Battery Surgery

I have a story to tell about todays events.

After some more manual research our team figured out how the battery management system (BMS) should be switched on in the start of its use. It was not very clearly said anywhere in the manual so thats why it took so long to figure it out. Once we got the BMS working we found something disturbing.

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BMS showing battery status.

In the picture above the is one thing that is not right. The middle bar is the 4th cell of one of our batteries and that cells voltage is only 2.9 volts while others were well above 3.8 V. When we tried to charge the battery with a balancer the cell voltage dropped down right after disconnecting the charger. Because of one cell malfunctioning the whole batttery is useless. It is comparable when human has a organ that fails the human could pass away almost certainly. That is why we were already giving up on the battery and calling the time of death.

While we were looking for a replacement batteries a miracle happend. We found an old cell that could replace the broken one! But that meant that we needed to do some surgery on the battery which is dangerous and should be done carefully.

The Head of Battery Cell Surgery Dr. Vepsäläinen and the Electric Engineering Surgeon Dr. Autiosalo decided to perform an cell replacement surgery.

All along the operation it is very similar to the kids game “Operation”. You guys remember that? The only difference is that if you fail and hit the edges of metal, instead of a error light and sound there is relatively big arc of light and possibly loud explotion.

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The operation game from the 90’s.

With this “penalty” in mind the two first time Doctors took their job seriously and wore the appropriate safety gear. Operating while wearing those is quite hot and clumsy as some of these pictures from the operation show.

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Dr. Autiosalo’s precise and accurate manouvers.
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The skin removed to see the organs.

After the battery’s cover was removed it was time to extract the dead cell and replace it. This is was the tricky part since the cell contacts are very thin (less than 1 mm) and might rip out easy. At this part the operation had been going on for about 45 minutes.

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Critical artery cut. The stakes have never been higher.

Once we got the bad cell removed the syphtomps were validated. The cell had swelled about two times the nominal thickness from one corner. This cell was long gone.

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This bad boy was gone. Rest in pieces.

The old cell we found was in rather good shape but it didn’t have holes in the same places of the contacts as the other cell. Then Dr. Autiosalo performed a quick round of shots to the contactors.

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It is not engineering if you are not using a hammer.

After the the delicate handeling of the newbie cell it was time to put the battery back into one piece. We had done good documenting of what goes where so the assembly was pretty straightforward.

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Good as new!

After 2 hours and 11 minutes the operation ended succesfully. We hope that the patient is fully recovered and after some rest it should be better than ever.

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The new cell is reaching to the same potential as his new friends.
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We Have a Lift Off!

Today was the biggest day of the project for us. It was a new test drive with the new electric drivetrain. First we had to hook up the cables to the batteries. The cables are so thick that they don’t bend very well hence the Dr.Octopus -look.

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Wiring up. Tape is best for prototyping insulation.
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Finishing touches here and there…

This was. Jyry was on the moped. The excitement and suspense was mixed in the darkness of Tuesday evening. After few moments we would know how well we have calculated the chain transmission and whats the quality of our self-made parts.

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Deep thoughts. What is going happen in a few seconds?

How was it? Everything worked! Just as expected 🙂 Actually better than expected. We though that the moped would make some noise as it did inside but when the motor had some load all that disappeared. The moped was more silent than a bicycle. It also moved very graciously compared to the RC “toy”-setup that we had installed in the fall.

This is just the beginning!

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“Woooooooooooh!” – Jyry

A lot of hassle

We had quite many things to do for today and we did get most of them done. First thing was finishing the adapter for front gearwheel to our axle. We had to make a keyway and we did the old fashion way with a hydraulic press and a keywaysaw.

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Making the keyway.
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Finished keyway.

Next we corrected the position of the motor and attached it firmly to the frame of the moped. When the motor was on place it was time to get the front gear in place.

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Front gear in place. It’s like art, don’t you think?

Some rewiring also needed to be done because the wires were a mess. We got some of it done but there is a lot more wire that has to be wired to be out of sight and protected from external loads. After the rewiring we tried to get the back brake to work but after hours of oil bleeding we came to the conclusion that the bleed nipple or the brake saddle itself is broken. We are going to get a spare part for next time.

Last thing we did today was installing the chain to the gearwheels. With the chain the moped looks more like motorcycle.

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Chains in place.

Because the brake wasn’t working and it was already getting late we decided to put off the test drive to Tuesday eve. Still some enthusiasm was detected…

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Ready to go!

Appearance

The project has come to the point of desgining how the bike is going to look like. We decided to do 3D-printed bodywork as a test of what pros and cons come with it. I started modelling the Switchpad and dock for the displays. Here is a CAD model of something I’ve been working on.

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Switchpad and displaymodule for the handlebars.

Quite original, right? I don’t know if it is good or bad thing but sure is something 😀

One important protective cover is the motorcover so your pants or shoes wont get in touch with the chains or the axle. Here’s a sketch about that cover as well.

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Motor cover. Starting to see light at the end of tunnel…

I will be doing a lot of modelling and printing during the next few weeks and the rest of the team is focused on getting power to the backwheel. Exciting times, stay tooned!

Power of Electricity

Today we connected the batteries for the first time to the moped. It was quite scary beause working with these voltages (48 V) and the batteries being able to give 500+ amperes it is very dangerous to do these connections in a fuss. So we took our time and did it slowly and safely using the propper protective gear.

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Things going great. At least so far…

Before the battery operation we had a meeting about what needs to be done before Aalto Mechatronic Circus which at 7th of April. We listed priorities and we have two major things to do: 1. Get the Moped moving safely 2. Make it look good.

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Much text. Such wow.

To get the moped moving we need to know what is our gear ratio. The smallest gear ratio with standard moped gears is around 3. To determine this we of course needed to do some calculations. Me and Juuso did our own versions of these calculation. In the graphs below the gear ratio is shown as a function of wheel speed when the motor speed is kept constant.

Rock And ROLL!

Ladies and gentlemen we have a lift off!

After countless hours of debugging, frozen pizzas and terrible humor we finally got the motor running! Look how beautiful it rolls. This is definitely the greatest moment in the project so far. In the picture below we measured the max RPM of our motor to configure the needed gear ratio.

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Measuring RPM with IR measurement tool.

When we first plugged the Sevcon controller to our computer with CANbus we got five different errors. After a while we got it down to two. One of the faults was about contactors which use 12 volts. We though that we would have to regulate the 48 V from the Sevcon but actually Sevcon has an Analog output that can give the voltage required which in this case was the 12 volts.

The second fault was a bit more tricky. Our motor had no documentation with it about what encoder it uses or how the encoder wires are color coded. None of us had no knowledge of encoders beforehand so we had our share of homework to do. That wasn’t enough because on top of that we still needed to figure out the wiring. But eventually the hero of the week, Juuso, got it to work.

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If you have worked with Sevcon you know how this feels. No words to describe.