nitrosportsandrunner

I recently found out about antweight (one pound) battlebots and thought, hey I can make one real simple.

I thought I could use 2 standard size continuous rotation servos, a V-tail mixer, a 2s 500mah lipo and my flysky GTC3

But I have 2 problems:
big one: no matter what I try, the servos will not "center" or stop. The best I can get (by adjusting the trims and end points) is for it to want to creep forward very slowly. I know I have the V-tail mixer wired up right but why wont the servos center up (stop with no throttle/steering input)
Any ideas?

Second issue, servos don't turn very fast. Sure, I knew they would turn slow normally but I figured that powering the rx with a 2s lipo would give them twice the voltage of normal and thus twice the speed. Is flysky rx limiting the voltage to the servos to 3v? Any ideas how to get around this?

Mechanicaloverlord

I've never heard of a Rx limiting voltage to servo's. They put the voltage straight through from whatever the power source, be it a bec or battery pack. Most bec's are 5-6v, so 7.4v (I know it's nominal voltage) isn't going to be twice the voltage or twice as fast.

I have no experience with v tail mixers but I have an idea to try. You mention adjusting trims and I assume that means the normal trims, how about subtrim? Regular trims cut the range of travel on one side which might be screwing with the mixer's calibration. Subtrim just moves the center without effecting the travel, might be able to trick the mixer this way.

nitrosportsandrunner

It could be that the servos are getting 6v and they just "seem" slow to me, or slower than I had hoped they would be.

I tried a older radio from a evader and was able to adjust the throttle trim and got it to work properly. I guess the GTC3 just doesn't have enough adjustment to work with these servos. I tried the GTC3 with the V tail mixer on a set of regular servos and it worked fine, but the continuous rotation servos just dont like that radio.

The GTC3 has throttle and steering trims, expo, reversing, and end points. No combo of any settings worked. And it only seems that the throttle channel cant center...the steering centers just fine. When its "crawling" when Im not giving it any input, both wheels are turning the same speed. If I pull the trigger just a tad (maybe 1/8th inch) then both servos stop. So "center" or neutral on the GTC3 seems I cant trim it far enough to make these servos happy.

I guess now I have to make some larger tires if I want more speed. I also need a 4ch radio for the second bot. I prefer two sticks to control the wheels, but my son is 6yo and I wanted his to be controlled with a pistol radio since that's what he is used to.
It is neat how the V tail mixes things. If you steer with full throttle, one side turns and the other doesn't. If you steer full but without any throttle input, both sides spin opposite for 360 spins. So this bot will turn fairly quick even though the servos are not very fast.

Mechanicaloverlord

Too bad the radio doesn't have subtrim. Subtrim would adjust the center or neutral and fix that problem according to what you've posted.

Like I said I've never heard of a receiver that adjusts voltage in any way, they just pass it straight through. I'm curious if the mixer is sapping power though. It should act just the receiver and pass the voltage on through but you never know. Maybe try hooking the servo's up directly to the receiver to compare going through the mixer just to experiment.

The only other explanation, besides the servo's just being slower than expected, is the battery. Voltage always drops under load, the smaller the battery and/or the higher the load the more voltage drop there is. Hook up a meter to the battery, apply a load and watch the voltage drop. I k is they're just servo's but they're driving a vehicle (fairly high load) and the battery is a little guy. Doesn't hurt to test it out.

nitrosportsandrunner

The current "vehicle" weight is only 7.5 oz, so the load on the servos isn't very high.

I tried using the duratrax radio without the v tail mixer but the speed was the same

but then I tried the flysky radio without the v tail mixer (it trims just fine without the mixer) and the speed was slightly faster. Not a huge difference, but enough you notice. Maybe the old duratrax radio just isn't as efficient, allowing more power to flow to the servos?

Not sure what I will do at this point. Running the mixer on the old radio slows it down a bit, but is easier to control. Running on the flysky without the mixer means you have to do the mixing in your head but it drives a bit quicker. If I get a 4ch plane radio I will have to mod the throttle stick to center itself. Almost starting to wish Id bought gear motors and 2 small ESC's. Ive run 2 ESCs off a v tail mixer before on the flysky radio and didn't have any issues with trimming. But 2 gear motors and 2 ESCs (enough for 1 bot) would have cost as much as the 5 servos I bought (enough for 2 bots and 1 weapon)

nitrosportsandrunner

current state of the bot
Idea is to have a solid base/driveline that I can attach a foam board/duct tape body to.
I want something that can be "damaged" but easily and cheaply replaced.

SyCo_VeNoM

needs a flame thrower


umm one option disconnect the servo's board, and solder on a cheap and tiny ESC to the motor that might work with the throttle properly

Other option use a radio for an airplane, and modify it so the right stick auto centers, and do it tank like steering.

EXT2Rob

My Feedback: (1)

I don't think FlySky receivers are rated for 7.4V. You might fry the receiver.

SyCo_VeNoM

I know the older ones definitely are not, and will fry as one of our members who used to use a Tamiya ESC kept frying ESC's cause it didn't have a BEC on board, and was pumping the full voltage into his RX.

Now I'm not sure if they changed them since, but I would really doubt it

nitrosportsandrunner

I have 3 prototypes now
1 has the vtail mixer and is running on 2s
The other 2 are using 4ch radios (twin stick steering) and are running on 9v batteries

So far the Rx's are OK. All three are flysky (or flysky compatible)

Flippin disaster did burn up the MG996r flipping servo pretty fast (15 minutes or so) but that could be the voltage, or it could be that I had end points set to 120% or some mixture of the 2

Flippin disaster is the one running the vtail and I made some progress regarding the creeping issue. Turns out these 360degree servos have adjustable pots (small hole in the case) and when I adjusted those I was able to get it to sit still without any throttle input. However, now one servo turns a bit slower when going in reverse. It drives the same speed going forward and turning is great. I can live with this quirk better than it always wanting to creep backwards.

Flippin disaster also has a glitch buster added (bought it today) as Ive read that what usually causes Rx's to die when running high voltage is when there is a sudden current draw on them and that the glitch buster can help solve that. It was $7, which is a bit cheaper than a flysky rx.

Youll notice Ive tried a lego frame as well. The servos are hot glued to blocks, which can then be built into any shape chassis you like. Im not going to do any actual comps, I just want 2 or 3 bots for me and my son to play with. I don't want them to be able to blow each other apart, but its no fun if you cant do some damage. so lego chassis may give some damage but be easy to repair and not cost anything when damaged either.
However, Ive watched a lot of antweight combat vids now and the majority of wins are by knocking your opponent out of the arena. A few bots can deal some serious damage (drum, horizontal, vert and full body spinners) but most are wedges or flippers or grabbers to push your opponent around.

This time next year, I hope to be living in north Carolina...and Ive read there are some battlebot events there. Im hoping the RC hobby in general is more popular there. Not much happens in this area of maine.