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Unread 01-18-2005, 07:01 AM
Gdeaver Gdeaver is offline
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Re: THE Fisher-Price Motor Spec Sheet

If the FP motor gear box is used for an arm, limiting PWM is a bad thing. In certain positions the motor is going to be starting under a considerable load. It might be better to start the motor at full and reduce down once its moving.
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Unread 01-18-2005, 08:48 AM
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Re: THE Fisher-Price Motor Spec Sheet

Yeah, I generally do not like hard limiting anything. At least leave a "boost" button on the joystick or something to let you go to max power. Even if you end up frying your motor, you may need that last push at the end of the match.
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Unread 01-18-2005, 10:44 AM
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Data

I have some data, not as solid as I might like, but at least I have something.

#1, I counted teeth and I concur with Paul Copioli's count.

#2, I clocked one transmission at 12 V, no load:
100 Revolutions in 49.5 Seconds = 2.0 Rev/Sec = 120 RPM Close enough to Paul's prediction of 132 RPM when you consider that the gears DO actually provide some load to the motor even if the output shaft of the motor is "free"

#3 Current things get murky because of my test set up.
I only had a power supply with a current out meter. Also, I only had aligator clip type jumpers to power the motor -- looking at the data, I think that these must have affected my data.

In theory, the resistance of the motor should be 0.081 Ohm.

Voltage Current A Current B 1 4
2 14
3 22 20 4 30 30 5 40 39 6 48 47 10 75 74 Slope 0.125 0.131
The slopes are much higher than .08 Ohms! I was disappointed but I think it is more a function of my test set up.

I do not have time to repeat the test with a better set up right now, but I think that we can fairly safely say that the motor AS SPECed is the motor AS SHIPPED.

Feel free to confirm my test with your own data. If you do, please share.

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Unread 01-18-2005, 01:18 PM
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Re: THE Fisher-Price Motor Spec Sheet

I seem to be kind of slow (midterms are over time to get it together). Does any body have the accurate specs of the F-P motor or are they not avalible because theres confusion over what voltage the motor can be ran at?
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Unread 01-18-2005, 02:04 PM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by troy_573
I seem to be kind of slow (midterms are over time to get it together). Does any body have the accurate specs of the F-P motor or are they not avalible because theres confusion over what voltage the motor can be ran at?
In my mind, I am convinced that the specs as published are the spec of the motor we have (excepting any mixed lot parts that where shipped by mistake -- but it seems that that is the minority of parts, if any).

The issue of what voltage you can run them at is an open one. The motor can "stand" 12V. If the motor is not loaded too highly, 12V will be just fine. If you load the motor down, you are asking for trouble.

Bottom line for me: Keep V*I Power from becoming m*Cp*(dT/dt) Power and you will keep your motors cool and happy. Run too close to the stall point for too long and the acrid smell of burnt motor windings will fill the air ;-)

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Unread 01-18-2005, 08:43 PM
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Re: THE Fisher-Price Motor Spec Sheet

Thx alot dr. joe but i must say after our meeting today i am even more mind bottled. Every body keeps saying "the F-P is the strongest motor in the kit. I know im not the best in the world at math but a some people have checked my math and its correct i got the following


F-P has 5.364 FT LBS @ 126 RPM

The Van Door has 22.1 FT LBS @ 75 RPM

The Denso has 6.78 FT LBS @ 92 RPM

The Jideco has 6.144 FT LBS @ 85 RPM

Please would some body check this information to make sure it is correct because if it isnt i dont want others to use it (me) and i would like to know what mistakes i made in calculating these numbers

Also if these number are correct although at diffrent RMP's isnt the Van Door stronger than the F-P .... thats what makes me think i have made a error.

Also ive read that the van door is not good for arms and needs to be operated at high rpms .... well lets say we needed 90 ft lbs and gave the van door hmmm 5 to 1 ratio would the rpm of the van door drop to about 15 ..... if so is that safe for the van door because i know theres some sort of fan inside
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Unread 01-19-2005, 09:32 PM
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Re: THE Fisher-Price Motor Spec Sheet

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Unread 01-19-2005, 11:49 PM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by troy_573
Also if these number are correct although at diffrent RMP's isnt the Van Door stronger than the F-P .... thats what makes me think i have made a error.
I think you may be confusing torque with power. Power is torque times angular rotation.

The FP is the most powerful motor in this year's kit. If you gear all the motors to the same speed, the FP will have more torque (if we are to believe the spec sheets).
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Unread 01-23-2005, 09:33 PM
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Re: THE Fisher-Price Motor Spec Sheet

Another thing to think about...

If the FP GB was designed to work with this motor at 6v, what are the plastic gear teeth going to do when you stall it at 12v?

Is it reasonable to expect that they over-designed the gear teeth by a factor of 4x? (2x to account for the 2x of the motor and an additional 2x so that you have your standard safety factor.)

In 2002, we pushed the FP gear teeth beyond their normal operating range and spit out teeth in every match.

Just one more thing to watch out for.
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Unread 01-23-2005, 09:55 PM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by Andrew
Another thing to think about...

If the FP GB was designed to work with this motor at 6v, what are the plastic gear teeth going to do when you stall it at 12v?

Is it reasonable to expect that they over-designed the gear teeth by a factor of 4x? (2x to account for the 2x of the motor and an additional 2x so that you have your standard safety factor.)

In 2002, we pushed the FP gear teeth beyond their normal operating range and spit out teeth in every match.

Just one more thing to watch out for.
The last stage of the F-P gearboxes is not strong enough for a drivetrain; not comfortably anyway. Modifications that 188 made in the (distant) past included metal gears in the last stage, and new (metal) shafts for all of the gears, to replace the plastic ones. We've avoided the F-P gearbox altogether since 2000.
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