Reflection Ten

Over the last week i have been incredibly busy, Tim Economu came over and looked over what i had so far. He said we needed a new sprocket, i had to have overnight shipping and that slowed progress down a bit. as soon as it came, Tim came over again, but becaused it needed to be machined all i could do that day was a few little things like talking about how to mount the throttle and driling the mounting bracket. the next day, Tim came over again and with the machined part i installed the motor and secured the wire from the throttle (i had installed the handlebars before Tim had showed up) and ut the controller in place and started mounting the dashboard. i would talk about what else i did, but i as so busy today that i forgot less than half of it. On Wednesday i finished putting all the insturments on the dashboard, fliped out when i couldnt find the wire i had gotten spceifically for this, looked around the garage for a few hours, finally found it in the bottom of the plumbing drawer of the least used cabnet in the entire garage. installed all the wire, after preparing the wire. got it all together and found out it didnt do anything, went over all the connections and checked all the wires. i found out that i was missing a wire, luckly i had just enough spare wire that i was able to sucsessfully plug the wire in on both ends without electrocuting myself. i then had to switch three wires around till i got the motor to run as it should. then i got in for a test run, knocked a wire loose had to fix it with out getting electrocuted. then i started it up and it started going in reverse and when i switched the wires around one of the connectors fell off the wire end, so i had to relace it with a new one. after that the only problem was a loose chain that tends to jump off the gear if it bumps around too much. Thats not really a problem and is easy to fix. At a later date.

Annotated Bibliography

Neal Allen

Level 3 Escalation Engineer

Fluke Networks Technical Support Center

Neal Allen (my dad) has been helping me since day one. And by helping i mean he was urging me to do as much as humanly possible. Unfortunantly i didnt listen so i was up late on the last day doing my bibliography and powerpoint. Neal also helped by telling me when i was about to destroy something because i was doing something wrong.

Neal wishes that he could have been here for the last few days of the project. Neal timed me during the original time trials. Neal also maned the radar speed gun during the time trials. Neal was very helpful during the whole project, and i coudnt have done it without him.

Tim Economu

Offgrid Engineering LLC

4131 Springwater Rd.

Clinton, WA 98236

360-579-2117 office

offgrid@whidbey.com

Tim Economu was by far the most helpful person during my project. Being an electrical engineer, he had all the materials i didnt. Without his assistance i can be 100% sure that this project would have failed. Because of Tim's help i will pass 8th grade and have a awesome go-cart to show for it.

Tim Was looking over my sholder during the last few days to make sure i didnt screw it up big time right befor the presentations. Right before i bought anything  i always ran it by Tim so i wouldnt buy the wrong part. And i know that if he wasnt busy he would have been there to supervise the wireing process and told me if i should be worried when the batteries make a poping noise when i connected them to the main circut. I am can say with certanty that if i had tryed this on my own without Tim, i would have two speeds; on, and off.

electricvehiclesusa.com

From this website i not only got all of my parts for my go-cart. But also was able to browse there online store for technical specs on all the parts i buy. One of the best things about the site is that they sell parts in bundles based on compatibility. Because of that feature i as sure all the parts were going to work together before i even purchased them.

I could also reasearch parts to see what stores have the cheapest parts. The site also recommends parts that would work with your last purchase. Its very handy because its online, and you dont have to drive anywhere to browse. And if you dont want to free-style it you can get one of the kits they sell to build your own street-legal car.

Reflection nine

This week i have made a lot of progress. i have talked to Tim economu and showed him what i have so far. he found out the size of the gear and ordered it, it should be here on Monday 18, 2009. i have fixed the floor plate with a bolt. i then mounted the batteries using two cargo straps. i found a piece of metal that will become the mounting bracket at island recycling, i will drill the holes in it on Monday. Tim will probably be at my house helping me out on Monday. just to clarify things, when i said that i bolted the floor plate back on, that means i took a bolt that would fit through the hole i made in the frame, shoved it thought with the help of a sledge hammer, took some bolt cutters and chopped off half of it, then used the sledge hammer again to force the bolt around the frame. i then spray painted the frame flat black.

Reflection eight

This week i have not achieved much. i talked to my dad about what i needed to get, received shipment of #2 wire and a circuit breaker. i have removed the engine and looked at the size of the motors existing gear, its too small so im getting a new one, were not sure what size it is yet.

