Thunders Grasshopper EVO Project

[ThunderDragonCy]

Wordy title, but you get the gist. Hornet Evo has definitely got a lot of love, and does speak to me as a person who has - on multiple occasions - grafted proper suspension onto tamiya swing axle buggies. 

However, I am not a huge fan of the execution of the rear of the Hornet Evo. I understand why they did it, but I don't like the rear motor look on those old buggies, and the wildly mismatched track widths is just poor effort IMO. 

I played around with a version earlier in the year just for a fun thing to think about on dark winter evenings, and it definitely caught my imagination. I wanted a Hornet Evo with mid motor, and matched track widths, but still able to use the original wheels. After many iterations, this is what I have:

 

 

 

The plan uses a Thundershot transmission for the midmotor setup. It has my design arms as the middle length dogbones required to get the width right. There is a couple of shock holes and the option for a rear sway bar.

I have done uprights (with toe in), and shock tower for CVA short shocks built with 41.5mm shafts at around 81mm Eye to eye length. Shock tower is custom design to reduce height, as there isn't room for the stock Thundershot tower under the body of the older buggies.

It uses an hsp dog bone of 55mm pin centres to give a width across the kit rear wheels of a little over 240mm, to match the Hornet Evo front end. I wanted to use a tamiya tc01/xm01 54mm prop shaft but these are very hard to get. Axles will be Hornet EVO to fit either original wheels (grey in pics) or GH2 wheels (black).

This is the first grasshopper/hornet chassis i have attempted this on do I don't know a lot of details yet. I think/hope grasshopper axle pod mounts can be modified to mount the bottom holes of the thundershot trans. I don't know how the top transmission mounts will mount yet. Hoping for something similar to my side plates I have on the Grasshopper 2 chassis on Ultra G, but I know the original Grasshopper chassis is quite different here to the GH2.

I got the parts 3D printed with some work stuff a couple of weeks ago

White part is a first try at a 380 adaptor for a Thundershot trans. May or May not get used. This won't be eligible for 380 club racing. 

Main reason this is slow burn is that funds are tight this year and i didn't know how or when i might get going. But, my Dad has put some money in the toy car fund for my upcoming birthday (can't imagine he expected to still be buying me toy cars for my 49th birthday!) so a Grasshopper will be coming along to start the measuring and fitting up. Yes, Grasshopper. Partly because I think the axle pod mount is what I need, partly because I always preferred it to the Hornet and I have never owned one. I plan to use the original wheels, just to see how it goes. Never used those old wheels, but hoping it's part of the fun. 

Front suspension is still open to consideration. I have done a few design ideas with variants of the Ultra buggies, but nothing hits the spot yet. I might yet just buy Hornet Evo parts trees, but there appear to be a few small flaws in that setup. Main point is to get rear sorted. Front should hopefully be less of a design project. We will see....

 

 

 

 

 

[Krustybus]

This sounds like another interesting project, look forward to seeing it develop 🙂

[jonboy1]

awesome stuff! following this with interest. I was playing around with ideas myself a while back but got completely stuck with the front end. Having seen your other builds I'm sure you will come up with a cracking idea  

[ThunderDragonCy]

6 hours ago, jonboy1 said:

awesome stuff! following this with interest. I was playing around with ideas myself a while back but got completely stuck with the front end. Having seen your other builds I'm sure you will come up with a cracking idea  

Thanks Jon. I would like to try something with the Evo front arms, but might involve doing other bits myself 

[officepizzaparty]

Looking forward to this, I love these major suspension conversions on old chassis

[ThunderDragonCy]

Baby steps. Got a small package from Sir Tony of Tamiya which included Hornet EVO rear axles (which as far as I can tell are unique to the Hornet EVO) and the shafts for the upright/arm pivot. 

The bearings are nice tight fit, and the GH2 wheel hub seems to fit well, so although i sold the grey GH2 Black Edition rear wheels as i didn'tneed them at the time, it looks like fitting the balloon tyres of some description is going to work.

Also shown are the HSP shafts. They are listed on those vendors on ebay by overall length, which is really unhelpful! These are listed as 61mm, and they are 56mm pin to pin centres which what I designed for. 

