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Author Topic: Help Finding Drive Motors  (Read 147 times)

rsoko

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Help Finding Drive Motors
« on: March 03, 2018, 12:57:31 am »
I have built a 10.6lb combat robot with 12v 1000rpm motors and 4 inch 3D printed TPU tires (6 motors for drive- 3 each side on tank controls).  The bot can barely get enough torque to start any type of movement on a level surface.  My brushed ESCs are capable to 4s (16.8v) and I needed advise on motors to get for the bot.  I need the bot to be able to push around other bots, so speed is not as critical.  Any ideas?

zacodonnell

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Re: Help Finding Drive Motors
« Reply #1 on: March 04, 2018, 09:49:33 pm »
Hi Rsoko, welcome to this crazy game. I'm sorry to hear you're having troubles with your drivetrain. From your description it sounds like you're trying to build a robot to compete in the 12lb combat class, and you're aiming for pushing power over speed, is that right?  If so, 6x kitbots 1000RPM motors with 4 inch wheels would be pretty undersized, and I think you'd run into gearbox and overheating problems.  The good news is that there are lots of options out there for you.

The tried-and-true standard in the 12 and 30 pound class has been the BaneBots P60 gearbox for a while now. It offers a very reliable and compact setup for not too much money. Because it can be used in the 30 pound class it comes in a little heavy for the 12s, but if you're looking to push other bots around and maybe going with a simple wedge bot for this machine it can be a great fit. It also provides you with lots of room to grow in the future as the parts are very common, flexible, and available.

The drive setup is made up of several parts:
Motor - http://www.banebots.com/product/M5-RS550-12.html
There are lots of sizes. The RS550 is heavy-duty for a 12 pound bot, and a little light for an unweaponed 30lber. If you're close on weight then the RS-395 motor is a good choice, but you'll have to get the smaller pinion and the 300 series gearbox version.

Pinion - http://www.banebots.com/product/P60P-GM54.html
This is the little gear that connects the motor to the rest of the gearbox. This requires a small press or bench vise to install as a tight press onto the motor shaft. Because it presses on the motor, the hole in the gear must match the motor shaft. Banebots sells all kinds of pinions - you'll just need to get the one that matches your motor and gearbox choice.

Gearbox - http://www.banebots.com/product/P60S-44-5.html
The gearbox is where all the magic happens. This takes the super-high-speed motor output and slows it way down into something usable for a wheel. It multiplies the torque as it reduces the speed, so a 16:1 box will make it 16x slower and 16x as much pushing power. This ratio is a good fit for this motor and class with a 4" wheel. It would be ok to go with even a little more reduction, like maybe the 26:1 box if you want even more control, but you'll need the 5:1 pinion for that. The banebots gearboxes are custom made with threaded mounting holes and decent shaft support. For a simple setup you can just bolt them to the baseplate and put a wheel on the shaft and go. Of course, it is even stronger to use a pulley on the gearbox shaft to drive a wheel that is mounted separately, but that gets a lot more complicated.

Hub - http://www.banebots.com/product/T81H-RS81.html
The hub goes inside the wheel and is used to link the shaft to the wheel. This hub is made to fit on the stock output shaft of the P60 gearbox because both are a .5" diameter. The square part of the hub locks into the wheel to make sure it turns when the hub does.

Wheel - http://www.banebots.com/product/T81P-395BA.html
Wheels are important too. They have to match the hub you're using to the shaft. This wheel is the closest banebots has to the 4" wheel you mentioned. They offer three different hardnesses for this size, and the one I linked to is on the harder end. They won't wear as fast as the other types and should provide reasonable traction in the arena.

Motor controller - You mentioned that you already have brushed controllers that support up to 4S Lipo, but you didn't mention the current rating. This setup would work well with a controller that can handle around 15A continuous. If yours are rated for less than that you might want to get some bigger ones. The BotBitz 30A controllers are not too expensive and popular, but there are a few others in this size range that work reasonably well. http://ttrobotics.com/botbitz-30amp-esc/
A good alternative is the RobotPower WASP: http://www.robotpower.com/products/wasp_info.html

Hope this info helps!
-Zac

rcjunky

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Re: Help Finding Drive Motors
« Reply #2 on: March 04, 2018, 11:57:19 pm »
I second Zacs reply, its very complete. The gearboxes include the needed pinion but have spares doesn't hurt. 1 of those set ups per side will drive your bot quite well.
Andrew Burghgraef
Canadian Carnage Robotics

Great Hobbies- Canada's leading retailer of radio controlled models and related hobby supplies