Reflection 7

So far i have done only reasearch. I now need to find the last few parts to compleate my beast. i need the following parts: #2 cable, brackets, a circit breaker, eyelets, and i need to get my motor mount cut. it takes more parts than i thought to make a go-cart run and not kill pedestrians or the driver. my best source is by far this site. I have have been going at about  4 this week (out of 1-10).

interview

Here is what you are going to look for in your motor. You are going to ask yourself in whatever motor you are looking at, obviously size is important - what size are am I going to look for.  What voltage is important. Size, Voltage, and Current. Those three things are really important, actually they are all interrelated.  And maybe power level, because when you are looking for motors they won’t always tell you the power, they won’t always tell you the current.  They will give you little hints.  It’s like, well wait a minute.  How do I do this?

 

There is an easy equation to figure the power of a motor. And your dad can help you with this if you get in trouble, but you should take this down.  To figure the power of a motor sometimes they will tell you it is 100 watts say, and they will tell you it is a 10 volt motor, and it takes10 amps.  But they might not tell you all three

 

The watts of a motor equals the volts times amps.  That is part of Ohms Law.

 

If you know this equation, you only need two pieces of information.  Because if they give you, say, volts and amps then you can calculate watts.  If they give me a spec on an engine as 10 volts and 10 amps, what is my power?

 

T: 100 watts?

 

Easy, right?  So now I know that is a 100 watt motor.  They may not have told me that but now I have that information.  Here is a little trick that they won’t tell you.  Say that I run that 10 volt motor momentarily at 20 volts, what is my power now?

 

T:  Ahh,  200?

 

Exactly, because I can still run it at 10 amps. So momentarily…, say I want a continuous rating of 100 watts but I needed a punch every now and then to climb a short hill you could give it more voltage, or using this formula I could give it more current.  I could use 10 volts but give it 20 amps.  That is where your controller comes into play. 

 

So the controller you use actually determines two things: the volts and the amps. So, what am I saying; that it is not just the motor controlling the power, it is the controller.  It is actually the controller controlling the motor.  The motor is going to give you the power to run the car.  So that is why the other day your dad and I were tossing ideas back and forth about motors and controllers and decided “lets look at a package of motor and controller if we can” because you know that somebody has matched them – probably better than we can.

 

I have got lots of motors, in fact, I can give you one if it turns out that’s the size you need. 

(4 min)

 

You could buy 100 motors and 100 controllers and only have matches for half of them.  And the other half wouldn’t be very well matched at all.  We don’t often have a lot of information. You could read the data sheet and be a nerd like me, and go through and read the data sheet completely, and I think I understand it, and not have it register completely.  It’s like, they have given me all this data, but if the controller data and the motor data don’t describe the same things then I don’t really know.  If you see a package, then at least the distributor is saying “hey, these things go together.  These two should work.”  And if they don’t then you can return them to the dealer and ask for something that works together.  So that might be another thing that is important at this stage.  Without being an engine motor designer you are looking for a package, or at least a recommendation from a dealer.  Hey, you buy this motor from me, and this controller, you will have a good deal.

 

I have been studying motors for years. I remember, when I was your age, I was rewinding slot cars.  Do you know what a slot car is? We used to have big ones with pretty large motors, really.   We used to take them apart and rewind them for speed.  Man, we used to hop those things up!  They wouldn’t last very long, but boy they were fast!

 

So, I have been studying motors all my life and I still can’t look at the catalog and know what the matches are unless they say this ac motor matches this controller.

 

(6 min)

 

So: batteries, controller, motor.  Is there enough information there?  Were you looking for some more information on motors?  You were selecting …

 

N: We had no idea, looking at specs online, what would tell us what we needed to know.  If we went down to someplace in Everett, and they had an electric motor on the shelf, and even if it was too big for what we wanted, we had no idea if it would even come close.  If it would have enough torque to move the car, or …

 

The torque on a motor, this kind of another motor fact, is equivalent to the current put into the motor.  Zero current, zero torque.  A whole bunch of current, a whole bunch of torque.  Pretty much any motor – up to a certain point – I mean, you can’t go down to a two inch motor and get 100 foot-pounds of torque out of it.  So there is a lower limit on what you can use on your car and still move the car.  There are formulas for that, and I can give you those formulas.  We can talk about what that is.  The weight of the car – the mass – and the current it will take to move it, and that sort of thing.  But you also have a budget to keep.  You are kind of capped on the lower end by what sort of motor will move it, and you are capped on the upper end by how much you want to spend.  You don’t want to spend a fortune on a go-cart, because no good engineer spends more than absolutely necessary.  We are all cheap – as we should be.

