Electric Help

Ok, I've always wondered about this, and now it's time to ask. My friend and I are building an RC car, and I need to create a few microcontrollers for it since we're making everything (the chasis will be made of wood with holes and compartments for the wiring, and outside will be covered w/ metal). Now let's say I get 4 motors from Radioshack, each using 9-18 volts DC. At max it spins at 24K RPM, and it's 2 inches long. Now this can probably take a 2-3 pound load easily, especially since there will be 1 per each wheel. How can I create a microcontroller that will regulate voltages for lesser and higher rpms? Additionally, would it be better to regulate the voltages of the front 2 wheels when making turns or use a chasis that actually moves to turn left or right? Finally, any reccomendations for an 18V power supply for the car. Note: it must be a battery and rechargeable. Can I just hook up several battery packs together?

All the things I really like to do are either illegal, immoral, or fattening.

Any online place (PDF or website) that describes this stuff?

All the things I really like to do are either illegal, immoral, or fattening.

Steering the car by slowing down or shutting off one side of the car would be the weak way to do it . But, it is the easy way. If you wanted to do steering, which is the cool way, you'd have to figure out the proper way to make it so the inside wheel turns more than the outside wheel, which would be a little tricky. If you don't so this then you'd have to deal with wheel skipping while turning.

To regulate the voltages you could use a variable resistor, also called a potentiometer. What this is is a little dude that has resistance that depends on how much a knob on it is turned. So, if you hook that up to a servo motor that is hooked to an remote controller reciever, you can vary the resistance of the line going into the motor from the battery. By varying the resistance, you can regulate the voltage drop that the resistor gives to your circtuit.

I found the motors you are looking at getting on Radishacks website. It says at 9-volt operation, it wants to draw 1.86 A of current. So, to get a voltage drop of 9-volts through your potentiometer, you would need to set the resistance to R= 9v/1.86A= 4.83 ohm, which might be hard to get exact.

Yes, to get higher voltages, just hook up several batteries together.

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<font color=blue> "Trying is the first step towards failure." </font color=blue>

O, and another thing: can this potentiometer be used to make the car go backwards? It'd just take reversing the electrical poles sent to the motors, right?

All the things I really like to do are either illegal, immoral, or fattening.

You know what might be a thing to look into for your power source is companies like DeWalt now have 18V cordless powertools that operate on rechargable battery packs. They might be a bit heavy, but check them out if you go down to the hardware store sometime soon. Those suckers pack tons of juice. The cordless drills can suck a screw through 1/2 inch plywood no problem. See if you can just get the battery back and charger and then find a way to adapt it to your car.

Some day I'll be rich and famous for inventing a device that allows you to stab people in the face over the internet.

Oh oh oh, you could put a little "NOS" on it too! Get a couple of capacitors and figure out a way to wire them up so a push of a button discharges them into an extra burst of energy to the motors. That'd rawk!

Some day I'll be rich and famous for inventing a device that allows you to stab people in the face over the internet.

Yes, by turn I meant their actual physical direction, or angle, not rotational speed.

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<font color=blue> "Trying is the first step towards failure." </font color=blue>

This car will be tricked out. If I'm spending $400- $500 on it, it better be tricked out hehe. How goes this torque translate into how much load the car can actually carry, ie we have the wheels hooked onto the motors and then there's the load on top of the car. How many rpms can I expect from that, and also what gears would you suggest?

All the things I really like to do are either illegal, immoral, or fattening.

Hmm, for this car I'd need a radio that can do left right, back forward, speed, button to release spikes when icy, and then an extra for stuff we may do later- that amounts to a 4 channel radio it seems. Let's assume the spikes and extra are only 1 channel- up or down.

All the things I really like to do are either illegal, immoral, or fattening.

More info for you...

Now, those motors have their maximum efficiency ratings at 18000rpm at 18v, drawing 1.98amps of current. You really want to have the motors constantly operating at this speed. If you don't, then the motors will draw more current, get hotter, and suck the batteries dry faster. This means that at 100% efficiency you have about 0.05 horsepower to work with. I wish it said what their efficiency was at that RPM, but it doesn't. Assuming an 80% efficiency (which is probably around what it would be) at 18000rpm, you have about 0.04 horsepower to work with. If you use 4 motors, then you have about 0.16 horsepower to work with.

