TIC Racing Terminator GT12 - Build and Review
Background The GT12 class is a fairly recent addition to the 12th scale section of the BRCA and has been running as a support cla...
https://www.thercracer.com/2014/03/tic-racing-terminator-gt12-build-and.html
Background
The class has a number of restrictions in place to cap costs. The rolling chassis kit must be available at a RRP of under £100 including tyres, but does not have to include a bodyshell. The chassis must extend the full length of the car, which prevents LMP12 style pods and chassis being used so as to limit performance. No camber change is allowed during front suspension compression, so LMP style dynamic strut front ends cannot be used. No oil filled dampers are allowed on the car; only tube type or friction types, again to reduce costs.
The class's roots hail from the 12th oval scene with the original Mardave GT12 car being a circuit version of their oval car. The Schumacher Supastox was a new design from the ground up as Schumacher's recent history has been in touring cars and off road classes. TIC Racing have won multiple oval championships and the Terminator GT12 is a development of TIC Racing's oval car.
The Car
The car is of a simple design with a one piece fibreglass chassis, sliding pillar front suspension with an upper brace for the kingpins, a rear pod of similar design to the Mardave AC12 with a centre pivot and a pair of springs at the rear to give suspension in roll and vertically, and a centre chassis brace that doubles up as a cell holder.The car is supplied with a solid rear axle, the same as it's competitors, which makes it eligible for the GT12 Production Cup class. A differential can be fitted, but then the car would have to run in the BRCA Super Cup class There is nothing radical about the design and it is extremely simple to assemble following the instructions. The build took a whole 40 minutes, minus the electrics.
The chassis is of 1.6mm fibreglass. This was chosen as it allows a degree of chassis flex to help absorb any bumps. Ideal at club level where the tracks aren't always smooth, as it reduces any skittishness in the car making it easy to drive. However, due to the material thickness, the chassis is not countersunk, so the chassis ride height has to be a little higher to give the screw heads the minimum 3mm ground clearance required within the rules. The front brace, which isn't shown in the photos, helps reduce any play in the kingpins and provides support in the case of a crash. This is carried over from the oval car.
The rules for the class specify 13.5 brushless motors with a speedo using non-timing or 'blinky' mode. This is the same equipment as used in the LMP12 13.5 class allowing cross sharing of electrics if someone wanted to change classes. Cells are the same 1S 3.7v LiPo.
The kit is supplied with one of the most popular GT12 shells, the Kamtec Ascari shell. Mine did not come with tyres, but wheels were included. As the RRP is more than £10 below the maximum limit, there is ample scope for the tyres of your choice to be purchased and still stay below the price limit. And don't forget, the shell is included unlike rival kits.
As built from the box, the car has already proven competitive in the Production Cup class in an RC magazine report, so I won't repeat that here. I was looking to run the car in the Super Cup class, so I carried out a number of minor, cost effective modifications to make the most of the car.
Modifications
I intended to run the car to Super Cup rules, as this is the most popular class at my local clubs. To this end I purchased a Mardave differential and ride height adjustable pod. The kit pod allows you to adjust ride height by adjusting the tension on the rear springs. I preferred the Mardave pod as it allows you to leave the suspension settings alone once you have them right, and adjust the height of the axle using offset axle bearing holders as on an LMP car.
The Mardave differential is reportedly not as smooth as the Schumacher option, both of which will fit. However, the Mardave diff is significantly cheaper, and as I was trying to improve the car for the minimum outlay, I went for this option. I made a couple of changes to the diff to improve its performance using parts lying around in my pitbox. The first change was to fit a Kimbrough 69 tooth spur gear. The reason for this was not to improve performance of the diff, but to allow me to achieve the correct gearing using the pinions I already had to hand in my pitbox. I did however use 12 1/8" diff balls which allows the diff to be run with less tension due to the greater contact area. I also superglued the diff rings in place to prevent them slipping, after sanding the surfaces flat on both sides. Once bedded in, the diff wasn't that far off my LMP diff! When I fitted the wheel on the diff side, this changed though. As the wheel retaining nut tightens on to the wheel, it in turn partially locked the diff. I've heard people run the nut loose to counter this, but any side load on the wheel would cause it to rub and bind on the nut. The solution is shown below and was very simple. I opened out the hole on the outside of the wheel using an 8mm drill bit, turned by hand, just deep enough to fit a 5x8mm bearing. This was a spare Tamiya bearing. I also ran a 5.5mm drill bit all the way through the wheel so that it did not rub on the axle. I was now able to secure the wheel fully without affecting the diff performance. I repeated this on the other rear wheel so I can easily swap wheels from side to side to allow for even wear.
My next changes were to the rear pod. The pod is kept central by sliding up and down on a guide pin located at the rear of the pod between the springs. As the pod moves up and down in an arc, it was binding slightly on the guide pin. It would be tight at the bottom as the rear of the hole rubbed on the pin, then go loose until the front of the hole rubbed as the pod was level. Then loose again until it went tight at the top. The solution was to file a small flat on the front and rear of the guide pin as shown.