 

(8 min)

 

So, torque and current.  Since you are going to be using batteries that are pretty large, even motorcycle batteries.  Motorcycle batteries will give up 100 amps, 200 amps for short periods of time quite easily.  What determines the amount of current that a battery will give up is called the internal resistance.  It kind of makes sense, the lower the internal resistance to current would be, the more current they give up.  It’s kind of intuitive.  The way that works is another formula.

 

The battery voltage is equal to the current times the resistance.  That is called Ohms Law.

 

Resistance is measured in ohms.  Your dad can help you look at the data sheets and figure that out.

 

What that means is that the lower this goes, the higher the current can go.  So, they are sort of inversely proportional there.  And of course that also means the higher the voltage, the more the current you can get out of there – generally speaking.  Or the more power you get, because of this thing (gesture at formula) we were talking about earlier.  So, volts, amps, and resistance are all kind of equivalent in that way.

 

N:  There was another thing you mentioned which I had not considered.  I was looking at the specs online and if it said it was a 36 volt motor, then we are fixed at 36 volts.  But you are saying you could run it on 12 or 24 volts.

 

Absolutely!  That is the nice thing about a dc motor.  DC motors have a range.  And you will notice that they give you a “volts at this rpm”.  Why would they do that?  Because the volts actually determine the rpm of the motor.  You know how I just said current equals the torque, the more current the more torque? Well volts equals the rpm.

 

(10 min)

 

There is actually a constant.  They call it a technical voltage or rpm constant.  That is the rpm of the motor.  So it might be a 36 volt motor rated at 4000 rpm.  Well, what is it at 18 volts?  Half of it would be 2000 rpm.

 

N:  And the throttle…we were talking about the variable resistance throttle. That is deciding how much of the 36 volts you are going to give it right now. 

 

That is exactly right.

 

N: So, using fewer batteries would just mean you didn’t go to full throttle.

T: Yup.

 

What is kind of cool with batteries, you can play around with this.  As long as .. well there is a technical detail – but we will forget that for the moment.  Say you eventually wanted to have three batteries, but you wanted to try it on one.  The one thing with an electric vehicle that I will heartily recommend: you try it with a much reduced voltage first.  Why?  Because you are going to screw up.  The first time you build it I guarantee you will screw something up.  A bolt will be loose. Something.  I don’t know.  The chain won’t quite be tight.  You want to limit the damage.  So when you start it up, use a really … If you can find a lantern battery, just something so you can get the… just put the car up on blocks and just to see thing spin.  Put a really small battery in there.  Like a drill battery or something.  If it runs, everything is smooth, the chain is nice an tight, grease the chain a little bit.  Let it run again.  If it is a new motor let it run for awhile.  Let it run for 10 minutes to break in the motor.  If you get a dc motor, a brush type motor, will want to have a little break-in time with no load.  Let it run a bit.  “this is cool, I can’t wait to get in it..” 

 

(12 min)

 

Then, and make sure everything is greased up, then when you do let it down – even if you are using two or three batteries – put only one battery in it first and run it around the yard.  You know, this is pretty cool.  And from that you might say, this is it.  This is all we need.  Or, oh man, I am only doing two miles per hour.  I need more speed.  That is a good way to build up to it.  You will have designed it to know how many batteries you think you need.  But that is a nice way to inch up on things.  Especially with a new electric vehicle.  These things can be dangerous.  You have got gears there and a lot of torque.  And especially with a chain and gears.  You want to watch your clothes.  You don’t want to catch your clothes or your fingers in it.  You can only say Ouch once.

