Pinions And Spurs

It has been a while since I have written but have been busy with work and other projects including setting up HD for video production and setting up and building the Tamiya F104 pro (stay tuned).

I have to say the HPI Sprint 2 RTR is an amazing RTR package, the car is well built and handles well on the track. For a RTR it is hard to find kits that are so competitively priced and can run as well as this chassis, I have really enjoyed doing the brushless conversion and testing the car.

The mamba max system was chosen and used the 5700kv motor for now, the only thing other than the brushless system I used is a Robinson Racing 48p 22t pinion, everything else is bone stock on the car and it runs very well.

I am using Trakpower 2s lipo so had to make some small modifications on the battery tray, such as adding double sided tape to the bottom of the tray without taking the other sticker off. This is to ensure that the thinnner lighter lipo battery stays on the battery tray along with using dremel on the top of the battery mount so I can pass the two positive and negative power cables through.

This is a short video of the recent run I did on this car, I have to admit this is one Tamiya chassis that I am least impressed with.

It is definitly more adjustable from the TT01E but if you are thinking about upgrading I would say just go for the Ta05 or better. The car does not seem to handle brushless systems too well, the fastest motor you can use in my experience is the super stock from Tamiya anything more you will start to rip the car apart or just keep burning through spur gears.

Took the Ta05 speed passion 2.5R combo for a run as well, nothing changed on the car setup except for rear wing addition and FPV video gear. The car ran very well, as expected the added weight of the FPV gear made the car a little unstable at high speeds nearing 50mph. 

I have radar tested this setup for 50mph in windy conditions along with rear wing, I would say it was pretty near that target given that it was not windy that day. 

The video is more fuzzy on this car, I beleive this is mainly due to the car being setup lighter than the TC5R and so on corners and little bumps the car shakes more and thus causes more video disturbance..

I will hopefully be working on some kind of universal chassis of some kind that can hold the FPV gear better and definitly upgrading to 5.8ghz system when I can.

So finally got around to test out the new motor/gear/25c lipo setup on the TC5r. It was an extremely hot day, average ambient temperature was about 90-96. The car performed well, but ended up blowing the left rear tire and crashing as a result

The Mamba Max 5700 combo 87/22 gearing with Trakpower 3s 4900 25c combo is very very good, I enjoyed running the car. However the FPV equipment it self is pretty heavy along with the 3s lipo made the car somewhat unstable at high speeds, I estimate the car was topping out at around 60mph I did not get a chance to use the radar gun to make sure but given the setup and my calculations it should be doing at least that much.

I intend to get an OSD setup soon and perhaps in time upgrade to a 5.8ghz video system so I get better reception, the whole project has been challening because there are a lot of moving parts. The video gear and the car the electrics all need to be setup well and mounted on the car so they dont make the vehicle unstable.

I think I’ll be doing this in phases, next one will definitly be the OSD so we can start seeing some data like motor temperature, RPM and of course GPS based speed.

My digital camera seems to have come back from the dead some how, so thought I would write a post on what I have been up to. 

I am currently working on selecting the best motor/esc/lipo setup for fastest 3s lipo race able car, so far I have tried the good old Novak 3.5R, the Mamba 7700kv and Traxxas 3500kv motor. 

All three motors were run on the TC5R  chassis using the VXL3S speed control, they all survived the 11.1v of power mostly because they probably were never able to exceed their rpm limits and perhaps with a lot of luck as well.

The problem is that the lower turn motors like the speed passion 2.5R run very very fast on 2s but seem to max out at or around 60mph. That is plenty fast for racing, but I just have the itch to see if we can go faster, maybe around 70-80 clean on top speed and still be reasonably racable.

The TC5R with the above motors sits pretty heavy and I have had to use harder roll-bars so it does not hit the ground everytime I make a fast corner. The over all stability seems better due  to added weight but I still need a solid motor/gear combo that can give me over 60mph and be able to go around a large track without too many issues.

