Introduction
The Hot Bodies TC-FD is the sucessor to the previous TC-D chassis. The TC-D was vastly popular adapting the mid-ship motor positioning for a RC Drift Spec chassis. The TC-FD was released in middle of 2011 and has since been idle in the RC Dori scene. As we were big fans of the original HB TC-D, we felt this was a good chance to finally get one. After several months with this chassis, we felt it was lacking in aftermarket support. Hot Bodies recently announced a CS kit for this chassis, but that aside, nothing else is available for this. Feeling that it lacked modern capability of the current CS generation, we decided it was a good candidate for a Drift Mission custom modification.
The Modifications
This chassis lacked steering angle for countersteer, especially with high CS modifications ratio. This would require changing the steering geometry of the chassis. The stock steering angle is approximately 35 degrees, which is ok for low 50/50 and counter-steer ratio under 1.5. But we were aiming for a higher CS ratio, so more would be required. Stock geometry does include Ackerman angle, so the steering modification will also address the issue.
We also felt the stock suspension arm setup was weak, and may not be capable of high angle. The limits lie in the bulky suspension arm, C-hub and steering knuckle. Even if we gain more steering angle, it will eventually ran into a limit of about 40 degrees. We decided the best mod for this would be changing the entire front quarters (steering hub, C-hub, lower suspension arm). We have always felt the Street Jam OTA-R31 suspension is a good system and more than capable to handle high steering angles. Replacing the front quarters would require the following parts.
- R2Hobbies TEH-R31 front suspension arms
- Eagle Racing R31 10 degrees caster hubs
- Eagle Racing R31 steering knuckles
- Eagle Racing R31 universal driveshafts (51mm)
For the counter-steer modification, we will be aiming for a 2.0 CS ratio. This will be accomplished using the following components:
- 39T front pulley with front ball diff
- 14T D-like center front pulley
- 23T R2 hobbies center rear pulley
- 32T rear pulley from a sprint 2
Front Suspension System Modification
Luckily the inner hinge pins of the HB TC-FD fit with the R31 suspension arms. The outer hinge pin from the TC-FD will not fit, so we used the R31 outer hinge pins to fasten the C-hub to the lower suspension arm. You will also need a set of ball connectors for the top of the C-hub. The R31 knuckle requires the use of a 10x15x4mm ball bearing for the inner bearing. The stock TCFD 5x10x4mm outer bearings will fit the R31 steering knuckle. The Eagle 51mm universals is a good fit into the stock ball diff as well. The 48.5mm universals are just long enough to reach the clamping ring of the ball diff (the aluminium ring that attaches to the end of ball diff). Not sure which one is best for a Front One-way diff because we dont have one for this chassis. With the R31 suspension system, the TC-FD is now capable of more than 55 degrees of steering without the universal driveshafts binding. Now that the front quarters are more capable, it is time to move onto the steering mods.
Steering Modification
The steering modification has undergone 2 different revisions now and it is still not satisfactory. Initially we changed the mounting position of the steering knuckle by adding small pieces of carbon to the stock steering bridge. Attaching horn shaped extentions to the steering bridge does yield slightly more angle, approximately 40 degrees. This quite a good result, but we really wanted to achieve as much as possible. Here is some pictures of version 1 of the steering mod.
Version 2 of the steering mount would be similar to the Active Hobby carbon support mount for the TA05/06. The idea is to place the steering ball connectors right behind the king pin, this will not only yield more steering angle, but also reduce Ackerman angle. Since we chose to use the Eagle aluminium version of the steering knuckle, we had no choice but to create a new carbon extender to solve the problem. If we had used the plastic knuckle, a hole could be drilled directly behind the king pin and the problem would be solved. This method is one of the easiest and most effective ways to increase steering angle. After some cutting and drilling, here is version 2 of the steering mod. It works for the time being, but has some problems.
Version 2 will be the temporary solution until we can find a better way to do it. We will draw the entire assembly into CAD to find a better permanent solution. We feel that the entire steering assembly is weak and needs to be drastically changed. The current mod is not the prettiest, but it works for the time being, until we can figure out a new solution.
Countersteer Modification
The 32T sprint 2 pulley requires some slight modifications to fit into the TC-FD rear spool. The 23T R2 hobbies pulley is quite useful for anyone doing CS mods, but the material is lower quality than a conventional alloy pulley. The following components would yield a 2.0CS ratio, 100% overdrive should make the TC-FD more fun. Both front and rear belts have been replaced to accomodate the new gears. The front belt is a 213mm and the rear is 489 belt, with the stock tensioners everything fits perfectly. Now the TCFD is more capable at 2.0 CS ratio. HPI/HB will be releasing a CS kit for this chassis in 2012, which will include 16T and 20T center pulleys, 32T rear pulley with a both front and rear belts. The official HPI/HB kit will yield a maximum CS ratio of 1.52. If you are patient enough to wait for it…
Conclusion
This is all the modifications that we have performed on this chassis so far. Now the Hot Bodies TC-FD is more capable than the original stock version. The only big problem that remains in the steering assembly. The CAD drawings should yield a better solution, but will likely be fully custom machined parts. This project has been really fun and quite successful. Look forward to future mods for this TC-FD, we believe that there are a few more things that we can improve on this chassis.
