aminnich

Adding more motors for more torque and speed?

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Hi guys, 

I am not sure how to really explain this.... 

All numbers are just for example, nothing is legitimate.  If I had;

1 motor with 1lb ft of torque and 1 mph output speed

2 motors 1 lb ft of torque per motor, but geared up to give me 2 mph output speed

3 motors 1 lb ft of torque per motor, but geared up to give me 3 mph output speed

Does that make sense? I am not taking battery box supply into effect, but basically do more motors give me more torque and speed? 

 

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Of course they do !

PS: Zblj had 8 XLs when he pulled a car with his truck.

Edited by IA creations

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I don't think that would be true, you have tgo add into your equation the motor torque reduction due to gearing up, the weight increase, the friction that is created to such a high amount of gears...

It's not that direct , but if I'm correct , without any gearing you would get better acceleration , but if you add gearing, things get more complex...

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It make sense - but only in an ideal world. In the real world adding gearing reduces speed AND torque, about 10% - 20% depending on the type of gears used.

Like @LXF said, it's better to use motors without gearing if possible - especially when gearing up. 

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Hey aminnich, "how many gears is too many?" is a very open question which is impossible to answer outright due to the number of gears not being the only contributing factor to loss of torque and rpm due to friction.

Other things which MUST be considered are; type of gears used (spiral, bevel, spur etc), placement and housing design (if the housing is not rigid and flexes this can add friction due to the structure that the gears are built into being twisted when torque is applied through the input shaft(s), length of shafts (a drive train may not be able to withstand the torque being supplied if any one shaft is too long and can flex), the drive motor (different motors have different rpm/torque outputs and the performance drop for each motor will be different depending on the given number of gears between motor and final drive.

Hope this helps!

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Hi Aminnich, what type of model you have in mind?, because i might be able to give you some tips about torque and rpm and the gears if i know what kind of model you want to make; to answer your first question, you are right in that, adding more motors adds more mechanical power (which is both torque and rpm), so theoretically, if you double the quantity of motors you double the power, but as it has been said before, that only happens in a perfect world (which means: no friction, no power losses and no external factors which alter the power), about the gears, i think that you should try to avoid them as long as you can, i think that it is better to use the right motor for the duty instead on adding an excessive number of gears (which cause a lot of power loss), you should use them only when too much speed or torque is required or if you dont have the right motor; i hope this helps you a little bit and i will try to give you more information if you need it.

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There is one way to find out how many gears is too many.  Experiment with the motors and gears you plan to use.  That's how I do my GBCs since I do not remember my engineering math stuff.  :laugh:

 

 

 

 

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Theoretically, yes, speed and torque are lost due to friction when many gears are involved.  I won't do the leg work and re-look this up, but if I am not mistaken, that was one of the problems identified in the Porsche set, early on, by Paul (aka Crowkillers I think it was) as to why the gearbox was not functioning properly.  I can't remember exactly how many gears drive was passing through, but it was well into double digits. 

However, I think for practical purposes, unless you are having drive transmitted through like over double-digit individual gears, the power lost will be negligible.  This all depends, as mentioned by others, on which motor you are using, weight of machine, etc.  But if the build is somewhere in the "normal" range (say 1500-3000 pieces) and you are using XL motors, I don't see using many gears as a huge problem.  The drive in my Unimog in my signature block went through five individual gear meshings, for an incredibly inefficient final output of 35:1, but still, at around 2000 pieces and over 1000 grams in tires alone, was able to travel through over six inches of water, mud, gunk, etc with no problem.  It was powered by a very powerful LPE, but still, I think the friction in the five gear parings did not have a horrible effect on my output.  On a more recent project that I will not repost, a crawler powered by Buwizz (in the Buwizz thread if interested), I had only three gear pairings, but one of which was planetary gears through a Bionicle wheel with cleats (and flanges, BL part 64712).  For anyone who has ever tried this configuration they will know that it is entirely inefficient and costs much power due to friction, but the crawler still performed marvelously; able to climb a curb with no problem.  

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I want to rebuild my battle not, except without any constraints. I want to see if I can build it any better. It needs lots of speed and torque.

i have enough L motors and XL motors. 

What you guys are saying makes a lot of sense 

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11 hours ago, aminnich said:

I am not taking battery box supply into effect, but basically do more motors give me more torque and speed? 

Both @MattL600 and myself have recently seen better performance when separate batteries (i.e. standard Lego's 9v box) were used to power separate motors - fyi, in case you have any doubt that the added weight won't be worthwhile :laugh:.

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I was thinking 10-12 L motors and like 4 battery boxes.  I think that would be a good amount of power supplied for that amount of motors 

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14 minutes ago, aminnich said:

I was thinking 10-12 L motors and like 4 battery boxes.  I think that would be a good amount of power supplied for that amount of motors 

That'll be about 1 battery box per 2-3 L motors - will still perform better than 1 L motor... but I would go for 1 L motor per battery box, but that's me :tongue:

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1 battery box per motor will not happen haha, Do you wanna buy all those batteries for me???

