RCCrawler Forums

RXcrawler · 08-09-2006, 03:35 PM

Here's my set up on the TXT:
GP 3300 mAh batteries, SR ESC, Magnetic Mayhem motor, GD-600, 2 Hitec 805 1/4 scale servos, 6.0V 2000 mAh reciever pack. Rx pack goes to a Y-harness one side plugs into the rear servo the other plugs into the reciever, other servo plugs into the receiver.

Same setup since late last year...no problem until lately.

Problem when the truck gets into a bind with the wheels turned it won't go, if I let off and don't turn the wheels it will usually go then. Sometimes it will do the same thing when its not in a huge bind. I originally thought it was from the reciever pack batteries going dead, but testing it today it would do it before the rx pack should be dead. I now think the motor is going bad: how do you tell if a motor is going bad. I compared the brushes to anothet MM and they were almost ½ the length, but the spring still holds them tight. Would new brushes help?

Since the servos are ran off the rx pack and the motor has its own battery; why would the rx pack going dead cause the motor to lose power. In the past when the rx pack goes dead you can still drive the truck but when you start to turn the wheels it will lose all power (like you let off the throttle) Are the two batteries still somewhat connected since the rx pack is plugged into the reciever. When I plug up the rx pack the ESC comes one even though it's switch is off (which I assume is normal, the ESC getting its power from the reciever bypassing the ESC's BEC). Did I just answer my own question with that?

JohnRobHolmes · 08-09-2006, 04:06 PM

Could be a few things. Your motor probably needs a comm cut and new brushes for one. If the RX pack is very old, it could be suffering from voltage depression under load. What kind of cells are they? Those mammoth servos could stress the pack enough to drop the voltage down and cause the ESC to shut off.

SVEN · 08-09-2006, 04:08 PM

Half!?!?! dang dude, change those brushes. And check the commutator while you are at it. If it appears to be worn (blackened) or bowed, it may need to be turned on a comm. lathe. Now I wish I hadn't sold my comm. lathe, or I could do it for you. Since I started using a brushless motor in the triple-X (before I started crawling), I never thought I would go back to brushed motors...oops. If there is a hobby shop nearby, they may be able to do it for a small fee.

RXcrawler · 08-09-2006, 04:33 PM

The rx pack is 5AA cells 2000mAh. I orginally thought the problem was form them being old(about 1 year old) but I had one I had never used and it did the same thing. What is "voltage depression under load" if this is happening will the pack still take a regular full charge. Would Hitec 5995 servos stress the pack as much as these 1/ scale servos.

RXcrawler · 08-09-2006, 04:35 PM

Is there a specific type of brushes to buy? Is there a type that is better for crawling?

JohnRobHolmes · 08-09-2006, 04:47 PM

Im ignorant on brushes for the most part, i will pass that Q to someone else.

Voltage depression happens to a battery when the load exceeds the capability of the battery. For example: GP 3300 cells drop to 0 volts when the load exceeds 400 amps for any period of time- fully charged or not. Smaller batteries like the AA's you are using will depress under a lower amperage. Most new AA's will start to drop rapidly in voltage when the load exceeds 15 amps. I doubt you are drawing that much power, but as the cells get older from manufacture date they handle less amperage.

Old cells will still appear to take a full charge, and they can dish that full charge back out if the load doesnt "stress" them too much. Once you exceed the discharge capacity, the severe voltage depression begins.

SVEN · 08-09-2006, 05:02 PM

For an Integy lathe motor, you will need laydown brushes (rather than standup). Here is a great guide to motor tuning: http://www.motortuningsecrets.com/tunestockmotor.html

I don't know of anyone testing different types of brush face cut patterns (in a crawler). But I really don't think crawlers will see any of the advantages of the different cuts that a racer will notice.

slobin3d · 08-09-2006, 05:13 PM

ive heard of people using stiffer springs to guard against brush hop under heavy stress but lathes dont spin all that fast so i dont know if its worth doing.

HVFracingwilly · 08-09-2006, 05:33 PM

for racing ive always used "f-brushes" or reedy 767's both are great brushes. make sure you true the comm b4 you replace the brushes or it will be worthless.

