HPI RS32 Mods Thread - RC Groups
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Feb 12, 2012, 04:49 AM
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Evil Twin's Avatar

HPI RS32 Mods Thread

With a few mods, this car may be the ultimate budget micro indoor/garage racer. Below I list the pros and cons, and then follow with some mods to solve the cons.

1. It’s 2.4Ghz so you should be able to race a bunch at once.

2. It runs great on cheap 1s 3.7V lipo batteries, which can be bulk charged 3 at a time on a 3s charger with a simple adapter.

3. It costs ~$100 so your friends are more likely to join.

1. The stock battery is not easily swappable which makes racing a hassle. You need to take off the body which is a pain with this car, and then you need to undo 3 screws. Once you get to the battery the connector is difficult to unplug.

2. The stock motor is too slow even with the biggest pinion gear (9t), and it’s real draggy so it tends to break the back wheels loose especially on low traction surfaces like concrete.

3. No easy way to buy ball bearings

To address the motor issue, the stock motor was replaced with a coreless motor from a Blade mSR helicopter. The mSR motor is much faster than the stock motor, I estimate the car is 1/3 faster with a coreless motore and 6t pinion than the stock motor is with a 9t pinion. Also, coreless motors have almost no drag so they don’t tend to break the rear end loose on corners. To solve the battery swap issue the body is mounted with magnets, now 20 second battery swaps are possible. Blade mCP X batteries and connectors are used, which should give long run times and the connectors are easier to disconnect.

Part 1: Motor Upgrade
I recommend doing this mod first, you will see a big performance gain. The battery mod gives you longer run time and easier battery swaps.

Parts/tools needed
1. Stock Blade mSR motor EFLH3003 or equivalent. I've also used EPS8 from hobbyking.

2. 5/16-18 Nylon Hex nut part 881553 It’s for the motor mount, purchased from Lowes

3. Brass tubing: 9831 Thin Wall Brass Tube 1.5mm OD x .225mm I bought mine from advantagehobby

4. 2 small tapered wood/plastic screws, I used 9 gram servo (HXT900) mounting screws

5. Drill press

6. Drill bits ~1mm, ~1.6mm and 11/32”

8. Very small file

1. Remove the stock brass pinion gear from the MSR motor, DO NOT TRY TO PRY THE PINION GEAR OFF or you will ruin the motor. These motors don’t take axial loads very well so be very gentle removing and installing pinions on them. To remove it, take a pair of pliers and crush the pinion rotating the pinion 90 degrees between each squeeze. After ~3 squeezes it will fall off.

2. Sand 1 face of the nylon nut so it is flat, the beveled edges will make drilling mounting holes difficult.

3. Drill out the center of the nylon nut using the 11/32” bit. Pre drilling with a smaller bit will help keep the hole centered.

4. Drill mounting holes in two opposite corners. Use a sharp nail to mark the nut halfway between the edge of the hole and the outside of the corner. Drill with the ~1mm bit first and then the ~1.6mm bit. Test the mounting screws.

5. The new motor mount holes will be a little wider than the stock motor holes, so the holes on the car will need to be widened a few millimeters to allow the screws to pass through. I used a small round file to remove some plastic.

6. Cut a piece of brass tubing 5.6mm long by rolling it on a hard surface while scoring with a hobby knife. To protect the bushing put a pin hole in cling wrap, and insert the shaft through the hole. Lightly sand the shaft or the glue won't hold.

7. Insert the brass tube into the 6t pinion, then glue the tube onto the shaft with super glue. Remove the cling wrap.

8. Removing the wheel helps when mounting the motor. Adjust the position of the pinion so the gears are meshing properly.

Part 2: Battery Upgrade
To be continued....

Last edited by Evil Twin; May 24, 2012 at 06:25 AM. Reason: Changed pinion mounting method
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Feb 12, 2012, 05:07 AM
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Evil Twin's Avatar
Here's a video of micro-t's racing on my garage track (Wu Tang Track). Once I get the rs32 dialed in I'll post a video of it on the same track and then a moded Micro-t vs moded RS32 show down! By the way this same motor mounting method works great on the micro-t, use the smallest micro-t pinion.

Losi Micro-T race (1 min 52 sec)
Feb 15, 2012, 01:36 PM
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iPearl's Avatar
Nice !!!

I made mods my self.

Bigger Wider Tires heavier Tires
New Body
Modded Chassis to accommodate the bigger tires for Turning radios w/o rubbing

Here is the build thread.

