Author Topic: 4,5 kg/cm for 15 kg wheelie thing  (Read 1922 times)

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Offline arexxTopic starter

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4,5 kg/cm for 15 kg wheelie thing
« on: November 21, 2010, 08:19:54 AM »
2 motors with roughly 9 kg/cm of stall torque are enough for a 2 wheeled car with around 30 kg of weight? the wanted rps is around 1.

Ive used the RMF, but all servos ive found have the torque in kg/cm, yet here its kg/m. and if im doing the math correctly, ill need a gazzilion servos, lol

cheers

Offline waltr

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Re: 4,5 kg/cm for 15 kg wheelie thing
« Reply #1 on: November 21, 2010, 09:58:51 AM »
There are many on-line conversion apps to convert the torque units which are handy to check your math.

You may not find large enough hobby servos for this although there are some very large servos made.
A better choice would be gear motors and a motor driver/controller circuit.

Offline arexxTopic starter

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Re: 4,5 kg/cm for 15 kg wheelie thing
« Reply #2 on: November 21, 2010, 10:30:53 AM »
There are many on-line conversion apps to convert the torque units which are handy to check your math.

You may not find large enough hobby servos for this although there are some very large servos made.
A better choice would be gear motors and a motor driver/controller circuit.



So the servos in question will NOT work? crap :S.

by gear motors you mean DC, i suppose. I was thinking about using an arduino board, what else will I need to get?

Offline rbtying

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Re: 4,5 kg/cm for 15 kg wheelie thing
« Reply #3 on: November 21, 2010, 10:57:14 AM »
There are many on-line conversion apps to convert the torque units which are handy to check your math.

You may not find large enough hobby servos for this although there are some very large servos made.
A better choice would be gear motors and a motor driver/controller circuit.



So the servos in question will NOT work? crap :S.

by gear motors you mean DC, i suppose. I was thinking about using an arduino board, what else will I need to get?

You'll need a motor driver that can handle the voltage and current passing through the motors, and probably some sort of feedback to make a closed-loop control system. 

Just a note:  Most of the robots that run on modified servos mass < 3kg.  It's not really surprising that a 30kg bot can't use them.

Offline waltr

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Re: 4,5 kg/cm for 15 kg wheelie thing
« Reply #4 on: November 21, 2010, 11:54:02 AM »
Quote
what else will I need to get?
As I posted above:
Quote
and a motor driver/controller circuit


Offline arex

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Re: 4,5 kg/cm for 15 kg wheelie thing
« Reply #5 on: November 23, 2010, 05:19:58 PM »
And can two servos with 20kg cm stall torque move a wheelie with 15kg?

Offline Soeren

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Re: 4,5 kg/cm for 15 kg wheelie thing
« Reply #6 on: November 23, 2010, 08:32:16 PM »
Hi,

And can two servos with 20kg cm stall torque move a wheelie with 15kg?
Stall torque is not the only important parameter, but assuming you didn't put 15kg on their axles and they each has got 20kg-cm, yes, they would be able to move it, very slowly, on a level plane, as long as your wheels are less than 5.3cm in diameter - make the wheels 5.4cm and it won't budge.
The output shafts on a regular servo won't like the load or the direction of same, but it could be coupled to an axle mounted in bearings.

Servo motors are ridiculously small though and get their strength at the cost of slow speed due to heavy gearing. If you want your vehicle to move in a fashion that'll keep you from dosing off, use gear motors.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline arexxTopic starter

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Re: 4,5 kg/cm for 15 kg wheelie thing
« Reply #7 on: November 24, 2010, 10:31:03 AM »
Thanks for the reply!

I need 1 rps roughly, so it should be ok?

and, in case i end up using DC motors, any suggestions on the switch control on the H bridge? with an arduino board and the ports id like to close and open the switches... ive thought about some LED and LDR system to control the passage of current, but I dont really see that working

thanks A LOT :P

 


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