Let's Make Robots!

Treads?

Hey guys, I have a question for you. I see many of you guys using the track and wheel set from Tamiya (http://www.sparkfun.com/commerce/product_info.php?products_id=321) that is special built to be compatible with their dual geared motors. For such a cheap price you get a very versatile tread kit that allows endless combinations of tread length and design, however, it seems what's gained in inexpense, is lost in quality. Many who I've spoke to say you get what you pay for when purchasing this item, especially when it comes to the motors (http://www.sparkfun.com/commerce/product_info.php?products_id=319) The motors seem to be great, you can adjust the gearing ratio to balance out your required speed and torque, however, it seems they never balance. When you increase torque, the motors move too slow, and when you increase speed, it's too fast! I was about to purchase these until I found what may be a better solution.

 The tread kit from Solarbotics! (http://www.solarbotics.com/products/gmtpkg/) This kit comes with, what apprears to be, great adjustable tracks, 2 motors, 2 cogs, and 2 idlers. This package is more expensive, however, there is more documentation on all of the parts, and more options as far as motor choice goes. But, as I mentioned, it's more expensive; add in the extra cost of more idlers and longer track pieces if you want a better design, and you'll be running some bucks. I see a few robots that utilize these tracks here as well.

 

Well my question is, based on your experiece with whatever tread kit, which one do you recommend?

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Wow...those are looking like some nice treads! Grasi.

Rubber, grip.. be aware! Tracks must be able to slide over the surface!

http://letsmakerobots.com/node/387

 

 

Check out these from Lynxmotion http://www.lynxmotion.com/Category.aspx?CategoryID=94

They have a kit too http://www.lynxmotion.com/Category.aspx?CategoryID=120 but I'd heard it was a good idea to replace the Lynx motors with some Banebots types.

I wouldn't say that the people I talk to have little experience with drive circuits, I just think that upon comparison with the solarbotic geared motors, the Tamiya may seem a little cheap, as well as the motors. I don't know that for sure, but I supect that's where their negitivity arose from.

 

Are their any other treads that you'd recommend?

I used the tamiya treads and motors on my first robot, and am now using the solarbotics ones for my 2nd robot.

The tamiya treads are rubber, so turning on carpet or rugs will usually throw the track off but smooth floor gives good grip. They stretch a little though, so getting the right tension can be tricky. The only gripe I have with the gearbox is it`s a bit noisy, plus you can get fluff and junk stuck in the gears unless you cover the open areas.

The solarbotics treads look great, are made from a hard plastic so it won`t catch in carpet and will definitely last longer than the tamiya ones. Individual links can be added or removed, making size adjustment easy. When I put my set together the connecting pins were very stiff. I ended up having to pullit apart and run a tiny file through the holes. Also laying the completed track flat from end to end there was about a 30 degree twist to the whole thing :/ Maybe I just ended up with a dud.

 

Honestly I`d get both. The tamiya for knocking up something quick/cheap/functional and the solarbotics for looks/form/quality.

For a beginner, and for fun & cute little things that act more like platforms than anyting else, I'd go for the Solarbotics ones. They are used on the Yellow Drum Machine.

If I was to make something that I wanted to behave more like a tank, something in which I was considering it's ability to climb over a doorstep etc, I'd go tor the Tamiya ones.

If I was to build something that should drive outside in the open & get dirty, I'd consider none of these! 

Ok, so lets say one would consider the tamiya treads, would you also recommend the gear box motors? Because quite frankly that seems to be my only gripe about them, but then wondering how easily compatable the treads would be with other motors.

I have a couple of sets of the Tamiya. I've never had the speed/torque issue. I think people don't make allowances for the wheel size. For example Frits has the gearbox listed in the component section with a comment about setting it up in it's low range due to lack of torque but when you look at the robot he shows using them he is using large diameter wheels, thus the need for a higher torque setting.When using the track kit with the tamiya gearbox you also get two different sized drive wheels, using the smaller drive wheel will give you an intermediate speed/torque setting.

I am also suspect of the drive circuit on some of these robots. Junior is a very heavy robot (around 1Kg) and his gear ratio is set at "B" (58:1). His only problem was that I had current limiting resistors of too high a value limiting the stall current to half an amp (it was supposed to be about 2A). I'm now waiting on parts.

You must remember that not only do a lot of these "H" bridge ICs drop the voltage to the motor but they also have a certain amount of resistance that limits current to the motor. If you use a FET "H" bridge or a relay/FET combination you will get the maximum power to your motors. If it goes too fast, use PWM to slow it down with minimal loss of torque. Another factor is frequency when using pulse width modulation. The higher the frequency the higher the inductive reactance of the motor windings. This is noticable in Junior when his clockspeed is set to 16Mhz as this affects the PWM frequency and one of the reasons I've had to drop the value of my shunt resistors.

All in all I think some people are too quick to blame the gearbox as they don't have enough experience with drive circuits. The only downside to this gearbox is that because the gears are exposed they are prone to dust/dirt/carpet fluff.