Dear fellow EZ-robotisits,

I purchased a 2x12 and got my hands on a couple windshield wiper motors from the junkyard. The motors are not only extremely heavy, but the worm gear attached makes them unsuitable for differential drive on smaller robots as the RPM's are too low. I have been researching my motor options for the optimal balance of torque and speed for a robot weighing under 20 pounds and wheels with a circumference of 31.4 cm. I would like my robot to achieve a maximum speed of 5mph. Thus, I have determined the motors should be capable of 2000+ RPM.

I have not found any documentation for the appropriate range of motor specifications, but have read of instances where people fried the sabertooth by driving motors that pulled too much current. So my questions are:

1. Assuming the output is 12v and =<25amps, how small of a motor can be driven by the 2x12 before the motor's resistance causes damage to itself or the sabertooth?

2. Given the specific demands of my robot, should i use a 2x5 instead?

3. Is there a specific motor any EZ-robot users have experienced success with under similar scenarios?

video of my robot before sabertooth upgrade, driven by continuous rotation servos: http://vimeo.com/83097440

Thanks, Brad

Sabertooth motor controllers are really tough. However you need to get the proper size rated for the load your pulling out of them. That means they need to be rated for under the amount of amps your motors are capable of sucking out of your power source. If you say your motor is rated at =< 25 amps then you need to get a 2X25 Sabertooth. The "25" in Sabertooth's name depicts the amount of amps the controller is rated for each of the two motors. Dimension Engineering makes it simple to find the right size controller you need to by by putting the Amp rating right into the name. So to answer your question; No the 2X5 Sabertooth will not push a motor rated at =< 25 amps. The 2X5 will only be acceptable for two motors rated at less then 5 amps each.

Hope this helps.

Dave,

Thanks for your reply. One of the problems I am running into is that motors often only list the operating voltage, and with most 12v motors that do list amperage they put it around something like 0.5 amps. My understanding of an electronic speed controller is that it basically maintains voltage while modulating amperage output. What I do not know is what will happen if I push 12amps through a small motor (let's say 12v 0.5amps). Will the motor's resistance cause thermal overload? I know the ceiling for a 2x12 is 12A (or 25A at peak) to be safe, but where is the floor?

By the way, your Robbie robot is crazy dope! how did you sync the lights with the speech? Do you have some kind of amplitude sensor in your circuit?

@kap10cartoon ... I think you got it backwards... Devices draw amps... you can't force amps on any device... Amps or mA are a pool for a device to draw from.... A car battery is 12V and around 60 amps capacity a motorcycle battery is also 12V but only around a 10amp capacity... Hook any 12V device up to the car then the bike battery and of course the car battery with it's larger capacity will (theoretically) run that device 6 times longer... So what Dave is saying is your motors will draw too much power (amps) for the sabertooth 2 x 5 to be able to provide... What I am saying is that your motors will need a certain amount of power to run (ma or amps)... the motor controller's job (and battery of course) is to see to it that the motors get the current they require... A small motor will work on a sabertooth 2 x 5 or 2 x 12, because it doesn't draw (relatively) as much power so either sabertooth can provide it with it's power needs... A big motor like a wheel chair motor will easily over draw on the smaller sabertooth 2 x 5 so you'll need a 2 x 12 or in some cases a 2 x 25...

Thanks for the nice words @kap10cartoon. That means a lot. However if you call my B9 robot, Robbie to his face he'll tell you his name is Robot, just Robot. Robbie was from the Forbidden Plaint movie. Both classic robots were designed by the same guy though, Robert kinoshita. So I guess you could say they are bothers.

I get the chest neon to flash with a cool product by Tech 22, The Neon Power Company. It has a lead that attaches to one Channel of a speaker output on an AMP and when it senses a voice pulse it will trigger the transformer of the neon and flash it. Here's a link if your interested:

Tech 22