Low Voltage H-Bridges

[nickelflippr]

I've been playing with some tamiya dual gearbox motors mounted on a Tamiya tracked vehicle chassis kit. Thru a mostly trial and error process, some reasonable operation is obtained, using a Pic 16f684, TI 754410 dual h bridge, with a software PWM. The h bridge inputs/outputs are paralleled to handle the 2.1A stall current of the motor, so only driving one side right now.

The problem with the TI 754410 h bridge is that the input motor voltage is from 4.5-36V. So four Ni-mh cells are not going to do the job. Using six Ni-mh cells right now for the breadboard operation, but this is likely to be too heavy.

Found a low voltage part, MPC1550EL from Motorola/Freescale, that is made for 2.5-5.5V operation. The problem with this part is that its in a VMFP package.

Anyone know of a low voltage dual h bridge part, in a more friendly package? A Soic package is about as small as I can solder.

 

[mneary]

Are you constrained for space? You can always use discrete MOSFETs at that voltage.

A good example is IRF7309, about $3 in small quantities. You'll need four of them.

Another option is to use 2/3 size NiMH cells, more voltage, less current.

 

[3v0]

Why do you feel that 6 Ni-mh (AA's?) cells are too heavy? The Tamiya dual (twin or double?) gearbox and motor are more then up to the load. To some degree weight should be a plus for a tracked vehicle.

I have a Tamiya 70168 Double Gearbox setup at the lowest gear ratio 344:1 using Tamiya 70145 narrow tires (like Mongoose uses). I am driving it with 6 AA's into a bipolar H-Bridge, it has plenty of torque.

What is you take on the tracked vehicle kit? Is it worth getting?

 

[nickelflippr]

mneary: Thanks for the useful ideas. Right now looking at a 2 sq. in. area. Really like the idea of a prepackaged h-bridge, as there was a smokey experience when trying a discreet h-bridge previously.

3vO: The tracked vehicle seems like a good value. But until the treads hit the road, carpet, lawn etc. its hard to say how it will perform. The four cell pack would be nice because it fits between the front of the motors and the front axle. Will have to build a mezanine for it anyways and could put the batteries up there. Would rather keep the center of gravity low if possible, maybe four below, two on top.

By the way, the dual gearbox (and twin motor?) is a direct drop in for the tracked vehicle chassis, as the axle is the same width.

Was hoping to use it with a Vex R/C transmitter, as per previous thread.

 

[Hank Fletcher]

How about using four Lithium AAs? They're light, last longer than any other AA, and give you 1.5V each. They're the most expensive, of course. Pick 'em up at your local camera store.

 

[3v0]

Here is a ready to go solution. It the Pololu Low-Voltage Dual Serial Motor Controller.

**broken link removed**

It will handle 5 Amps per motor and the price is not bad at $32.

 

[nickelflippr]

More good ideas, Thanks. Saw that Pololu controller, which got me thinking about the low voltage solution.

Just ordered another SN754410 dual h-bridge. Will be going with the six cell Nimh's for now, to stay on the budget side of things.