# Tracked Vehicle - Lotus Tank based off a CV90



## Rusted B&B (Nov 6, 2020)

Sometimes you just have to start a dream project. I've tried in the past but really didn't know what I was doing and useing those times as a learning instance. So I finally bought a bunch of DOM tubing, parts and starting building and designing. after I felt I was ready I starting filming and building.

Basic info as of right now is:
-DOM frame
-Lexus gs450h electric motor
-differential steering
- seating for 4
-solar charging for 12v system and maybe HV

More to come as I hash things out and start building


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## brian_ (Feb 7, 2017)

In an electrically driven differential-steered vehicle, why would you use a single motor and some mechanical steering arrangement instead of just using separate motors for each track?


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## Rusted B&B (Nov 6, 2020)

brian_ said:


> In an electrically driven differential-steered vehicle, why would you use a single motor and some mechanical steering arrangement instead of just using separate motors for each track?


Comes down to funds. Not only would you need another motor, gearing, battery and even more battery. Im simply doing the best I can with what I have. I would love to use two but I simply dont have the funds for it


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## Rusted B&B (Nov 6, 2020)

Also it much more simple


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## brian_ (Feb 7, 2017)

Rusted B&B said:


> Comes down to funds. Not only would you need another motor, gearing, battery and even more battery.





Rusted B&B said:


> Also it much more simple


It would not take any more battery, since the same total power would be required. Yes, it would need two motors and two gearboxes, but unless you are building an exceptionally high-speed vehicle there is no need for the mechanical complexity of the GS450h transmission (or its dual internal motors and planetary power-splitter gearing) - simple fixed-ratio gear reducers (from almost any EV) would work. The two-motor approach would eliminate the mechanical complexity of whatever is being planned for differential steering. The biggest expense would be for two controllers and whatever would be used to coordinate them.

The simplest possible differentially steered electric powertrain is two motors, each with a fixed-ratio gearbox. It's how every child's toy and robotics hobbyist basic chassis that can turn on the spot works.



Rusted B&B said:


> Im simply doing the best I can with what I have. I would love to use two but I simply dont have the funds for it


I'm not sure I understand the logic of buying an inappropriate drive unit, then saying that choice prevents building a better design of vehicle, but I do understand making do with the stuff you have (even when it was selected for a very different vehicle). Enjoy the project!


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## Electric Land Cruiser (Dec 30, 2020)

Steering will be done by two disc brakes and a lever for each hand. He can probably build it for less than $100 from parts out of a junkyard. I approve of this build! KISS!


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## MattsAwesomeStuff (Aug 10, 2017)

I think the real answer here is "I'm doing what I want to because I want to", in which case, general advice is not necessary or useful, only specific troubleshooting.


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## Rusted B&B (Nov 6, 2020)

MattsAwesomeStuff said:


> I think the real answer here is "I'm doing what I want to because I want to", in which case, general advice is not necessary or useful, only specific troubleshooting.


yes and what I can do to achieve what I want to do - I love advice and would love to build this with someone but I have a tight budget and can only do what my skill capacity is. Thats why I love DIY forums like this because most these builds people are building what's in there head and it's just so cool! Plus I have a film degree and I'm finally putting it to use editing these video


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## Rusted B&B (Nov 6, 2020)

Electric Land Cruiser said:


> Steering will be done by two disc brakes and a lever for each hand. He can probably build it for less than $100 from parts out of a junkyard. I approve of this build! KISS!



It will actually have three disc brakes, one before the 4.1 LSD and one on each side. The sides will provide the Differitial steering provided by a steering wheel and thus turning as pressure is applied to the opposite side. I could go with clutches and torque vectoring but again thats not this project. The brake before the lsd will be the actual brakes and this is a simple design based off of rock crawlers and monster trucks , needing the least about of force to apply the great results. KISS if def what this is, and glad to have you along!


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## brian_ (Feb 7, 2017)

Rusted B&B said:


> It will actually have three disc brakes, one before the 4.1 LSD and one on each side. The sides will provide the Differitial steering provided by a steering wheel and thus turning as pressure is applied to the opposite side.
> ...
> The brake before the lsd will be the actual brakes and this is a simple design based off of rock crawlers and monster trucks...


That works, and for the steering portion is the system used by basic 6-wheel and 8-wheel ATV's (such as the Argo), but it's very crude.

