gearing the minibot

[JP Carlin]

We are currently looking into running our tetrix motors for our minibot without the attached gearboxes. we have mounted the motor and can not find a way to now gear the motor to the wheel 2:1 for power given the holes in the aluminum. if any teams have a solution to this without drilling new holes into the aluminum thanks for the help

[Bill_B]

Originally Posted by JP Carlin

We are currently looking into running our tetrix motors for our minibot without the attached gearboxes. we have mounted the motor and can not find a way to now gear the motor to the wheel 2:1 for power given the holes in the aluminum. if any teams have a solution to this without drilling new holes into the aluminum thanks for the help

1. how did you mount the motor without a gearbox?

2. into what aluminum are you averse to drilling holes?

3. wheel? 2:1? do you want the wheel to spin twice as fast as the motor? I saw a video which had a tetrix wheel hitched to a gearboxless motor. It spun so fast that the rubber tread was thrown off.

pictures will help. They should show what you have tried so far. Just asking the readers here to solve another problem in addition to the ones we're already trying to solve for ourselves might not get much more response than this one.

[JP Carlin]

Sorry for lack of info. It is mouted by just using some eletrical tape woulnd around it to have it large enough to be held by the mounts. The main issue I'm having now is now gearing it to make up for some of the power lost by removing the gearbox. I tried going from the smallest gear on the motor to the medium gear on the wheel today only to find that that did not provide enough torque to lift the robot and almost burned out a motor although I'm not sure if this might be because of the battery not being fully charged. Tomorrow I will try replacing the 80 tooth gear on the wheel with the 120 tooth wheel to see if that will provide enough torque to lift the bot up the bar And the gear ratio I am going to use is not for speed but for power as I feel the way the tetrix gearbox on the motor sacrifices too much speed so I am replacing it with a gear ratio to give it enough power to lift itself without sacrificing too much speed

[vamfun]

Originally Posted by JP Carlin

We are currently looking into running our tetrix motors for our minibot without the attached gearboxes. we have mounted the motor and can not find a way to now gear the motor to the wheel 2:1 for power given the holes in the aluminum. if any teams have a solution to this without drilling new holes into the aluminum thanks for the help

If you are planning on using your existing wheels, e.g. a 4 in diameter wheel then you will need to provide a similar gearing that the gear box provided. When you removed the box, the motor speed/torque are now 8775.00 rpm/10.47 oz in. A 4.5lb robot going up a pole with 4 in wheels needs around a 1:29 to operate at the peak power point. However, you can use a tiny tire, say, 0.3 in in diameter and do pretty well without a gearbox

[JP Carlin]

So using only the 4inch wheels and a 3:1 gear ratio it is pretty much impossible to loft a five pound bot

[Alex.q]

Originally Posted by vamfun

If you are planning on using your existing wheels, e.g. a 4 in diameter wheel then you will need to provide a similar gearing that the gear box provided. When you removed the box, the motor speed/torque are now 8775.00 rpm/10.47 oz in. A 4.5lb robot going up a pole with 4 in wheels needs around a 1:29 to operate at the peak power point. However, you can use a tiny tire, say, 0.3 in in diameter and do pretty well without a gearbox

How would I calculate this?

Also, do you have any suggestions on how to modify the tetrix gear box?

[Jeffy]

Originally Posted by Alex.q

How would I calculate this?

Also, do you have any suggestions on how to modify the tetrix gear box?

A simple way to get mostly accurate results is to use the potential energy gained at the top compared to the power output of the motors.

Gravitaional potential energy: mass*gravity*height (mass*gravity=weight)

Once you know the potential energy you have, you can divide it by the power output of the motors, and it will give you the time it will take. I would add about 20% to that time to give you a buffer zone aswell. Power ratings for the motors can be found here: http://www.chiefdelphi.com/forums/sh...ghlight=tetrix

Speed calculations are pretty straight forward, and I would assume you know how to do them because you should use them for your drivetrain as well.

[vamfun]

Originally Posted by Alex.q

How would I calculate this?

Also, do you have any suggestions on how to modify the tetrix gear box?

theoretical gear ratio at a given %torq_used for steaty state climb.
Peak power requires %torq_used = .5.

gear_ratio=r_m*(m_kg*9.8+drag_force)/(tq_max_nm*eff*num_mot*%torq_used)

tq_max_nm = max motor torq in nm
%torq_used = .5 for peak power. .3 to lower your current
num_mot = number of motors,
eff = gearing effectiveness
drag_force = bearing_coeff_frict*Normal_force (eg .22*Normal_force)
m_kg = mass in kg
r_m = radius of tire in meters