BLDC Motor Controller Schematic

11 10 2012

Hi all,

Power section of BLDC motor controller for recumbent electric bicycle.

This is the schematic for the alpha version of the power section within the motor controller I am designing for my electric recumbent. It is fully untested so use at your own risk. It will be run by an Arduino on my project but I have designed it so that nearly any micro-controller with TTL logic levels can be used. I am in the middle of designing the PCB and will upload all of the files to github once I’m finished. Also, an explanation of the circuit will be put up soon too and yes I am aware that the hall effect sensors are missing. I am not sure if I will be adding them to this board or making a separate one for them. If I do add them then I will post an update.

Hope you all enjoy and let me know if I’ve made any silly mistakes or if you think I should add something.



Bare Probe Temperature Test

3 10 2012

I’ve completed a preliminary temperature test with the probe I made on the solar cooker today. All went fairly well, up until the point that I got bitten by a green ant in between my toes during one of the measurements. This resulted in me accidentally pulling the probe off of the cooking rack and, hence, ending the experiment prematurely. I did get good results none the less.

Bare probe on the cooking rack

One thing that I did note is that the wind had a big effect on my temperature readings. As can be seen in the data plot below, whenever a small breeze came up, the temperature would drop dramatically.

Graph of temperature readings during the test.

This makes me want to redo the experiment with the probe inside a glass jar, with possibly a slight vacuum applied. This way I can get some more accurate results and some more extreme temperatures if I apply a vacuum.

Bare Probe Test Data

As mentioned during the post on building the probe, I think that the temperature readings I am getting are lower then the actual temperature because of the exposed bit of the probe. Before the experiment was brought to a premature end by the ant bite, I was planning on using a pair of pliers to see if I could pull the probe from the graphite straight after removing it from the cooker. Since solder melts at approximately 190 degrees C, if the probe pulled out I would know instantly that the measurements were off. Why I think it may be that far out is because, directly after inserting the probe into the graphite during construction, I had a reading on my multimeter of approximately 140 to 150 degrees C. This is a far cry from the > 190 degrees I was expecting. However, I did not preheat the probe before I put it in so that could also result in the lower reading.

Anyway, I am pretty happy with these results, considering the wind factor. I may revisit these tests at a later date, but for now at least, I am going to refocus my energy onto my two major projects (the recumbent bicycle and high altitude balloon).

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.