Make your own free website on Tripod.com

RC OBSSESSION

Big Block Drill Motors

Home
Discussion Thread
Coming soon, Novak 3.5R Evader ST Pro!!
Track
Helicopters
Pictures
Live Market Place
Tips and Troubleshooting
Motor Cleaning
Related Links
Contact Me

755vc_motor.jpg

The stock motors that are installed in the E-Maxx are very good motors. They produce lots of torque, require little maintenance, and if not abused they can last for years.  However, as Tim Allen is fond of saying, “everything can use more power.”

With this in mind, the easiest way to give an E-Maxx more power is to run it with 14 cells (rather than 12).  After that, though, we're looking at upgrading the motors.

There are three different paths one can take when upgrading the motors.  First, there are brushless motors.  Many people consider this the ultimate motor upgrade.  If you want the fastest possible electric R/C vehicle there's no question that brushless is the way to go.  It's going to cost you, though.  Depending on the system you select, you're looking to drop $350 - $600 or more.  Second, there are modified motors.  True, these will give you more speed, but they're not cheap and they need frequent rebuilds.  Lastly, there are 'traditional' maintenance free electric motors (like the Titans).  Since these motors are designed to power riding toys (Power Wheels), drills, circular saws, etc. they've been designed to be powerful, dependable, and long lasting.  In addition, they're cheap.  Keep in mind though, that you can't generally run out and buy such a motor.  However, with a little research you should be able to find them at a surplus or wholesale distributor.

After some research, I was able to find the manufacturer and model of the stock Titan motors.  They're RS-550VC motors manufactured by Mabuchi. Mabuchi also makes a motor that can be considered the Titan's big brother, the RS-755VC.  Here's how the two motors compare:

Model

Voltage

No Load

At Max Efficiency

Stall

Operatin g Range

Nomina l

Speed (r/min)

Curre nt (a)

Speed (r/min)

Curre nt (a)

Torque

Outpu t (w)

Torque

Curren t (a)

RS-550VC

6.0 ~ 14.4

14.4V

19,800

1.30

17,620

10.5

64.7 mN-m

660 g-cm

119

588 mN-m

599 4 g-cm

85.0

RS-755VC

6.0 ~ 14.4

14.4V

20,500

2.40

17,730

15.3

94.2 mN-m

960 g-cm

175

696 mN-m

709 5 g-cm

98.0

Here's a Titan next to an RS-755VC.  As you can see, the RS-755VC is about 50% bigger!

titan_and_drill_motor.jpg

The RS-755VC motor is not a direct swap for the Titan.  For example, the motor needs to be 'prepped' before it can be used.  Prepping is simple.  First, since the motor's shaft doesn't have a flat spot for the pinion gear's set screw to bite, a flat spot needs to be created. This is simple enough. 

The RS-755VC motor is not a direct swap for the Titan.  For example, the motor needs to be 'prepped' before it can be used.  Prepping is simple.  First, since the motor's shaft doesn't have a flat spot for the pinion gear's set screw to bite, a flat spot needs to be created. This is simple enough. 

Simply grind the shaft with a Dremel or a bench grinder.  Take care not to let the shaft get too hot or you'll ruin the motor.  The other thing you'll need to do is to attach two 0.1 uF 50V capacitors to the electrodes and the motor's can.  This is to eliminate the radio interference that the motor would otherwise generate.  Use the stock Titan as a guide for installation.

Since the RS-755VC is so much bigger than the stock Titans, you'll need to buy new pinion gears (Titan's shaft is 3mm and the RS-755VC is 5mm, pinions can be purchased at www.finedesignrc.com) and you'll need to either modify your existing motor mount plate or make a new one.  The reason for this is the distance between the two mounting screw holes on the motor's can are 4mm further apart than the Titan's (29mm v. 25mm).

I decided to make a new motor mounting plate rather than modify the stock plate because I wanted to have the option to put the Titans back on and given the torque these motors generate, I felt a thicker, stronger mounting plate was necessary.  The stock mounting plate is 1/8" thick.  If you take it in your hands and try to bend it you'll see that it does have some flex to it (unless you're Superman, you won't be able to bend it!).  The lightest, strongest, cheapest, and most durable metal for making a new mounting plate is 6061-T6 aluminum.  Since I wanted my new plate to be stronger than the stock plate I decided to use aluminum that's 3/16" thick.

flat_stock_aluminum.jpg

There are a number of places you can go to buy this material.  I choose to use Online Metals (www.onlinemetals.com).  Here's a shot of the flat stock when I first got it.  Its dimensions are 12" X 12" X 3/16".  This is much more aluminum than I'll need to build a mounting plate but I'll have plenty left over in case I mess up or for other projects.

I want the overall size and shape of the new mounting plate to be the same as the stock plate so the stock gear shroud will fit.  So, the first order of business is to trace the stock plate onto the

aluminum.  It's also critical that the mounting holes line up perfectly with the screw holes on the transmission or the plate won't fit the truck.  To accomplish this, I traced the stock plate onto the flat stock with an awl.