 

Say you decide on a whatever motor, 24 volt motor lets say.  You can run that at 12 volts, you can run that at 36 volts.  Why do they call it a 24 volt motor? Because that is what they designed it for, that is the design voltage.  Most motors will take two times the design voltage for periods of time, until they overheat.  Could be half an hour, an hour, or even a day. 

 

One problem with that, the only downside of that is your controller.  The controllers often have what is called a low-voltage disconnect (LVD). What that does is, when you buy a controller it will have an LVD – look at the spec sheet.  Say it is a 24 volt controller.  It might have an LVD of 6 volts. That means, great, I can run it on a 6 volt battery or a 12 volt battery and be fine.

 

(14 min)

 

It might also have an HVD, a high voltage disconnect.  That means that is as high a battery you can put on it with that controller and still have the motor run. So it might be a 24 volt controller with a 38 volt High Voltage Disconnect.  Well, you are not going to be running that with 40 volts.

 

N: The disconnect on the high end is to protect the controller?

 

Right. And on the low end it is to take care of the batteries.  [Running a battery dry is bad for it.]

 

Let me show you a controller.  Kinda heavy, huh?  It is full of epoxy, it is “potted”.  We bought this one for the solar car.  It has connections for your motor, battery plus, battery minus, and some other connections.  What those are is your throttle.  You connect your throttle to “those”.

 

This is a 300 amp controller that is good for 24 - 48 volts.  So there are your low and high voltage disconnects.  And it is programmable.

 

(16 min)

 

you take this off, you connect your laptop computer, and you can change stuff.  You can change the low and high voltage settings, and the current trips on them.  You won’t want them this fancy.  This is for golf carts that run at 24 to 36 volts and run all day on them.

 

The one you get will probably be half this size. In all likelihood you don’t want a 300 amp controller. A 100 amp controller is probably going to be fine. It depends on how much you want to burn your tires. How quick of an acceleration you want.  The voltage is going to set your top speed with your gear ratio.  You guys know how to work out your gear ratio?  You can work out the ratio to know what your speed will be?  Your speed will be determined by the diameter of the wheel, the diameter of your drive wheel your gear ratio size, and the speed your motor is running at.  Your acceleration will be determined by how much torque you get from the motor which is determined by how much current.  The two are proportional.

 

The bigger controller, the more current.  But the bigger the controller the more bucks too.

 

My gut feel is 100 amps.  If you run 24 volts at 100 amps your power will be 2400 watts. Amps times volts.

 

There are a couple ways to look at 2400 watts.  Lance Armstrong running full bore in the Tour ‘D France puts out a continuous 400 watts.  He is moving a 30 pound bike and himself, he is moving about 200 pounds.

 

What do you weigh?

 

T: 120 pounds?

 

And the cart, that is about 200 pounds.  Lance can move 30 miles per hour on 400 watts.  So you can say all we need is 400 watts.  Well, probably not.  He does not accelerate as fast as you are going to accelerate.  You guys want to throw up dirt… My gut feel is that 1000 watts would be pretty nice.  That is a pretty nice size, and a pretty nice price range.  You can go more, you could go to 200 amps but the price…

 

(20 min)

 

One way to look at that is to divide by (738?) is 3.25 horse power.  That is an interesting number.  That is really close to the motor you have on there. But it is way different.  Horse power is power.  Remember how I was telling you about torque?  Electric motors versus gas motors – when you press the accelerator on a gas motor, it will go r r rr rrr RRRRR and wind up from idle to 3000 rpm.  As it is picking up, … I will show you the graph.

 

(concept only, don’t scale drawing)

 

As it is picking up.  Say this is 3000 RPM out here.  It is going like this, it is leveling off.  By 3000 rpm it is at maximum torque.

 

But an electric motor it starts at full torque and falls of just a little at 3000 rpm, but mostly stay constant.

 

 

Look at the torque difference. At, say 1000 rpm look at the torque difference. I have twice as much torque off my electric motor. That means that when you floor it you feel it instantaneously.