The car rolls smoother. Turns Left Twitchy. It is stuck as hell.
Runs more like a 1/12 pancar


Feb 19, 2012, 06:36 AM
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Evil Twin's Avatar
Adjustable height magnetic body mount and Lipo battery conversion mod

This mod replaces the cumbersome stock body mounting system so you can quickly pull the body off to swap batteries and allows a 200 to 300mah 1s Lipo to be used. Iíve tested the motor/battery/body mount combo on hard wood floors, it is very fast even on the smallest 6t pinion. Iíll report back after I try it on the track.

Parts/tools needed
1. Rare earth magnets, I used 5mm x 5mm x 2mm. One dimension needs to be between ~4mm to ~6mm to make the body fit right. Magnets from an old Sonicare tooth brush head will probably work.

2. Hot melt glue gun

3. ~2mm outside diameter stiff plastic tubing, I used 2mm teflon tubing. A coffee stirrer with a ~1.5 mm inside diameter will probably work.

4. Small files

5. Thread locker

6. Stock eflite MCPX battery 1s 3.7V 200mah part # EFLB2001S25 or possibly Nanotech 300 for the solo pro 100 if the connector is replaced. Nanotech 300 for the MCPX is too long!

7. Connectors for the speed control and charger. Digi-Key Part Number 455-1704-ND
Link: http://search.digikey.com/us/en/prod...1704-ND/926611

8. Lipo charger for MCPX batteries. If you have a regular lipo balancing charger, you can use the connectors above to make a wiring adapter.

1. Remove the black plastic body mount from the body, then cut out the center section as per the picture. In front cut it about 10mm behind the screw. In back cut it off just forward of the tabs which is about 35mm in front of the screws.

2. Screw in the modified body mounts. For the back body mount spread the body out a bit with your fingers and put a drop of hot melt glue in between the body and the outside of the mount to support it.

3. Remove the rear shock and battery cover, noting how the front of the shock mounts. You will not use the battery cover, the car is stiff enough without it and it will prevent lipoís from fitting.

4. Test fit the plastic tubing with the rear shock, the shaft should slide easily in but the spring will be stopped. Hot glue ~20mm of the tubing to the front of the chassis as per the picture. The tubing will extend the same amount into the battery compartment as the original rear shock mounting hole, about 1mm.

5. Replace the screws from the battery cover with some thread locker. The screws will stick to the magnets and allow the body height to be adjusted, with 5mm magnets my screws are backed out about 1mm.

4. Use hot melt glue to attach the magnets into the body as per the picture, mine are standing on edge to make the spacing correct.

5. Replace the rear shock.

6. Test fit the battery, if it doesnít quite fit under the shock, note where it is hitting the chassis, you may have to file a bit of plastic away.

7. Test the body fit adjusting the battery cover screws until the body clearance is correct. Be careful not to pull on the rear pod when removing the body.

8. Put a new connector on the speed control. I spliced in cat 5 wire from an old network patch cable to make the wires long enough. Solder the wires to the connector at a 90 degree angle as close to the connector as possible, see the picture. You will need every millimeter of space. Cut the excess leads off the end of the connector and place a dab of hot melt glue on the exposed leads to insulate them.
Last edited by Evil Twin; May 08, 2012 at 03:20 AM.
May 08, 2012, 02:57 AM
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Evil Twin's Avatar

Lipo battery update

Progress has been made with the battery, the nano-tech 300mah for the solo-pro fits as well as the stock e-flite blade mcpx 200mah battery, and the connector is compatible with the stock RS32 connector from the speed control! Luckily I saved the stock connector, I'm going to put it back on.

Turnigy nano-tech 300mah 1S 35~70C Lipo Pack (Fits Nine Eagles Solo-Pro 100) PRODUCT ID: 9210000001
Last edited by Evil Twin; May 08, 2012 at 03:17 AM.
May 09, 2012, 11:31 PM
in memory of dez RIP
rcphreak's Avatar
any video of it running now vs stock ??
also around how much is this conversion going to cost ??
also with thses mods and the car being faster can it handle the extra speed and be driveable / raceable . thanks in advance .
May 13, 2012, 02:40 AM
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Evil Twin's Avatar
I tried to make a video, but the pinion came loose. I'm going to try using brass tubing on the motor shaft to improve the mounting or find a pinion with a smaller hole. The motor seems too fast for racing even with the 6 tooth pinion. I have some ideas for slowing it down, perhaps a resistor in series, a magnet stuck to the outside of the motor case, or a slower motor.

The blade msr motor is ~$10, but hobbyking has an equivalent for $2 that I'll try. No load current is within 5% of the msr motor so I think it will be about the same speed. The nanotech 300 solo pro battery is ~$2 at hobbyking. Lipo charger was ~$6 from hobbyking. The connectors are ~$0.25 a piece from digikey.
May 24, 2012, 06:02 AM
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Evil Twin's Avatar
Test drive video.

