Test stand for Smart Drive Motor

2 10 2012

I made a little bit of progress on the recumbent bicycle front today. I’ve made a makeshift test stand for the Smart Drive motor so I can start testing some control board designs before I put in the effort of installing the motor on a bicycle frame. This way the motor has no load connected to it, which will keep the current required to run the motor to a minimum during testing.

The stand basically consists of the shell from an uninterruptible power supply (UPS), bolted to a piece of steel plate, with the nylon hub of the motor cable tied to the UPS frame. The first thing I did was strip the UPS frame and reinforce it with a couple of cable ties.

The bare UPS frame with cable ties to prevent it from wobbling.

Four matching holes were drilled into the cover of the UPS and a piece of scrap steel I bought for $5 and then they were bolted together using M4 bolts and nuts. I had to buy this piece of steel because, it wasn’t until after I gave the steel case of the washing machine to the scrap metal merchant, I realised I could of cut it out of that instead of having to buy more. But, that is a lesson learnt I suppose.

Lid of UPS bolted to steel plate using M4 bolts and matching nuts

Basic stand after UPS frame is bolted back into its lid and attached steel plate.

I then cable tied the motor hub to the basic frame through the holes that were already present in the bottom of the UPS. The motor does have a bit of movement after it has been secured. However, if this becomes an issue during testing I will probably just put some double sided foam tape down between the motor hub and the UPS frame to prevent it sliding about. Time will tell on that front.

The motor secured to the frame via cable ties around the motors bearing hub.

After all is said and done, I think I have managed to slap together a passable test stand that should get me through to the time that I have to actually mount the motor onto the bicycle frame.

Finished test stand. The steel plate was connected so that more of it was on the side that the motor would be on. Due to the centre of gravity of it not being directly over the hub, but underneath the actual motor. This way it stops the stand from falling over.


Maximum Temperature Test Probe

2 10 2012

Today I’ve been working on a graphite probe to test the maximum temperature that I can achieve with the solar cooker I made. I went with graphite because it is black and it can handle extremely high temperatures without melting or breaking down. To make the probe I have used some graphite sticks I got from an art supply store and a high temperature thermocouple probe for my multimeter that I got from work.

Drawing graphite and double sided foam tape. The tape is used to hold the graphite in the vice on my drill press.

The specifications of the probe say that it is very accurate when measuring the temperature of a gas or a liquid. Since I am measuring the temperature of a solid, I decided to drill a hole into the graphite, fill it with solder, then insert the probe into it. This way the solder will melt and give accurate readings. I am hoping that I will still get some accuracy when the solder is still solid.

First I stuck some double sided tape onto opposite sides of one of the 8B graphite sticks so I could put it in my vice on my drill press without it shattering. I made sure to leave the backing paper on the tape so that it wouldn’t stick to the face of the vice. I used the 8B to start with because I wasn’t sure if I could manage to drill into graphite without it breaking.

Double sided foam tape (with backing paper left on) is applied to opposite sides of the graphite so the jaws of the vice don’t apply too much force and make the graphite shatter.

Next I put the stick of graphite into the vice as low as it would go and then drilled a hole down the length of it. I started with a 2mm drill bit and worked my way up to a 5mm drill bit. The diameter of the thermocouple is 4mm, so the 5mm hole allows enough room for the solder to surround the probe.

5mm hole drilled to accept the thermocouple with some space around it for solder.

Once the hole was drilled to a reasonable depth, I chopped off strands of 60/40 rosin core solder in the hole until I couldn’t fit any more in.

Hole filled with solder

I then melted the solder using a hot air gun. I had to add more solder afterwards until I had completely filled the hole and then I inserted the probe while the solder was still molten.Then topped off the hole because too much of the solder shot out when the thermocouple went in.

Probe inserted into the graphite and held in with the solder.

I made sure to have the probe connected to the multimeter while the solder cooled so I could read the temperature. After it had cooled to a temperature I could safely handle, I checked that the probe had a good solid connection with the graphite. All that is left to do now is fire up the solar cooker on the next clear day and give the probe a try.

