Let's Make Robots!

Controlling belts

I set out to make an aggresive little tank and I got this far. It runs like a dream when I put a battery directly on the motors... in a straigt line. Any ideas on how to control it, so it can turn on a plate. All wireless.

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Everything was made from old bits and pieces. I havent spend any money yet. 

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You need to use a motor driver or some other way to reverse one of the motors. If one turns forward and the other backward it will spin in a circle.

That looks like an awesome start, will be a great robot. Do you have any information about the motors? Like voltage, stall current, etcetra. That would be helpful to suggest an h-bridge to use on it.

To drive the h-bridge, you would also need a microcontroller or some other way to get the signals in. Have you done any programming? Anything you like?

Simple answer, to just get it moving, would be to have 2 double pole double throw switches, to change the connection of the battery terminals to the motors.  This would be wired control though. You could conceivable have the switches activated using RC servos, from a regular radio set like Futaba or Hitec or Airtronics.

A step up would be using relays.  But that would add drivers for the relay coils, etc.

It's a nice pice of work. Is it fast? Looks like about a 4:1 reduction gear. Some reduction inthe belt drive, too, but I imagine it would be fast unles there's a gearbox in the motors. They look like big motors. If an H-bridge looks complicated or expensive, we can show you how to build one out of inexpensive telephone relays...

Where did youy get the tracks? They're the best...!

 

 

I too am curious where you got the tracks, and the chassis too. It looks really familiar, I think I might have seen it on some site, but I can't remember where it might have been. Looks really nice.

Dan

Motors are 12V from a cars windshield viper (no gears in the motors) and the track are from an old toy tank with tiny motors and wirecontrol. Chassis is all homemade. I trashed the original plastic one, because I wanted to be able to drive everywhere... incl. jumping over fire.

Programming experience: 0.

I thought I would have to get 2 RC speedcontrollers but I'm not sure thats going to work. I'm confused. Working with relays sounds interesting too.

Are they wiper motors or WINDER motors. Here are wiper motors. They're big, they have a worm gear and they draw 10A each.

Don't worry about having no programming experience. Pick a product, read the manual, we'll supply loads of examples.

RC speed controllers are a good, simple, high-current option, but I find them expensive. You need to be careful with relays that you don't switch from full forward to full reverse, they click when you change direction and you need to make sure you're not switching them on and off repeatedly for prolonged periods. Cheaper, but they need work.

I think they are wiper motors - but then again - I didn't take them out of a car myself ? They were mounted in plastic gearboxes that looked very car'ish.

Car motors, whether windshield or window, get into high current draws. But some RC car speed constrols are rated for high current. But they are also typically a lower voltage (7.2 to 8,4) than the 12v the motors are capable of. Additionally, the reverse may not be there, or may be at a lower rate then the forward.I guess you could try looking for the speed controllers that are reversing first of all, then looking to see if they'll take a higher voltage, unless you wanted to use a 7.2 or 8.4 voltage pack to drive the tank.

I've got some  window motors that I'd seen rated a 3 A in free run, not sure about stall. I've used a Pololu Dual VNH2SP30 MD03A driver for them, and don't really expect problems unless I stall a lot. I expect a 12 to 15A stall, but the driver should handle that for a number of seconds, till I can shut it off. Windshield wiper motors can be a little beefier and have a greater current draw than window motors. That Pololu driver might still handle them ok, and would probably be cheaper than 2 RC spped controls.

Ok, I'm just not awake yet. Pololu has a "motion controller" that accepts RC singals to drive (from a regular Futaba or Hitec radio receiver)  and will drive 2 motors at 12 volts. Its tha TReX dual DMC01 and could work pretty well. $100 but that's a pretty good price for what it does. There's also the Scorpion XL from Robot-power little stronger for $120.And the Dimension Engineering Sabertooth 2x25 at $125. All these reverse, are capble of 12 volts, and can connect to either an RC radio, or a microcontroller.