supercooper's RedCat Super Mods (aka how to make an RC Super almost acceptable)

[supercooper]

Since Andre N and I started modding our RedCat Supers about the same time, this thread parallels his and documents my journey to turn a cheap POS to at least a mediocre super class crawler.

So, the journey began about a year ago when I naively purchased a RedCat Super for $175 USD delivered. Since I wasn't sure I'd get hooked on the sport, I didn't want to PO the spouse by spending too much at that time .

The fallacy, of course, is that once you get hooked you want more performance than a budget priced entry product provides - this, of course, costs you more money. And then the cycle repeats, you spend hours figuring out how to mod your POS into something better and spend more money, and then you tinker some more, and.... well, you get the picture. The irony is that your spouse gets PO'd at you anyway for spending too much time in your shop instead of with her, as well as spending too much money. so, you might as well of spent more money in the beginning to buy a better man toy.

For me, however, as I suspect it is with many other hobbyists, it's the challenge of making something on your own that does what you want it to that provides the greatest satisfaction.

So, if you have RedCat Super or one of the knockoffs lying around and want a challenge, read on.

7/26/2012 Update: Over the past few months my design has evolved from the RedCat stock "version 1.0" to an aluminum frame version 2.0 to the current plastic bodiless version 3.0, "FrankenCat". The evolution is shown in thumbnail pictures below:

[supercooper]

Here are some of my mods (still a work in progress):
1) moved battery (6 cell NMH) to front axle, notched "batwings" to hold battery pack in place lateraly, stock velcro strap holds it vertically. Picture on the left has arrows pointing to the notches.

[supercooper]

2) trimmed radius of wheel foams by 1/4 inch and added 8 oz of BBs in each wheel for traction - this made a huge improvement ; cost: $7 USD for 2 lbs of BBs
3) replaced center chassis with HM aluminum, 2 inches wide at bottom (to limit center hangup), 4 1/4 inches wide at the top; cost: ~$15 USD for rod and flat stock from Home Depot.
Note that the bottom "standoff" made of 1/2 inch Al rod is actually a "rock roller" that rotates on the machine screw axles and prevents the chassis from getting stuck high centered on rocks, logs, etc.

[supercooper]

4) reversed top links so center pivot is on axle using HM aluminum bracket due to narrower bottom link mounts (will probably replace these with a real 4 link setup in the future)

[supercooper]

5) added skid plates from 1/8 inch Delrin over bottoms of transmissions and motors (my motors were getting scratched up on the rocks). I used countersunk 1/4 inch small sheet metal screws to attach the skid plates to the plastic rails under the transmission and extended the plates to protect the motors; cost $0, as I had Delrin on hand left over from a previous project
6) replaced motors with Integy 75T and replaced 10 tooth pinions with 8 tooth ones from RedCat (combined these increase torque by about 50%) - BTW, it took 24 hours of continuous running at ~ 1.8V with no load from a benchtop power supply to break in the brushes on the Integy motors, but well worth the improvement in control and increase in torque over square ended stock brushes; cost: $32 USD shipped

[supercooper]

7) replaced radio and receiver with Sanwa (aka Airtronics) MT4 and added second RedCat ESC for electronic Dig/Burn (this radio lets you proportion power between front and rear motors under your control); cost: $220 USD for MT4 plus $42 for second ESC

[supercooper]

9) replaced the funky 1/10th scale body with a true 1/8 MaxStone 8 body; cost: $24 USD shipped

[supercooper]

10) did a little suspension tuning by moving the rear links on the axle up from the original low mounting points to the upper ones vacated by the original upper link ends (the red arrow in the left pic shows the move). This brought the uncompressed wheelbase down by about 1 inch or so to 16 1/4 inches, but more importantly, reduced the change in wheelbase when the suspension is compressed from 2 inches to 3/4 inch, so the crawler is now comp legal
Articulation is still quite good at about 10 inches

[supercooper]

11) Well, as I was programming my shiny new MT4 radio for 4WS and dig/burn modes, everything was going well on the bench. I had the crawler blocked up so all 4 wheels were spinning in air to adjust the throttle trim. On a second adjustment, I flipped both switches for the ESCs on in rapid succession and heard a pop from the front ESC. the voltage transient from turning on the second ESC zapped the first and it went up in smoke, literally. To make matters worse, it shorted the battery and I had to unplug it quickly to avoid a fire and a fired battery pack. (Andre N, I think I jinxed myself when I replied to your post about the same problem and said I hadn't had any issues with mine - well it's in the dustbin now, too)

Solution: I ordered a Novak M2 Dig dual brushed ESC for a mere $125 USD shipped - boy, the spouse is really PO'ed at me now

Next steps: install new ESC when it arrives (hopefully by the next weekend), program the MT4 and hit the rocks!

[jjj649]

That thing is pretty cool with your mods. I have one too. I love mine. One thing you might wat to try is have dual batteries. You'll have a lot longer run time and a lot more power.

[supercooper]

12) I decided that the BBs added too much dynamic mass to the tires, so I removed them and made new dual density tire foams using furniture foam from WalMart. The foam is 1" thick, so two layers would be a little too much, so I made the inner rings a little smaller in diameter so they are stretched about a 1/4" in radius to go onto the wheel hubs. This compresses the foam and allows the outer layer to be softer. the denser foam is on the right side of the picture. Seems to be about the right softness and the sidewalls are well supported (I made the foams 1/4" wider than the tires). The second picture shows the notching I did on the tires to create more edges for better grip and make them more flexible. 144 cuts per tire x 4 tires = sore fingers .