Finished thermocouple probe. I’m not sure how accurate this will end up being because not all of the probe is inside the graphite, which could lead to a lower reading then it should be.

Making of a Cheap Solar Cooker

27 09 2012

This is a little side project I’ve been working on over the last few days. I’ve wanted to build a solar cooker for a while now, so when the opportunity came up to score this Ku Band satellite dish for free, I couldn’t resist myself. These dishes aren’t perfectly circular, but more elliptical, because they are designed to be the cut out of a circle projected onto a parabolic surface but slightly off to one side of it from centre. In this way, the horn that contains the receiver and transmitter is not in the way of the incoming signal. Hence, you get more surface area to collect the signal but, more importantly, you don’t get weird effects, like scattering, degrading the incoming signal.

Ku Band Satellite Dish with Stand

The first thing to do was to go into work and grab some aluminium tape and get cracking. I cleaned the surface first of course.

The aluminium tape I used

First strip on

Curvature begins to be a problem

At this point the curvature of the dish starts to cause a fair bit of ripples in the tape, it also begins to get harder to line up the tape for a straight run across the dish. So, I changed to applying the tape vertically, in line with the major axis, instead of horizontally, in line with the minor axis.

Halfway there.

My five year old taking a photo of me whilst I am working. He does love cameras.

The dish with the reflective surface finished

As you can tell from this photo, obviously mirrors would have better reflectivity. But, I don’t really feel like cutting that many square pieces of mirror and then attaching them to the dish. This was much easier and will get a similar result cooking wise. If I were building a solar powered metal foundry, as at one point I have planned to, then I would rethink my choice.

After this, I removed the horn and then flipped the mount on the back of the dish around. I did this so I could have the focal point above the dish, instead of in front of it. That way I would get the sun light concentrated onto the bottom of my cooking pot, instead of on the side, which will allow for more even cooking.

Dish mount in original direction


Dish mount in new direction

Next, I tied a rope between the main boom of the stand, that came with the dish, and one of the support legs because I had problems with it sliding out when I tried to mount the dish on it.

The stand that came with the dish

The dish is all mounted and ready to go

Once it was all together, I had a little bit of fun with a piece of paper. The reflector didn’t have enough power to burn through plain white paper. But, if you put a black dot on it, using a permanent marker, then it catches on fire pretty much straight away.

*insert evil laugh here* IT WORKS!!!

I can’t believe he’s still smiling after that.

After I had my bit of fun, I attended to the problem of being able to hold a pot at the focal point. I ended up using a section of wire fencing I had laying around for my initial tests but I may end up making a hanging arrangement later on. This is because I’m not too sure how it will go during late afternoons or early mornings when the Sun is lower in the sky. All the contents may shift to one side and spill out. That will be one test for a later date.

All I had to do to mount the cooking rack was take off the coupler that is used to hold the horn and the three support legs together. Then slide the poles through the holes in the rack, then re-attach the coupler. With this set up, the rack is held in place very well by the support poles attached to the minor axis, but moves a bit up and down on the pole attached to the major axis. This may actually help in the long run, as it will allow for a little bit of adjustment when trying to make the cooking pot level.

Cooking rack installed

I then did a test to see how long it would take for the cooker to heat up 500mL of water in the pot I bought ages ago just for this purpose. I got the pot in a set of two for AUD$5 from a local clearance store. Mainly because they were cheap and had a black enamel coating on the bottom. This greatly enhances the effectiveness of a solar cooker due to the black absorbing more of the incoming radiation and, hence, transferring it into more heat energy for cooking.

Solar cooker aligned and with cooking pot in place.

The pot only just fits in between the support poles and required a little bit of wriggling to persuade it into place. You can see the yellow thermocouple I used to measure the temperature of the water in this picture. At the end of the experiment, I realised that either the thermocouple isn’t very accurate at measuring temperature, or the multimeter I used it with isn’t. Because, when the water was happily boiling away, I was getting a reading of only 97.6 degrees centigrade not the 100 degrees that I was suppose to be getting.