Now, in order to determine what speeds/gearing, you will want to know in advance what wheel sizes you will be using. You will need to gear these motors down, or else with 3" diameter wheels it would want to do a top speed of 160mph at 18000rpm, which is of course not possible. So, you'll need to figure out what wheel sizes you want, what top speed you want, how your controller is set up to handle the different voltages, then eventually what gearing you will need to do to accomplish what you need. Of course you don't HAVE to necessarily do all that, but you may want to to make this thing really cool.

Now, theoretically you could then figure out approximate battery life by figuring out how much energy is stored in the batteries you plan on using. This would then let you know how much time you can draw whatever amount of power you are using.

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<font color=blue> "Trying is the first step towards failure." </font color=blue>

Now, what speed the back wheels out to go in turning would depend on the width of your car and the radius of the turn. As the radius of the turn increases, the outer rear wheel needs to spin faster (or the inner wheel spin slower, whatever you like). See, cars get away with this by having a differential just automatically do it so you don't have to worry at all about turning radius or wheelbase, but you don't have that luxury. But, you can buy model car differentials, which would solve that problem. This would then let you use all motors hooked up to one drive line, and the differential would do the work for you. But, if you said you want to do everything yourself, then you'd have to figure another way around the problem. That would be hard which would mean you may just have to deal with wheels slipping. This wouldn't be too big of a problem if you plan on using it in dirt rather than on pavement, as the dirt would just spray rather than the wheel skip.

You should go 2 wheel drive. You could hook all 4 motors (or just 1 big motor) to one drive axle and not worry about cornering issues. That's not trick though . You'd then only want to regulate voltage to regulate speed, which shouldn't be too hard.

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<font color=blue> "Trying is the first step towards failure." </font color=blue>

You know what most battery packs are? A bunch of AA batteries connected and shrinkwrapped. If this is a custom job, I'd just pick up a battery tray at Radio Shack. When I converted my mom's bicycle horn from 3v to 12v (hard to find 3v buzzers), I picked one up that held 8 AA batteries and was about the size of the two original D cells.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>

Woah, as it turns out a C alkaline battery has ~7800 mAh, so 12 of those would be fine, and they weigh in at like 1.7 pounds! NICE! D's would weigh 3.5 pounds, which is fine. They'd give 16500 mAh, which is a lot. I have a recharger for alkaline batteries- do those really work well? I haven't used it for anything that I'd notice a worse battery...

All the things I really like to do are either illegal, immoral, or fattening.

I think the car will be able to handle 12 D, I mean if each is 2 inches in length and 1" in diameter, then that means the car must be at least 1 foot long and 2 inches wide, but it will be more like 8-14 inches wide and up to 1.5 feet long. This leaves room to mount the camera and radio equipment up top. Would alkalines handle well under 10 amp load?

All the things I really like to do are either illegal, immoral, or fattening.<P ID="edit"><FONT SIZE=-1><EM>Edited by flamethrower205 on 06/14/03 02:37 AM.</EM></FONT></P>

I was thinking about front wheel differentials and how to make em turn and all with the motors, and I think I may have figured something out. After finals are done I'll try it out wiht toothpicks to see if it works.

All the things I really like to do are either illegal, immoral, or fattening.

Know of any circuits that could fix that? If there were something that monitors rpm and regulates voltage accordingly so that it's at the speed of the slowest motor. Otherwise, I'll use the axel.
Another question: when hooking up multiple batteries, to get the total mAh, do I add all of them up, so 12 4000 mAh batteries would give 48000mAh or is it always going to be 4000mAh?

All the things I really like to do are either illegal, immoral, or fattening.

Hmm, this is my theory: wiring up several batteries that don't touch to an object yields higher amps, placing sveral batteries so they do touch yields same amp, higher voltage. I was thinking this while eating, now watch it get slammed down

All the things I really like to do are either illegal, immoral, or fattening.

oh, and here i was thinking that u needed a electrical "stimulator"

<font color=blue>Many modern games <b>must</b> be played multiplayer. And those you encounter online are, almost as a rule, <b>complete and utter cockmongers.</b></font color=blue>

Right then. A couple of years ago I was looking at building a battlebot, and went through most of the same questions you are asking.

Batteries: I recommend <A HREF="http://www.battlepack.com" target="_new">http://www.battlepack.com</A>, they're light, powerful, rechargeable, but not cheep. You can defiantly save money by doing it yourself instead, but you won't be able to get any lighter.

