ICE Battlebot

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1

Since seeing how pretty and strong the attatchment chain is, I have been enamored with the idea of using it to create a Battlebot (preferably a 12 lber).
x12.putfile.com/1/1608052332-thumb.jpg
What I’d really like to do, though, is use two ICE’s (internal combustion engines) to power the treads.

In searching for small ICE’s, the smallest that I’ve been able to come up with are the two-stroke RC car glow engines.
The problem with these, though, are their extreemly high output rpm.

With 30,000+ peak rpm’s and weighing under a pound, these little devils would be amazing, if I could convert all that unneeded (and, in an enclosed arena, harmful) speed into torque.
To do that, I’d need a 60:1 gear reduction, however…

I haven’t been able to find any gearboxes that could handle an input of 30,000 rpm’s.
:cry:
The best that I’ve seen is this site, which sells a 1lb $200 planetary gearbox that can handle a 10,000 rpm input.

So, I could use a four stroke glow engine, or a small gas engine, since both types are geared towards lower rpm’s and higher torque (here’s the gas engine that I’m thinking of using):
www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJYN7&P=0

The only real problem that these two types of engines share, is their low power to weight ratio (at least, in comparison with the glow engines).
The one in the link above is 3.6 lbs, which really puts using two of them out of the question.
Although, I’m told that I could use a single one with a clutch system to operate one side at a time, when I need to turn, but that’ll mean slower an less “dime-like” turns.
The other problem, is that these motors are made for airplanes and boats (they need higher torque to spin a propeller, since it’s less efficient than a tire).
That, though, shouldn’t be too much of a hurdle, since I should be able to convert the output shaft of the airplane motors.

So, after a few weeks of excited reasearch, I’m stuck.
If anyone has any ideas, I’d be really grateful.

Also, I’ve been meaning to get a better understanding of the full drive-system of an RC car, and have been falling short.
I’ve found many sites that give descriptions of individual component’s mechanisms, but I can’t find a site that shows the overall setup of the internals.
It’s nice to know how each component works, but I need to see how they fit together, as well.
So, if anyone has a link to a site that’d help, I’d again be very grateful.

Thanks.

2

having dabbled (sp?) in RC everything for many years i might be able to shed some light on the situation.

first rc cars typically use a special glow engines different from planes because they dont get the air flow for cooling you will most likely encounter a similar situation. the output of the engine has a centrifugal clutch with a pinion gear (~10-15 teeth) embedded onto it which will drive a wide array of gear arrangements dependent on use. im only familiar with the single gear pass (~ 6:1 upto 10:1) as i like speed. to have reverse(pretty rare on IC cars) you must add complicated transmission components which is not worth the expense.

if you are using tracks, drive them with the smallest drive gear you can find, and i would suggest a belt reduction.

in all honesty though in a 12 lb bot you will find similar power output from two 540 size brushless motors and you don’t have to deal with fuel and tuning (which you would soon discover is quite hard for a beginner and it is exceedingly easy to destroy an engine within minutes). further more you gain reverseing capabilities and brushless motor far outlive even well maintained RC car glow engines

nick

3

Sigh…
That’s depressing.
I was hoping to be the only guy around with a 12lber that ROOOOOAAAAARRRRRRRS.
:laughing:

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…
:blush:

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?

Thanks again.

4

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 :smiling_imp:

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

5

Go here: robotmarketplace.com/store.html
Click on the motors section and look for small ones, if they are too large try the antweight section.

6

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!

7

Well, I’ve looked at those, before, and there was 4.69 reasons why not to use them.
:wink:

That kind of weight would force me into making a 60lb bot, in which case, there are other engines that output much higher torque for the same weight.

I’m putting this project on the backburner, for a while…

Right now, I’m working on a secret project…

Muahahaha.

If all goes well, you’ll be seeing it in the near future (probably within a month).
If it doesn’t go well, I’ll post it here, anyway.
:stuck_out_tongue:

8

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.

users.erols.com/diesel/wada/gp9specs.html#

9

Wow!

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.

Thanks.
:smiley:

10

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)

11

Hmm…

If I have to put a battery on-board, then that defeats the whole purpose.

:frowning:

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?

12

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.

13

Thanks for the info, WTW!

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.

Thanks.
^.^

14

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!
:unamused:

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?

Thanks.
:smiley:

15

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.

16

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.

http://image44.webshots.com/44/3/24/44/374432444BJxZQv_ph.jpg

17

Hey Nick,

You need one of these. It has electric start… :laughing:

http://www.conleyprecision.com/pics/supercharge.jpg

18

OH MY GOD! That thing is awesome. How many cc’s is that thing? How much horsepower does it put out? Is it yours?

19

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!

20

It’s just too bad that 5,000+ dollars is WAAAAAY out of my price range.

:stuck_out_tongue: