Let's Make Robots!

Outdoor robot with 2 large 78amp hour batteries

I want to build a large outdoor robot around a power source I have recently aquired for free - 2 12 volt 78 amp hour batteries.

The primary purpose of the robot will be to roam around my garden outside and scare off squirrels and racoons and rabbits that like to eat from the garden.

Here are my questions:

1. What would be the optimal size of motors/gearbox to pair with this power source -plan to use skid steering?

2. Is pressure treated wood a good material to use for making the body of the robot (I'm pretty handy with wood)?

3. I thought I might use mountain bike tires and rims for the wheels - sturdy and fairly cheap. Is this a good idea?

4. Are infrared sensors good enough to spot critters/movement in the garden area? Is there a better way?

5. Any other information you think would be helpful to make this project successful?

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That motor would be one option, yes. But you will:

A) probably need 2 of them


B) can get a better deal on 2 motors (including the wheels)


Based on the feedback here, I'm thinking something like this would be ideal:

Wheelchair motor

Did not think about fuses. But, with this kind of power, I agree that they are essential.

You have talked me out of drill motors. I will see what kind of deal I can find on scooter/mobility motors.

I have used drill motors for quite a while now on my robot Walter. I have gotten them to work, and they work well but I would not recommend them. First off, they are way too fast. I use a chain drive (reduced twice) coming from the drill. I start with a 3:1 ratio going to a 7:1 ratio then a 12" wheel. The motors are DeWalt 14.4v drills running on a 12v SLA. Even with this double gearing, and the drills in the "low" gear, the robot can still do almost 5' a second. If you go with drills, you MUST use a secondary gearing-down of some kind.

Next is the current draw.... The DeWalt's are quite happy just driving around. On average they pull about 4-6 (maybe 8) amps each. Now, when you throw a chain and lock the drills up, they turn into little arc-welders. We are talking about incredible juice here --somewhere in the 60A (yes, sixty amps) range. Fuses are your friend.

Lastly, drills are much more efficient going forward. Because one motor will always be going "backward", in that it is on the "other" side of the robot, you will be in a constant state of trying to keep them balanced. This offset changes quite a bit as the battery level drops so if you want your robot to go straight, encoders are a must as well as code that can be used "in real time" as the robot travels to keep everything straight.

Have I talked you out of it yet? --If you end up going this way, please get a hold of me. I have figured out most if not all of the tricks needed to get these guys going and I can save you from tearing your hair out.

My suggestion would be to go ahead and drop the $150 or $200 on wheel chair motors from Ebay. A small investment up front here is going to save you a lot of agrivation in the long run.

Oh, and did I mention fuses? Whatever system you chose, USE THEM!!! Use a main fuse or a fuse on each motor, whatever you want --just be sure you use them. And buy spares!! The truth is that you will be working on your robot, blow a fuse without a spare and to keep working, you will stick a paperclip in there. Soon after, you robot and/or house will be on fire. Fuses, fuses, fuses.

  1. You'll need some beefy motors. Krumlink suggested good sources. Cordless drill motors have their pros and cons, but could be another choice. Differential steering with two wheels is a fine choice. A tracked vehicle is nice for handling all types of terrain, but may chew up your lawn a bit.
  2. Pressure treated wood is heavy. You might be better off with tubular steel or aluminium, U-channel or square-tube, etc. If you can weld that opens up a lot of options. You might find a frame ready made from a kids ride-on toy, mobility scooter, or other thing. If you use wood, you can always give it some good paint or spar varnish to protect it from the elements.
  3. Those are some big wheels. If you want smaller ones, maybe look at wheels from kids' bikes. Then you can still use the same bicycle sprockets, etc, but have smaller wheels.
  4. IR doesn't work well in sunlight. You might want a variety of sensors for day/night conditions. Also maybe include some headlights and a camera.
  5. Check this site for robots like hardmouse's tracked lawnmower, CtC's Walter, FrenchGuy's tracked RC vehicles, and Jad Berro's MIGHWAR, Krumlink's tank or even my own YardGnome for ideas.

1. Electric scooter motors, CIM motors, Windshield wiper motors are all powerful contenders. Also Power wheels motors, which are like 330 watt motors.

2. Wood is okay, aluminum is better.

3. Yes if you can incorporate electric scooter motors using 35 pitch chain.

4. Depends on sunlight, color of object, distance, etc. LIDAR or even SONAR would be best I think.

5. Is this your first project?

I have a lot of handyman type experience and woodworking. I don't know how to weld but would like to learn. I have built small robot kit type things and know my way around microcontrollers and electronics. But, I recognize that this is an ambitous project. I like the idea of an alunimum frame - light but strong. The batteries are very heavy and might not be the best to use for something like this. But, I got them for free and do not have a better use in mind.

Thank you for the quick feedback. This is a wonderful site.