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speedy_w_beans

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Everything posted by speedy_w_beans

  1. Not sure what 4.5V cutoffs are for, but they are not compatible with lipo. 1S lipo: - 3.0 to 3.2V cutoff - 4.2V full charge - 3.7V storage charge Multiply these voltages by 2, 3, 4, etc. depending on the number of cells in your pack. Going below the cutoff voltage or going above the full charge voltage is asking for trouble - damaged cells, puffed packs, or fire hazard possibly. An accurate balance charger and correct cutoff reduces these risks to near zero (nothing is ever zero risk), so don't let these voltage requirements scare you.
  2. For a 2S lipo: - 6 to 6.4V cutoff voltage - 8.4V full charge voltage - roughly 7.4V storage voltage if you're not using the pack for some months. Also throw the pack in a refrigerator (not freezer) to increase storage life as well. Multiply these voltages by 1.5 for a 3S pack, and by 2 for a 4S pack. For a crawler it seems like you would "T" the cutoff output to both ESCs so they both stop at the same time.
  3. Take a look at either Futaba S3305 or Turnigy 1258TG. I've used a few S3305s and they have been reliable, but I recently tried a 1258TG because it's supposed to have higher torque and faster speed at about the same price. So far the 1258TG has worked well with no issues for me, but I don't have the run time and number of units installed to declare it my new favorite servo. My ESC has a 6V, 5A BEC in it, so your mileage may vary depending on the specs of your ESC. Edit: This assumes you even need a high torque servo. I've been using Futaba S3003s in several basic Tamiya kits with no problems. Usually the servo savers will give before the S3003 runs out of torque. I'm probably going to cross-shop for similar Turnigy servos in the future to either save some money or get better specs at the same price.
  4. I'd go for a CR01 if the budget allows. Many of the same bodies are available on either CC01 or CR01, but the CR01 is more capable off road.
  5. DB01R. It's a DB01 with all the nice option parts (slipper, reinforced drive belts, CVDs, motor mount heat sink, threaded aluminum dampers, aluminum suspension mounts, carbon reinforced parts, etc.). It's a fantastic 1/10 scale buggy for general driving and racing. -Paul
  6. Here's the Atmel AVR ISP MkII programming pod. It costs about $35 from Digikey.com. One end of the pod plugs into the programming header installed in the radio; the other end plugs into a PC's USB port. There are less expensive programmers out there with open source drivers and utilities, but I opted to use Atmel's Studio 6 (a free download from their site). Here's the pod attached to the radio. And here's the programming in action. It's difficult to see, but the window open on the PC is a programming utility that's part of Studio 6. After selecting the pod and the processor part number, it's as easy as connecting the pod, turning on power on the transmitter, and then reading out the original firmware and EEPROM settings into files. I did this in case the Open9X firmware had problems; that way I could put the original firmware back in the radio and still use it instead of having a useless brick. Once the original firmware and settings were backed up, then I selected the Open9X programming file and had the tool to write it all to memory. Erasing memory before writing it is enabled by default and is necessary. And, it worked just as expected! The first time Open9X boots, it complains about an EEPROM data error and then formats it to default values. Everything seems to be working; now it's a matter of skimming the manual again, configuring some outputs, binding a receiver, and checking it out with a servo. I'm going to declare success at this point and play with it more later. -Paul
  7. Here's the cable installed. I used a small adhesive square and a zip tie to provide some strain relief to the connections. I had seen where other people had cut holes in their transmitter to expose a connector for programming, but I didn't want to alter the housing if I could avoid it. I found that the battery compartment had a little bit of spare room in it, and there were already slots in the battery compartment for passing wiring through. End result. I put a layer of black duct tape on the end of the battery holder so none of the programming pins would touch power by accident. Now I can push the connector down and close the battery compartment door, or I can pull the connector out by about 2 cm to attach a programming pod if necessary. This way I can continue to update the firmware without opening the transmitter again. Just making sure it still works!