Once I finished this, I cut the new mounting plate out of the flat stock.  I intentionally made the cut bigger than the stock plate to accommodate any cutting errors I would make.

Initially I had a lot of difficulty cutting the metal.  Since aluminum is so soft I though the blade would go through it like butta' ! However, after only 1/2 inch of cutting the metal would melt and choke up the blade's teeth. I would then have to stop and clean the aluminum out of the blade.  Thinking that there had to be a better way, I grabbed a blade designed for cutting wood and installed it into my jig saw.  Amazingly, this blade did the trick.  It cut through the aluminum just as easily as if it were hard wood, like oak. Below are pictures of the blades.

metal_saw_blade.jpg

metal_saw_blade_close_up.jpg

wood_saw_blade.jpg

raw_mount_plate.jpg

Here's the freshly cut piece.  As you can see, I still have a lot of work to do. If you look closely you can see the traced image of the stock plate.  It's a little hard to see in the photo.

The next step is to cut and grind the piece to shape.  Rather than use a grinding wheel, which is a big no-no because the aluminum will choke up the wheel causing it to shatter, I used a hand drill with

a router bit (an old router bit!) attached.  This allowed me o work the piece to the exact shape I wanted.  Once finished, I drilled and counter sunk the five transmission mounting holes.  Counter sinking was necessary because of the added thickness of this material.  The next thing I needed to do is to drill and tap the four holes required to mount the shroud.

After that, it was time to map out and cut the holes for the motors. This was the most difficult part of the project since most of these holes are not round but sausage shaped.  First, I had to plan exactly where the holes should be. Any mistake in the measurements and the pinion gears would not properly mesh with the spur gear. Next, I 'rough cut' the holes by drilling 1/16" holes along the hole's perimeter. Then I used my Dremel with the cutting wheel attachment to finish cutting out the holes.  Lastly, I used the drill and routing bit to smooth out all the rough edges. After ensuring that everything fit properly by installing the mount on the truck, I took it back off and finished up the job.  I buffed the mount with a brass wire wheel to give it a lustrous brushed finish.  Here's a shot of the finished mount!

finished_mount_plate.jpg

Here are a couple of shots with the mount installed.  These motors look a lot bigger than the Titans when installed in the truck.  I'm glad I went with the thicker mount plate because the stock plate would look way too thin for these things.

finished_job_side_view.jpg

finished_job_top_view.jpg

Now that everything's done, it's time to test my creation.  For my first run, I took it really easy on the truck to make sure everything held together and to get used to the new motors.  Next, it was time to see what these things can do.  I installed two freshly charged battery packs (12 cells) and ran the truck pretty hard.  The torque these motors put out is very impressive.  Knowing these things generate a lot of torque, I went with 21 tooth pinions.  Even still, the truck is quicker and has a higher top speed than the stock Titans on 14 cells.  For example, if the throttle is 'punched' while the truck is in first gear it will flip right over onto its back.  In second gear, it wheelies with little effort.  Despite the extra weight of these motors, the truck's overall handling seemed to be unaffected.

After the run, which lasted about 15 minutes, the motors were only warm to the touch.  A similar run with Titans would have left them nice and toasty.  So now, it's time to pull out all the stops and see what these motors can do.  For this run, I installed two 7 cell packs constructed from GP 3300 batteries.  With 14 high power cells, the speed and power of these motors is insane.  Though not as fast as a brushless setup, it makes the Titans look weak by comparison.  Rather than wheelie in second gear, the truck flips over.  I'm convinced that I can run pinions with either 22 or even 23 teeth without over taxing the motors.  I would gladly give up some torque in second gear for a little more top speed.

Shortly into this run disaster struck.  I punched the throttle from a standing start while in first gear and a horrible grinding sound instantly came from the rear differential case (think nuts and bolts in a blender).  Suddenly my truck was converted from 4 wheel drive to front wheel drive!  I blew the rear differential!

Back at the shop, I took the rear differential apart and discovered that I stripped the spider gears.  Based on this, I decided to replace the rear differential with a spool. This will strengthen this part of the truck and provide better traction.  If you’re not familiar with a spool, it simply replaces the rear differential and has the effect of locking the rear drive-shafts together.  The only downside with a spool is the truck will tend to under-steer when driving on high traction material.  Additionally, I loosened the spring on the slipper clutch slightly so it will absorb more of the 'torque shock'.

Trashed Spider Gears
spider_gears.jpg

Spool
diff_spool.jpg

In the end, I feel that this was a very worthwhile modification.  The new motors provide the truck with a substantial increase in speed and torque with a negligible decrease in runtime and for a nominal monetary cost.  The motors are inexpensive (if you can find a seller!) and require minor prepping to make them ready to use in the truck.  By far the hardest part of this project is making the motor mount plate. If you are comfortable with metal working or if you know someone who is, fabricating a mount plate will take about 5 hours.

Enter supporting content here