P-Power hacksaw

Between the novel drive (wiper motor) and the novel material (printed) this project sounds like it would make a great article for the MEW magazine. It sort of combines old-school ideas like the reciprocating hacksaw and cheap motor drive with modern technology of the 3D printer. IT would make interesting reading and pics in an article for sure. It is certainly something that has never been covered before (AFAIK).

Edited By Hopper on 19/04/2017 11:36:07

Back to the original question of the wiper motor running too hot, it might just be a cheap aftermarket Chinese part that simply is not very good. It happens all the time. Maybe better to get an Original Equipment Manufacturer part, even a used one can be better than the poor quaility Chinese reproductions. I see this type of thing all the time with motorcycle parts.

I bought this motor in UK, so I thought that would be an genuine part...?

Hopper,

After that last remark I immediately did a search on YouTube, and guess what...It has been done before...!
Shame on me......

Chris

Hopper is probably right that it's an after-market motor. The ebay small-print says: "Part Manufacturer: Unbranded".

I can't say if being unbranded is the problem or not. I don't know how hot is normal for a wiper motor and I can't easily get at the one in my Corsa.

Dave

Hey guys,

Did some additional testing. Somewhere in one of the posts higher up I read that the casing itself could be the "-" (ground).
So I connected the powerunit's negative lead to the motor's casing and connected one of the (2) wires coming from the motor to the "+" and it worked to. The yellow wire gave me a higher speed and the white one a lower speed. 75 and 40 rpm.
But.. It also got hot, just the same as before when I connected the two leads white/yellow directly to the powerunit. This resulted in a speed of (about) 100rpm.

Chris

Since you dismantled part of the motor to look at the gears, you may as well look inside the motor and see what's is in there. (and hopefully report back)

The wormwheel in your photograph seemed to show the slipring section that I would expect as part of the parking mechanism but I dont see any wiring to the brush contacts.

The two speed technique I have seen in other automotive motors is with a third brush on the commutator. The two normal brushes at 180 degrees to each other are used for the normal/slow speed. One of those brushes is used with a third which might be say, 150 degrees to it. The supply current is then much higher because there are less commutator segments and less copper in the circuit. The motor is a lot less efficient but its a cheap way of getting the results for the manufacturer.

Nowadays I would have thought that motor speed might be controlled electronically but maybe not in entry level cars.

The printed saw you linked top looked quite good (although a bit of it looked to be wobbling) so I think yours has a lot going for it.

Ian P

Edited By Ian Phillips on 19/04/2017 18:27:11

If you read the fine print at the bottom of your linked eBay posting, it says "Brand New Aftermarket Part". That could very well be your problem right there. They really do make some rubbish over there. It works good enough to move the wipers and maybe last the 12 month warranty period, or maybe not in which case they give you another unit that costs them about $5 to buy from China. It's a racket. The heat would be from where the aftermarket motor does not have the same amount of copper windings as the original (expensive) and/or smaller, cheaper magnets, so the motor is underbuilt, underpowered and working harder. Wheareas the original OEM part might last 10 or 20 years, the aftermarket part will last one or two years.

Edited By Hopper on 19/04/2017 23:52:40

I mean it has not been covered in MEW magazine before and just seems like exactly the type of article that would suit. INteresting video though.

Another thought, you might try to get a heavier duty wiper motor of a larger car like a Toyota LandCruiser four-whee-drive or large American pickup truck etc that would have more power to start with, as it is designed for larger wipers. LandCruiser parts are very solid indeed. More so than little Vauxhall cars, although we don't get that brand here in in Oz these days so I am making assumptions there.

Some more pictures while cannibalizing it even more.
Two brushes are angled at 180° and a third one is angled at (about) 60°.
So that explains it about the two different speeds I suppose.

Well it is definitely a two speed motor. For your application the motor will be best on the slow (180 degree) brushes.

Can I suggest you undo the brush carrier plate and lift it slightly to see which wire goes where (or whether there are any other bits lurking)

Strange that the self parking mechanism is not apparent. Maybe on modern cars its done with an optical sensor on the blade mechanism.

The other oddity is that in order to stop the wipers dead in the parked position the usual method is to short out the motor. This would be done on the 180 degree brushes regardless of what speed the motor was running at. The is shorting might nowadays be done by whatever electronics is controlling the motor.

Ian P

I did mention this previously about the motor having two speeds.......obviously missed by many I guess....

If you connected your supply directly to the two wires rather than one wire and the casing, it will make the motor run hot!

"Have you considered that the motor may be a two speed job?

The negative connected to the body of the motor and the positive connected to one of the two wires for the two speeds?

Ordinarily, the brushes would  be opposite each other with half of the armature connected across the supply, with a third brush contacting a reduced number of coils, would give a higher speed but an increase in current....."

Edited By John Rudd on 20/04/2017 09:23:01

No no I didnt miss it at all John, that's why in the end I disassembeled it. Thanks for the tip..!

In the second picture of the last post the yellow lead(on the right) is 180° sepparated with the "-" lead(far left) and result in the higher speed. The 60° brush(center in the picture), connected to the white lead gives me the slower speed.

So now we have a third wire! (originally you said there were two wires coming from the motor)

So white and yellow go direct to brushholders, what is the third brush connected to, and what is the third wire connected to?

Ian P

Earlier you mentioned the possible difficulty of attaching a crank to the tapered and splined shaft. What I have done is created a taper hole (I used a hand taper reamer) that is somewhere near the right size and used the nut to pull the part up very tight to 'bed' the splines. As you are only adding a single crank the precise alignment is not critical if the crank does not pull up dead square. My crankpin was a ball joint which give a lot of leeway.

If you add locking compound into the equation it will be more than strong enough as the end result will be limited by the plastic gear on the shaft.

Ian P

Basically there are two wires that go to the brushes (yellow/white). The third one is the one I added and is connected to the outside of the casing. That's the black one in the picture.

If you look closely at the last picture, you'll see that the left brush is connected directly to the casing(with a screw) The brush on the right is connected to the yellow lead via a connecting-nippel
Sorry if I was not clear the first time...

This is my old hacksaw that will be replaced. Like I said before it takes up to many space in my workshop.
On the far right you'll notice a windscreen-wiper-motor. That one is getting hot to.
This saw runs at 60rpm, I'd like to speed up the new one a bit. I'm aiming at 80 maybe 100 rpm

In the vise a 50mm -2"- brass rod.

There are three brushes......there are two wires.

Two wires go to two brushes.

The third brush is connected to the motor casing= 3rd wire....

That covers it even better, thanks John.
In my post at 10:00:03 I should have added : The second wire(white) is connected to the most upper brush in the picture(barely visible)

Thanks again John..

Yesterday I was parting of a thick piece of brass with my old power hacksaw. For some reason my saw got stuck without me noticing it. It stayed blocked for an estimate 1.5 hours. Entering my workshop after that amount of time I immediately was alarmed by the unmistakable smell of burned electronics.
To make a long story short. Powerunit was not working anymore and was rather hot. The windscreen-wiper-motor was boiling hot. So that was the end of it, lucky me I was planning to make a new one. And lucky me that nothing worse had happened.
Next day al was cooled down and I thought why not, lets try that thing and see what happens. Guess what, if as nothing had happened the day before, that hacksaw started to work again. And what's more I used the same (computer)powerunit to power that hacksaw. Big surprise, that was absolutely not what I expected.

Point of this story : No need to be afraid anymore; windscreen-wiper-motors can handle this kind of abuse...