  8. Here's an even closer look at the microcontroller and surrounding circuitry. I was extremely fortunate to stumble upon a posting by another person who had used the same programming tool I had bought, and he had found it necessary to swap out a capacitor and three resistors to get the in-circuit programming interface to work. This isn't a tool issue; it's more an issue of how Turnigy implemented the interface on their board. It's possible the interface works fine in an automated in-circuit test process in a factory where pogo pins touch the silver pads and then program the flash, but with a low-end desktop programmer some of the parts on the board interfered with operation. This is a comment Gerd wrote in the installation section of th9x, a predecessor to Open9X. I'm quoting this verbatim; the original text can be found at http://code.google.c...ion_de?wl=en-US. "Hello, I used the Atmel AVRISP mkII to program the FW. It works well but following steps are required: 1) convert the downloaded .BIN file to .HEX using a hex2bin converter (I don't remember where I downloaded it, just google for it, it is a common tool). 2) As already mentioned by some people above, Flysky's engineers have a bit strange way to design electronic circuits... (not sure they know what they are doing...). The big 4.7uF on reset is much to big, the programmer is not able to discharge it in a fast enough time and reports an error. Replace it with 100nF ceramic one. Removing it totally works as well, but it is a good habit to keep a decoupling cap on the reset pin for avoiding the processor to reset on a glitch. 3) The filtering resistors on the PB pins (also where the SPI programming signals are taken) are configured in a strange way. I do not really understand what they wanted to do with... I would have reversed them (capacitors on the mcu pins then resistors to the switches), but the goal is not to re-do the design... In current configuration, the resistor values are too small and the capacitor values too big. The SPI signals from the programmer is "seeing" too much of the these big capacitors and is not able to drive the lines. To get the system working, the resistor values must be increased. From the Atmel spec, the programmer is able to drive a line impedance of 820 ohm or higher. The resistor values should therefore increased at least to this value to be safe. I used 2.2Kohm. The modifications are easy to do if you are used to solder SMD components. After these 2 steps, the programming is works smoothly Gerd" So with these comments in mind, I replaced the small yellow capacitor under and to the right of the processor with a smaller value, and then replaced the resistors associated some of the programming pads, changing from 200 ohms to 2.2k. This preparation was needed before installing a cable. My programming cable is made with a six-pin header, some ribbon cable, and some heat shrink tubing. Finished cable. Now, how to hook up this cable? Again, at the same th9x installation page there are pictures of the silver pads that need to have the wires attached. These pads are labeled, "VCC," "GND," "RST," "MOSI," "MISO," and "SCK." These are signals for power, reset, and serial communication to the processor. The programming pod I have also has these signals, and they're assigned to certain pins on the programming cable. The pinout of the connector is here. For my ribbon cable, I have the following color-to-signal assignments: Red = MISO (lines up with the red wire on the programming pod) Orange = VCC Yellow = SCK Green = MOSI Blue = RST Purple = GND
  9. I decided to try loading Open9X on the Turnigy 9X transmitter tonight. This involved installing a programming cable in the transmitter itself, installing some Atmel software tools, reading/saving the original firmware and EEPROM settings from the transmitter, and then burning new firmware into the ATmega64A processor. I opted to do this at work after hours since my company has better tools than I do when it comes to surface mount electronics. I knew going into this I would have to swap a few components on the board and then tack on some wires, so it's really nice to have a microscope, tweezers, and a nice soldering iron for doing the work. Here's the victim, er, patient... It only takes six screws to remove the back cover from the front bezel. The connection between the rear board and front board is made with a white single row connector. The battery pack actually plugs into the rear board. I looked throughout the whole assembly and didn't see any signs of hot melt glue, so maybe another transmitter in their lineup is built that way. This one seemed pretty conventional to me. A little closer view of the front board. The black square at the bottom of the transmitter is the microcontroller that reads all of the sticks, switches, and potentiometers, performs calculations/functions on those inputs, and then generates a PPM output to the V2 radio transmitter module on the back of the unit. The firmware that's inside that chip is what I'm replacing so the functions and calculations are more configurable and less tailored towards aircraft. I took a look under a magnifying glass and found markings, "Atmel ATmega64A."
