1,

1.98:1,

and 2.78:1

Will updated as I progress.

*edit:

I have uploaded a video of my testing last night for your amusement (and some pics of the experimental vehicle)

My Experimental Vehicle:

Edited January 13, 2016 by ARXD

[oracid]

Depends what your goal is.

Two XLs will work fine from one battery box / IR receiver.

The question I ask myself, regardless of the power problems, is it dangerous for the internal gears of the motors to couple two motors XL to double the power of an specific action ?

Edited January 13, 2016 by oracid

[aminnich]

This is what I was thinking you could do.

except, this builder has the output drive shaft down gearing for more torque, you could gear up and speed up depending on what kind of weight you have on your model.

[ARXD]

The question I ask myself, regardless of the power problems, it is dangerous for the internal gears of the motors to couple two motors XL to double the power of an specific action ?

YES and NO

It depend HOW you do it,

"Hard-Coupling" is a simple solution, this is good for M or L Motors, but can be harmful for motors with heavy load/torque

The safest way is to use Adders, but that also add friction, wight and take space in a design

adder makes use of a differential in order to equalize the differences between two (or more) inputs and to drive a single output.

I like to build powerful designs so for safety I always use adders.

Edited January 13, 2016 by ARXD

[oracid]

YES and NO

It depend HOW you do it,

"Hard-Coupling" is a simple solution, this is good for M or L Motors, but can be harmful for motors with heavy load/torque

The safest way is to use Adders, but that also add friction, wight and take space in a design

Do you mean that any differences in speed of the two motors can break the gears?

One can quite easily turn the axis motors XL, so I thought reciprocal attenuation solved this problem..

I feel that your two solutions are equivalent.

[ARXD]

Do you mean that any differences in speed of the two motors can break the gears?

One can quite easily turn the axis motors XL, so I thought reciprocal attenuation solved this problem..

I feel that your two solutions are equivalent.

They are not equivalent.

In hard Coupling, one motor is attached directly to the second motor, any speed variation will put strain on both motors.

In adders, any difference between speed inputs will be equalized by the system of the differential’s inner gears. The output will be driven by the sum of the inputs’ torques and the average of their speeds.

[zux]

"Hard-Coupling" is a simple solution, this is good for M or L Motors, but can be harmful for motors with heavy load/torque

Is there a real issue using two hard coupled XL motors if they are connected to same point on IR Receiver? They would work simultaneously, with same speed. Unless you think that two motors may have their specs slightly different?

[ARXD]

Is there a real issue using two hard coupled XL motors if they are connected to same point on IR Receiver? They would work simultaneously, with same speed. Unless you think that two motors may have their specs slightly different?

Yes, this is a real issue.

All motors has some differences in tolerances and spec PLUS it's own footprint of wear and tear (How it was used/played history)

No motor is exactly the same, and when you coupled motors you need to take that to account, especially large motors (XL or RC)

Hope it's helps.

Edited January 13, 2016 by ARXD

[Blakbird]

Hard coupling electric motors is absolutely no problem at all. Yes it's true that no two are exactly alike and therefore the power they provide will not be equal. They will therefore draw slightly different currents. But as long as they are on the same channel there is no chance of one backdriving the other. This is exactly how many real life systems are coupled and I do it all the time. Philo did a practical study on this some time ago.

[Samer]

I did some builds with M motor steering:

M-Motor + rubber band or

M-Motor + this(better):

P.S. I love this discussion about coupling motors, useful ideas..

[oracid]

Hard coupling electric motors is absolutely no problem at all.

I agree, but here it is with integrated motor speed reducer in output.

They are not equivalent.

In hard Coupling, one motor is attached directly to the second motor, any speed variation will put strain on both motors.

In adders, any difference between speed inputs will be equalized by the system of the differential’s inner gears. The output will be driven by the sum of the inputs’ torques and the average of their speeds.

I'm sure you're right, but I still do not understand. That is my problem.

Anyway, thank you for your explanation, I take good notes.