Stump the genius quiz (help!!!)

[alamo]

Hello RC geniuses,

I'm putting proportional steering and speed control in a scale tractor-trailer rig that basically started out as a realistic-looking plastic toy. It is designed to run on fairly smooth surfaces like tractor-trailer trucks do. My truck will run on floors and patios so I have no suspension to worry about.

Rather than speed, I'm building it for prototypically slow big rig city operation. I am using a Tamiya gearbox geared for higher torque and lower speed. Slow speed is necessary to precisely park, drop off or pick up trailers as well as being able to maneuver tight turns of city street driving. While I'm willing to sacrifice top end speed considering the small running spaces, I do hope it will do At Least 30 scale MPH - which about 225 wheel revs per minute in this size.

OK, so here's the problem. The gearbox comes with a Mabuchi RC-260 motor.
The motor specs are:
Operation Voltage: 3.0V
On-Load Speed: 10,500 RPM
Stall Torque: 15 gcm
Current: 1.0 A
I can't find information anywhere on the number of turns in the 260 - even after much time Googleing and calling both Tamiya and Mabuchi. I haven't found anyone who knows how many turns it has.

At any rate, I am currently using a HiTec Ranger 2 stick Tx and Rx and an Airtronics ES-01 reversible speed control powered by a 4.8v battery. The problem is that there is a large dead space on either side of stop - then as I apply throttle, almost 100% of the speed is reached as the throttle moves about 1/8" in either direction past the 1/8" either side dead spot. So I have 100% control in about 40% of the throttle movement!!! The Tx and ESC are not adjustable and I'm very disappointed in the Tx Small range of throw in the fine control zone since I definitely do not have surgeon fingers.

I'm writing because I would like to have ideas of what could help me get better speed control in this project. Is there a better reversible ESC and maybe Tx also, not too expensive either. I've been considering the Airtronics Blazer Tx (not Sport) because of its adjustability and the Duratrax Intellispeed Auto Sport with Fwd/Rev and a setup. Would something like this work better or is the little 3 volt motor hopelessly out of manageable control for this application? btw, the guy from Mabuchi suggested I go to Radio Shack and buy a potentiometer and control the pot with another mini servo??? But would this work? What size pot? How is it wired?

I want to operate this little big rig and would deeply appreciate any suggestions to help me tame this little 3v beast.

Thanks
Mike

[iluvtruenos]

Hey,

First off, I agree with your idea of getting new electronics. They will definately help you in terms of control and scale appearance. Don't worry about using the ESC with such a small motor. I've used a DTX 12t Rev ESC with a 130 sized motor, or whichever one is in the MRS4.

Also, can you provide pics or some sort of measurement based on weight and size of the said rig? If you have something pretty big and heavy, maybe you should think about a bigger motor but with more gear reduction?

Last, I strongly suggest the Tamiya universal gearbox. That thing has a huge number of gear ratios, and I'm sure you can find a gearset with enough torque/speed to make you smile.

In any case, keep us updated, it sounds really cool!

[chaimo123]

Listen to truenos, he knows his stuff!

[iluvtruenos]

Thanks Danny.

[DanteXIII]

A new ESC, would be your best bet, you want one that's programable, at least to the point of finding the endpoints on your Tx. Yes the potentiometer will work, it would just be a pain in the butt. You would go to radio shack, and find a pot (short for potentiometer for those not in the know) rated for 5v there are only 2 main sizes that they carry that I know of, one will be to big, the other will look about right. Sometimes they only have one size. Regardless, theoretically. You would have the battery connected to the Rx and the motor in parallel. You would have the pot wired in series between the motor and battery. Either side should be fine (pos or neg). Then you hook up the micro servo so that it will turn said pot proprtional to how far you pull the trigger. The problem with this is that it will be complex, and if you don't have an Rx with endpoint adjustment, you will have to do it all mechanically which, again, will be a PITA. Therefore, I would just go to your LHS, tell them what your doing, and find out what ESC they think you should get for it. Honestly, I couldn't reccomend an ESC for the job, but I'm sure that there are plenty who can. Good luck, and post pics when your done!

[alamo]

Thanks for your quick responses.

Truenos, Yes, good ideas on my project. Regarding weight and size info, Using a balancing rod, the nearest I can determine without a small scale is that both the tractor and the trailer weigh about 1.25 lbs each. That's the truck with all the RC gear and a van trailer (empty ;) ).

Here's a link showing the truck I'm working on with size dimensions. Click the photo for a big picture or check out their menus to see other trucks they have. They are not too expensive on the shipping either. I found lots of 1/32 places that are.
http://store.extremecustomtoys.com/1scin99ixwga.html

I'm using the planetary geargbox which has 6 different ratios. It seemed to fit in the truck body with less screaming and it also has a good range of probable gear ratios - but it is actually untried - as of yet.

I'm still tinkering with the truck rear end working to keep all 8 drive wheels on the ground and level with the elastic band transmission I have.

Dante,
You mentioned "A new ESC, would be your best bet, you want one that's programmable, at least to the point of finding the endpoints on your Tx." I agree completely. I sure hope someone can give me a name of one - I know you mentioned going by my LHS but I don't think they quite get the project yet and I haven't spent enough time there to edumacate them with my model in hand. They don't carry DuraTrax for some reason.

I'm keeping your pot wiring idea in case I need it. Thank you for all your trouble describing the connection to me. btw, The picture of my finished project won't look too different from the photo above - I hope ;)

I'm still in need of some info on inexpensive endpoint selectable ESCs with reverse, but I bet my 2 stick Tx is just not right for the job either. I am brand new to RC cars and am learning lots on this project. I have never tried a pistol Tx either. What fun!

So thanks again,
Mike

[DanteXIII]

First off, since you said your new to the hobby, welcome aboard! The planetary set should be all you need, although, as I remeber it, the lowest of all speed settings it's capable of may be way too low for your project, although I haven't used one in about 2 years, so I don't remember, no big deal though, you can change it around. As far as radio gear goes, I'd just get an inexpensive futaba, it'll probably have all the features you need, and it'll be a good reliable radio. ESC wise you may be best suited to look around on a site like www.towerhobby.com for awhile. Most ESCs have specs on the bottom telling you how many cells they will handle. This way you can look around, read up on some features and specs, then get a good idea of what's availible, and what would best suit your project. I still wouldn't recomend the pot idea though, you would have to fabricate some parts, and do some wiring to get it to work, but if your comfotable with it, go for it. Like I said though, it'll be way simpler to just get a new ESC. I am pretty sure, but I think that most ESCs designed for bigger cars will work just fine in this project, just be sure to read the specs. Ideally you want something that can do 4-6 or 7 cells. Just don't forget, the ESC will never put out more than it takes in. So, if you use a 4 cell battery, the motor will never see more than 4.8 volts. As far as the motor itself goes, even though it says it's rated for 3V, I used to run them at 6V all the time, and they don't have a problem with it, so 4.8V will be just about right.