If levers are actually used, there should be a system to keep both brakes from being applied at the same time when trying to just steer, because that would just waste power if used together. A wheel can be used instead of two levers (and tanks do routinely use a steering wheel); off-roaders routinely use a single lever rocking between two hydraulic cylinders (but they normally make the lever move forward and backward, which would be weird for steering). There would presumably also be a brake pedal for slowing down, which would work with either the separate driveshaft brake or with the same brakes as used for steering. This is a typical single-lever cutting brake control, from Wilwood:








Of course a version home-built from two clutch master cylinders and a random bar would be much cheaper, but the operating principle is the same. The pushrod for each cylinder goes slack when the other cylinder is pushed - it can't be arranged so that the lever pulls on the unused cylinder.

Braking even one track when not trying to slow down is a waste of energy, which is always an issue in an EV. A power-splitter gearset could be used on each output to reduce that, but that would be more complication again. The loss could be reduced by applying the retarding torque with generators and recycling the power to the drive motor, but that would mean creating two custom transmission systems, ironically each of the type which is sitting - unused - in that Toyota hybrid transmission.

But complications and efficiency aside, the worst part is that the brake-to-steer method doesn't even work well. Rock crawlers and monster trucks (and the tractors, etc. that they copied this system from) use differential braking (which they commonly call "cutting brakes") only to help in tight turns - they primarily use normally steered wheels. You might think that holding both brakes off (both levers forward or steering wheel straight) results in going straight ahead, but it doesn't; it just means completely uncontrolled direction. The differential ensures the each track gets approximately the same torque, but those tracks can run at any speed. It's like driving a car with rear wheel drive, an open diff, and no one holding on to the steering wheel: the vehicle wanders at the whim of any factors affecting or side forces, such as slopes, changes in the ground softness or material, or whatever. As a result, the driver has to continually tweak the steering brakes... almost like steering that car with two loose ropes connected to the steering wheel, which can't be used to hold the wheel still in any position because only one can be pulled at a time.

There are tracked vehicles which do use braking to turn and which go straight well, but in those (such as traditional bulldozers) there is no differential and pulling a lever (or pushing a pedal) opens a clutch for that side then brakes - that's more mechanical complication (although a differential isn't needed) and to provide a range of degrees of turning radius (or even the ability to rotate in place) a more complicated system of gearing is sometimes used.

Differential steering transmissions are a fascinating mechanical challenge, but in an EV they're all pointless, since the best solution is no mechanical connection between the sides at all. I do realize that this is about something that can be easily built at minimal cost, rather than something that works well, but I think expectations should be kept at a realistic level... and I hope it will never be expected to travel at significant speed.


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## Electric Land Cruiser (Dec 30, 2020)

@Rusted B&B stated that he is going to use a LSD, or limited-slip differential. That will eliminate most of the issues with direction control that you are talking about @brian_ and send equal torque to both sets of tracks.


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## Rusted B&B (Nov 6, 2020)

Electric Land Cruiser said:


> @Rusted B&B stated that he is going to use a LSD, or limited-slip differential. That will eliminate most of the issues with direction control that you are talking about @brian_ and send equal torque to both sets of tracks.


I have no idea why @brian_ is attacking my build so much, or me for that matter. but this has been done many times and I just wanted to share my ideas and you nailed it on the head. LSD eliminates these issue and is very reliable 

Like these guys








Bentley Continental GT On Tracks Is World's Most Luxurious Tank


A group of Russians has created a custom Bentley Continental GT that rides on tank treads. It should be able to go anywhere when the project is complete.




www.motor1.com


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## Electric Land Cruiser (Dec 30, 2020)

Yep, I recognized it as something that has been built many times before


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## brian_ (Feb 7, 2017)

Electric Land Cruiser said:


> @Rusted B&B stated that he is going to use a LSD, or limited-slip differential. That will eliminate most of the issues with direction control that you are talking about @brian_ and send equal torque to both sets of tracks.


Good catch - I had skipped past the limited slip diff, which is exactly the opposite of what will work well. The nature of the problem will depend on the type of LSD:

with a worm gear type (Torsen, Quaife) LSD, when the driver attempts to steer by braking one track so it turns more slowly, the LSD will respond by fighting that, applying more torque to the slower-turning track
with a clutch-pack LSD that squeezes the clutch packs in response to drive torque, the LSD will make the vehicle harder to turn when more power is applied; yes, in a straight line full power would be most stable (but still not really straight), but it will become unstable as soon as power is reduced
a Detroit Locker is more extreme: it will completely prevent any steering above some level of applied torque, and revert to simply open below that level
In fact, an open diff is the only type which will actually send equal torque to both tracks. The entire purpose of any limited-slip diff is to apply unequal torque in an attempt to get more equal speed, reducing the tendency of one wheel to spin (otherwise known as "turning").