HPI RS32 with Blade mCP X LiPo battery, Blade mSR coreless motor (0 min 35 sec)

I finally got the pinion to stay on, I had to lightly sand the motor shaft otherwise the pinion would fall off after a few minutes even with super glue. Without mods the mSR motor is too fast for the car, the rear wheels break loose even on carpet at half throttle. I ended up adding a 1ohm resistor in series with the motor to slow it down.

I updated the motor pinion mounting upgrade directions in the original post to include the brass tubing.
Last edited by Evil Twin; May 24, 2012 at 07:10 AM.
May 24, 2012, 07:03 AM
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Evil Twin's Avatar

governor mod...

I had to put a resistor in series with the motor to slow it down. The resistor is inserted into the speed control connector so it can be quickly changed to suit the driver and track. The blue speed control wire was cut and the motor leads were soldered to each end of the cut, putting the resistor in series. I've tried 1/8 watt 1ohm, 2.2ohm and a staple in the connector. The video is with 1ohm. I was concerned that 1/8 watt wouldn't be enough but it wasn't even warm after the test runs.

The resistors are from Radio Shack, I bought the 1/8-Watt Carbon Film Resistors 500-Piece Value Pack for $10. For the non-electrical engineer types brown black gold gold is 1ohm and red red gold gold is 2.2 ohms.

I timed a battery swap, it was 20 seconds with no practice including removing and replacing the body! Possibly a world record for this car?

Next step is to clear out my garage and set up the track for an RS32 vs Micro-T showdown!
May 27, 2012, 04:32 AM
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Evil Twin's Avatar


I found some info on bearings in another thread, front bearings are 2x5x1.5mm and 4 are needed, rears are 3x6x2mm and 2 are needed.

The front bearings are hard to find because 1.5mm is not a common thickness. I ordered a set of 10 for $7 including shipping from ebay. The item was called '10pcs 2x5x1.5 MM BALL BEARING FOR TAMIYA KYOSHO TRAXXAS HPI'

The rear bearings are more common, I'll order these on my next hobbyking order. 'HK190 Out Shaft Bearing 3 x 6 x 2mm (2pc)' $1.82.

Edit 7/24/12: The bearings above fit perfectly, I've installed them in two cars.
Last edited by Evil Twin; Jul 24, 2012 at 05:47 AM. Reason: added info on bearings
Jul 24, 2012, 05:43 AM
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Evil Twin's Avatar

HPI RS32 stock motor vs Blade MSR rolling resistance demo

The blue car has a Blade MSR motor, the white one has the stock motor. The MSR motor is coreless, so it has very little rolling resistance which helps prevent spinning out on corners. Even though the cars are sitting on a piece of sandpaper to give better traction the white car skids down the ramp at about 30 degrees, never turning the motor and the blue car starts rolling at about 5 degrees.

HPI RS32 stock motor vs Blade MSR rolling resistance demo (0 min 8 sec)
Aug 17, 2012, 08:55 AM
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Evil Twin's Avatar

LiPo battery mount option #2

The nanotech 300 1s 35c for Solo Pro also fits at the rear of the car with a slight modification. The plastic silver piece at the rear of the car had be removed, see the attached pic. It was removed with fingers without too much effort. Currently the speed control wires aren't long enough to allow battery swaps without removing the body, but if they are lengthened it should be possible! Currently the battery is just taped in with clear tape, in the future velcro or a thin plastic shelf may be used.

Moving the battery to the rear also helps with the forward/back weight distribution if the Blade mSR motor is used because it is much lighter than the stock motor. Below are weights of each end of the car and the total. The total was read on the scale so it is a little off from adding the back and front weights.

RS32 with stock battery and stock motor, back is +14.1g
57.9g (back) 43.8g (front) 100.3g (total)

RS32 with Blade mSR motor and rear mounted LiPo, back is +14.1g which is close to the stock ratio
49.8g (back) 35.7g (front) 85.9g (total)

RS32 with Blade mSR motor and mid mounted LiPo, back is +4g which differs considerably from the stock ratio
44.8g (back) 40.8g (front) 85.8g (total)

I'm still testing/tweaking the car on the track. I like the way the car handles more with the rear battery mount, it helps prevent oversteer on smooth concrete.
Last edited by Evil Twin; Aug 17, 2012 at 09:12 AM.
Aug 23, 2012, 05:43 PM
in memory of dez RIP
rcphreak's Avatar
great home work on this car seems your making good progress keep up the excellent work .
Aug 24, 2012, 02:24 AM
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Evil Twin's Avatar
Thanks for the props, I've enjoyed working on the car and hopefully it will be our next standard garage racer. Progress has stalled, I've run into an issue with spin outs on left turns only, I just started a new thread to get some help. 'HPI RS32 spins out on left turns?!?'.

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