  10. Thanks for the comparison information. Yes, 2000 rpm at the spindle is a bit much for metal - I'm used to just a few hundred rpm on the big machines. Between this week and next week (Christmas break) I should get this built up for a project I have in mind... -Paul
  11. My criteria for selecting only one: - Usable on-road or off-road - Fast acceleration - High top speed - Great handling - Durable - Lots of tunability - Parts readily available Touring cars are out due to the off-road requirement. Monster trucks are out due to handling. Scalers/crawlers/tractor trailers/tanks are out due to top speed. That pretty much leaves me with buggies, and I prefer 4WD over 2WD. At this moment in time I'd have to pick my OFNA NEXX8 1/8 scale e-buggy. It's nicely equipped, built to last, and a blast to drive. If I didn't have the NEXX8, my second choice would be a Tamiya DB01R for many of the same reasons. -Paul
  12. That looks just about perfect (to me)! I'm not really attracted to rock crawling persay, but using a CR01 as a highly articulated scale trail runner looks awesome! -Paul
  13. The first test run went pretty well. I took it easy at first, just trying to get a feel for how the chassis behaves, and it turned out to be very easy to drive. In the video below I'm pretty gentle with it, coasting into turns and rolling onto the throttle. I didn't do any really hard launches as there was a parked car on the street that I didn't want to hit. I only used full throttle a few times to get some top speed measurements; in the grass I probably used half throttle at most. Acceleration is excellent; there's plenty of torque on tap for getting up to speed. Top speed is ok at 45 mph / 72 km/hr with stock 13/46 gearing (3.54 motor pinion/spur, 3.31 diff pinion/ring, 11.72 final ratio). The ESC heat sink stayed cold to the touch; the motor was warm but not hot. I haven't touched any of the ESC default settings yet, so maybe I can lower the motor timing to reduce the temperature some. I'd like to find the optimum combination of motor timing and pinion size if possible. The suspension was great, but my first run was pretty basic with asphalt and grass. The asphalt is very smooth and doesn't challenge the suspension much; the grass has some roughness to it, but nothing major. A few people on RCTech felt that the stock springs are soft, and I think I can see that given how much the suspension moves under relatively easy conditions. There's enough weight installed in the chassis now that it actually may require adjusting the ride height. Along with finding the optimum motor setup, I can see playing with some stiffer springs, heavier damper oils, and adjusting the ride height a little. The rear sway bar really does work. Tight turns with a little bit of speed and braking cause the inside rear tire to lift off the ground as the outside rear suspension compresses under load. It's neat to see that work. There's a lot of playing and tuning to try in the future. For now I'm very happy with the initial results. http://www.youtube.com/watch?v=682DLM31btI
  14. I was able to get the chassis finished today and took it outside for a test run; here are some pics of the completed buggy without a body. I'll get around to painting the body soon and stick in my showroom. For now just seeing it run and getting a sense of how it performs is good enough...
  15. I'm curious about the torque steer issue claimed for shaft drive buggies. If it's so bad, why has the RC10B44 family won so many national championships in 4WD mod class? It's essentially a DF02 style drive train with ball diffs instead of gear diffs (but with nicer hardware, better chassis structure, and better layout). I know I'm simplifying the comparison between a B44 and a DF02 quite a bit, but they are both shaft drive 4WD buggies... -Paul
  16. I love all the carbon and aluminum; this is looking really nice! -Paul
  17. I mounted the ESC and ON/OFF switch with servo tape to the center tray, then routed the ESC's BEC and signal wiring to the radio box. The steering servo wiring went inside the radio box as well. The receiver was mounted with servo tape, then the wiring was bundled and connected. The coaxial antenna lead was coiled and routed to the antenna tube holder. All in all, a pretty clean result... Here's the radio box installed and the servo connected to the steering rack. I tried to follow the manual's recommendations for turnbuckle length, but the way the servo splines lined up and the length of the turnbuckle worked against me and I had to install the servo arm one notch off. I may have to take this apart and cut the turnbuckle down a little in the future to get the most balanced steering; it seemed to get too tight at one point and I didn't want to risk stretching a connector. This buggy is just about ready to test. I did confirm all the electronics were working as I was installing them, so it's more a matter of enjoying that first run and tweaking settings. In the morning I'll glue the tires, solder up some charging leads, and get some cap screws for the motor mount. -Paul
  18. Electronics are installed. I started with attaching the motor mount cam to the motor, installing the pinion, and checking the wire lengths versus the placement of the ESC. I didn't have any M4 cap head screws for securing the cam, so I'll have to make a run to the local hardware store in the morning and get a few. The wires were a little long, but not long enough to trim. A little slack is good for routing the wiring. I debated on whether to install bullet connectors or just solder the motor wires to the ESC. In the end, I went for directly soldering just to be sure there wasn't any extra resistance due to connectors. I also braided the motor wires to reduce the amount of radio interference generated. The red and black battery wires are soldered to the ESC and have 4 mm bullets to connect to the batteries. The yellow wire is a jumper to connect the two packs in series; it also has 4 mm bullets installed. The jumper is a convenient way to break the circuit between the packs when the ESC is shut off. Another view... And another view...
