Author Topic: 2 servos connected = more power?  (Read 4031 times)

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Offline garriwilsonTopic starter

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2 servos connected = more power?
« on: October 08, 2007, 07:33:34 PM »
If you have a sprocket as a servo arm for two equal servos and you connect them, will they go twice as fast or the same speed? Will they have more torque but the same speed?

Edit: If I make a tank like tread on each side of my robot/rc car, with two servos on each tread will it go faster or just have lots more torque? (This has always confused and I didn't know anyone who to ask. I hope it gives more speed,  :P)
« Last Edit: October 08, 2007, 07:35:52 PM by garriwilson »

Offline paulstreats

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Re: 2 servos connected = more power?
« Reply #1 on: October 08, 2007, 07:47:27 PM »
sorry, but youll just get more torque at the same speed.
i have noticed though during normal servo operation that the faster you send your pulses ie. the low pulse length, the faster the servo moves to position, this would probably work well for a modified servo (if the low pulse is too short on an unmodified servo, it makes the servo jitter once it reaches position but because an unmodified servo never reaches position you can probably take it right below the usual 20-25ms).

Offline h3ro

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Re: 2 servos connected = more power?
« Reply #2 on: October 08, 2007, 07:52:22 PM »
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with two servos on each tread

This is probably going to give you a lot of pain. The whole thing would fail/break if the two servos does not move at the exact same speed.

Offline creedcradle

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Re: 2 servos connected = more power?
« Reply #3 on: October 08, 2007, 07:55:13 PM »
"the greater the torque, the lesser the speed"

so if you want to have a greater speed then look for a motor tha has a lesser torque .... ;D
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Offline Tsukubadaisei

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Re: 2 servos connected = more power?
« Reply #4 on: October 08, 2007, 08:24:49 PM »
"the greater the torque, the lesser the speed"

so if you want to have a greater speed then look for a motor tha has a lesser torque .... ;D

No.
You can have high torque with high speeds as well. The best thing to do is do the maths, read datasheets and adjust what you bought  by controlling voltage, current, PWM and using gearboxes/sets.
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Offline garriwilsonTopic starter

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Re: 2 servos connected = more power?
« Reply #5 on: October 08, 2007, 08:41:31 PM »
Quote
This is probably going to give you a lot of pain. The whole thing would fail/break if the two servos does not move at the exact same speed.

So you're saying I should use only one servo per tread? That won't work will it?

And should I just get 4 motors from servo city, an rc transmitter+receiver, and a motor controller (H-Bridge)? Then put two motors on each side since electrical have more speed but less torque, the speed will stay the same but I'll get more torque with 4 motors?

Also, if I wanted to use one servo per tread, how would I do that? I don't know how to explain it but what I imagine with one motor looks weird. Because a tread usually has a couple of wheels...

Quote
i have noticed though during normal servo operation that the faster you send your pulses ie. the low pulse length, the faster the servo moves to position, this would probably work well for a modified servo (if the low pulse is too short on an unmodified servo, it makes the servo jitter once it reaches position but because an unmodified servo never reaches position you can probably take it right below the usual 20-25ms).

I'm going to make this robot RC and how do you send different pulses with a transmitter? (sorry I'm new to this stuff :-[)

Offline creedcradle

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Re: 2 servos connected = more power?
« Reply #6 on: October 08, 2007, 09:31:32 PM »
"the greater the torque, the lesser the speed"

so if you want to have a greater speed then look for a motor tha has a lesser torque .... ;D

No.
You can have high torque with high speeds as well. The best thing to do is do the maths, read datasheets and adjust what you bought  by controlling voltage, current, PWM and using gearboxes/sets.


i see... what if i have a motor with the following:
6000 RPM for my motor - when i am going to put a couple of gears, that won't increase the speed though it increases the torque - thus, it still follow the physics rule- "the greater the torque, the lesser the speed" -just correct me if im wrong.. ;D
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Offline Tsukubadaisei

