Wednesday, April 2, 2008

High Speed Pursuits

While I'm in love with the dragster, I felt like I needed a more general purpose RC vehicle. I wanted to keep my parts current so I decided to look for another vehicle that runs on brushless & lipo power. I think that if and when my dragster starts running consistent 100mph passes, I will probably retire the chassis and put the motor and battery in another vehicle since it would be a tragedy to let them sit on the shelf. Now this lead me to the conclusion that I need to build 2 vehicles. Why? Because 2 is more fun than 1. My next 2 victims will be a stadium truck and a pan/touring car. I chose these because they are both 2wd, and both can run on the parts I already have. So in my mind at least I'm getting a 3 for 1 deal. I also can test a variety of parts in many different setups so that anyone wanting to know how a particular combination works doesn't need to spend their time and money working out details that many people have already tried.

The Stadium Truck

In a game of chance I have acquired a Traxxas VXL Brushless Rustler. For the Naive the rustler is this: . Traxxas claims that it is "The Fastest Ready-To-Race electric stadium truck you can buy." I thought it would be a good idea to hold Traxxas to their word and test out the truck.

This truck already has a brushless motor in it, the "Velineon Brushless Power System." While this should go pretty fast, at some point the Mamba will find its way into the truck and well see if that makes a difference.

For a few magic beans I managed to get a 3s 11.1V 5000mah Lipo pack from Max Amps. Traxxas says I need a 6000mah lipo and gearing, but whatever, the 5000mah came in the RTR run kit. The kit also included a pretty cool Hyperion charger (More on this in another post) and a Lipo bag (to conceal explosions?). . Going along with Traxxas's claim this kit portends to propell my little rustler to 70+mph. Sounds fun.

I don't have any real goals for this vehicle except to make it fun. I wanted something that I can play around this at the beach or the parking lot, yet is really fast, and this seems to be the thing. I will review the VXL truck in depth next week, so check back for an ultra boring a long post about it.

I have modified the truck already. There seems to be a glut of wheelie bars and wheelie bar accessories for this truck. This led me to the conclusion that this truck might do a wheelie with the high voltage battery that I chose for it. so on go the wheelie bars. Pictures will come soon.
Formula 1 Cars are fast.
The Touring Car I spoke of will be a Tamiya F103GT Pan/Touring car chassis. I chose this because it has direct 2wd, it is light, and it is cheap. It also has many option parts, and my components that I already have should fit right in. This chassis is made to accept regular touring car bodies and tires, so that makes it easy to complete. It does come with a little scrawny brushed motor, which will either be annihilated by my lipo pack or never used. I have not received this kit yet, but when I do ill include some build photos and the modified parts I choose for it.
My goal with the touring car is just to hit 100mph. Will my Mamba Max + Lipo combo do it? Maybe, but if not I'll get as close as I Can and switch to a more capable setup. This car still operates within my original parameters, so I don't need to change my own rules.

Tuesday, April 1, 2008

Shiny Green + 63,000RPM = Fast?

Mamba Max Time

What sounds like a catchy intro for tonight’s episode of dancing with the stars (don’t ask why I know that) is actually an intro to the motor I’ve chosen for my dragster.

The Mamba Max is a motor made by castle creations that offers brushless power & high RPM’s for a decent price. I ended up choosing the Mamba Max for 3 reasons.
The price. I snagged mine off of eBay with shipping for around $100 less than what the other packages cost. This enables me to stay within my original budget goal.
Allot of people are using them. Drag racing, off road racing, carpet racing. They all seem to agree that the Mamba line of motors is versatile enough for all of these applications.
The RPM rating makes it a capable candidate for my 100mph project. Also it will fit in a touring car or a truck, so it enables me to try to reach 100mph in a variety of platforms.

For my application I chose the model that will spin at 5700 RPM per volt. They do make a Mamba Max 6600, and a Mamba Max 7700, but those are limited to 2s lipo packs. They are limited to prevent mechanical failure so a quick estimate of the math shows:

7700RPM x 7.4V (2s Lipo) = 56,980
6600RPM x 7.4V (2s Lipo) = 48,840
5700RPM x 11.1V (3s Lipo) = 63,270 RPMs!!!

Here is s nice link castle puts out that shows the capabilities of their products. (Ignore the speed results that they have since those are with different gearing & weight than what I will use.)

