Is there a good compromise between speed and power?

[LLeveik]

Hello there,

as the title says, I'm looking for a good transmission or gear setup to achieve both speed and power.

That's what I need it for : I'm currently building an articulated bus, nothing special (no doors, no tilting, but with(at least at the steered axle)suspension and a two speed gearbox.

After building the chassis I'm doing the bodywork now, which led to the problem, that the bus is getting relatively heavy, about 1,7 kilograms.

I use Sariels Heavy Duty Gearbox and three XL Motors for propulsion, one M Motor to shift the gears and one M Motor to steer.

At the moment the bodywork is 1/3 done, I've already tried to save weight by only using one 1x5x11 plate every 9 oder 13 pinholes. The 1x5x11 plates support the weight of the roof and give good insight at the parts I used in there. So having "holes" on the sides is acceptable, but I can't leave out more parts, as the roof would collapse then.

The roof itself is build out of 1x5x11 parts and 1x1x11 to 1x1x15 arms.

I thought adding additional motors (from one up to the three I've currently built in) would help to increase both speed and power, but only if the gear ratio is 1:3 the bus moves well.

So :

- should I add (a) motor(s) to the rear axle, as the middle axle is the only one which is driven, to increase power?

- should I change from PF to NXT, as the motors are able to move with diffrent speed-levels?

- should I change the gearing? If yes, how?

LLeveik

Edited July 17, 2011 by LLeveik

[Milan]

You probably don't need 3 Xls to power <2kg vehicle. One or at max 2 Xls would do the job, and provide both power and speed.

Take a look at Pauls video of TT races-

-there are lots of very big and heavy trucks pushed to the limit on rough terrain and most of them have one, or rarely two XL for drive.

Sure, they are slow, but the buses are not much faster?

-Question is how much speed do you want from your bus?

-Also, if you don't provide enough energy to those XLs of yours, you wont get their full power.

-No need for NXT if you have PF, you can use PF speed controlled to obtain 7 speeds in both directions.

[DLuders]

I recommend looking at Nico71's "TTools v2.0" -- an online "simple web software which calculates some usefull data for TruckTrial and Lego vehicles." Nico71 describes it in this BrickTruckTrial.com article:

"Features

This web-software allows you to calculate some usefull data which are :

• -Linear speed (max and in charge)

• -Torque (in charge and max)

• -Mechanical power (on motor, on wheels)

• -Electrical power

• -Lost power (mechanical and electrical)

• -Efficiency (motors and drivetrain)

• -General efficiency of the vehicule

• -Autonomy (normal use and in charge)

• -Usefull angles (approach, departure and clearance)

Instructions For Use

To calculate this data, it’s very simple :

• -Choose your motor(s) and the number of motor(s)

• -Choose your battery (9V or 7V) and capacity

• -Choose your gears

• -Enter dimensions of your vehicule (wheels base, wheels diameter...)

• -Press "Calculate the data"

It’s a web-software, then just click and try ! -TTools V2.0

About TTools V2.0 - Calculation

• Linear Speed : functions of type of motors, battery , gear reductions and wheel diameter.

• Torque : functions of type of motors, number and gear reductions.

• Electrical power : functions of type of motor(s) and number.

• Mechanical power : functions of type of motors, number and drivetrain

• Efficiency of drivetrain : functions of gears (worm, knob, spur, bevel)

• General efficiency : functions of motor(s) and drivetrain efficiency.

•Lost mechanical power : functions of drivetrain : Worm screw and Knob gears reduce the efficiency. The software detects worm gears, knob gears and spur gears automaticaly.

• Clearing Abilities : functions of dimensions of your vehicule. It’s based on trigonometrical functions.

Normally, the software doesn’t bug if you try absurd values. By the way, if you have bugs, please leave a comment to inform me. Also, this software is under development so if you need other usefull calculated data, please ask me ;)

Note regarding the climbing abilities : At the moment, it’s too complicate to calculate the climbing abilities angle, causes lot of complicated values (wheel, grip, weight distribution, type of constructions, bearing systems friction and roll friction)."

Edited July 16, 2011 by DLuders

[LLeveik]

Thanks for the fast responses!

@Dluders, thanks I will give it a try :)

@Milan : Currently the setups are A)motors-knobwheels-12tooth:20tooth-16tooth:16tooth-20tooth:differential

B)motors-knobwheels-20tooth:12tooth-16tooth:16tooth-20tooth:differential

A) is for slower movement and I'd like to have another speed that is noticeable faster ;)

I weighed the bus and it's weight is about 2,6 kilograms ;)

LLeveik