More power in a smaller package
In every issue, ROBOT will report on new technologies that improve hobby robot performance. Here, we look at the benefits of using new brushless motor packages in smaller robots. These motors have recently emerged in the RC car market and, as you’ll see, are plug & play solutions for many robotics applications.
NOVAK HV-MAXX BRUSHLESS
The largest motor we are taking a peak at is Novak’s sensored brushless motor kit, the HV-MAXX. Novak is just as serious about the exploding robot marketplace as Castle and Astro Flight; and they are showing that dedication with their latest brushless ESC package by offering a motor that has been wound a bit differently just for the robot crowd. The sensored, brushless HV-MAXX kit was initially designed to replace two 550 brushed motors in a model truck so you know it packs some impressive power. The standard HV-MAXX motor is the same diameter, and just slightly longer than standard 550 motors. The ‘robotwound’ motor is the same size but produces even more torque than the stock HV-MAXX motor. I did a little torque and amp testing of this motor compared to a Trinity Monster Maxx brushed DC motor and was amazed at the power of this offering from Novak. Contact Novak for pricing information.
I’ll be offering expanded reports on the “combat performance” of these various mills in future issues of ROBOT, so stay tuned!
Now that we, at Team LOGICOM, have started to design and build more of the smaller combat robots, I have been doing research on how to pack extra power into these pugnacious petite pugilists. My search for maximum power in the minimum volume first led me to Castle Creation’s Mamba 25 reversible, brushless motor kits. These little kits are a nice, dense package able to generate a lot of torque for such a small ESC and small diameter motor. The kit boasts some other impressive numbers too. Like being able to operate reliably with voltage as low as that produced by four NiCd/NiMH cells (nominally 4.8 volts), or as high as 12 nickel cells (14.4V) or with 2 – 3 lithium polymer (Li-Poly) cells in series. The ample torque available with this system stems from the controller’s ability to handle some serious current: 25 amps continuously and 50 amps of surge current.
How can the controller survive at these current levels without a heat sink or active cooling? It is possible, owing to the remarkably low RTSON FET resistance of just 0.0045 Ohms. Just when you think all the surprises are over, Castle Creations packs in a bunch more features. Combat robot guys tend to want fullbraking, full-current and full-speed reversing with little (or preferably no) reverse delay. The Mamba speed control features a variety of braking and reversing options.
The programmable low-voltage cutout will protect Li-Poly packs from excessive discharge and keep the battery eliminator circuit (BEC) alive for reliable radio communications. I know I mentioned it before, but it deserves a repeat—this ESC is really small for the power it dishes out. It is a diminutive 0.95×1.72×0.4 inches and weighs only .9 ounces (24.5 grams). Since there’s no heat sink or active cooling needed, you can pack this little guy into the tightest of places.
The Mamba motor is a mere 0.79 inches (20mm) in diameter and 1.3 inches long, and it weighs only 1.7 ounces (48 grams). The controller comes set up nicely right out of the box, but Castle has a great USB enabled programming package available via Castle link hardware, and Mamba link beta software. Right now, you can program a custom throttle response curve and a custom brake response curve; and very soon, Castle reports, you’ll be able to program your own punch control, brake strength and custom reverse power. Plus, you’ll be able to save your profile setup files.
Let’s take a look at the motor that comes with this kit. Initially, I was concerned on how to get the rpm down to a manageable level for drive power in a little bot. I looked at designing and building a spur gear reduction, a multi-stage belt reduction and a multi-stage chain reduction; but all of these custom designs were getting big, heavy, complicated and expensive. What about a plug & play solution? (See page 84).
There is an excellent alternative brushless motor available right now from Astro Flight that is a good match for the Mamba 10 or 25 brushless controllers. This is the Astro Flight MIGHTY MICRO 801P-19 Planetary Robot Motor. It is a gear-head motor, which means the motor and reduction come together as a package. This is nice because the package has already been tested extensively. This reduces prototyping time if you are designing your own bot. The Astro Flight motor is a slightly larger diameter motor than the Mamba at 25 mm, but the integral metal planetary gearbox is a smaller diameter than the motor at 17 mm, and this means the total package size is smaller than the Castle motor and Tamiya gearbox. The Astro Flight 01 motor is rated at 100 watts and will operate reliably with voltage as high as 12 NiCd/NiMH cells (or up to 3S Li- Poly). The gearbox comes standard with a 19:1 ratio and is available in several reductions from around 4:4 to around 64:1 (each system of planetaries increases reduction by an additional 4:4 ratio). The gearbox has a flat-sided 3 mm output shaft so you can easily attach a set screw or preferably a collet-type prop adapter. From that connection, you can attach a wheel directly or easily connect the gear-head to the rest of your robot’s drivetrain.