  19. Nice to see it come together. I hope you enjoy it; I really like mine! -Paul
  20. Thanks guys. Even with the issues found through a teardown, I still like the buggy quite a bit and look forward to running it. Filling the diffs, finding some alternate fasteners, applying thread lock to a few fasteners, adding a few O-rings -- these issues aren't too bad by themselves, but it's not a true RTR if you have to strip it down and check these things. The fitment of the top brace was maybe the biggest disappointment, but that's not an OFNA part. I really should contact the vendor and see what he has to say -- maybe it was a batch problem. I'm not upset and I know the vendor sells many good carbon parts; it may just be a fluke. Anyhow, I'm hoping to get on with some electronics tonight... -Paul
  21. Some spare parts -- Rear dogbones, axles, and 4 mm grub screws replaced with UJ axles and 3 mm grub screws. Standard wheel hexes replaced with serrated wheel hexes. Long screws replaced with shorter screws for the diff brace. Kit motor mount and front diff mount replaced with one-piece cam motor mount. Diff cover no longer needed with thicker chassis. 3 mm chassis replaced with 4 mm chassis. I know it seems like a lot of work to basically end up where I started, but at least now I know the screws are torqued and locked, the dampers and diffs are full, and some upgrades are now in place. I'll want to do something about a front brace eventually, but for now I think the next step will be to get some electronics installed and go for a test run. -Paul
  22. Unfortunately the front diff was about the same as the center diff. There wasn't much fluid in there at all. At least all the screw lengths matched. I filled it up with 5,000 cst oil, installed a new gasket, and put it all back together. I also checked the pinion/ring gear mesh and found I could improve it by shifting one of the shims from one side of the diff to the other side of the diff. The front end went back together in reverse order. Install the four big screws, install the four little screws for the sway bar mounts, install the two e-clips... I adjusted the grub screws in the sway bar mounts to eliminate most of the slop in the bar while still allowing free rotation. I also opened up both front dampers and checked the fluid; they were both filled completely. They went back in place, then it was time to install the front end on the chassis. At this point I was looking at the front prop shaft side play, and installed an O-ring in the center diff cup so there was an O-ring at both ends of the shaft. This eliminated most of the side play, but still left enough for chassis flex under running conditions. I was going to install the SNR carbon fiber chassis brace / top deck, but another problem came up. Some of the holes for the center diff mounts were not drilled in the right locations! I also found the top deck required leaving the original steering brace in place, so the kit screws were not long enough for the extra 4mm thickness of this bracing. Furthermore, I found both the SNR aftermarket part and the original kit piece did not have holes correctly drilled for the aluminum motor mount/diff mount I had installed earlier. At this point the SNR brace was out due to the wrong hole locations, and I just installed the original piece to retain the wire clips I'll need later. That was also a hassle as the original long screws were too long and I had to find shorter screws to thread into the aluminum mount. The new 4 mm chassis is definitely stiffer than the old 3 mm chassis, but if I ever want to stiffen the chassis more I think I'll just make an aluminum diff brace and then run one or two turnbuckles between the steering brace and the diff brace. There's not much to report about the rear end; it was the same story as the front for the most part. All of the screws were torqued pretty well. The dampers were full. The diff was empty, so I filled it with 1,000 cst oil and installed a fresh gasket. I replaced the kit dogbones and axles with universal joint axles (UJs) and discovered the original 4 mm grub screws would not work in the UJ axles, so I had to find some 3 mm grub screws instead. Another O-ring went into the center diff drive cup to take out the side play of the rear prop shaft. Serrated wheel hexes were installed all the way around. So, at this point it's back together...
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