 

So it is not quite apples-to-apples.  But it is still 3 hp.  That is a pretty good size.  My gut feel is that is a pretty good size to shoot for.  Why you are having such a tough time is because people do all sorts of different things.  Some people want 30 hp.  That motor you found first puts out a prodigious amount of power, but it didn’t come with a controller.  What was it, a 35 volt motor?  It was almost 7 inches in diameter and 13 inches long.  That motor would make that go cart into a dragster.  You could do zero to 60 in maybe 4 seconds.. if you had enough batteries on it.  I see you like that idea… but you would also kill yourself!  That thing would be way over-powered.  You couldn’t even steer.  You would lose control.  If you built with that motor, what you would do is put it in your truck, take it down to Portland international raceway, and race it with all the electric cars when they show up on Saturday night.  They do that a couple times each summer.  It is literally drag racing.  You would kill some gas cars (Hondas, Mustangs...)  It would be a smoker…  you could probably get 30 hp out of that motor for the few seconds it takes to drag race.

 

Especially if you use this kind of batteries.  Lithium batteries.  This (holding up a short cylinder with battery cells in it, looks a bit like bullets in a revolver), here are 10 batteries – that is a small battery pack.  This is from a miniature hub motor.  We will talk about that.

 

That 1000 watt range is pretty nice.  It is like the 3 hp gas motor you have but with more acceleration.  That is a really good size.  You still need to provide 24 volts, but you could still test at 12 volts.

 

(24 min)

 

If you felt you needed more power you could step it up to 36 volts, and that would give you 50% more power.  50% more voltage is going to give you 50% more power.  So, you have a lot of options if you go in that range.  And the prices are pretty good.  Around a 1000 watts there are a lot of little motors in that range.

 

I even have a little 1000 watt one. Remind me to show it to you on the way out.  I can even give it to you if that is what you decide to go with.

 

Motors.  Controllers.  Batteries.

 

Go with a sealed battery.  For sure, go with a sealed battery.  Just for the tipping. You don’t want any liquid electrolyte splashing around if something goes wrong, if you tip over.  You don’t expect anything to go wrong, but you want to plan for it.

 

N: Plan for the worst, hope for the best.

 

That is right!  That is exactly what you want to do.  You are the designer now.  You are going to want to feel smart. If something does go wrong you want to feel: I didn’t expect this to happen, but I did design for it.

 

Any questions?  You need to digest it.  There is a lot of stuff here. Motors are amazing.

 

What about charging?  What are you thinking for recharging batteries?

 

T: We have a car battery charger.

 

Ok, so one at a time.  Take them out and recharge them separately?  Nothing wrong with that.

 

N: That will also give them time to cool.

 

(26 min)

 

Yeah, one thing, if you take it out and run it hard you probably want to give them an hour to cool.  Batteries have a lot of mass and keep heat for a long time.  Give them a little time to cool down.  They charge better when they are cooler.

 

N: If you use other types of batteries they don’t like to charge hot.  NMH will develop a “memory” if they are charged hot, and you can’t fully charge them.

 

I wouldn’t recommend NMH for your application. 

 

N: We are considering motorcycle batteries.

 

There are some AGM’s.  Tell you what, these might be a little bigger than you were thinking.  You can have them.  These might be a little larger than you were thinking.  They are wheelchair batteries.  They are 12 volt AGM batteries, there is no liquid in them.  AGM batteries put out a lot of current, they have very low internal resistance.

 

N: Is that the brand?

 

(28 min)

 

No, AGM is “absorbed glass mat”.  It is like a gel battery.  In this they have gone one step further.  They have taken the liquid electrolyte and made it into a paste.  Then absorbed it into .. kind of like a cardboard filler.  So the electrolyte is not liquid.  It is like a solid immobilized liquid.  And so, because of that, you can tip them.  You can mount them on their side. You can mount them in any orientation. You could mount them upside-down (it would be kind of crazy because the posts are down…), but you could if the mounting worked best.

 

The other big thing is they never take liquid.  Those caps never have to open.  Actually, if you expose the electrolyte you deactivate it.  You never open them for the life of the battery. 

 

This battery is fairly old, but I use it for inverter testing. My inverters, this are the style of inverter I design.  They will pull 400-500 amps.  They (the battery) will actually do that for a very short period of time.  They are a really incredible battery.  If you do test, test with only one battery first.  They will put out an incredible amount of current.  They will handle whatever controller you chose. Why don’t you try those.  Worst case, if they are not as good as they used to be, that will let you test your system with a compromised battery.