Things should pick up a bit now. It's my birthday tomorrow and there is a kit sized box from Time Tunnel Models sitting in the living room, which should contain a Grasshopper.

 

[Krustybus]

Happy Birthday for tomorrow Cy!

[Grumpy pants]

Happy birthday for tomorrow 🎉

[Andreas W]

Happy birthday, Cy. 

[ThunderDragonCy]

Well this can really get going now. My Dad obviously went shopping at Time Tunnel because the big box had this in it

And also this packed underneath

As an aside, the Grasshopper box art is just the coolest.

Pulled a few bits out of boxes to get a feel for what I am dealing with.

 

Fitted the axle mounts and cut the Saint Dragon rear trans off the A parts tree to see what it looks like. Way toonarrow to fit straight into the Grasshopper parts is the answer. However, some fairly cheap bobbin type parts could easily bridge the gap.

Trans is much more snug that on a GH2 tub, but i think there is something that can be figured out to anchor it all together.

[ThunderDragonCy]

Bit more loose assembly today. I printed the B8 rear arm mounts so I could sell on the B parts tree complete (I will end up parting out most of the Saint Dragon kit) so did a trial fit with rear arms

 

Couple of small things to address here. Firstly the arm catches on the outdrive bearing boss on the transmission case, so I will need to file that down a little. Secondly, something I missed in the model was that using the B8 "flipped" to add toe in, reduce wheelbase (to keep it  as Geasshopper looking as possible) and get a straight driveshaft (Thundershot is quite swept back), also makes it all move in an arc I  stead of straight up and down, so my solid inner camber link mount won't work because the pivot isn't in the same plane as the arm. Shame as it would lend stiffness (I printed a few od them ages ago for Ultra G to stiffen up the Thundershot blue arms), but I can replace with a more usual inner ball connector easily enough.

Next thing was to check the wheel

I had some old rally car foams so stuffed them in. They don't fill the tyre much, but it will help reduce bounciness a bit.

I have never built these wheels before, and I really enjoyed it. The three pieces, all the little screws and nuts. I feel like I have just moved through a Tamiya right of passage!

 

All fits nicely. No binding or catching. i meadured across the wheel to the centre (ish) and its going to end up a touch over 240mm wide, which is about right I think. 

I am a little short of 1150 bearings so I am waiting on those before I can put transmission internals in, button it up and start really figuring stuff out. I really don't want to start trying to mount it until I know where the motor sits.

[ThunderDragonCy]

Got my RC Bearings order and some ball connectors from Tony Tamiya, so time to button up the rear trans. As there aren't a lot of Thundershot chassis builds on here I think I'd do a few of the details:

Not completely sealed, but much smoother and more enclosed than earlier Hotshot diffs. 

The diff gets metal bevels as standard and buttons up with the kit supplied 2.6mm screws. Forgot you need so many of these for this build, so I am very glad I bought a cheap kit to get all the parts. 1150 bearings pushed into the trans halves.

Counter/spur gear. I put one of the kit plastic 1150 in this because it doesn't actually spin. I don't know if this gear was in another kit at some point, but it's always been a weird feature to my mind. 

850 bearings for the layshaft, and fitted together. It's effectively a 2 gear trans so it's tightly packed. This also shows the relatively narrow crown gear on the diff. If I could get someone to make a ball diff gear this thickness with 47t you could fit it to the DT03 ball diff parts and have a diff upgrade. 

I wanted to show this picture because when building these 2wd buggies with this trans, I have found it's better to put one of the prop shaft bevel gears on and a 1150 bearing on the end to support the layshaft. Makes the teeny tiny 850 bearings it otherwise runs on last much longer. Also needed another 4 of the 2.6mm screws from the kit to fit the bevel gear cover part too. 

Cheapest way I am aware of to get 4 x 48.5mm suspension shafts.

Trans all buttoned up. The inner camber link mounts are some ball nuts with M3 x 10 screws through the outer tab of the upper arm mount, where the screwpin would bite into on the regular kit built. Replaced my inner pivot part with a long adjuster and checked the driveshaft fit. All moves nice a free. Next thing will be fitting the right hand suspension, building rear shocks and fitting them to my custom shock tower, then putting a motor in it. Once all that is done I can offer it up the chassis tub and see how I can fit it to the car. 

