Fast axle for heavy vehicle

[Richter]

Hello! Can anybody please give some hints or tips or even some instructions how to make a heavier model to drive fast using gears? Im currently building K2000 model weighing some 3kg and the axle I built is quite slow, so Im looking for alternative axle designs which would make the car move abit more quickly

Thanks!

Edited November 24, 2014 by Richter

[Corvette3]

At 3kg im not sure if fast is even possible, what kind of motors are you using?

[Richter]

At 3kg im not sure if fast is even possible, what kind of motors are you using?

Im using one XL engine. The Axle I have produced have the gears with four round teeth on them, to prevent the grinding.

[Corvette3]

Two might work better, but im not sure what other gear ratios you need, the ball gears only produce a 1:1 ratio have you got a pic of your models drivetrain?

[Richter]

Two might work better, but im not sure what other gear ratios you need, the ball gears only produce a 1:1 ratio have you got a pic of your models drivetrain?

My drivetrain

http://www.upload.ee/image/4376965/drivetrain.jpg

[Zerobricks]

The heavier the machine the more power you need to overcome friction.. I suggest you tise lego hubs, because they can support lots of weight with little frivtion. Also use as low gear number a spossible. A picture of the whole thing would also help.

[Richter]

A picture of the whole thing would also help.

Some pictures of the whole vehicle

http://www.upload.ee/image/4377055/knight.jpg

http://www.upload.ee/image/4377056/knight2.jpg

http://www.upload.ee/image/4377059/knight3.jpg

http://www.upload.ee/image/4377061/knight4.jpg

[AndyCW]

The key to having a fast vehicle is weight/power.

The PF motors only put out a little power and so weight reduction is a key element.

Anytime you make it faster, it has less torque.

You could try to gear up the motor with a 20t DB pinion gear and a 12t B ring gear. All other things equal, this will give you 67% more speed, but a 67% reduction in torque.

If you watch RC lego videos on YouTube, you will see very few fast ones.

v/r

Andy

[andythenorth]

The knob wheels are high friction.

Instead of one motor for the axle (with a 90 degree turn) I would try one motor per wheel, ideally direct drive, no gearing.

1 M motor per wheel might have enough torque, and would be faster than XL.

[Boxerlego]

Gears don't want to work like this when being heavy is involved. Its better to use a bigger and stronger motor that is geared down to produce the required torque to drive the heavy designs. Once in motion this is where transmissions come in to play in where you can put that heavy weight and momentum in to action and be able to reach speeds that you couldn't if you were to go from a dead start because the design is to heavy to start in that high gear selection.

Edited November 25, 2014 by Boxerlego

[Richter]

But how do you gear up/down the motors?

[Rockbrick]

you need the torque to overcome the inertia to get the thing moving - so maybe some sort of variable transmission would help

or just a simple LO-HI ratio gear box

[SNIPE]

How about using the motors as part of the chassis so a lot of the weight just sits on top of the motor's casing?

Edited November 25, 2014 by SNIPE

[aol000xw]

But 3 Kg with only 1 XL motor is going to be slow no matter what, isnt it?

[andythenorth]

To give you a reference point, this is about 2.5Kg. 8x L Motor, 2x battery box. It's geared for pulling power not speed (it will pull at least 10x own weight).

https://www.flickr.c...th/14071162377/

Apologies in advance if the flickr video doesn't play, flickr video is borked in some browsers.

Sariel has made some insanely fast MOCs (can be found on this forum). Low weight is the key.

Edited November 25, 2014 by andythenorth

[Tommy Styrvoky]

I would suggest using several XL motors, at least 2-4 or use L motors for each axle.

[andythenorth]

I would suggest using several XL motors, at least 2-4 or use L motors for each axle.

Agreed. I would suggest starting with 2x L Motors per wheel (4 in total). This is the maximum that can be practically driven from one battery pack.

Based on Philo's charts (if I've read them correctly), 2x L is less efficient than one XL, but it gives more flexibility over mounting, and the motors rotate faster. The XL will need gearing up though to get an acceptable speed. Gearing up = friction losses, more space needed, and parts will break. http://www.philohome...ec/pfcurves.htm

Ignore all the suggestions about gearboxes, they're not robust enough to deal with the amount of torque you need to get into that single axle. You'll have split gears, stripped gear teeth, or the clutches will slip under load (or all 3).

Try the train controller to have variable speeds, I'm 100% guessing here, but I think it uses PWM, which I think means it regulates frequency rather than voltage (which means on the low setting the motor gets a brief kick at full voltage every n ms). But I'm pure guessing, and it's half my life away since I studied electrical machines, and I wasn't good then.

The point being that on low speed setting the motor will get enough torque to start the vehicle without trying to apply full torque (and tearing up parts). That's my experience anyway, but it might be way off reality.

Edited November 26, 2014 by andythenorth

[Tommy Styrvoky]

Ignore all the suggestions about gearboxes, they're not robust enough to deal with the amount of torque you need to get into that single axle. You'll have split gears, stripped gear teeth, or the clutches will slip under load (or all 3).

Yeah go as robust as possible, use double bevel gears and knob gears for driving the axles, spur gears are prone to chewing teeth and breaking in half.

[SNIPE]

I thought there was 2+ motors?

Edited November 25, 2014 by SNIPE

[piterx]

3kg won't go fast :P ever

maybe you could try with a gearbox and a clutch but i can guarantee that it's not going to go fast anyway

if you want something fast it needs to stay below 900g and has to use 2RC motors :P

[Blakbird]

3kg won't go fast :P ever

It can go fast in a free fall!

[Mikuri]

Put 1-2 RC motors and it should help :P

But I would try 1 L-motor on each wheel. Should be enough.

[SNIPE]

After googling how much KG is in stone I now will say:

Impossible!

[andythenorth]

There's fast and there's fast.

If the original poster is just looking for 'faster than with one XL using high friction knob gears', that's no way impossible.

[Richter]

Thanks for the suggestions guys!My only problem right now is that I have 2 XL motors but one's broken apparently, so I have to use only one atm until I get a new one. Ill try to upload a video about the car moving soon!