Sigh…
That’s depressing.
I was hoping to be the only guy around with a 12lber that ROOOOOAAAAARRRRRRRS.
About the air cooling, yea, I noticed that yesterday, but I stupidly told myself that I could just put a fan in there.
HELLO, EARTH TO NICK!
I hadn’t even thought about the weight of the batteries for the fan, nor the fan itself…
I didn’t know that brushless motors could output that high of an rpm, though!
It seems as if they’d beat a modified-for-reverse car starter motor, if they’re geared down.
One such brushless that I found had 5,800 rpm’s per volt, which would put me back at 30,000+ rpm’s again, if I went with 6 volts.
Can planetary motor gearboxes handle 30,000 rpm’s?
If need be, I can gear it down in steps, but the first gearbox in the chain still has to handle 30,000+ rpm’s, doesn’t it?
Any recommendations for ones with low rpm and high torque?
with a grain of salt you can assume that with some of the latest brushless set-ups can compete pound for pound amoung glow set-ups. so you wont loss to much of that ower you want, and you can always run a weapon off a glow engine
brushless motors come with a kv and kt rating, though you hardly ever see the kt posted. the higher the kv rating the higher the rpm per volt, higher kt equals more torque per amp. generally speaking if you find a family of brushless motors, their power output (rpm X torque) will all be similair so go with a lower kv rated motors and you will get more torque
there are also two different flavors of brushless, the one you will be interested in is called an outrunner amoung other names. the electromagnets are on the inside and the bell housing spins, this gives some extra torque as opposed to a typical motor type of setup.
choosing the motor is more about the money you want to spend. if you want some high quality stuff your going to pay for it through the nose, on the other hand you can buy some 25 dollar kits and wind your own so you can custom tune it for your application.
the hand wound is the route i would choose if only to learn some more.
Nick why not try something like a 23cc engine? They use them on the Marders, HPI Baja, DuraCrap 1/5th scale cars.
Only thing bad about the RC engines (2 stroke glow ones) is if you don’t tune them good, depending on the engine, they’ll flameout. I remember my TRX 2.5 would not run for anything, if I didn’t have it tuned good!
Nick, Have you considered Diesel-Electric? It would give you the ‘ROOOOOAAAAARRRRRRR’ factor without the transmission headaches. Wada in Japan builds nitro-methane powered diesel-electric model railroad engines.
What a neat idea…
Of course, the one’s they make are way out of my price-range, but it looks like I could make my own.
I read that site, and checked the three links that it had on the subject, but I can’t seem to find anything in-depth on how to determine what motor is suitable to which ICE.
I did some general googling, but I can’t seem to find out much of anything on DC generators, except that they need to have commutators and brushes.
Is any dc motor going to be suitable to be a generator?
I suppose that the motor and ICE should have equivalent rpm’s, as a low-rpm dc motor would restrict the ICE…
I’d also like to find out how I can determine the amperage and voltage that the generator produces at a given input rpm and torque.
If anyone can explain these things, or point me to places that can, I’d be very grateful.
The Wada’s are indeed pricy. That reflects the craftsmanship and modeling detail at least as much as the propulsion technology. I know of one home-brew implementation of this approach for model railroads. As I recall he used a marine engine coupled to a cordless drill motor for a generator. Heat was an issue, but that was mostly due to the limited ventilation inside the model locomotive body.
RPMs aren’t as important as the voltage/current produced. You adjust the throttle to produce a bit more than you need, then regulate it down. For a robot application, the current requirements are likely to be uneven, with high peak demands. In this case, a battery system could be charged up during off-peak loads to provide supplemental current on demand. (much like a hybrid car)
If I have to put a battery on-board, then that defeats the whole purpose.
I understand what you’re saying about the voltage and amperage, but I still don’t see how I can determine the output voltage and amperage before actually buying the engine and motor.
After scouring google without much luck, I resolutely turned to wikipedia…
But, even they didn’t have an equation/relation (isn’t that illegal, or something? I always thought that they knew EVERYTHING.).
They did have an equation for finding the AC resistance, but that doesn’t help.
Does anyone know how to determine the amperage and voltage produced by a generator at x rpm’s?
I don’t have any hard numbers or equations, but here’s some rough material to start with:
A horsepower is roughly 750 watts. Even with the conversion losses, that 2.2 Hp Fuji should be able to generate a kilowatt of juice.
Assuming 100% efficiency, the generator would have to be the same size and turn at the expected max speed of the drive motor. I have seen claims for DC generators with better than 90% efficiency. I’d plan on getting somewhat less.
The battery is not a requirement, just another option to consider. It wouldn’t have to be big. Just enough to supply a quick burst of current on demand. Remember that there will be some throttle lag with the ICE.
You might look at smaller portable generators for ideas (or maybe even parts). For example, the Honda EU1000I is a 1.8 hp - 1 KW model.