As an aside I got a good look at my friends Hornet EVO last weekend, and I have to say I'm not massively impressed with the front end. The arms are nice, but it still has lots of bump steer and there were a couple of other details I didn't like, so I think I am going to go my own way with the front. I might yet use the arms, but they're not cheap at about £18 a set! I suspect something more along the lines of Ultra G will be the thing, maybe dying a pair of the Thundershot arms I have already in the Saint Dragon kit. It would be nice to do something a little different though. Open to suggestions if anyone can think of some nice front arms to have a go with. I am 99% sure I will need to chop the front shock mounts off and do something different anyway, so it won't be limited by that.

[ThunderDragonCy]

Bit of post-work CAD looking at the front end design. Thought I would do something a little different to the usual and modify an idea from AMPRO. This is his offset mount from arms so you can use a CVA mini shock on a Hornet/Grasshopper with standard narrow track

I have taken the idea and done my own arm that mounts in the kit pivot points. I think a 3mm hole through this and then put a 3mm steel rod in it should make it strong enough in SLS Nylon. I have measured up the GH kit front setup and it has a track width of about 200mm. I modelled up a rough version of the kit front arm and them started a new set up as a double wishbone that will sit at about 235mm with the standard GH/Hornet front wheels. Got and arm and C hub roughed out

Getting the camber link to miss the shock is the next thing to solve, but I like this. It's not something I have done before on the Ultra conversions, and feels a bit more appropriate for an Evo version of the original. What do you think?

[MadAnt]

9 hours ago, ThunderDragonCy said:

As an aside I got a good look at my friends Hornet EVO last weekend, and I have to say I'm not massively impressed with the front end. The arms are nice, but it still has lots of bump steer and there were a couple of other details I didn't like, so I think I am going to go my own way with the front.

The front end does have a few flaws, but the fix for some of it is easy and I cover it on my Hornet EVO build thread. If you are going ahead with your own design, may I suggest have the front control arm shock mount be ramped in the front? From my experience running the evo and using the ampro design that little bit of support sticking out the bottom can catch on things in the ground. Having the front rounded or ramped forward could allow the control arm to slide over objects or obstacles rather than crashing into them.

[ThunderDragonCy]

Thanks for the feedback on actually using those arms. Good to know. I will re-read your thread.

[ThunderDragonCy]

Little bit of fit up and checking this afternoon. I got a motor fitted to the transmission. Although it's not the right lateral spacing, the bottom mount does fit in the Grasshopper swingaxle boss

 

As you can see, this is touching, which means some combinations of pinion won't fit ad the motor will move.

Issue two, floor height mismatch

With the trans mounted to the kit bosses with the floor parallel to the ground, it is about 4-5mm above the floor height of the tub. This does however help solve the next issue 

Having never had a Grasshopper before, I forgot the battery door slides, rather than flipping out like it doesitn the Grasshopper2. The mismatch in floor height does allow the door to slide out.

At this point I am a bit torn about what to do. I suspect will be able to build some combo of rear shock length length to get the ride height ok, but the mismatch does both me. I measured the distance from the swingaxle mount to the rear axle on the Grasshopper and it is 55mm. Same distance from mounting boss to axle on the thundershot trans is 60mm, so it's already longer. However, I want to make sure the motor clears and I would ideally like to drop the trans down a little. I think this is pointing me towards doing my own tub to trans mounts. A little more compact to avoid the motor, maybe 5mm further back so hopefully I can avoid the sliding battery door.

[MadAnt]

2 hours ago, ThunderDragonCy said:

little more compact to avoid the motor, maybe 5mm further back so hopefully I can avoid the sliding battery door.

If it works, go for it. If you want to shorten the wheelbase in the future maybe by a few millimeters, you could design some offset control arms or knuckles.

[Andreas W]

Would it be an idea to use a battery door with mount a'la Ampro,  which uses two bodyclips for locking? It's a way better solution than the OE anyway. 

