Electric Conversion Pinions etc advice? Ideas?

[Jools 0]

Here's my conversion project. I'd appreciate any input guys...

Hard-starter Force 15 gas engine removed and my installation of an Astro 05 FAI motor ('classic' beautifully engineered cobalt motor - it's a 5 turn, 3214 revs/volt).

Q: Pinions. I've assumed that I need to use a motor pinion to approximate the driveshaft gear revs, accounting for the difference in motor revs as follows:

Gas Motor revs 30,000. Motor pinion was 14 tooth, Mainshaft drive pinion is 42 tooth = 3:1 ratio

Astro Motor revs 17,500. Motor pinion (my conversion) 29 tooth, Mainshaft drive pinion 42 tooth = 1.44:1 ratio

Luckily I found this 29 tooth nylon pinion in a junk shop and I've turned up an adaptor to fit it to the Astro shaft. (I realise that nylon is not ideal, but it'll work as a test, and has the advantage of having two pinions on it so I can experiment with gearing by shifting the motor mount). I know the ratios/revs sum isn't precise but it seems close enough to me for a first test.

Does this all seem ballpark?

In case the nylon pinion doesn't cut it, or that I need a different sized motor pinion, does anyone know a good source of alloy pinions in various sizes?

Cheers

Jools

[speedy_w_beans 4272]

Check out Robinson Racing for pinion gears: http://www.robinsonracing.com/.

Since this was a gas car to start, I'm guessing it used 32 pitch gears? Here's Robinson's page on 32 pitch pinions: http://www.robinsonracing.com/catalog/32pitchpinion.html.

-Paul

[Backlash 481]

Hi Jools,

Great project you have there..

In regard to your gear ratio equasion that you are using... I feel that this would work fine as long as the electric motor has the same output power rating (HP) that the old .15 gas motor had, but I doubt that the electric motor will be as powerful as the gas motor.. Maybe I'm wrong, I'm not familiar with those Cobalt motors..

You may also want to consider redesigning a new top deck, and relocating the steering servo onto the main chassis in front of the motor to make room for your battery on the opposite side of the chassis to the motor.... You may as well discard the throttle/brake servo and brake parts, as this will no longer be required as all of your braking will now be done via the electric motor..

Goodluck

[Jools 0]

Thanks guys. Speedy, good link for pinions, ta, I'll be using that.

Backlash, useful input. The Astro is a pretty hot motor, a 5 turn, can handle at least 50 amps (check those big external brush holders). But you're right, it probably won't put out 0.7 hp as the gas motor, - prob more like 350 -450w which I guess is more like 0.5 -0.6 hp. Still it'll run it and once I get a feel for how it goes I can re-gear to optimise.

Good tips re: revised top deck / general arrangement. I may end up doing this, but in the meantime I'm moulding a 'truggie' style body for it which has enough height at the back for the battpack.

BTW I'm a new member so don't have much idea of the forum 'history', - I haven't seen much/any info on moulding a body. Do you think it would be useful for me to do an instructional thread on styling, shaping, and making a moulded fibreglass body?

(I have a ton of experience creating aircraft, including big gas turbine models).

-Jools

[TA-Mark 195]

Most nitro powered 1:10s and 1:8s use 1.0MOD sized gearing. These are available for nitro to electric conversions, but are usually available as a 5mm bore only. Avoid aluminium pinions/gears and use steel or hardened steel gears.

No idea on the Cobalt motor to know what gearing to use.

The conversion I did was on a 1:10 HPI MT2 by using a Castle MambaMax 5700Kv running on 3S2P Li-Po (~60,000rpm). I needed to use the largest spur gear and smaller pinion than was used on the nitro engine. It flies! Much faster than the Force 15 that was fitted to it with a longer runtime than the 75cc fuel tank.

If I were doing the same conversion today I would use the larger 1:8 brushless systems (MambaMax Monster) with larger 1:8 2,200Kv motor and 4S Li-Po (~32,000rpm) with a similar gearing to the nitro engine. If this can power the heavier 1:8 Savage monster truck well, then it'd be just pure nuts in a 1:10 4WD stadium truck.