Did I forget to mention that I will be using lipo packs for this project? Ah yes, the new “black gold” of electric power, lipo (lithium polymer) batteries offer more voltage at a higher discharge rate for a longer period of time than similar Nickel Cadmium batteries. The problem? Lipos can catch on fire if they get too hot, too low in charge, or too much of just about anything. So you must have a specific charger, and other equipment to properly charge the batteries. This sounds like a big deal, but there has been a ton of literature written on the subject, and it seems straightforward. I haven’t used the lipos yet, but Ill post any explosive results I get with these little powerhouses. I ordered My LiPo’s from Max Amps. I’ll do a full review when I’ve used them in multiple vehicles.

Back to the motor
So as you can see from my calculations the Mamba Max 5700 has a higher RPM rating when being used with the recommended batteries. In order to stay within my rules of being able to operate the car after the run, I decided doing what the manufacturer says to do would be best. Now if I break the 100mph barrier and decide to test the limits, you can bet I will strap one of the 7700 Mamba Max’s to my dragster and see what happens.

Friday, March 14, 2008

Powerplant Wanted

Now that the chassis is assembled I need to find a motor that will push it over 100mph. Electric motors have come a long way in a short period of time, and that makes my project significantly easier.

I am by no means an expert in RC or motors, but I will try to provide a brief description of what I have found out (please feel free to add to this in the comments if you feel compelled to do so).

For a long time the remote controlled car was powered by the brushed motor, this motor offered speed and affordability, but the performance could not meet that of a nitro motor. Also the brushed motor has miniature brushes that need to be replaced periodically that adds to cost and downtime. The brushed motor kept RC cars stuck at a certain ceiling of performance and durability for a long time. I think it should be noted that there have been several 100mph passes made with brushed motors in the past, so the limits on performance are not absolute, but 100mph runs were defiantly the exceptions.

Along came the brushless motor into model aircraft. This motor offers durability and high performance that could compare with some nitro engines. The brushless motors are essentially turned inside out so that the magnets rotate inside of the motor, instead of the fixed magnets in a brushed motor. This configuration allows the car builder to forgo the necessary rebuilds, and set the limits higher that previously restricted electric motor performance.

This wikipedia article sums it better than I can so you can get the idea

I think Its easy to see why I chose a brushless motor for my car project. In my search for the perfect powerplant I considered 3 different brushless motors and electronic speed controller combinations.

Neu motors – These are model airplane engines. They come in a wide range of RPMs, shapes, and electrical parameters. The current RC world record holder of 134mph used a Neu motor for his car. The drawback in one of these is the cost, and the fact that they don’t come matched to an ESC. In fact the cost of the engine alone is more than many of the motor + ESC combinations that I’m considering for this project.

Novak Motors – Novak offers a High Voltage brushless motor and ESC combination. This would allow me to run several LiPo(See future article) batteries, so generate sustained RPMs that are needed to run at high speeds. The motor and ESC combination is cheaper than the NEU motor, but seems to have less performance capabilities also. This is still an expensive combination, and seems limited in its capabilities. At the World speed record challenge there was a car that used this setup to make several 100mph passes.

Castle Creations – The mamba line from Castle creations seems to be very popular among the drag racing crowd, so it immediately grabbed my attention. The recent release of the 1/10 Mamba Max seems to be very popular right now. These motors are capable of the ~60,000rpms that are needed to go over 100mph. They also come packaged with an ESC that is programmable from a laptop. This means that you can adjust different parameters that control aspects of the motors performance from your laptop. The best feature of this motor is the price. Of the 3 I reviewed it has the lowest price tag, and the ceiling of performance is yet to be determined.

I think that any of the 3 above motors will propel my dragster to the desired speed. Check back later this weekend and ill photos of the winning combination.

Tuesday, March 11, 2008

Physics, Math, and Other Stuff

Well I hope nobody thought I was going to get to 100mph without a little help from our little friend math. Thankfully I found an online computer that takes into account your tire size, gear ratio, battery Voltage, motor RPM, and just about any other variable so that you don't have to relive 10th grade trigonometry.

I haven't posted what motor I'm going to use yet because I'm still waiting for it to be delivered, so at that point I'll post my initial setup ideas. If anyone has any advice or insight at this point please post it.

The Dragster Chassis

Here is what I've decided to use as the initial chassis for my 100mph car. Its a 1/10 scale Grand Motorsports GMS Dragster kit.

This kit weighs about 1/2 of a pound and allows for a central weight distribution. If I am able to break the 100mph barrier with this chassis, I will move on and try a touring car, but initially this will give me the best shot to break the speed limit on a budget.

I would like to say that Grand motorsports did an excellent job with this kit. The fit and finish is excellent. The Carbon/Graphite is very precisely machined, and the anodized aluminum parts look very nice.

