Small DC wiper motor burnout

[Sam Neall]

I’m building a racing simulator and due to a potentiometer issue I think one of my motors burnt out. It made my whole room smell and when I opened up the case I saw that a group of the coil was black. The motor now does not have enough power to move my rig. Is there any way to fix the motor? Also if I were to buy a new motor should I buy a replacement for the other one too? The reason I ask is because the motors are pretty old. I don’t want a lot of inconsistency in how the motors respond to certain power and their potential torque if I have a brand new motor and keep the one that is old for the other side of the rig. Basically how much does old age (I’d say the motors are a few years old) deteriorate a motor and how much will it differ from a brand new one. I posted a couple pictures below to give you a better idea of what I’m dealing with.
Thanks!

 

[BrianPetersen]

You can't put the smoke back in after it comes out!

Only way to fix it is to rewind it. No idea if that is a practical or viable option.

 

[Sam Neall]

@BrianPetersen Thanks for the info haha. A new motor runs me about 30 bucks so it’s best to buy a new one. What about the deterioration of a motor like that over a few years. Will there be noticeable differences in how the motor operates when compared to a new one or do you think it will be unnoticeable if I have a new and old motor running different sides of my build?

 

[BrianPetersen]

If they were built the same, they should work the same. Only thing I can think of that might change over time, is if the bearings start going tight or brushes start wearing out, but if either of those is enough to make much difference, the motor is probably almost done anyhow.

 

[Sam Neall]

I will most likely get both. I forgot that there is a lot of vertical play in the motor shaft. Like I can lift the rig up a couple centimeters because of it and you could probably see how in action, when the weight is shifting constantly, it will be a problem. There is a bit of backlash too but that is normal. Do you think having around 100 lbs pushing on the lever attached to the shaft will bend the shaft if I get a new one? I attached a picture so you can see what I’m talking about. Basically do you think the bearing or whatever is holding that shaft in a perpendicular position to the motor is strong enough to withstand that leverage on it? The play is something I can deal with but it’s something that I’d rather get rid of if new motors will fix it and not bend over time due to the design of the rig.

 

[BrianE22]

If the motor is old then maybe the insulation on the wires has been breaking down over the years. If adjacent wires are shorted within the coils then the speed/torque would be different then it would be on a new motor - another good reason to get new motors or rewind both motors.

I can't tell how that lever is coupled to the motor shaft. You should do a free body analysis of the motor shaft to determine the loads on the motor bearings. Then check with the motor specs or the motor manufacturer to see if the loads are o.k. If there is bending of the motor shaft then you should check the bending stress on the shaft.

 

[Sam Neall]

I posted better pictures of it. Thanks For the info. I don’t know who makes the motor. I could probably get in contact with a generic wiper motor manufacturer, but is that something that they are going to record? Wiper motors don’t undergo that kind of downward pressure on the shaft in normal use.

 

[BrianE22]

Ah, looks like you have a right angle gearbox on the motor? If so, then you probably don't have to worry about loads on the motor shaft. The gearbox though....

 

[dArsonval]

The prominently burned single armature coil and burned brush/spring holder in photo labeled "image 6" reveals a STALLED motor condition.

Something mechanical likely caused the motor to seize up and stop.
Investigate what may have prohibited the motor arrangement from spinning freely or otherwise you'll
be replacing a new motor with another new motor.

John

 

[Sam Neall]

@dArsonval Yes like I said it was because of a potentiometer issue that this happened. I fixed it already. Basically the potentiometer slipped and read that the lowest position that the motor was in was the midpoint so it tried to go below the physical boundaries of the lever. The main issue is that I didn’t notice it for a good 15 seconds. It turns out it was slipping because the set screws in that blue coupler were riding on the threads in the motor axle. Idk how I overlooked that haha. I JB Welded the axle so that the axle is smooth. It was old JB Weld so I won’t have problems getting the axle off. This whole thing is DIY so I have to design how everything is attached.

 

[BrianE22]

John -

Would that single armature coil being burned also apply to universal motors? Every once in a while we get one back from the field with the same failure. I know people stall our device. I thought there might be a defect in the one coil that was burned.

 

[Sam Neall]

@BrianE22 Sorry I meant the shaft coming out of the gearbox not the motor itself.

 

[Compositepro]

For want of a fuse the motor was lost. Don't let it happen again.

 

[Sam Neall]

@BrianE22 So now that you have a better understanding of what I’m working with here, just speaking generically, would a motor bearing (or whatever is holding the output shaft in place) that size be able to withstand around 100 lbs applied about an inch away from the actual output (since the lever is bent out a little as you can see in the pics attached). If It’s a dumb question and there’s no telling, I just need to find a workaround to the vertical play because when the weight in the simulator shifts from one side to another, you can really feel the play rock the upper platform. Maybe I could weld a larger bearing with the same ID as the output shaft onto the bracket. I’m only 17 so I’m still learning about this stuff. I’m not 100% sure what I’m doing so pardon my lack of knowledge haha.

 

[waross]

You must live somewhere warm.
In most of Canada it is common in the winter for the wiper blades to by stalled by several inches of heavy wet snow.
At other times the wiper blades may become frozen to the windshield.
The gearbox and shaft easily withstand stalled rotor torque.
In an automobile an automatic resetting circuit breaker protects the wiper motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Sam Neall]

I’m not really worried about rotational torque. I’m worried about the pressure that is being put on the gearbox shaft downward. I attached a picture of the entire rig so you can see what I’m talking about. Other pictures haven’t probably been too descriptive. I’m specifically worried about that silver Shaft that connects the upper platform to the motor putting to much downward pressure on the gearbox shaft and bending it.

 

[BrianE22]

Sam -

I think I know what you have - gearbox output shaft with a crank installed. I'm guessing the bearing you mention is supporting the gearbox output shaft. Can you make a sketch of what you have? The only way to know for sure is to construct a free body diagram. As far as the backlash is concerned, it looks to me like there is weight on the rod connected to the crank. The weight would keep the linkage "preloaded" to a degree and should mitigate backlash problems.

I think Bill's point about the robustness of wiper motors also applies to the gearboxes. They would need to be designed to handle the moments the wipers produce. Still, you need that FBD (free body diagram).