If any LSD is used, the worm gear type is likely the most desirable, because it reacts to output speeds speeds (which is what you want to control) rather than drive torque (which is unrelated to the need for directional stability).

The Russian project in the YouTube video uses an open diff, according to the captions in the linked episode; they also say "That's not quite correct, but we will try to use on drive tests", and in that episode nothing is operating. There are a lot of videos of it running, but I don't know if any explain what was wrong with the original plan. In the "first run" video it does go down the nice smooth road at up to 50 km/h, wandering all over it while the driver saws away at the steering wheel... with an unknown type of differential. This vehicle apparently does get driven a lot, but judging from these two videos there is likely no useful technical information ever shared.


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## Electric Land Cruiser (Dec 30, 2020)

brian_ said:


> Good catch - I had skipped past the limited slip diff, which is exactly the opposite of what will work well. The nature of the problem will depend on the type of LSD:
> 
> with a gear-type (Torsen, Quaife) LSD, when the driver attempts to steer by braking one track so it turns more slowly, the LSD will respond by fighting that, applying more torque to the slower-turning track


This is the type of LSD he is using, my guess, but your interpretation is wrong. Differentials are designed to differentiate, first. Torsen is short for Torque-Sensing and the geometry of the differential gears allows to diff to differentiate when there is a great difference in speed between two sides of the diff, like for instance a racecar coming out of a tight hairpin bend or a tank skid-steering. But when there is a smaller difference in speed between both sides, then it starts to lock up, like for instance a hard acceleration run where both rear tires are struggling for traction. If it worked like you say then out of the hairpin corner the racecar would have the inside tire spin up in a smokeshow, which is actually what happens in an open differential.


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## brian_ (Feb 7, 2017)

Rusted B&B said:


> I have no idea why @brian_ is attacking my build so much, or me for that matter.


I'm not attacking anyone. It's a discussion of a vehicle design... but apparently you don't want that. Video blog away, and again, enjoy your project.


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## brian_ (Feb 7, 2017)

Electric Land Cruiser said:


> This is the type of LSD he is using, my guess, but your interpretation is wrong. Differentials are designed to differentiate, first. Torsen is short for Torque-Sensing and the geometry of the differential gears allows to diff to differentiate when there is a great difference in speed between two sides of the diff, like for instance a racecar coming out of a tight hairpin bend or a tank skid-steering. But when there is a smaller difference in speed between both sides, then it starts to lock up, like for instance a hard acceleration run where both rear tires are struggling for traction.


The marketing name is cute, but a Torsen doesn't sense torque at all. Quaife probably sells more of these things in the aftermarket than JTEKT (the current owner of the Torsen name and design), and Quaife calls it their Automatic Torque Biasing (ATB) limited slip differential - torque bias is the output, torque isn't the input. By connecting the output sides through a nearly one-way gear drive (that's why the worm gears in some versions), it only allows the slower-turning output to receive more torque; it is effectively speed-sensing, rather than torque-sensing. Torsen documentation refers to the Torque Bias Ratio, and that's the result of the gear action, not the input to it. The side which turns faster transfers torque to the slower-turning side, as in any reasonable LSD.



Electric Land Cruiser said:


> If it worked like you say then out of the hairpin corner the racecar would have the inside tire spin up in a smokeshow, which is actually what happens in an open differential.


The scenario of the inside tire spinning wildly doesn't occur with a Torsen because as soon as it is the faster-turning tire it gets less torque. An open differential puts the same torque to both outputs, so when one has less load and thus less traction - typically the inside tire in a turn but also the tire on a patch with less traction or the tire with less load on it or even lifting due to uneven ground - it continues to get the same torque as the other side and slips.

But as I said, a LSD will make the vehicle harder to turn, which is indeed directional stability... just stability that the driver has to fight.


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## Electric Land Cruiser (Dec 30, 2020)

Well, yes, torque will increase on the braked side but speed will decrease and as it comes to a stop the diff will fully open like an open diff. Luckily with a disc brake there will be more than enough mechanical advantage to overcome the torque. Maybe you've just started thinking about a vehicle like this today, but a recreational tank like this not a new concept and is a common build for gearheads all over the world using this tried and tested formula.


