New Bosch Motors desoldered?

[mrobrien]

With a 40 amp breaker in place and our Bosch motors being stalled, the wires that are soldered to the end of the motors desoldered themselves. Has anyone else had a simular problem? Is it generally safe to run with 40A breakers?

[team222badbrad]

UMM that is not good....... If your motors are stalled and are not rotating they become heaters.

In otherwords: Your motors became the Soldering Iron

You probably have your robot geared too high or your wheels, gears, or axles are binding.

GOOD LUCK!!!!!!

[mrobrien]

I wasn't asking why the motors were stalled, that was because a team member got in the way. The motor had a 40 amp breaker on it. When the motors are stalling I assume they draw enough amps to trip the breaker. I also assume FIRST requires that breaker in order to prevent the motors from drawing too much current and getting too hot. However (I wasn't there to see it) the motor apparently had enough time to desolder its wires before the breaker tripped. I was wondering if this was some freak occurrence or if these motors can't handle themselves properly at 40 amps. From what I understand it was a freak occurrence, but I wanted to make sure.

[Andy A.]

heating up motors till they fail is no fluke. It happens fairly often, often during testing.

The motors can handle 40 amps no problem.

They can't handle stall current (well above 100 amps) for long. The problem is that the 40 amp breakers are thermal, and as such do not trip at 40 amps. They trip if you stay above 40 amps. How long that takes depends on how much current you are pulling. With the high currents the new motors are capable of pulling, the breakers should trip fairly quickly at stall.

However, testing a robot means running it for long periods of time. While the breakers may have time to cool in between stalling, the motors will stay much hotter much longer.

When testing, take breaks to let the motors cool.

-Andy A.

[Al Skierkiewicz]

The new drill motors have a stall current of 129 Amps, and the breakers surely would have tripped at that point. To melt the solder at the terminals, that point in the motor had to reach more the 400 degrees. (the melting point of most solders) If that is really the case, (and not a short in the motor due to dropped shavings or other foreign objects) I would consider the motor is now dead. That high a temperature internal to the motor has probably caused the varnish insulation of the motor windings to either fail or be very close to failure. Take a good whiff of the motor near the brush assy. and if it smells burned replace the motor.
Some teams have reported that the brush assy is easily broken and FIRST is recommending that teams DO NOT solder new wires to the motors as the brush assy is plastic and easily melted. Is it possible that brush assy was damaged before this incident and the brushes were actually shorting? Please let us know what you found.

[Joe Ross]

The wire that is already soldered onto the motor looks like 16 guage to me. According to Belden's page 16 awg wire can only carry 26 amps with 105 degree C insulation. Even with 200 degree C insulation, it's only 35 amps. And yet, we have a 40 amp breaker on it. And now, if you look at Ensil's solder melting point page you will see that many types of solder melt at around 200 degree C or below.

Because of this, I'm worried that more teams will experience their wires desoldering. I really hope that there is a flaw in my logic, and that someone more experience then me will point it out.

[Al Skierkiewicz]

Joe,
Notice on your reference page that most solders are in the 350-400 F melting range. These are measured on just the melting of the solder product under controlled conditions and are usually thought of as absolute minimums. In practice on soldered connections in is necessary to get the connection over 400 degrees in order to form a good bond with all the metals. (i.e. non cold solder joint) Please remember that the current capability of wire is expressed in terms of a fixed length in open air or conduit for a fixed temperature rise at a fixed (constant) current over a fixed length of time. Although I haven't determined the wire gauge yet, a short piece of #16 with good connections at both ends would sink some of the heat generated, raising the allowable current before failure.
Also of note, now that specs are published, the motor is reaching peak efficiency at a 25-35 amp range so I don't think most teams will have much of a problem.

[Adam Y.]

Well at least you didn't desolder the wires before you put the robot together. Dohhhhh!!!! This is the last time I will listen to the rules.