I also found the pivot ball for the pod a tight fit. This is fine for oval racing where the cars only turn in one direction and take a 'set' in the suspension. For circuit though, this should ideally be looser to allow the pod to move freely in all directions and allow the car to level up out of a turn and be ready for the next change of direction. A number of people have modified their Mardave pod plates to accept the MI5 pivot ball assembly from Schumacher. Having seen this though, there is too much play, which allows for axle tramp in acceleration - basically the back axle hops. A quick raid of the spares box provided me with a spare pivot ball assembly off my Speedmerchant LMP12. This is a 2 hole version of the 4 hole pivot balls found on 12th scale t-bar cars. A 4 hole can easily be cut down to suit. To fit, I just opened out the moulding on the pod plate using a body reamer until the pivot ball housing would fit, then made 2 holes for the screws. The plastic is soft enough to run a drill bit through by hand. I could then adjust the tension on the screws to allow the pivot ball to move freely with no play.
My final change to the rear was to fit a spare damper tube to allow for damping in roll. One end attaches to the pod and the other to the battery brace, picking up on existing holes. The first tube I used was off a V-Dezign 12th car. This did not give enough damping though as it was one half of a twin damper setup. I then remembered my spare Tamiya damper tube off my RM01X, which was designed to operate on its own. I fitted this with 2000wt diff oil and achieved the desired result. I did have to fit longer ball cups to it to allow it to fit. Sadly, I do not have a picture of it as I am now trying something different again!
The front of the car comes equipped with in-line axles and non-ballraced wheels. This is fine for Production Cup where the lack of a diff requires the extra bite of inline steering. Having fitted a diff though, the car would be too twitchy with inline axles, so I wanted to change to a trailing axle. I chose to fit a pair of spare Xenon steering blocks off my RM01X with a 1 degree camber insert. This allowed me to fit a pair of Mardave axles to take ballraced wheels, and also put some camber in to the front wheels. The kit front end does not allow for static camber change, so the steering blocks put some in and also would tame the front end down in high grip conditions by not putting the outside wheel flat to the carpet when turning. I fitted the insert the opposite way round to on my LMP12 to give negative camber.
However, the standard kingpins are 3mm diameter and the Xenon steering blocks are 1/8". If I didn't want to add the negative camber, I could have used the standard kingpins and fitted a pair of Yokomo LMP steering blocks with Mardave axles, as Yokomo use a 3mm hole. Instead, I spent a bit of money on a pair of Associated TC3 shock shafts and cut them down as shown using a Dremel to achieve the desired result.
I know had a very smooth running front end. I also replaced the springs with a pair of 0.45mm LMP springs from my pit box. The top brace had to be removed however, as the trailing axles moved the wheels rearward slightly, causing them to rub on the brace. I plan to make a new brace when I find time and the drawing will be fed back to TIC Racing. I decided to put a small amount of castor in the front end too by using a washer under the forward mounting hole for the front arms, which would tip the arm back slightly.
Running the Car
The car was now ready to run so I took it to my local track at Crewe. I set the ride height to 5mm all round to allow for the screw heads. With the car fully laden I also set the gap between the rear of the pod plate and the chassis at 2mm. Front tyres were Jap46 and rears were medium pinks. Having never driven this class before, I trundled down the straight to trim the steering, then just opened it up and drove it. It was so easy to drive! It is probably the easiest car I have driven in 30 years of driving. The steering was easily balanced on the throttle and the car went exactly where you pointed it. Running in a 10 car heat with a 'bit' more contact than I'm used too hampered me a little though. Also, the car was so easy to drive that it did not have the extra edge to get round the twisty bits quickly enough. It was thoroughly enjoyable though.
Next time out was at Derby club, where the track is more open and the heats are less crowded. Three runs resulted in a best to average on the night of under 0.3 seconds. The only mistake in 3 runs was from catching a piece of lifting tape causing a half spin. This again proved how easy the car was to drive. As this is lined up for my daughter's first car, it's ideal. I still wanted a little bit more of an edge to it though.
Final Mod
A quick raid of the spares box again, and a trip to the garage to cut a piece of fibreglass, resulted in the above change in place of the tube damper. It is a friction plate damper off my Tamiya F1, similar in design to the older 12th scale t-bar car damper set up. I've kept to the rules by not adding any holes in the chassis. The hole used is the redundant hole from the pivot ball security clip I never used, as I changed the pivot ball. I copied this hole into the battery brace to allow the post setup to be fitted. And you can see the result. The car is now damped not only in roll, but in bounce. Damping can be adjusted by putting different weight diff lube on the plates, or by adjusting the tension on the springs.
I have only run this set up once so far, on the same track at Derby, where I found a 9 second improvement from my previous visit. The car could turn much tighter and understeered less on power, giving it the edge I was looking for. I did overdo it in the final run though by clamping the plates too much, and ended up cocking the inside rear wheel on most corners! Just a little fine tuning required though.
Watch this space for any future improvements.