500mL of water boiling vigorously.

It only took approximately 14 minutes to get the 500mL of water to fully start boiling. So, I call this a massive success. I can’t wait to see how this thing performs in the middle of an Australian summer.

After I finished testing, I took a measurement of the ambient air temperature with my multimeter and compared it to the reading from my cheap wireless weather station that I was using for timing. The weather station took a reading of 29.2 degrees C whilst the multimeter took a reading of 24.8 degrees C. Considering my weather station is one of the cheapest available, with only indoor and outdoor temperature readings as well as humidity and barometric pressure, I don’t think it is giving a very good reading either. But it does illustrate the inaccuracies that I didn’t foresee at the start.

Anyway, here is a plot of the data I acquired during testing and a copy of the spread sheet I wrote up to go along with it.
One thing I did notice is the linearity of the plot. I must admit that I was expecting it to trail off at the end but it didn’t. This would imply to me that this thing has a lot more potential for heating up more things then just water. I’m going to try and find a carbon brick from somewhere and heat that up. That should give me a real idea of its true power.

Plot of the time it took for 500mL of water to reach full boil.

Water Boil Test

I think I’m going to have a bunch of fun with this in the future.

Fisher and Paykel Smart Drive Schematic

25 09 2012

I’ve spent my free time over the last few days reverse engineering the control board out of the Fisher and Paykel washing machine I bought. I managed to find details on all of the components except one. I know it’s a MOSFET but, beyond that, I don’t have any more specifications. It is labelled H75309 G814BE and is a 4 pin SOT-223 package. If anyone has any more information on it, I eould very much appreciate it. I used this codebook to help find all the parts with SMD markings on them, which was exceptionally helpful and I would highly recommend it. I rewrote the schematic in KiCAD (Build: (2010-00-09 BZR 23xx)-stable), which I will share with you all here. Please note that this is not a complete schematic of the control board but only a partial of the power section that drives the motor. I wasn’t really interested in the rest of it and it took a long time just to do this part. So, I’m not going to bother doing the rest, except for the hall effect sensor section at a later date. I’ve also included the libraries I created for the parts that KiCAD didn’t have as standard. They must be added to your library list before the software can use them.

Next, I’m going to attempt to remove as many parts as I can off the board to reuse, then use them to develop a prototype for my controller. Hope this all helps somebody.


Electric Recumbent Motor

22 09 2012

The journey has begun for my electrically assisted recumbent bicycle. I’ve collected a lot of parts, including the donor bicycles, some steel for construction, some of the batteries and the all important motor. I’ve decided to use a BLDC motor from a Fisher & Paykel washing machine (must be a model with the Smart Drive motor). This is for a few reasons; they are cheap to get, powerful and have permanent magnets in the rotor. Cheapness is important to me as I am a low income earner, I got the entire washing machine for AUD$5.50 off Ebay. So, for an approximately 1kW motor, that is a pretty awesome deal I think. The permanent magnet side of things is also important because I am wanting to investigate regenerative braking on this build and I am led to believe that these are more efficient in that regard. Most people that use these motors as generators usually rewire them for better voltages, but I am going to go with the stock motor first and see how it goes.

Here are some pictures of the tear down of the washing machine and preparation of the motor for mounting. I got the washing machine for cheap because it had stopped working and after the previous owners spent some money replacing the water pump, they gave up on it when it still wouldn’t go. Most of the time the power drive transistors on the control board burn out on these models and a handful of components can get them working again. But, I’m not interested in riding a washing machine all day, I’m interested in bicycles and how to make them go fast.

Fisher and Paykel washing machine with Smart Drive motor. Bought off Ebay for cheap.

To remove the tub and motor assembly, the four support rods on either corner have to be removed first. The top right has already been taken off in this photo. I just grabbed hold of the motor shaft inside the tub and lifted slightly to be able to lift off the grey holders on each corner. It worked well for me.