I found some nice Du-Bro, aluminum-wheeled, rubbertired airplane wheels at my local Hobby Town and drilled them out to fit the 5 mm shaft of the prop adapter. In mere minutes, I had a complete robot drive package consisting of a motor, reduction, and wheel, ready to be bolted into my next project. Astro Flight is justifiably proud that they make their motors themselves, so you can be assured of American-made quality. Price—$120.00 (Astro 801P-19 geared brushless).
TAMIYA PLANETARY GEARBOX
I happened to think about some of those Tamiya planetary gearboxes (No. 72001) I had laying around from another project. Given my design preferences, the gearbox was larger in diameter than I would have liked, about 37 mm high from the mount to the top case screw as compared to the motor’s 20 mm diameter, but the Tamiya pinion gear pressed on perfectly to the Mamba’s 2 mm shaft. That meant I only had to design a motor adapter instead of a whole gearbox. SWEET! And the Tamiya had the perfect 25:1 reduction that I was looking for!
The Tamiya planetary kit is a nice setup. It comes with two X4 planetary stages and two X5 planetary stages that you can mix and match to form ratios from 4:1 (one X4 stage) all the way to 400:1 (all four stages, X4 X4 X5 X5). The output shaft connects directly to Tamiya wheel kits and the whole package comes with the mounts, motors, and everything. Of course, we robot guys are never satisfied running stock motors and that is where the Mamba 25 kit hits the sweet spot.
OK, I connected the Mamba 25 motor to the input stage of the Tamiya planetary kit and ran the motor a bit – then a bit more – then a long time. I then ran the geared setup for a really long time. “SCREEEEECH.” The gearbox seized. This brushless motor had spun so fast that the plastic from one stage of the planetary carrier had welded to the gearbox case. With a new reduction stage and a better lube job, I was back in business. It looks like this little motor has some really nice potential, so you are sure to see some Team LOGICOM bots powered by this little monster in the near future. Price—$139.95 (Mamba 25 motor and speed controller); $18.50 (Tamiya planetary gearbox).
DURALITE LI-POLY BATTERIES
A perfect match-up for these new generation brushless motor kits comes to us from the well-established brand of Duralite. The e-PLUS SILVER and e-PLUS GOLD lithium polymer batteries are extremely light and well packaged. These high-tech battery packs offer 10.5C continuous and 14C peak current which means that you can draw an incredible 70 amps from some of these packs!
The e-PLUS SILVER battery packs are strengthened with kapton fiber and the e-PLUS GOLD packs are strengthened with 1 mm thick carbon fiber sheets on each side of the pack. These external armor plates add torsional rigidity, impact resistance and puncture resistance. All the e- PLUS packs also sport a unique airflow design for uniform cooling and consistent cell temperature. Duralite knows that adequate cooling of lithium polymer batteries is essential for maximum performance and reliability, so these ventilated packs are heat-shrink free and have silicone separating discs between the cells. This unique design allows for airflow between the cells and lets you see each individual cell to check for damage or over-heating.
One of the really cool things about the Duralite e-PLUS packs isn’t even a battery. It is the optional Stay Balance ModuleTM for e-PLUS Li- Poly Batteries. Duralite recognized early on that keeping all the internal cells at the same potential is essential with the latest high-performance Lithium polymer battery packs. Cell balancing is key for optimized pack capacity and performance and the Stay Balance Module does this effortlessly. The Stay Balance Module connects directly to Duralite e-PLUS batteries with the included plug and continuously monitors each individual cell in the pack while charging and keeping them all perfectly balanced. Please contact Duralite for pricing information.
Astro Flight Inc.
www.astroflight.com, (310) 821-6242
www.dubro.com, (800) 848-9411
www.castlecreations.com, (785) 883-4519
www.duralitebatteries.com, (877) 744-3685
Novak Electronics Inc.
www.teamnovak.com, (949) 833-8873
Tamiya America Inc.
www.tamiyausa.com, (800) 826-4922
Team Whyachi LLC
www.teamwhyachi.com, (715) 654-5000
Trinity Products Inc.
www.teamtrinity.com, (732) 635-1600
Words by Brian Nave