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Re: 2 servos connected = more power?
« Reply #7 on: October 09, 2007, 06:01:57 AM »
The greater the torque the lesser the speed is valid only, and only if the rpm under no load(or constant load and voltage) is constant. If you have constant rpm you can adjust the final speed/torque using gears. One could say that the mathematical relation between those 2 properties would be: Torque*Speed=constant.
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Offline TrickyNekro

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Re: 2 servos connected = more power?
« Reply #8 on: October 09, 2007, 03:35:35 PM »
For the tread idea:

Not sure for that but if he uses same motors (not exact same) and the same source of power (meaning that he will connect the motors in parallel) then shouldn't he be OK!!!
This idea could work for very very small motor speed difference, of course!!! Because the motors share the same current!!!

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Offline jsmoker

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Re: 2 servos connected = more power?
« Reply #9 on: October 10, 2007, 09:00:51 AM »
I would also suggest going with one motor per tread.  Just use some dummy wheels for the other side of the tread, you also might want a wheel for tensioning purposes (ie to keep the tread taught.  Spacing the wheels just the perfect distance apart can be tricky, if you have a tensioner (a wheel that's spring loaded) it will keep the tread taught without having to make the tread a perfect length, but that's up to you).  In terms of the said speed vs torque trade off, this is true when you have the same motor inside of the servo. They're just switching the gear ratios inside to give you what you want, speed or torque.  I'm not sure what kind of speed you're looking for but this is a nice easy way to start for a gear box and motor.

http://www.sparkfun.com/commerce/product_info.php?products_id=319

again for the other side of the tread you would use free spinning wheels.  This gear box has a good deal of torque even though it uses small motors.  I don't know if it has the speed you want though.  There are three different settings (gear ratios) that you can set it up on.

I'm not sure what paulstreats was talking about with the servo pulses.  With an unmodified servo. the pulse length corrisponds to a position for the servo with the center being something like 1.52ms, when you go to around 2ms it goes to one extreme and 1ms gives you the other (plus or minus 0.something milliseconds).   The further away from the desired position the servo is, the faster it will go to get there.  So if you give it 1.5ms pulse, and you're at one extreme, the servo will *start moving* slower than if you give it a 1ms pulse and you're at the 2ms point (the other end) this is called proportional control.  When you modify the servo you're taking out the part(potentiometer) that tells the servo where you are and lying to it.  usually it's set up so the servo always thinks it's in the middle so the more extreme signal you give it (closer to 2ms or 1ms) the faster it will try to get there, but of course the potentiometer is not telling so the servo continues to revolve at that speed.  The jitter comes when you try to feed the servo the pulses at a speed it's not designed for.  It get's all confused at jumps around.


Offline paulstreats

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Re: 2 servos connected = more power?
« Reply #10 on: October 10, 2007, 04:10:57 PM »
Quote
I'm not sure what paulstreats was talking about with the servo pulses.  With an unmodified servo. the pulse length corrisponds to a position for the servo with the center being something like 1.52ms,


taking about the low pulse width not the high one (the time in between high pulses)


          ---------          ---------          ----------              <---high pulse width
          |       |         |       |          |        |
~~~~~       ~~~~~        ~~~~~         ~~~~     <--low pulse width

Offline Admin

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Re: 2 servos connected = more power?
« Reply #11 on: October 19, 2007, 08:04:56 PM »
There seems to be confusion about speed and torque for motors . . .

A slower motor doesn't mean it has more torque than a faster motor.

Suppose you take motor A, and then gear it. If the speed is reduced by half, the torque is doubled (ignoring gear inefficiency). This is a rule for gear reduction.

Its not a feature of motors, its a feature of mechanical advantage. ;D

Offline Tsukubadaisei

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Re: 2 servos connected = more power?
« Reply #12 on: October 20, 2007, 05:18:42 AM »
Yeah, I posted that a while ago in this thread but people just dont listen.
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Offline garriwilsonTopic starter

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Re: 2 servos connected = more power?
« Reply #13 on: October 22, 2007, 10:33:40 PM »
So speed and torque are directly proportional. I think you write it like this (I learned this in Physics class today!)
speed~torque
right?

 


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