Anyone figure out MA jumping to motor?

ejaf · #1 11-21-2002, 10:33 PM

Just curious about some of the findings I've read about...

There was a great thread on MM readings to the ZZ motor, fluctuating between 60 and 110 mA.

Decided to try for myself, and lo and behold, I confirmed that finding (jeez, I wish I hadn't thrown out my analog when I bought the digital).

Anyone know what's up wit dat?

E

Azimov · #2 11-23-2002, 10:22 AM

Is that on the same car or do you get different readings of output from one car to the next?

And what is MM by the way?

wild03 · #3 11-23-2002, 11:58 AM

Quote:

Originally posted by ejaf
Just curious about some of the findings I've read about...

There was a great thread on MM readings to the ZZ motor, fluctuating between 60 and 110 mA.

Decided to try for myself, and lo and behold, I confirmed that finding (jeez, I wish I hadn't thrown out my analog when I bought the digital).

Anyone know what's up wit dat?

E

Cheap motors!?!?

If you put a similar load using a resistor I bet that the current will be constant. It might have to do with the poor quality of the motor that as it turns different friction at different points might cause the resistance and current to vary...wild guess!

Azimov · #4 11-23-2002, 12:16 PM

Sounds reasonable to me. Could also be due to friction in the gears fluctuating and increasing or decreasing load.

ejaf · #5 11-23-2002, 12:24 PM

Can't be the motor....measurements were taken between the motor contact points without the motor in the car.

There was a previous thread regarding the measurements, and whether the current was pulse modulated. I was wondering whether that is truly the case, and what advantages PM would give the car.

wild03 · #6 11-24-2002, 02:40 AM

Quote:

Originally posted by ejaf
Can't be the motor....measurements were taken between the motor contact points without the motor in the car.

There was a previous thread regarding the measurements, and whether the current was pulse modulated. I was wondering whether that is truly the case, and what advantages PM would give the car.

I am no expert but as far as I know an amp meter is a short circuit to other circuits and should never be placed across a power source. by doing that type of measurement you are creating a short-circuit on the board. when you measure amps you do it with the circuit intact. the meter itself provides no load on the circuit, making it a strait wire. The correct way should be between the motor casing and the tab at the on the chassis floor
I measured 13 or so mA this way!

ejaf · #7 11-24-2002, 11:41 AM

Got you on leaving the circuit intact...I'm no EE, but measuring amps has to be done in series, and you are losing the resistance of the motor.

I was following the measurements and points taken by Namuna on this thread:
http://www.tinyrc.com/forums/showthr...t=pulse+mod%2A

Measurements aside, however, what would be the advantages of this current being pulse modulated?

wild03 · #8 11-24-2002, 08:35 PM

Quote:

Originally posted by ejaf
Got you on leaving the circuit intact...I'm no EE, but measuring amps has to be done in series, and you are losing the resistance of the motor.

I was following the measurements and points taken by Namuna on this thread:
http://www.tinyrc.com/forums/showthr...t=pulse+mod%2A

Measurements aside, however, what would be the advantages of this current being pulse modulated?

Yes amps are measured in series and with the motor you will be measuring actual working amps on the circuit, taking the measurement without the load makes no sense. The batteries could be sending 500AMPS and the motor will only use 10mA or 15mA, that's what the circuit will show. the batteries will always supply more than enough, it's the actual device that you want to measure. At a constant voltage in order for the amps to increase the motor will have to have less resistance. I'm no EE either but I know plenty of them at work, I'll have to ask them and get back to you. but I'm almost sure that you are shorting something out and that could be the cause of your amp measurements being all over the place!

I did the measurement with the motor and the amps were fairly constant at around 10mA to 15mA

ejaf · #9 11-24-2002, 08:59 PM

Interesting...could be shorting something out. Good that you know some EE's at work...all I know from people at work are C sharp (the "new" language), java beans, and what not (I'll stay on the data side of things, thank you).

Funny thing though...even if I am shorting things out, the measurements taken that way jump on the ZZ, yet on my bit clone (I just checked my Shen Qi Wei), the amp measurement is a CONSTANT 291 mA (same exact measurement points, without the motor in the car). That's what probably allows higher RPM motors, right?

Quote:

The correct way should be between the motor casing and the tab at the on the chassis floor

Exactly what do you mean by "tab at the on the chassis floor"? Let me know, so that I can measure that way too, to see if I get the same reading.

If the meter has to be in series, how could I break the circuit with the motor still in place?

Azimov:
Sorry I didn't answer you earlier...
MM = Multimeter

Quote:

Is that on the same car or do you get different readings of output from one car to the next?

I checked the readings without the motor in between 1 ZZ and one bit clone (Shen Qi Wei....boy, is that fast...)

wild03 · #10 11-25-2002, 11:54 AM

Quote:

(I'll stay on the data side of things, thank you).