My plan was to order the Mamba Max 5700 system which I have installed and done some inital testing, everything looks good just hope the weather is clear this weekend so I can do some good test. Also this time around I plan to be in FPV mode, essentially a wireless camera mounted on the car so I can get a feel of the car and power as if I was actually sitting in it.

Since my Novak GTB 3.5 has blown up most likely due to gearing issues, I decided to upgrade the TA05 and TC5R to break my current 53mph record with Novak GTB and TC5R combination setup. So the first test was to run the TA05,  it was a very windy day and I was also experimenting with HPI X-pattern wheel/tires on both cars so was not able to get my target 60mph top speed. 

According to my calculations tha TA05 should have hit approximately 60mph, however clocked a clean 50mph (previous top speed 43mph) run using a Speed Passion 2.5R motor. This is a fantastic motor, not only does it have plenty of torque (using Trakpower 2S 5400mah 16c lipo) but an outstanding 13800 rpm/volt and it sounds awsome.  I think if it was not as windy and I was not using the rear wing, I reckon I should have hit close to 60 but that will have to wait since I am waiting to receive a Trakpower 2s 4900 25C lipo pack.

The 4900mah 25C rating should give me 4.9 x 25 = 122.5 amps, currently with the 5400mah 16c I am getting 5.4 x 16 = 86.4 amps. The Mamba Max ESC is rated 100amps max so with the 4900 25c pack I should definitly get more torque and hopefully my target 60mph top speed.

In all I am very happy with the overall performance, the motor is very light and the TA05 with everything weighs only 1472grams. I think once I get the 25c rated lipo, I will do another speed run to try for 60mph again, hopefully it’s not too windy again.

The TC5R I decided to turn to a traxxas VXL 3S system that I had bought a while back, but never really used it much. The reason behind using this system was essentially research on the internet and realizing that I will need much more torque i.e. battery power to hit traget speeds of 70-80mph. And boy does this thing have some serious power, the motor is 3500kv and I am running 48p 75/35, since this is a low kv motor I am able to use trakpower 3s 5400 16c lipo.The car is definitly heavier but that is increasing general stability and straight running, the torque on this thing is so nice the car continous to wheel spin even when reaching higher speeds. The problem however during this run is that I was unable to do enough runs to actually clock the speed by my bushnell radar gun. 

In only a two test runs I lost traction big time and the car flew about 4-5 feet in the air after hitting the grass. Fortunately there was no major damage, I lost the right rear suspension holder and the spur gear (kimborough spur) seems to have disintegrated, not sure if this was caused due to heat or simply got crushed due to too much power.

Please note that this post is not about an experiment, this is simply a warning about the dangers of this hobby. I recently rebuilt a new scale Ferrari Enzo body for my Team Associated TC5R, including things like scale air ducts to reduce wind resistance and increase motor cooling. ( Testing to get ready for the next speed run test)

The car had been sitting on the shelf for the past couple of weeks, and within minutes of running it in a very cool environment the car started to cogg heavily. I started this video with the intention of shooting high speed cornering of the TC5, at first I noticed the car does not brake as well getting out of the corner.

Moments later it starts to cogg significantly and then stops and goes into flames, so far nothing special had been done to the Novak brushless system except for a recent changed motor. The last motor had locked up after a speed run that I did a couple of months back, and now a completlely blown ESC.

The following are some links I found of people who experienced similar issues with this brushless system:

1. http://www.rctech.net/forum/rookie-zone/271957-novak-gtb-ss-smoking.html
2. http://www.rctech.net/forum/radio-electronics/202571-want-instantly-fry-your-novak-gtb-spread-spectrum.html
3. http://www.rcuniverse.com/forum/m_7831236/printable.htm
4. http://www.rcracechat.com/vb/showthread.php?t=39466
5. http://www.forums.radiocontrolzone.com/archive/index.php/t-243720.html

At this point I am unable to clearly figure out what caused the fire. However I intend to document here some important safety matters to keep in mind, the following however are some key observations I found in my setup along with research on other blogs and rc groups