If you have any questions about the dragster please ask.

Monday, March 10, 2008

Choosing a 100mph Chassis

The platform I use to build the car will have to fit within my own rules and will only be limited by its purpose.

1. Must be lightweight – I’m going to use carbon fiber initially because it’s the lightest, strongest, and abundant material that many manufacturers already make high performance chassis from.

2. Must have enough space to hold all of my electronics - This car will need a high RPM motor, an electronic speed control, a high capacity battery pack, a steering servo, a RPM meter, and a speedometer. Based on this I think the car must bat at least 1/12 scale, and possible 1/10 scale.

3. Must be durable & usable in standard race classes – See above reasoning for using carbon fiber.

4. 2 Wheel drive may be the easiest way to go – Many of the current electric on-road cars are 4wd, and while this would be a more impressive engineering feat, it adds more parts. To me more parts in the car mean more parts to break. By keeping it 2wd I eliminate the need for a belt drive that could possible break, and the need for a differential that would not be meant for excessive RPM’s. This should cut down on my broken parts and down time. I will look at both front and rear engine designs, but initially I will be focusing on a rear engine car mainly because that’s what the manufactures produce.

5. Central battery & engine location – This will help keep the car running straight and the load equally balanced bilaterally on the tires.

Based on my above ideas I came to the conclusion that I will use either an electric 2wd touring car with a central battery mount, or a drag car that is within my 24 inch wheelbase rule.

The best touring cars that I have found are the Calandra Racing Concepts Gen10X, the CRC Gen12X, the team associated RC12L4, and the Tamiya F103GT. There are probably many others that I’m not aware of that would do the job, so ill update this list as I find and try new possibilities. I haven’t tested any of these cars, so all of my ideas are based on speculation.

The drag cars I have considered for this project are all of them. Seriously, every platform has the lightweight, center weight, short wheelbase, and durability that I’m looking for. Currently there are drag classes for Pro Stock, Funny Car, Top Fuel and many others. There seems to be 3 companies that make electric drag car chassis.

Grand Motorsports – Make all classes of chassis out of carbon fiber & aluminum. These are priced around $200 and seem to be a popular choice for many racers.

RJ Speed – Make a 24” wheelbase dragster, 11” pro-stock, and 13” funny car. These models are tagged as the “entry level” cars, and are priced at under $100. I’m not sure what they are made of or their quality, but for under $100 they would be ideal if you start breaking parts.

Any other RC drag car would possibly work. I will list them as I find them, and please feel free to comment and I will update the posts.

In the next post ill let you know what platform I chose for my initial run.

My Goal With This Blog

Basically my goal is to build a remote controlled car that will go at least 100mph. This blog will chronicle my progress so that others may be able to also achieve this. Any speed over 100mph will be an added bonus, and eventually I may enter a car I build into the world record RC top speed challenge that RCCA Magazine holds each year. Many people have reached 100mph before me, so this is nothing new. I would like to reach it efficiently and affordable while using a solid platform that could be used to achieve an extreme top speed.

In meeting my goals I’m setting some perimeters for myself. These are loosely based on the rules that RCCA uses for its challenge:

1. The wheelbase must be 24” or less.

2. The car must resemble some vehicle & have a place for a driver.

3. Electric or Nitro powered (I’m using electric).

4. The car must be drivable after the top speed run.

5. The top speed run will be verified initially with an onboard speedometer, then verified with radar.

Outside of the “rules” I set for myself I’m setting some goals for my car.

1. The car will be made with parts that can be bought online or at most hobby shops (this means no extreme fabrication will be used until I fail miserably and go all out to reach my own arbitrary goal).

2. Based on the above goal I would like to keep this project affordable for anyone to build. Ideally the car should cost less than $500.

3. The car will be able to race in some form of current class when the run is over (Oval, Touring, Drag, ect…). This is mainly for my piece of mind that I didn’t build a single purpose speed machine that will go to waste after I break the sound barrier (I’ll be happy breaking the speed limit).

4. The car will be electric. I think that electricity may power all of our cars in the future, so developing high speed electric vehicles seems to be a reasonable pursuit.

5. In a top speed setup, the car should be able to do roughly 20 100mph runs without a major rebuild.

I have already started the design phase & should be posting regularly as the car comes together.

I have done some research on the subject and found some other builders with parallel interests, so I would like to give them credit and allow people to see other parts of the hobby. I will provide links to anything I find on the web that may relate to high speed RC.