This is a picture of the tub and motor assembly once removed. The motor is the grey part on the bottom. The problem with this design is that it is hard to remove the motor from the tub. So, I decided to just cut away the tub right back to the part that holds the bearings and shaft.

First I drilled a hole in the side of the tub big enough to fit my jigsaw blade through, then cut around the perimeter to remove the top.

At this point I removed the rotor and stator then started cutting either side of the support sections that run out from the central hub up to the next cross support. After that it was just a matter of snapping each part out along the cross support. With the wider sections near the outer rim of the tub, I had to cut them into smaller sections before trying to snap them because, if I didn’t, they would only bend and not snap.

Cut down to the last lot of support sections.

This is as far as I could cut down the tub with my jigsaw.

To remove the last bits of the supports I tried both a hacksaw and rotary tool with a cut off disk inserted. The rotary tool won out at the end of the day but I had to be careful when cutting because it melts the, what I assume to be, nylon and it can wrap itself around the shaft. As it builds up it ends up snapping the cutting disc. I got around this by cutting through in layers and removing the build up around the cut as I went.

I used the barrel sander attachment on my rotary tool to sand back the remaining stubs to leave a nice finish on the hub.


After the hub was finished I reassembled the motor. You can see on this photo that the stator has some cracks in it. Apparently this is a fairly common occurrence with these motors. I think I will end up impregnating the cracks with some epoxy using some kind of vacuum set up to prevent it splitting further.


Receiver Update

16 09 2012

I’ve had a chance to look into the destruction of the receiver module a little more. The verdict is, I had to end up buying a new receiver shield. I’m not sure why, but I replaced just the module and it wouldn’t work at all with it installed on the old shield. I bread boarded it and still couldn’t get it to work (I did forget to put the resistor in-line like the shield has though). I went and tried another module at the store I bought the first one from, before buying it, and it still wouldn’t work. At this point I gave up and just bought a new shield. This one doesn’t seem to be as sensitive as the previous one, as I am not getting as many packets as I was previously at the same distances. I’m going to redo my range tests with this new receiver and will post the results. This time I won’t point the antenna at any stray mobile phone towers šŸ˜‰

Fun and Destruction with Antennas

30 08 2012

Sorry about the slowness of my posts. I’m back at university now so my time is slightly limited. As promised I will now update you all on my adventures into the world of range optimisation for my transmitter/receiver circuit. I am just going to start rambling now so I hope it all makes sense. If not, then just hit me up in the comments.

Since I had a working connection between the transmitter and receiver, and was happily sending out “hello world!” for everybody to see, it was time to figure out if it is possible to get the required range out of these little modules for the distances that a HAB require. My initial set up had a half wave whip antenna on both the transmitter side and the receiver side, this allowed me to get to the green dot on the picture below

Fig 1 This is a map of how far I could get reception with different antenna combinations. The red dot is where the transmitter was set up. It was on the lounge room floor inside my house. The other dots are the different distances I achieved with the receiver before I lost reception completely.

After my initial trial run I found out that I should be using a quarter wave antenna on the transmitter end, not a half wave one. I’m not sure why this is but I will be doing some research to find out why in the future. So, after I replaced the transmitter antenna with a quarter wave whip, I managed to get reception up until the blue dot.

At this point, it was time to get a little bit fancy. I decided I was going to attempt to construct a Yagi-Udon antenna for the receiver. I understood enough about antennas that I was going to be connecting a balanced antenna onto an unbalanced cable back to the receiver module. This means that I was going to require a balun to connect the antenna to the cable. I followed the directions here on how to make a ferrite core 1:1 voltage balun and ended up with the following half wave dipole test antenna

Fig 2 Test balun with two pieces of solid core CAT5 cable strands acting as a simple dipole antenna.