1. Never leave the GTB connected to the battery in off position for too long ( I did this right before the run)
2. The capacitor if gone bad can cause the GTB to cogg significantly and may lead to a smoke/fire if not replaced ( my car was cogging a bit but I thought it was no big deal)
3. Be very carefuly with gearing as over gearing can over heat the motor and speed control
4. If you are using a Lipo make sure it is not over discharged, enable the cutoff on the GTB or get a lipo gaurd

So far the above are the only items I have uncovered, I have also contacted Novak to see what they have to say in this matter, my system has been running fine before this for couple of months and is not within the 120 day warranty. I plan to keep this post updated with my latest findings.

So finally got around to doing some speed runs!!! unfortunately the weather was still pretty bad. But it’s not all bad news, I got to test the car in the wet. I have to say the TA05 and Mamba Max combination is very good for the price.

The car handled really well and I was able to  squeeze in about 43mph on one of the runs. (I am using a radar gun). The small puddles of water were slowing me down a bit but over all it was a lot fun to run the car.

This is the same Ta05 that I have in part I and II, Ta05 with Mamba Max 7700kv, robinson racing 48p 75t spur and 22t pinion. I estimated the top speed to be 46.5mph so getting 43mph was not bad at all.

How to actually increase the top speed of my car has certainly been one of the most confusing aspects for me, will gearing make a difference? should I go with a brushless system? how do I know what the top speed of my car and is it possible to estimate top speeds given a certain setup.

Well I found the following were some key components to think about when attempting to increase the top speed of your vehicle

1. Aerodynamics – is the shape of your vehicle smooth enough to minimize air resistance?
2. Traction – depending on a 4wd  or 2wd setup and ample power, does the vehicle have a good ability to reduce or eliminate wheel spin
3. Ride height – generally the lower the car is the less air resistance it faces, so the vehicle should move faster
4. Power system – you can experiment with both brushed or brushless motor systems, but I would recommend a quality brushless system because not only it will last longer but will provide more power to your vehicle
5. Battery – definitely a key component the higher the quality the better the result
6. Gearing – a spur typically increases torque, a pinion will increase speed. So if you want to increase the speed of your stock car increase the number of tooth in your pinion by a few and drop a few teeth on the spur

I have created a simple spreadsheet with some of the cars I have along with brushless systems and gearing options, you can play around with the values to estimate top speed, torque and the effects of different combination of battery voltage and gears.

The TA05 has finally been rebuilt, using new precision differentials and black aramid drive belts so that it can better handle a brushless system. I am currently using the Mamba Max 7700 system. The car is geared with 48 pitch 75 tooth AE spur and 24 tooth Robinson Racing pinion. This gearing should produce anywhere between 45-50 mph depending on weather conditions and battery power. I am using the Trakpower 5400 mah 7.4v 2S lithium polymer battery, very reliable and high performance battery pack.

I think the Ta05 kit is a high quality and definitely high performance chassis, however only some key upgrades that I felt truly increased the performance of the car. There are a lot of hop-up available from Tamiya and other companies and I am sure they are all great, however while considering a reasonable budget I felt the following made a difference:

1. Aramid Drive belts (low heat producing, definitely a must if you will be going brushless)
2. Tamiya Precision differentials
3. Quality spur and pinion ( I prefer 48 pitch, to minimize damage from debris/stones)
4. Soft tires such as the JACO PRISM rubber (green)
5. TRF suspension kit from Tamiya, along with 30lbs purple springs from Team Associated
6. A good quality brushless system such as the Mamba Max 7700
7. High quality batteries, I chose the Trakpower 5400 mah 7.4v 2s lithium pack

The above are some of the basic things that can be done to a TA05 to get it moving faster and also be able to handle the extra power around corners and straight running. There is still plenty you can do, but I think above is the barebone to go brushless while ensuring that the mechanics of the car can respond to and be able to maintain the higher power.