Go here for the brushes and the even have a rebuild service! great guy he sponsors my other forms of racing!

www.axiommotors.com

08-09-2006, 03:35 PM	#1
RXcrawler Moderator Join Date: Apr 2004 Location: In my head Posts: 2,744	Okay smart guys help me understand this one! Here's my set up on the TXT: GP 3300 mAh batteries, SR ESC, Magnetic Mayhem motor, GD-600, 2 Hitec 805 1/4 scale servos, 6.0V 2000 mAh reciever pack. Rx pack goes to a Y-harness one side plugs into the rear servo the other plugs into the reciever, other servo plugs into the receiver. Same setup since late last year...no problem until lately. Problem when the truck gets into a bind with the wheels turned it won't go, if I let off and don't turn the wheels it will usually go then. Sometimes it will do the same thing when its not in a huge bind. I originally thought it was from the reciever pack batteries going dead, but testing it today it would do it before the rx pack should be dead. I now think the motor is going bad: how do you tell if a motor is going bad. I compared the brushes to anothet MM and they were almost ½ the length, but the spring still holds them tight. Would new brushes help? Since the servos are ran off the rx pack and the motor has its own battery; why would the rx pack going dead cause the motor to lose power. In the past when the rx pack goes dead you can still drive the truck but when you start to turn the wheels it will lose all power (like you let off the throttle) Are the two batteries still somewhat connected since the rx pack is plugged into the reciever. When I plug up the rx pack the ESC comes one even though it's switch is off (which I assume is normal, the ESC getting its power from the reciever bypassing the ESC's BEC). Did I just answer my own question with that? Last edited by RXcrawler; 08-09-2006 at 07:49 PM.

08-09-2006, 04:06 PM	#2
JohnRobHolmes owner, Holmes Hobbies LLC Join Date: Nov 2004 Location: Volt up! Gear down! Posts: 20,290	Could be a few things. Your motor probably needs a comm cut and new brushes for one. If the RX pack is very old, it could be suffering from voltage depression under load. What kind of cells are they? Those mammoth servos could stress the pack enough to drop the voltage down and cause the ESC to shut off.

08-09-2006, 04:08 PM	#3
SVEN I wanna be Dave Join Date: Feb 2005 Location: Burnsville Posts: 3,096	Half!?!?! dang dude, change those brushes. And check the commutator while you are at it. If it appears to be worn (blackened) or bowed, it may need to be turned on a comm. lathe. Now I wish I hadn't sold my comm. lathe, or I could do it for you. Since I started using a brushless motor in the triple-X (before I started crawling), I never thought I would go back to brushed motors...oops. If there is a hobby shop nearby, they may be able to do it for a small fee.

08-09-2006, 04:33 PM	#4
RXcrawler Moderator Join Date: Apr 2004 Location: In my head Posts: 2,744	The rx pack is 5AA cells 2000mAh. I orginally thought the problem was form them being old(about 1 year old) but I had one I had never used and it did the same thing. What is "voltage depression under load" if this is happening will the pack still take a regular full charge. Would Hitec 5995 servos stress the pack as much as these 1/ scale servos.

08-09-2006, 04:35 PM	#5
RXcrawler Moderator Join Date: Apr 2004 Location: In my head Posts: 2,744	Is there a specific type of brushes to buy? Is there a type that is better for crawling?

08-09-2006, 04:47 PM	#6
JohnRobHolmes owner, Holmes Hobbies LLC Join Date: Nov 2004 Location: Volt up! Gear down! Posts: 20,290	Im ignorant on brushes for the most part, i will pass that Q to someone else. Voltage depression happens to a battery when the load exceeds the capability of the battery. For example: GP 3300 cells drop to 0 volts when the load exceeds 400 amps for any period of time- fully charged or not. Smaller batteries like the AA's you are using will depress under a lower amperage. Most new AA's will start to drop rapidly in voltage when the load exceeds 15 amps. I doubt you are drawing that much power, but as the cells get older from manufacture date they handle less amperage. Old cells will still appear to take a full charge, and they can dish that full charge back out if the load doesnt "stress" them too much. Once you exceed the discharge capacity, the severe voltage depression begins.

08-09-2006, 05:02 PM	#7
SVEN I wanna be Dave Join Date: Feb 2005 Location: Burnsville Posts: 3,096	For an Integy lathe motor, you will need laydown brushes (rather than standup). Here is a great guide to motor tuning: http://www.motortuningsecrets.com/tunestockmotor.html I don't know of anyone testing different types of brush face cut patterns (in a crawler). But I really don't think crawlers will see any of the advantages of the different cuts that a racer will notice.

08-09-2006, 05:13 PM	#8
slobin3d I'm a stupid C U N T! Join Date: Jun 2005 Location: In the Garage! Posts: 4,307	ive heard of people using stiffer springs to guard against brush hop under heavy stress but lathes dont spin all that fast so i dont know if its worth doing.

08-09-2006, 05:33 PM	#9
HVFracingwilly Newbie Join Date: Dec 2005 Location: Oshkosh Posts: 26	for racing ive always used "f-brushes" or reedy 767's both are great brushes. make sure you true the comm b4 you replace the brushes or it will be worthless. Go here for the brushes and the even have a rebuild service! great guy he sponsors my other forms of racing! www.axiommotors.com

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