[speedy_w_beans 4272]

I'm interested in what you have to share for making bodies; there was another thread in the vintage section where the person was thinking about making bodies and polled everyone for ideas. How thick and heavy would a fiberglass body be? How much detail could it include? At a minimum making some internal top covers for rally car conversions would be on my list of things to do... So if you have a good, repeatable process to share with everyone, definitely make a new thread on this!

-Paul

[kaiser 8]

that astro flight cobalt is a nice peice of history, can i talk you into using a different motor?

i don't think it will like being in a truck at all. we used them on dirt and paved oval cars with much less weight and drag.

[Jools 0]

I don't expect this car to be a rocket. The idea came about just because I had the components to hand, -needed a project, and have minimal dough to spend.

It could well end up with a hot can or good brushless setup, but for now the Astro will do. Once I get the ESC from zac (cheers mate) I'll know what its potential is, (and I can ram more electrons into if necessary).

With some minor adaptation of the steering servo mounting I've been able to tuck the battery pack towards the rear LHS between the decks so c of g will be lower, much better.

I'll do a body body moulding thread so people can see the 'lost-foam' method of fibreglass moulding.

[Jools 0]

Well I've got this device running. Just an initial test, but it seems to be really rather good. It's fast, and only running 6 cells at the moment (I don't think 7 cells will be needed). Gearing seems about right, but my homemade shaft adaptor is not quite up to the job, so now I know the thing works I'll order a steel pinion from Robinsons. Only problem driving it is avoiding doing doughnuts! -Previous owner had removed the front drive components so it's rear wheel drive only. Fun but!!! Cost so far around $30. Like that! Once I get all the installations rigged I'll post a pic.

(If anyone has parts for these cars to spare let me know, it really needs the Front WD components -front driveshaft, front diff gears, front wheel driveshafts etc) .

Now, I'm a masochist (with another nice virgin motor waiting to be deflowered), so I'm planning another conversion of another Great Vigor gas car that came as a box of bits. I've got the major components but I do need various parts for it (see my Great Vigor wanted ad). Thanks for your input guys.

Jools

[stu22 12]

Ofna makes 3mm-to-5mm pinion adapters for their Hyper10/Jammin SCRT platforms.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZAG6

[Jools 0]

Good tip Stu, thanks. The Astro shaft is 5/32" though, so I guess the best option will be to get a Robinson pinion and drill it out to fit.

[Jools 0]

Just an update on this conversion. I had started with a 29 tooth motor pinion (which seemed about right to match the revs of the original nitro motor) because I had one available. I've now fitted a 20 tooth, which works better with the lower gearing, - not so fast, but better on the rough ground this thing has to run on. The ESC and motor are running cooler as well. Thanks to the generosity of another member I've been able to fit the Front drive components, which means at least I can now (more or less) control the donuts! I had to shorten the front drive dogbones, simply using K&S brass tubing sleeved over and soft soldered over the trimmed shafts. The Astro 05 FAI motor is a '*******er' as we say up here! I just machined a tight fitting brass plug for the 5mm hole in the pinion, loctited it in and then drilled it to 5/32 to fit the Astro shaft. Easy.

I might even put some oil in the shocks... that might help eh?

(Not to everyone's taste I'm sure, but I made a 'quickie' aluminium body for it inspired by the cars that run the annual Myrniong sprint hillclimbs up here in the Wombat Forest).

-Jools

[Percymon 2184]

Nice work.

This was always going to be a runner/basher project and no showpiece, although i do like the body

Get some oil in the shocks - something around 35wt is probably a good starting point.

[Sayer 742]

...Do you think it would be useful for me to do an instructional thread on styling, shaping, and making a moulded fibreglass body?...

Oh God, yes.

[Jools 0]

Oh God, yes.

Your wish is my command mate! -See moulding thread.

-Jools

[Jools 0]

Update: Alex kindly donated a set of long travel shockers, (and they've got damping!!!) -these, with some modification of the chassis plate has given me a whole 10mm more ground clearance and 25mm more suspension travel.

Great improvement as you can imagine. I now need a set of larger diameter tyres (with some tread would help!), I think that it's starting to become a bit of a weapon.

The one thing I need to sort next apart from the tyres is the weight. I'll be making a Carbon Fibre chassis plate for it, (an interesting idea here), and then slicing a little mass off various components.

I'll probably make a new fibreglass body too. The Astro motor is an absolute killer! Thanks for your encouragement guys.

-Jools