The BiT Bang Theory

Hi! As I mentioned in my latest post on how to make Tiny Encoders for DC Motors, some time ago I went to a junkyard to salvage two powerful high torque DC motors from car window lifting systems to use in a robot. I had to take my own tools and dismantle the doors from an old Renault Laguna myself  to get the motors and then managed to negotiate with the seller to buy both motors for 25€, which I think was quite cheap.

I tested the motors by connecting them to an old ATX power supply to the 5V and 12V lines and verified that both of them were working as desired. The current consumption was near 2.5A with 5V and near 3.5A for 12V which is more than I was expecting but nothing that I can’t work with.

The motors have a worm gear that gives them a very high torque and stops them from rotating if any mechanical force is applied to them. They only rotate if current is flowing through the coils of the motor.
The motors that I got have an interesting thing: the axle does not spin.

The only thing that rotates is the white plastic part with three teeth around the axle. Those three teeth fit together with a black rubber piece that has a total of 6 slots. I had to make a piece that would fit in the remaining three slots. I used my Dremel and a piece of Arnite plastic to make it.

Then I verified that the axle wasn’t long enough to hold the wheels that I wanted to use, which were two 100mm wheels from inline skates. Another thing that I had to do was to find a way of keeping the wheel in place. So, hacking of the motor was needed and I thought of a way of extending the axle using a piece of 8mm threaded rod where I could also put a nut to keep the wheel in place.

The first thing I had to do after cutting the piece of threaded rod with the size I found to be appropriate was to drill it through its center with a 3mm drill. However, the drill had to be perfectly aligned, so that the threaded rod would be perfectly aligned with the motor’s axle. To do it I used my bench drill and a small trick. 🙂 The trick is to first place the drill bit with the tip pointing upwards inside the chuck:

Then, tighten up the chuck and lower it until you are able to lock the drill bit in the vise:

After that, release the drill bit from the chuck and place the threaded rod piece inside the chuck:

This way, the drill bit will be stationary and perfectly vertically aligned with the chuck and the piece of threaded rod will rotate on top of the drill bit: 🙂

After drilling through the center of the threaded rod, I placed the wheel in the axle and used the drilled piece of threaded rod as a guide to make a hole in the center of the motor’s axle with a 2.5mm drill:

Then I used a 3mm tap set to tap the 2.5mm hole in the motor’s axle:

And finally used an M3 screw to attach the threaded rod to the motor’s axle:

Since the 8mm threaded rod actually has a diameter slightly smaller than 8mm and I wanted to have a better support for the bearing that fits inside the wheel, I used epoxy glue to add a little more thickness. Before applying the epoxy glue I covered the tip of the threaded rod with black tape, so that I could place a nut in it later:

And then sanded it down until I had the desired diameter:

After all this process, I still had to make another plastic part of Arnite to attach to the wheel. Again, using the Dremel I made a plastic part that would fit inside the wheel and glued with epoxy glue.

This piece was then glued to the other plastic piece with the same glue. A transparent plastic sheet with a printed encoder wheel was placed in the middle of both pieces:

Then I just had to use hot glue to attach the tiny encoders that I mentioned in my previous post to the motor, put the wheel in place and put a nut in the axle to hold it in place. 🙂

And that was it! After all this work I finally had the motor/wheel set ready to be used in a robot 🙂 . The funny thing about all of this work is that although it worked perfectly as desired, I ended up choosing to use bigger wheels and had to remake the whole thing in a different way that I’ll describe in another post later. Anyway, if you can get your hands onto some motors like this, the method that I described works just fine 🙂 . Below you can see a larger photo set of the whole process:

So, this was it. I hope it has enough details for you to replicate and use in your own projects 🙂

See you next time! 🙂

Update (10/05/2013): This post is now also available in Instructables.com. Check it out here.
Update (16/05/2013): This project has been featured in Hackaday! 🙂 Check it out here.

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