13) Well, the BEC on the Novak M2 puts out 6 VDC at up to 5 amps, compared to 4.8VDC at about 1 amp for the RedCat BEC, so guess what happened?
You guessed it, the plastic servo arm stripped its teeth right away. Went to my LHS and bought two Futaba-compatible (25T) aluminum arms and problem solved. FYI, I used Dynamite P/N DYN2530. The part fits fine but the throw is just a tad short. Unfortunately, there is not enough clearance between the servo arm and the transmission case to put a longer arm on with the stock "batwing" mounting. Which leads to the next stage...

14) Improving the steering angle and getting rid of the batwings while I'm at it. This will be more ambitious.

[supercooper]

14a) Before tackling the steering mods, I decided to add knuckle weights to the front axles. I used some 2" wide by 1/8" thick aluminum stock from Home Depot for support arms and drilled out a 7/8" diameter hole for a loose fit over the knuckle shaft housings. I made three 1/2" long spacers out of 3/8 AU rod for a total width of 3/4" which is the most you can fit onto the knuckle housings. The top two spacers are actually 0.7" long and are countersunk into the support arms by 0.1" each (these will be used to clamp the arms onto the axle housing later so the clamping force needs to be transmitted directly to the arms from the spacers). I used small sheet metal screws to hold these two spacers in place.

I then made cross pieces out of more 2" AU stock and cut the bottoms of both the cross pieces and the vertical arms on my band saw with 1-9/16 radius (the wheel hub inside diameter is 3-1/4", so this gave me 1/16" clearance). I made another spacer out of 3/4" copper plumbing pipe that fills up the axle holes. Bolted all this together and then used AU flashing to make a "cup" out of the wings to mould lead for the weight.

The pictures below show the mould before and after filling with 10 oz of lead (I used lead sinkers). The lead moulds around the vertical arms and the lower spacer so the combination locks the lead in place securely.

[supercooper]

After moulding the lead weight, I dissembled the cross pieces, cut a vertical slot into the support arms from the top to the axle hole and cross-drilled the top two spacers for a clamp bolt (use at least a 4mm or #8 bolts for this - don't ask me how I know smaller doesn't work ). I pre-squeezed the support arms together in a large vise until them were a snug fit on the axle housings. Final fit was done by adding one or two wraps of AU flashing around the axle housing. Then aligned them up and tightened the clamp bolts. Each weight weighs 12 oz which is about right for the new LiPo batteries which are 8 oz lighter than my old NiMH ones, giving me a total weight gain of 16 oz on the front wheels. I used to run 8 oz of BBs in each front wheel with the heavier battery, so this is about right.

[ekd]

Nicely done, and well documented.

[supercooper]

Thanks! More to come, as I've figured out how to eliminate the "bat wings" and relocate the steering servos and lower suspension arm pivots.

[supercooper]

15) BatWing removal: The reason was that with the axles clocked more the BatWing sticks out to the point where it is almost even with the tires, causing the truck to stall when approaching concave objects (like, err - rocks). So, the BatWings had to go. This required quite a bit of disassembly and retrofit. While I was at it, I decided to move the lower suspension link mounts higher and centered on the axles. I also kept the lower portion of the BatWings, as shown in the center of the picture below, so I could still mount my skid plates to protect the transmission and motor from rock scrapes. This also gives me the option to keep the lower suspension mounts in case the new axle mount method doesn't work out

[supercooper]

Here are pics of the new lower link mounts made from 1/16" AU angle bolted with 3mm bolts into the top halves of the axle tubes. I carefully bent the angle brackets to match the angle of the knuckle pivots and drilled and tapped the knuckles to provide more support to resist twisting of the brackets. I purchased new 3mm ball ends from Red Cat Racing because I couldn't find 3.5mm nylock nuts anywhere. The ball ends were reversed on the axle end of the links so they can be mounted on the inside of the new brackets.

[supercooper]

For the servos, I made new mounts from 1/8" thick 1-1/2" AU angle stock that through bolts to the transmission housings using two existing holes drilled out for 3mm bolts that are tapped into the new mounts. I made semicircular cut outs for the transmission hump and the motor. This piece is shown on the left in the first picture below. It also serves to support a vertical piece of flat stock that is the new upper link mount with three holes in it for some roll height adjustment. The cross piece shown on the right in the first pic bolts to the transmission bracket and supports two standoffs for the servo to mount below it as shown in the second picture below.

[supercooper]

Here's a shot of the front end with a wider top bracket to hold the battery as well as the servo. I used 2" AU flat stock for the top bracket because the batteries are about 1-3/4" wide and I wanted to keep the safety strap (even though the hook and loop fasteners are plenty strong enough). The astute observer will also notice that I extended the servo arms with a piece of 1/16" angle. The reason is that the Turnigy 1501 metal gear servos only have a rotational range of 120 degrees, as compared to the original equipment Lansu's 170 degree range. To compensate, I had to make the arms 50% longer to get full steering motion. This reduces the effective torque some, but I calculated the end result as follows: 238 oz-in / 1.5 = 159 oz-in, or about 60% more torque than the original servos.

Version 2.0 is complete!

[supercooper]

Post-mortem on Version 2.0: After taking this version (hint of more to come) on vacation in NC and doing some serious crawling, I found I was dissatisfied in the following areas:
1) with the really wide MOAB tires a single Turnigy 1501 servo doesn't provide enough torque, especially when weight shifts onto the rear wheels when climbing up a steep incline.
2) the heavy MaxStone body combined with the AU chassis has too high of a center of gravity making it tend to do endos (in fact I cracked the body when it endo'ed at the bottom of a descent)
3) the wheel base is a little too short at 16-1/2 inches