I’ve been doing a bit o’ reasearch, and I think that I’m going to restart this project as soon as I can get the capital (which looks like it’s going to be a couple months, at the rate that I’m currently burning money).
That’s not too much of an issue, though, as I have a lot to learn about the subject, and multiple other ongoing projects, anyhow.
The info on the Fuji generator is a bit skewed, as that motor is many times heavier than the average glow engine, and those 750 watts are all AC watts, but it does give me a reasonable idea of what ICE’s can do, though.
By the way, does anyone know if I actually need to use a muffler with glow engines?
Is it like a true car, where you rip off the headers and get a huge power boost from the lack of restriction, or is it too dangerous to do this?
And, does anyone know the details of how to control the throttle remotely?
And, what about starting it via remote control?
I’ve heard about using servos to do those, but I haven’t ever seen or heard the actual specifics of the setups.
Well, I stumbled onto what seems to be the only answer to my remote starting problem: http://www2.gpmd.com/image/t/tamg5091.jpg
That’s Tamiya’s .16 monster truck glow engine.
It seems to be the only engine at www.towerhobbies.com that has a starter motor.
Of course, it’s backorder only, woohoo!
I still haven’t figured out exactly how to fix the throttle problem…
I’m guessing that the black tab with the phillip’s screwhead on it that’s in the middle of the picture is the throttle, but I just don’t know these things…
Current questions:
Where’s the throttle?
Can I do without a muffler, safely?
Exactly how does this type of fuel tank input the fuel into the engine (they don’t seem to sell any hoses)? http://www2.gpmd.com/image/t/tamc4591.jpg
And, is there any way to make it so that the engine will still recieve fuel and run properly even when the bot is flipped over?
Yup, that little black thing on the side of the carburator is the throttle. Just hook up a servo via a pushrod to control it.
That brass piece on the other side of the carb looks like the connection for the fuel line. Search for “fuel line” on the Tower site for a number of tubing options.
Back when I played with RC airplanes, we ran without mufflers all the time. It works, but it is LOUD!!! It is bad enough outside. It would be painfully loud in an enclosed space.
Nick stay FAR FAR FAR away from traxxas engines along with those crappy electric starters. Trust me they are not worth your trouble. A good solid engine to go with would be something like a OS, they make nice reliable engines. You need to deside what kind of displacement and type of engine you want to go with. In your case a a desent .21-.25 engine would probably work nicely. If you want remote starting just fab somthing up your self. Its not hard to do trust me. Also get something with a slide carb with 3 tuning needles.
Also yes you have to have a muffler. These little 2-strokes need backpressure from the exhaust in order to function properly. Also if you want something on the quieter end then go with a 3 chamber pipe.
As far as gear boxes go you have many options. I would suggest a gearbox from a RC monster truck called the HPI savage. Its a proven design, all metal gears, possible 3 speeds w/reverse, and also has a slipper. And it will take all the power you throw at it, I garentee it.
If you have anymore questions I didnt answer just let me know. I have about 8 years expiriance in RC including glow engines.
I’m not sure how many cc’s it has or how much horse power, but I do know that it actually runs on fuel. It’s a real 1/4th scale blown V8 engine complete with a camshaft, lifters, rockers, distributor, etc.
The engine is not mine, I wish it was. I have seen videos of these engines running, and they sound just like top fuel drag engines but in a higher tone of course.
I would love to have one of those engines attached to my weed eater. Just think of the weeds you could whack!
I would look into the NOvak HV maxx brushless system, it is a 14 volt system that has a 820 motor size(geussing on that part) and outputs plenty of torque, my freind runs one in his revo, which is normally a nitro monster truck, and he cna compeete if not outrun all of the hopped up.32 nitro guys! if money was not an issue I would vouch for a couple of those. I think they are rated for like670 oz/in off tourqe. that sould be plenty and u shouldn’t need a huge gear reduction. if do just strap in a multi gear transission, the normal electric rc tranny takes 120oz/in of torque and 23,000 rpms and takes thaem down to 700 rpm and like 340oz/in of torque. with that kind of tranny(may take a little bit ofresearch) you should be fine.
Well, I’m pretty much decided on car starter motors.
Mostly because my brother can get me a couple for free.
When I get done building the bot (which will take a few months or more), I’ll consider swapping them for more-efficient motors, so I can get rid of the huge weight of the car battery.
All their deficiencies aside, these babies truly are powerhouses.
I believe (from a no-load viewing of them spinning) that they’ll have more than enough power to melt my wheels when they go up against a wall, once I tone down their rpm’s a bit.
My battlebot project has been stalled by two things, though.
(1) I just got my biped.
(2) I still haven’t found a place to buy a used weedwacker engine (or scraped together $100-150 for a new one).