I'm a programmer myself, mostly C++. they build them I make them move type of relationship. Most of them are out this week due to the holidays but as soon as I get a hold of one I'll get back to you,

Quote:

Exactly what do you mean by "tab at the on the chassis floor"? Let me know, so that I can measure that way too, to see if I get the same reading.

The tab that makes contact with the motor casing, It you want to read actual amps you would need to connect the positive wire on your meter on that tab, the negative wire on your meter on the motor case(I used an alligator clip to hold the motor) and hold the back of the motor so it will touch the other tab. THEN with your 3rd hand you will need to push the remote button foward, the motor should turn and you'll get the actual amps under load on the circuit. The amps without load mean nothing maybe how much load can the circuit handle but nothing more.

Quote:

That's what probably allows higher RPM motors, right?

Yes in theory the bits could handle a greater load.

Again, I'll get an experts opinion on this matter and get back to you.

Namuna · #11 11-25-2002, 02:17 PM

I updated the thread where I posted my results...http://tinyrc.com/forums/showthread....&threadid=1501

I made a little diagram with the PROPER way to test for current (in series) using a little ingenuity to make life easier for testing.

wild03 · #12 11-25-2002, 03:59 PM

Quote:

Originally posted by Namuna
I updated the thread where I posted my results...http://tinyrc.com/forums/showthread....&threadid=1501

I made a little diagram with the PROPER way to test for current (in series) using a little ingenuity to make life easier for testing.

Much better, I'm glad that we agree, Placing no load on the circuit will actually short it out.

You can also Put some tape on the motor case where it makes contact with the tab, then just put the meter on the outher casing and on the metal tab where it leaves the board. I think there's more room there than on the back of the motor.

ejaf · #13 11-25-2002, 10:36 PM

Thanks for the input, guys...

I couldn't take the measurement in series as in Namuna's post (couldn't get the damn probes anywhere near the tab that touches the motor), but what I did do was put it in series BEFORE the motor (tab on the bottom to the motor casing).

Interesting results:
ZZ ~ 20 mA
Shen Qi Wei ~ 42 mA
Panther ~ 59 mA

I would have loved to get the measurements AFTER as well, if only to see what resitance the motors are causing, but I probably need to pick up smaller diameter probes (I tried other ideas, but none worked).

I am now definitely leaning towards swapping the PCB from the Panther into the ZZ. I was going to do the dual battery mod, but giving the amperage numbers, even with the dual mod, if Ohm's law is in effect, I'm only going to increase the current to 2 times 20, or ~ 40 mA.

I can get that and more with the Panther PCB. Or am I missing something here? The more I think about it, the more I am leaning to this suggestion from Stridex, which was posted in another of my threads.

wild03 · #14 11-26-2002, 09:55 AM

Quote:

Originally posted by ejaf
Thanks for the input, guys...

I couldn't take the measurement in series as in Namuna's post (couldn't get the damn probes anywhere near the tab that touches the motor), but what I did do was put it in series BEFORE the motor (tab on the bottom to the motor casing).

Interesting results:
ZZ ~ 20 mA
Shen Qi Wei ~ 42 mA
Panther ~ 59 mA

I would have loved to get the measurements AFTER as well, if only to see what resitance the motors are causing, but I probably need to pick up smaller diameter probes (I tried other ideas, but none worked).

I am now definitely leaning towards swapping the PCB from the Panther into the ZZ. I was going to do the dual battery mod, but giving the amperage numbers, even with the dual mod, if Ohm's law is in effect, I'm only going to increase the current to 2 times 20, or ~ 40 mA.

I can get that and more with the Panther PCB. Or am I missing something here? The more I think about it, the more I am leaning to this suggestion from Stridex, which was posted in another of my threads.

Again I could be wrong but it doesn't matter if you take the measurement before or after the motor. Amps is = current flow and if the motor only allows 20mA that's what the circuit will transfer.

Swapping boards WILL NOT help you because the bottle neck is the motor, swapping boards will only help if you plan on going to lower resistance motors that allow more amps to flow, if the motor needs more amps than the circuit can supply then swapping to a Board that supplies more amps will help. Try the ZZ motor on the other cars and see if you get the 20mA again make sure all board supply the same volts or the amps will vary.

Dayfall · #15 11-26-2002, 12:59 PM

I believe that swaping out the PCB will make a diffrence. I made my measurements parllel to the motor and found that the resistance across the H-bridge on the ZZ was prety high. I was interested in knowing how much loss was in the transistors since those were the only parts I could replace.

Measuring in series to the motor will let you know how much power you are using. Volts*Amps=Watts I think. So using another motor will increase your current draw in the same way using another PCB would.

Also, I would like to suggest that the motor should not be allowed to turn when measuring in series to give the best idea of how much power the car has.

Oh, and there is definatly no pulse width modulation. I do hope somebody tries to send a PWM signal from the transmitter. Has anyone heard of someone succedding or failing at trying this?