[ThunderDragonCy]

1 hour ago, Andreas W said:

Would it be an idea to use a battery door with mount a'la Ampro,  which uses two bodyclips for locking? It's a way better solution than the OE anyway. 

I might do, but a whole battery door print will be quite pricey. I think I will see how it goes. However I do this the door will be tight on the transmission so maybe that will help.

[ThunderDragonCy]

Modelled up the side mounts and checked a few things and looked at the door again, and I think to avoid the door I need to leave the transmission high up as it is held by the stock grasshopper trans mounts. So, plan A is some extender bobbins to put on the ends of the Thundershot mount bosses to space them out to fit the Grasshopper parts. I will work about motor fitment later. I might end up with a 380 in this anyway. 

With that decided, when I hold up the transmission to the tub, one of the top surfaces comes very close to the underside of the old resistor mount on the tub, so drilling through and putting a screw and spacer here might be the first move towards mounting the transmission properly. 

I also did a rough model of the tub end to see about using the tub reset shock mounts as a further mounting point. I think this could work, bridging out to the rearmost trans mount bosses. Tired now, so turned the computer off, but I think there is the making of a solution here.

[ThunderDragonCy]

Bit more tonight on the front end. 

Tried doing a narrower version of the Ultra G EVO front end with schumacher gullwing arms and already uses grasshopper knuckles. Wasn't really working because I needed a very short camber link so I am not cutting the body. 

That being the case, I did something more based on original Ultra G because that works quite well with short arms and short camber link. Still not there because the long steering arm single central link steering system gives really bad bump steer with the Grasshopper knuckles. It's not a problem on Ultra G, but that uses modern sized wheels and DT03 front knuckles which make it work. The dt03 knuckles don't fit little Grasshopper front wheels. So, back to the drawing board. I think a shortish front arm will make the geometry good, but I need to go back to a double link and steering bar. That will give me a shorter link that should help the bumpsteer. 

It is amazing to me how hard this adaptation to the Grasshopper/Hornet has been compared to the GH2!

[MadAnt]

15 hours ago, ThunderDragonCy said:

It is amazing to me how hard this adaptation to the Grasshopper/Hornet has been compared to the GH2!

Hopefully it's satisfying when it's done, just keep pushing through.

[ThunderDragonCy]

Did another hour or so on this yesterday and I have come to the conclusion that I either need to cut off the tub towers and fit something else to use the yellow cva mini shocks from the Saint Dragon kit, or I need to ditch the yellow shocks, buy a Hornet evo front end and do that. Not sure.

Still quite taken with the idea of the yellow shocks as it's very 80s tamiya.

Thinking about something quite simple like the CRP mod from the 80s. Kinda like Wild One front towers that I would attach to the side of the tub. Maybe. Just can't seem to get a steering setup that doesn't give bumpsteer. 

[ThunderDragonCy]

Too hot for outside activities today, so I spent I nice few hours sorting this front suspension. 

I decided to go back to the front arms that mount like the kit arms that I started with, and another couple of ideas clicked into place.

 

Despite possible ground clearance issues i decided to go with the offset shock mount front arms and leave the front towers unmodified. I can use the mini cva shocks and although they bottom out before the tub hits the floor, it's not far off and no worse than Ultra G or Ultra Hornet. 

 

 

I managed to get the simple Ultra G style steering link working. Bumpsteer isn't completely eliminated, but it's pretty good. 

I modelled up the Grasshopper front arm and used that as some inspiration for some neater c hubs for the Grasshopper knuckles than I managed with Ultra G EVO, and I also used that geometry so the front wheels should be in almost same place as the Grasshopper to maintain the look and wheelbase as far as possible. 

Width is 230mm give or take a mm or two, so it's narrower than the Hornet EVO. As the rear end has come out around 245mm, should give it a nice stance. 

There is a hole through the inner pivot boss of the front arms so I can push a 3mm steel rod into it to reinforce that so hopefully should be robust enough. 

The c hubs are similar geometry around the pivots as a DT03 so I can use Hornet EVO or dt03 arms with a central mount is this doesn't work out.

Got some printing coming up for work so should be able to get these bits in the next few weeks.

 

[GTodd]

Bro your printing and 3modeling are next level!