[Bob Steele]

The wires that are soldered to the motors are only 16 ga.
We are supposed to use 10 ga wire to connect these motors.
Will this short piece of wire not act as a resistance? and heat up?

we had originally desoldered our motors (using heat sinks) in order to avoid this problem...

any ideas!!???

thanks

[Al Skierkiewicz]

Remember that wire has a specified resistance per unit length. In the case of #10 it is about .001 ohm per foot. Three inches would be about .00025 ohms. At 100 amps the above example would result in a .1 volt drop for 1 foot and a .025 volt drop for 3 inches or about 0.6% change. As far as heating goes in this example the 1' piece develops 10 watts while the 3" piece develops 2.5 watts.
As to replacing the wire, I have to refer to Team Update 7, "DO NOT attempt to unsolder the wires that are attached to the Skill-Bosch motors. The plastic housing that holds the brush assemblies will be damaged if you do. The high temperature of the soldering process causes the plastic to deform and destroys the motor. Teams should make their electrical power connections to the motors’ pre-attached wires, not directly to the brush holders." Hope everyone is keeping up with the updates!

[Adam Y.]

Hope everyone is keeping up with the updates!

Nah we don't have a problem keeping up with the updates we have a problem with the updates keeping up with the team.

[FotoPlasma]

Bob Steele:
Because of the fact that you are required to use 10awg wire to connect the drill, CIM, Fisher-Price, van door, and Globe motors, you're practically required to desolder the original wires attached to the drill motors, and replace them with 10awg wire.

If you can find them at an electronics store, you can use standard crimp-on connectors which are the perfect size to attach to the physical leads on the drill motor itself. This way, you don't have as much risk of physically damaging the motor if the wires are yanked, however that may happen, because they would just pull off, with enough force.

I believe I once heard my father refer to this type of connector as a washing machine connector, used for electical connections in washing machines, if I recall correctly. They typically have a firm plastic cover or shroud over the conductor.

<edit>
Ack. I guess this shows how much I read Team Update 7...
/me wonders if we've damaged our motors...
</edit>

[Adam Y.]

Ack. I guess this shows how much I read Team Update 7.../me wonders if we've damaged our motors...

Double check to make sure. We desoldered those wires and attacked those crimp connectors onto the motors the first time. Unfournatly we destroyed both of the motors doing that. It never hurts to double check.

[Richard Wallace]

The following is copied from the FIRST Q&A site
http://jive.ilearning.com/thread.jsp...=165&trange=15
-------------------
RayN303
Posts: 3
Registered: Jan, 2003
Drill motors
Posted: Jan 14, 2003 7:12 PM

Is it acceptable to wire the 10 AWG wires to the blue wires already soldered to the drill motors or will it be neccessary to connect the 10 AWG wire directly to the motor terminal.

first
Posts: 920
Registered: Dec, 2002
Re: Drill motors
Posted: Jan 17, 2003 10:55 AM

You can do it either way.

36F
------------------------
So I guess the rules don't prohibit removing the leads and attaching 10AWG if you want to.

More recently, Update #7 says under the heading "Cautionary Note About Skil-Bosch Drill Motors!!!!!," not to attempt to unsolder the motor lead wires.

My experience is that soldering heat will deform the plastic brush holder.

[Al Skierkiewicz]

I examined the motor very closely last night. The plastic that holds the brush assemblies in place is very thin. In all likelyhood the wires were soldered to the brush holders first and then assembled to the end plate. As such, I would not recommend soldering at this point either. The wires are #16 but are stamped as 200 C indicating a very high melting point on the insulation. So this is what I would recommend to teams...
1. Above all, protect the brush end of the motor, even aggressive bending on the #16 wires may damage the brush holders and their alignment.
2. Strain relief the #16 wires close to the motor before working on anything else.
3. Strain relief any wires you use to feed the motor.
4. If you decide to solder to the #16 wires, hold the wire with a pair of long nose pliers at the brush assy. The pliers will act as a heat sink and draw away any heat that might damage the brush assy.
You may be asking "Why?" on this motor but you have to remember that this motor was designed to go inside a hefty drill housing not a robot.