6 per box * 12 boxes...... 72 AA batteries 

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:grin: 

1 hour ago, aminnich said:

1 battery box per motor will not happen haha, Do you wanna buy all those batteries for me???

6 per box * 12 boxes...... 72 AA batteries 

 

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15 hours ago, aminnich said:

how many gears would you say is too many?

Probably more than 2 or 3, and try to keep it in a single stage (of gearing).

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Good example with my record racers:

- 28,47 km/h with 2 buggy motors and geared up 1:1,667, versus

- 32,71 km/h with 4 buggy motors geared up  1:2,5 (for now, it is a WIP), but in this case i had to add a lot of weight in the form a 2nd rc-unit (battery box)

Not by far linear results.

Consider that the axles will spin at insane speeds within its brackets, causing a lot of friction, grinding parts down or even melting them, especially when using smaller tires (they need more RPM for the same speed)

6 hours ago, aminnich said:

 

I was thinking 10-12 L motors and like 4 battery boxes.

 

Please let me know how this works out with the new battery boxes, but (i took this from  Philo's page on motor specs) a stalled L-motor can draw 1,3A, that is probably more then 1 box can handle, old boxes could handle around 800ma, i do not know what the new ones can take. Surely you will not stall the motors, but without load they already draw 120mA, and gearing them up will draw a lot higher current from the boxes, multiply that by 3 in your case. 

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4 hours ago, Marxpek said:

Good example with my record racers:

- 28,47 km/h with 2 buggy motors and geared up 1:1,667, versus

- 32,71 km/h with 4 buggy motors geared up  1:2,5

This is explained by the increase in torque - more torque overcomes more of the friction, making it closer to the theoretical speed. 

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Gears indeed reduce torque and overall efficiency of the motors. For example, 42065 has two motors directly attached to axles rotating the drive sprockets and one is in the front, the other in the back for a reason. I guess if the gearing wouldn't decrease performance, both motors would be placed in parallel to vehicle's length, alongside each other (then again, weight distribution is also important).

23 hours ago, Marxpek said:

Consider that the axles will spin at insane speeds within its brackets, causing a lot of friction, grinding parts down or even melting them

A VERY important thing when building the gearing is making it solid. For example, when using XL motor and small, 8-tooth gears (it was a must in my case of a quite compact RC C-model of 42030), the gears MUST be sandwiched between liftarms or connectors on both sides if the motor is used under even a slightest load. Otherwise, the gears will skip and wear super-fast.

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Rather than aiming for more force, more size, more weight (and therefore, more cost and more chances of damaging stuff), you also gain speed by scaling down: a smaller, lighter build will move faster than a larger build with the same power.

In the end, I think, it's about power-to-weight ratio. More motors mean more weight, more weight mean the motors have to do more work, so in the end, the power-to-weight ratio may be a little bit better, but I expect the actual improvement to improve only slightly, compared to the increased size and cost

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3 hours ago, Erik Leppen said:

Rather than aiming for more force, more size, more weight (and therefore, more cost and more chances of damaging stuff), you also gain speed by scaling down: a smaller, lighter build will move faster than a larger build with the same power.

Agreed, sometimes smaller - not bigger - is better :wink:, I always start as small as I can, and only increase the size as needed. 

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3 hours ago, Erik Leppen said:

Rather than aiming for more force, more size, more weight (and therefore, more cost and more chances of damaging stuff), you also gain speed by scaling down: a smaller, lighter build will move faster than a larger build with the same power.

In the end, I think, it's about power-to-weight ratio. More motors mean more weight, more weight mean the motors have to do more work, so in the end, the power-to-weight ratio may be a little bit better, but I expect the actual improvement to improve only slightly, compared to the increased size and cost

 

23 minutes ago, mocbuild101 said:

Agreed, sometimes smaller - not bigger - is better :wink:, I always start as small as I can, and only increase the size as needed. 

Also, if you need your build to be heavy (you want no holes and/or your design requires a lot of decorations etc.), try setting a low point of mass. The Wideguy Van I built (of 42030 parts, excl. wheels) is pretty heavy, but runs relatively fast on single XL motor. Said motor and servo are set as low as I could and they, just like the battery box, became the key elements of the frame (replacing the batteries is more difficult, I admit, but it was worth it). Adding numerous lighter parts above had no noticeable effect on speed and as I used a preposterous gear ratio (w/ sandwiched gears I mentioned a few posts above), it goes fast for a bulky and heavy vehicle. The battery box' upper "arms" are mounts for the exhausts, lower - for rear fenders. Motor is just below the floor on the right side of the vehicle and servo - on the left:
Wideguy Van RC

Edited by Immo

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sounds like there are pros and cons to using a bunch of motors.  I will just have to test it out and see what works the best. I am not sure what my next build will be, but it could be a larger model of my battle bot using what you have have been talking about the past couple days on this thread.  Thanks for all the feedback.  

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