At this point, I was beginning to run out of time (I had to pick up one of my boys from school). Also, I had a bit of an idea (yes they are dangerous words). I thought, I have one of these 43 element UHF television antennas sitting in the garage, maybe I can use that instead of going through the hassle of making one of my own since they operate on the 470 to 862MHz band and I was operating on 433MHz. I understood that the gain of the antenna would be severely diminished at that frequency, but I was willing to give it a try because I wouldn’t cost me much due to the fact that I already had the antenna. So, I put aside my home made balun/antenna and picked up my son from school. On the way I bought a PCB mount F59 socket to solder onto the receiver shield. This way I could easily attach a 1.5m RG6 cable between the antenna and shield. After we got home, I soldered on the connector and off we went for a quick range test. I left the transmitter set up at the same place as last time (red dot on picture below) and took the antenna, a camera tripod, receiver and pc to the test site (blue dot).

Fig 3 Red dot is where the transmitter was left at home. Blue dot is where I set up the UHF antenna attached to the receiver and pc. Purple dot is the unforeseen anomaly that will soon be discussed.

I clamped the antenna to the extending neck of the tripod so that I could have a convenient, and stable, way of pointing it to where I wanted without having to hold it by hand. I then started up the pc and the software, as well as connected the cable to the receiver shield. I then pointed the antenna in the rough direction that I thought was home. But when I plugged the arduino into the pc I thought I heard a pop come from the receiver. I couldn’t be sure though as there was a truck driving past at the time. Not thinking much of it, I opened up the serial monitor for the arduino and was delighted to be receiving some of the data that was being sent from the transmitter, although not very much. I thought, well that is good and bad. It was cool that I could get a cheap transmitter and receiver pair to work over that distance, but I was a little let down that I couldn’t get more out of it. I did a quick test to see what the effective “viewing” angle of the antenna was by rotating the antenna till I couldn’t receive any more data then sweeping it back through the reception area till I reached the other extreme of where I couldn’t get any more data. I found theĀ  effective viewing angle to be approximately 30 degrees, which was a lot bigger than I was expecting. We then packed up and headed home.

A couple of days went by before I could do some more tests. But when I got a chance, I decided to test out my home made balun/antenna. I took it out to where I lost reception with the half wave whip antenna and started up the serial monitor. I was a bit disappointed though when I was only receiving a very limited amount of data, “quiet oddly close to the amount I was getting from the television antenna” I thought. Even so, I had tested the other antenna combinations, except for the television antenna, to the maximum of there range, i.e. to the point where I couldn’t receive any data at all. So, I continued to walk down the alley way I was using for testing and into the park a block over before I finally lost all reception (see purple dot on Fig 1). On the walk back I decided to leave the serial monitor on to test at what point I could receive all of the packets. Strangely, I got all the way back inside my house and I was still getting the same amount of data that I was up the alley. Curiously, I disconnected my home made dipole antenna and reconnected the original half wave whip antenna. To my surprise, I was still getting very little data, even when the transmitter and receiver were about 1m apart.

At this point it clicked. That pop that I thought I heard when I was testing the television antenna was actually a popĀ  and it must have destroyed the module on my receiver shield. I was absolutely astounded at this thought. I was thinking “there is no way this antenna could get that much power from a little 3dBm transmitter module to be able to pop the receiver module”. I then started to think of other ways that it may have picked up enough power from something to be able to destroy it the way it did. It was then that I realised what I had most probably done. I have lived in my area all my life, so I know the ins and outs of all the streets pretty well. It was this knowledge that gave me the break through. A few blocks over from my house (the purple dot on Fig 3) sits the mobile phone tower for my area, this tower transmits on the ~900MHz band that the mobile phone providers use for their GSM networks. Since this is the only high powered transmitter anywhere in the area, my television antenna must have had enough gain at that frequency to create a huge power spike to be able to blow out the receiver module when I pointed it at the rough direction of what I thought was home. That is the only explanation that I can come up with that makes sense to me (feel free to correct me if you are better informed than I).

After all of this adventuring, I have managed to solder a new module into the shield but it didn’t work straight after installation and I haven’t had time to debug it since. Mainly due to me going back to university and also making a start on my other project (the recumbent bicycle). Anyway that’s it for now, but I will inform you all if I manage to get any time to work on it before the end of semester.