About this Blog

This is about the combination of two interests, Radio Control vehicles and Science Fiction models. Its also about vehicle design. The models have to satisfy two main precepts.

1. The vehicles have to work, ie be driveable, but not nescessarily win any races or rock crawling competitions.

2. The main thing is that they have to look cool.

Tuesday, 6 February 2018

Reverse Trike Part 1

I have at least 11, if not more, unfinished projects piling up in my shed. A few of them are so very close to being completed. The sensible thing to do would be to finish the nearly done ones off. What a good idea, I'll make it a new years resolution to not start anything new until I have finished at least two of the existing projects...

I started a new project...

I have been playing a little hill climbing style game on my phone called Prime Peaks. One of the vehicles I took a liking to in the game is called the Pealing Pea, it's a little reverse trike. I thought it might be fun to try and make an RC version some day and then I remembered I have a Traxxas Jato chassis with an almost complete set of front end parts lying around in a box, which may be able to be modded to work. I also have a pair of Imex Jumbo maxx Claw Dawgs wheels and tyres, one of which would make a cool big single rear wheel, and I also have a spare 540 motor with gear box sitting around as well.

Here is the first incarnation of the concept I put a couple of those weirdly scaled wrestler figures in some Axial Wraith seats to see how they fit.



I went with a single arm rear suspension made from some rectangular section aluminium. I  hack-sawed and filed a couple of 60 degree v slots along the length and bent the dog leg shape shown. The joins were brazed together with aluminium brazing rod and a propane torch.
The rear shock is a Traxxas GTR shock from a Slayer or Revo or Summit with a Slayer grade spring.
The arm pivots on an 8mm aluminium pin using a couple of 8x16 flanged bearings in the arm itself.
The mount is a piece of aluminium channel with another ali plate brazed on for the shock tower. I drilled a range of holes for shock placement but those GTR shocks are pretty stiff so I found the bottom hole worked best to balance with the front shocks which are stock Jato shocks, the same size as the rear shock just made from plastic. That's one of the things I like about using Traxxas parts for my creations is that the parts interchange fairly easily between models.



The motor mounts in a radius cut at the end of the arm and is held on with a chopped up hose clamp arrangement. It looks a bit crude but it works. The motor/gearbox combo is rated at 500rpm at 12 volts. It is not particularly heavy duty and after a little test drive all the gearbox retaining screws were found to be loose, I've since locktighted them all. It has only got a plain bearing (not ball) and I am sure it is not designed to take such an axial load, not to mention the hammering it will get if thrashed over jumps an off road tracks. However its what Ive got and it was cheap, only around $15.00 on ebay from China. I am pretty keen on this concept of a motor per wheel, I wish I could find something more robust and flatter that would fit inside the wheel but I suspect that even if such a beast exists it would be way out of my budget.



I came to the conclusion that those pesky wrestler figures just looked too small and the two of them didn't leave enough room for all the electronics and a battery that have to be crammed in there somewhere. So I ditched them in favour of a Tamiya driver figure that I calculate to be 1/8th scale.



As part of the re-arrangement of the driver I decided to flip the side the rear arm was facing. The weight of the motor and gear box tend to roll the vehicle to the side they are on so I thought to counteract that by placing the battery on the opposite side to them. The Jato chassis is asymmetrical in that one side is wider than the other, it is a gas powered car and the widest side is supposed to house the tuned pipe muffler, this is where the battery fitted the best so the arm had to be flipped, all the holes for the hose clamp and shock attachment redone. It wasn't fun flipping the arm, it is quite fiddly to remove and re-insert the pivot pin cause there are a couple of thin spacers made from a thin slice of brass tube that have to line up with the bearings so the pin will go through...aargh. It was a frustrating exercise but worth it as the trike now sits level instead of leaning to the motor side.



The driver figure is held on to a couple of metal standoffs with a couple of M4 screws. Those standoffs are mounted on a PVC false floor I made to give a flat surface to mount everything to. The Jato chassis floor has a lot of lumps and obstructions that got in the way. The false floor is attached to the chassis with 8 M3 counter sunk screws that use a bunch of existing holes that were already in the chassis plus a few extras thrown in for good measure. The underside of the floor is built up from a couple of layers of 3mm and 6mm pvc sheet superglued together. It also blocks some large holes in the Jato blue anodised aluminium chassis. I tried to save some weight but it still ended fairly heavy for what it does,. Grey PVC sheet is a relatively heavy material, but strong and easy to work, it can be drilled tapped, sanded, sawed, heated and bent, takes paint well and superglues extremely well. It cannot however be laser cut as the gases given off will corrode the laser itself and are very toxic.


 

For testing I used a LRP Runner plus Reverse ESC which is for an old school brushed motor. The ESC, reciever and battery are held down by self adhesive velcro, the standard i use is hooks to chassis and Loops on electronic components.
I cut down the Jato radio tray which locates the steering servo and made a couple of M3 tapped aluminium posts to support the cut end.



Next was the body and I first cut up some cardboard shapes to see how it would all fit before committing to 2mm Foamed PVC sheet. I chose the Foamed PVC sheet as a bit of an experiment to try out the material where before I would have used styrene. The foamed PVC is a bit more flexible than styrene and considerably less brittle though not as surface impact resistant, the surface of the foamed pvc sheet dings easily.






As I mentioned I have done a test drive on 7.4 volts (2S) which is adequate but not particularly fast. It would be pretty quick on a 4S or 14.4 volt battery with a suitable ESC and the motor can take the voltage but I fear the gear box would not be mechanically able to take the extra load for very long. A 3S or 11.1 volts may be the sweet spot for this project but that is a bit further on down the track yet.




More soon...

2 comments:

  1. Amazing.
    Please start more projects.

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  2. Don't worry there are a few projects that are already started but not blogged as they are still experimental, basically awaiting parts to see if the idea will work.
    I am setting myself the task to try and finish some that are already close to completion this year.

    ReplyDelete