You may also want to get a full blown speed controller. The Victor 833 available from <A HREF="http://teamdelta.com/products/elect.htm" target="_new">http://teamdelta.com/products/elect.htm</A> can cruise at 80 amps. It can be adjusted to compensate for unequal strength of the motors, doesn't wear down the batteries, makes the motors reversible, and weighs only 4 oz. Unfortunately it too is not cheep, and is probably overkill for your application.

And I would highly recommend a PCM receiver. The most common brand seems to be futaba <A HREF="http://www.futaba-rc.com" target="_new">http://www.futaba-rc.com</A>. They're programmable and can also do things such as compensate for unequal strength motors.

And all this may be overkill for an RC car. As I said I was planning on building a battlebot.

As for the wheels skipping, providing that you're using different direct drive motors on each wheel that shouldn't be a problem. Since each wheel is independent one can spin a little faster or slower without too much trouble. You may have some trouble with sharp turns at high speeds, but at the speeds where it will become a problem you'll likely spin out anyway.

Now if you're using a solid driveshaft (one motor powering 2 wheels) then yes you'll have a problem and will need a differential to compensate.

You also will defiantly need to gear down those motors. There's 2 ways to do it, with a worm gear/torque converters and with a chain or belt drive gear. Chain gears are cheaper but weigh more and are less reliable. Worm gears are smaller, weigh less and are more reliable, but are exceedingly difficult to find/make, and for that reason are more expensive. Most electric wheelchairs use worm gears while most home made robots/rc cars use chain/belt gears.

As for steering there's tank style and car style. Tank style slows the wheels on one side of the vehicle causing it to turn. The wheels themselves don't actually turn. It is easier/cheaper to set up (especially with a speed controller) and gives you a much smaller turn radius, but it's mostly ment for slow speed operations. Car style where the wheels actually turn is best for high speed operations, but can be a bit more difficult to set up. At the very least you'll need another much smaller motor to power the turning of the wheels.

How will you deploy the wheel spikes? Using pneumatics with a CO2 airgun cylinder? How are you planning on getting the air pressure into the tires? You'll have to use a hollow axel and channels cut into the wheel hub. In that case you're better off with a chain drive instead of a worm drive as it'll be easier to access the axel. You'll also likely have to use solid tires unless you're planning on getting incredibly complex. You're already going to have to figure out how to keep the spikes inside the wheels despite the large centrifical force pushing on them (springs perhaps?) while still allowing the air pressure to move them forwards and keep them deployed despite the weight of the vehicle pushing on them, as well as some way to bleed off the air when you want to retract the spikes.

You may also want to rig up some sort of a suspension system otherwise you'll be bouncing all over the place, especially at high speeds over rough terrain which is what you seem to plan on doing.

I love that capacitor idea as well.


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Knowan likes you. Knowan is your friend.

Those batteries don't seem to have the necessary amp requirements sadly. In terms of the radio system, I'm leaning towards a 4 channel FM radio, from tower hobbies themselves or a company like futaba. While looking around I saw that tower hobby's <A HREF="http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCUM2**&P=0" target="_new">4 channel radio</A> is the same price as their <A HREF="http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXNN65**&P=0" target="_new">6 channel</A>. Do you have any idea why, and does that look like a good radio. Also, can I mix servos, ie I have a mini one to turn the ptentiometer, another mini that simply turns a switch to pass a current to the spikes and then a heavy duty one for the steering. I may not use the full 6 functions, but who knows in time. Would this work? Being FM and all, what distance can I get from these? I'm hoping to be able to do at least a kilometer, since the video transmitter will be able to do that. Any way to make the radio controller have a stronger and farther?
In terms of the spikes, I was thinking of a small pressurized container inside the actual wheel that when an electrical shock is applied releases the air. This would inflate an inner tube to which the spikes are attached. There would be small holes in the outer tube that allow for the spikes to come out and to keep them out, the air pressure with a little curvy plastic piece that comes into position should do the trick. To keep the spikes in, I'd probably have to have some sort of spring system or use the plastic piece again so that in "off" position it stops expansion, in on if forces it to enlarge. The other thing I'm thinking about is you know those balls that you pull and they enlarge? They have em in all the science museums. Would it be possible to have something like that in the wheel. Hmm.

