Converting a Floppy Disk Drive into a Simple Robot (Part I)
By Chris Barron
The idea for this project was born from an unfinished website which had some important details missing. In essence the idea of converting a floppy disk drive into a small vehicle which could be made by someone just starting out in robotics, or even a kids summer camp, is easy enough to do once the practicalities of switching on the motor without having it connected to a PC is worked out.
A look at the pinouts of a standard floppy drive came in very useful and it has been simple to establish that all we need to do is to ground pins 12 and 16 on the edge connector and if you're as lucky as me, just supply the drive with 5V on its power connector. Once you've taped up the write protect switches the drive spins up immediately.
To identify the pins just have a look at the PCB around the area of the edge connector and you'll hopefully find that they are screenprinted to identify pin 1 or pin 34, or both, or even all pins !!
Turn the drive over so that the pins are like this:
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34With the exception of pin 3 which is +5V, all the odd numbered pins are ground. So to ground pins 12 and 16, squeeze 11 and 12 together with pliers and solder and do the same for 15 and 16.
The power connector should be to the left of this connector. If it is, the power plug pin nearest this long edge connector is our +5V input and the next one along is negative, 0V.
If the power plug is on the other side ,Though I've never seen one like that before, you will need to plug it into a PC power plug to get it right...The red wire of the power plug is +5V and the yellow is +12V, the two black ones in the middle are innevitably 0V
Assuming you have shorted the pins and connected 5V as explained you might think the drive should run. It wont do it unless either there is a disk drive which isnt write protected or you have taped up or soldered out the write protect switch.
It might be worth shorting out pins 11 with 12 and 15 with 16 some other way, perhaps with jumpers and then applying 5V to the power line BEFORE you do anything else more permanent, to make sure you have a drive which will work with just a single 5V supply. You could generate the 12V from a bank of AAA cells or a couple of 9V cells with a regulator if you had to.
Once you have established that your drive spins freely with these simple modifications you can be sure it will definately work for our purposes. So far, nothing you have done is irreversible you will be pleased to hear, just in case you have a change of heart.
The next step is to remove the internal disk carriage. These are very flimsy affairs and dont put up much of a fight. But be careful to leave the following untouched.
Some old hobby servo horns, a drill with a 3mm bit, some 3mm piano wire to make 2 axles from, some model plane 'wheel collars' 3/32" I bought 4 for 1 pound fifty and the ever popular cyanoacrylate glue 'superglue/cyano/crazy glue' as well as some fast setting epoxy, a 4xAA battery holder, some small cable ties and some wires, solder and a soldering iron.
Excluding the cost of the drive, this should make this project affordable to almost everyone.
So you have gutted your drive and are left with an alloy chassis with electronics on one side and nothing but a disk motor, a stepper motor and a sensor on the other. So lets build the drive system first, and see what problems crop up.
From your collection of old servo horns you need to pick two round disk ones, aproximately 30mm diameter and superglue these together with the larger flanges on the inside. Once the cyano has set, you might also want to fill the hole between these two disks with some of the fast setting epoxy to strengthen this, the drum assembly.
This is the winding drum which needs to be fitted, glued, directly to the disk motor platter, but before you do, file,scrape,otherwise remove any obtrusions which will prevent the drum assembly from sitting perfectly flush with the motor platter.
The next step is to make up the axle supports at the rear. This what the mountign rails were for.... If you turn these upside down and over so that they protrude from the back of the drive you can still get one of the mounting screw holes to line up. Take a bit of time to do this because you could be as lucky as me and find there are two nylon bearings on these rails. If so, attach the rails with these bearings as far away frome the drum motor as possible because we are going to put the rear axle into these bearings. But if you dont have nylon bushes on your rails you will still be able to use them because you can fit the rails in such a way that one of the old screw holes is at the farthest end away from the motor, they just might need drilling out a little to suit.
Next you need to cut the rear axle from the 3mm steel rod. Basically cut it to a length to give you an axle which extends 10-15mm beyond either chassis rail, when mounted in the bearings. The rear axle needs to be geared down a bit, due to the small diameter of the drum and we do this by glueing a cotton bobbin onto it. Theres a size of bobbin which is in between the common fat one and the small machine one and its one of these you want. Diameter is about 15mm. Probably you will find the internal diameter of the hole of the bobbin is so large that it cant be fitted centrally onto the 3mm axle shaft. If this is the case go and take a look at the guts of the drive you have already removed and you might find some spacers which will do the job nicely. If not try getting alluminium tubes from a model shop of increasing sizes from 3mm to the size of the bobbin hole. By slipping one piece of tube inside another and cutting it to length, you can make the bobbin fit snuggly. Another workaround is to wind sellotape onto the axle to bring the diameter up to the right size.
Now you have the axle cut to length slide it into its bearings, at the same time loosely sliding on whatever it is you are using to build up the axle diameter to fit the bobbin as well as the bobbin itself. Also fit one wheel collar to either side of the bobbin .
Then just glue all the parts together. With the tubes I recomend you slide them out of each other a little way and spread epoxy on them. Do both ends the same, and then glue the bobbin in place, also with epoxy, in such a way that it sits in the middle of the axle.
Once its all dry you can fit the drivebelt, which is just a rubber band, of the wide variety if at all possible. Just unscrew one of your chassis rails and slip the belt on. If you cant find the right length of rubber band its simple enough to double up a longer one, or use several narrower ones if need be. You'll need to experiment a little eith the length of the belt because if it is too tight its going to make too much friction. The reason for making the drive motor drum so large should now be evident ;because when you rotate the band through 90 degrees to fit it to the axle it leaves and returns to the drum at very obtuse angles.
One thing to be careful with too is the final alignment of the axle to the drum. You must get the centre of both these two to line up centrally as best you can before you finally glue the chassis rails in place or you will start and get too much friction between the edges of the drum and the drivebelt. Using a smaller diameter drum might help here if you have 20-25mm round control disks to hand. Then apply liberal ammounts of epoxy to the rails where they meet the disk drive frame to hold them in place. Once thats all dry you just need to make up a couple of wheels. I used 2 model aircraft wheels which look pretty good but something as simple as 2 more servo control disks would suffice. Again these can be fixed to the axle with the epoxy glue. Its a case of make do and mend . Another neat way to make wheels is to glue together some of the metal disks from the centres of floppy disks themselves, but mind you dont run them on polished floors !!!
Converting a floppy disk drive into a simple robot (Part II)
Article content copyright © Chris Barron, 2001.
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