 

N: We can borrow them, and return them. That will let us begin experimenting.

 

Fine, that will work for me too.  I do use them for testing occasionally.  But they are fully charged, and they are good batteries. 

 

(30 min)

 

This battery technology is actually also a gel.  The electrolyte is actually gelled in there, and they can be mounted in any orientation.  I used to use liquid batteries, and it was just a pain.  I can’t keep them “full.”  I am always charging and discharging them.  I use them for development work so they are always being cycled.  I am really bad at maintenance, and I just can’t keep them full.

 

You have to decide on your throttle method.  There is a thing called a “pot box”.  This (gesturing at PC screen) is a pot box.  It is just a potentiometer with a couple of wires.  It is overkill for what you are doing there, but it would work.  It looked like there was a metal arm coming back from the accelerator pedal on your go cart, and that arm could just tie in and …  You might be able to find one on eBay for $30-$40, that would be a deal.  You could design one yourself, but.  I have designed them myself.  You use some sheet metal, and a really nice analog pot, and it only costs you $10.  But look how much time you waste, a month?  You may be able to look around and find them cheaper.  Curtis makes them.  Curtis PMC (sp?) They also make some controllers.  Curtis, Altrac (sp?), and some others. 

 

(33 min)

 

This one we looked at before is 600 watts.  600 watts would work. For something like this something that is already kitted… I have heard good things about this motor.  And it comes in a couple different sizes.  This 1000 watt, 100 amp controller. That is what we were talking about. 100 amp, 24 volts, that is 2400 watts. 100 amps at 12 volts is 1200 watts.  That is pretty nice too.  These hub motors (gesturing at the bicycle motor on his desk) are about 250 watts.  So that is many times over a hub motor power.  Still plenty decent.

 

Another thing you can do is that you can use one.  And if you really like it you can still use two batteries, but put them in parallel instead of series.  I didn’t explain how that works to you yet.  But it is pretty cool.  You know how batteries work?  You have series and parallel circuits (starting to draw).  Your battery has a plus (+) and a minus (-) on it. You can hook another battery up, also plus and minus, let’s say they are12 volts just for argument.  Now what I have done is put them in parallel.  I can get two times the current that I can get from one.  Let’s say one battery is 50 amps.  With two in parallel I can get 100 amps.  I just pull off the two wires…

 

 

So that is a parallel circuit.  You could hook your system up that way.  You would have 12 volts, but twice the current.  There is also series.  I will hook them up plus to minus instead of plus to plus.  Now what I have done is doubled my voltage.  The parallel circuit is additive in current, the series circuit is additive in voltage. Either way you have doubled power.

 

Looking at the 600 watt motor, it isn’t bad, but the price difference for the 1000 watt isn’t that much.  You could run the 1000 watt motor at less power and be fine, or run it with more power and get more performance.

 

Next you need to mount the motor.  You need mounting ears, and bolt the motor to it, then bolt it to your chassis.  It will have to be pretty strong.  We are talking about 3 hp, and that is an amazing amount of power.

 

So we have a motor size range.  What will the acceleration be?  When you design race cars, or any car for that matter, you are looking at that torque curve.  Distance over time.  So you start at zero time and accelerate.

 

What will this curve be?  You can actually plot this.  Get your stopwatch out and mark off a distance.  Time how long it takes to get to each point and plot it.  Then you can work out a formula for it. 

 

Once you have that we can calculate what the electric motor and controller need to do to equal it.  We can decide where you want to be compared to the gas motor. 

 

At least you want to compare curves between the gas engine and the electric motor.  After you build this and ride it the first time you will have this big “EV” (electric vehicle) grin that just won’t go away.

 

 p.s images could not be uploaded

6th Reflection

This week i have gotten my gas motor running have most of my parts, just need fuses and #2 wire, i think. The gas motor was giving me considerable trouble, i relaced the carborator and the fule line. i checked the generator and it as fine, i assumed the wire was broken untill i disconnected the power from the spark plug and the engien ran better. turns out, the spark plug was bad. i got it running very fast untill the gas pedal came off, got stuck under the go-cart so it was pulling the throttle to maximum. that was a little freakey untill it it a wall and i was able to hit the emergency stop. this week i was doing about 5 out of 10, speed wise.