All the things I really like to do are either illegal, immoral, or fattening.

True. Now that I think of it they are ment to run a robot for a maximum of 5-8 minutes.

They use the same receiver. Also the transmitter is very similar. It probably only cost then about $5 to bring out the extra 2 channels.

yes you can do this.

In the US there's 3 different bands that a radio control can use. (actually there's 5, but the other 2 are rare and require exotic liscences/equipment). There's the AM 27 MHz frequency, the FM 72 MHz and FM 75 MHz bands.

The FM bands have greater range than the AM bands. The 72 MHz band is meant for flying aircrafts. The 75 MHz band is meant for ground control (cars and boats typicaly).

In most states it is illegal to use the 72 MHz band for ground effect vehicles. This basically is ment to prevent a ground control transmitter from interfering with an airplane's transmitter and causing it to crash.

The 75 MHz band has a slightly greater range when used for ground control anyway, maybe a 5% to 10% bonus.

Finally, there's PCM. PCM isn't it's own frequency, but is a protocol that can be used with either frequency, AM or FM. It basically encodes the transmitter signal, which is then decoded by the receiver. This encodong and decoding eliminates noise, for example from someone's cellphone, giving it a clearer signal. Typically this doesn't increase the range by much but it does increase the sensitivity and eliminates interferance.

Also PCM controllers are typicaly programmable. It allows you to do some mixing from the transmitter itself and have the reciever carry out the commands.

As for range, no manufacturer will gaurentee beyond 100 feet. Typically you can get to 250 feet. If you maintain line of sight you can probably go beyond that.

Ways to increase range include replacing the antenna, reducing/eliminating noise from the motors, reducing interferance, maintaining line of sight, and buying a signal amplifier (for example from <A HREF="http://teamdelta.com/products/prod2b.htm" target="_new">here for $10</A> ). Ways to decrease engine noise include something as simple as twisting the power lines to installing capaciters close to the engines. There's not much you can do with the transmitter beyond possibly replacing the antenna.

The only problem with that would be recharging the air cylinder. Plus you'll unbalance the wheel if you're not careful. It's probably easier to put the cylinder inside the car body and have a hose lead to the wheel. Plus then you can use a standard, cheap CO2 paintball gun cylinder.

You'll also have to do quite a bit of matth to get this right. you want the spikes to say inside, even when spinning at full speed with full centrifical force. Then you want them to extend when the cylinder discharges, even when at a stop with no centrifical force, and have them stay deployed despite the weight of the vehicle pushing down on them. Then you'll likely want them to be able to retract at any time as well, so you'll need some way to bleed off the air pressure when the CO2 valve is turned off. The tollerances are going to be very tight.

Perhaps you could have some sort of a latching system so that a sudden burst of CO2 will deploy the spikes and the latches will hold them in place? Then you'd need some sort of mechanism to release the latches in order to retract the spikes. Is that what you mean by a "curvey piece"?

You know, it may be easier just to have 2 sets of tires, a slick set and a knobby set, and change them by hand when needed.

I know what you're talking about but you'de still need some mechanism to deploy and retract them. Plus there's alot of hinges in those balls. That's alot of moving parts where something could break.

Here's an idea that I heard of once. Have 3 wheels in a triangle/star pattern rotating on a common axis. Make it so that all three wheels receive power and spin at the same time. Also make it so that only 2 wheels touch the ground at one time (thus the start or triangle pattern) and so that they rotate on a common pivot point. Now make the front wheel extend beyond the front of the car, beyond the bumper. Then have 2 rear wheels as well, putting 6 wheels on the ground at once and 2 wheels in the air.

Now what happens when the car hits a large object such as a stair? The front wheel is pushed back by the object, the wheel in the air is rotated forwards and becomes the front wheel, and the rear wheel is rotated into the air. The new front wheel is now on top of the object, pulling the car up it. That's how you make a car that can climb stairs.

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Knowan likes you. Knowan is your friend.

They're very helpful tho, I read it and didn't realize the length.
After some more thinking, this air pressurization could get a tad too tricky, and knowing how I build things, it'd end working, being complex out of its mind, and the whole thing would be help up by a string ready to break Instead, I've looked at some tires, and what if I just got some solid tire, drilled a few holes, then the middle piece is solid too and there is something like a piston for each hole that has total control over the spikes.

All the things I really like to do are either illegal, immoral, or fattening.