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## Rusted B&B (Nov 6, 2020)

Electric Land Cruiser said:


> Well, yes, torque will increase on the braked side but speed will decrease and as it comes to a stop the diff will fully open like an open diff. Luckily with a disc brake there will be more than enough mechanical advantage to overcome the torque. Maybe you've just started thinking about a vehicle like this today, but a recreational tank like this not a new concept and is a common build for gearheads all over the world using this tried and tested formula.


been done for decades and it's going to be a fun concept build - solar charging, carbonfiber, EV, moving turret - and all around foolery


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## Rusted B&B (Nov 6, 2020)

well here we go


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## Rusted B&B (Nov 6, 2020)

Just a slight update on where things are.


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## Rusted B&B (Nov 6, 2020)

Made some really good progress last night into the wee hours - also got the latest code uplaoded!









In other news I order a pedal and got this one by mistake by an ebay seller - got a refund and a free new pedal but I can't find the pin out on it. If anybody know it that would awesome!


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## schelle63 (Jan 3, 2018)

Someone told me that is is a redundant potentiometer, so this might be the answer.

On th other Hand, I also found this in the net (which probably is from another type of pedal, since there are pins # 7 and 8):









And finally here ist the (HELLA!)- pedal in my car (based on a Th!nk from Norway):








Please note that in this original wiring diagram there is one pin missing (cannot tell which one: #1 or #6), which needs to be connected to ground. The connections # 52, 7, 45, and 30 are at the controller.

Hope this does help.
Markus


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## schelle63 (Jan 3, 2018)

Will need to look at the car to find out which pin is connected to ground.


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## Rusted B&B (Nov 6, 2020)

schelle63 said:


> Will need to look at the car to find out which pin is connected to ground.


Thank you - very good info!


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## Rusted B&B (Nov 6, 2020)

Just more fabrication work getting done! In the back ground I have about 85% of the lexus wired up - will be testing that soon!


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## Rusted B&B (Nov 6, 2020)

So I've been playing with the idea of just locking the diff and putting a clutch on each side of it but I can't seem to find a stand alone clutch. That or my google skills are lacking. I looked at electronic clutches but that is not really what I need as I need it to ease in and out not just lock. I was debating of taking a regular clutch and the fabricating a housing and the clutch inside with an output and input. It shouldn't be too hard would just be a little pricy to get cnc'ed. I also thought about just getting two manual transmission cutting them up but that seems like to much a hack job for what I need.


If anyone know anything that would be amazing!


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## wjbitner (Apr 5, 2010)

Rusted B&B said:


> So I've been playing with the idea of just locking the diff and putting a clutch on each side of it but I can't seem to find a stand alone clutch. That or my google skills are lacking. I looked at electronic clutches but that is not really what I need as I need it to ease in and out not just lock. I was debating of taking a regular clutch and the fabricating a housing and the clutch inside with an output and input. It shouldn't be too hard would just be a little pricy to get cnc'ed. I also thought about just getting two manual transmission cutting them up but that seems like to much a hack job for what I need.
> 
> 
> If anyone know anything that would be amazing!


That's why it might make sense to go with 2 motors! lol You'll pay one way or another. That said, I'd go with the manual transmission route, since you are clearly good at fabrication. 
Bill


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## Rusted B&B (Nov 6, 2020)

wjbitner said:


> That's why it might make sense to go with 2 motors! lol You'll pay one way or another. That said, I'd go with the manual transmission route, since you are clearly good at fabrication.
> Bill


Yeah I've been playing with a ton of ideas with this guy as I work on it and how to save space in the actual tank and make it comfy for 4 people. My latest "idea" is have have the motor run a hydraulic pump system and run a articulated trailer in that it will hold the HV batteries and extra storage. I like this idea, as it makes running each track, turret, trailer all off a couple pumps. The only thing I'd be worried about is speed. I'm only shooting for 25mph but I'm not sure a hydraulic pump can reach that.
It will also add a level of safety if there is ever an issue with the HV battery when you stuck inside the tank. I got the idea after stumbling across a bunch of articulated tracked utv's. That or actually just run the GS450H motor in the trailer and a driveshaft through the articulation and an open diff brake system. Still plenty of time to figure it out but it's def been a blast learning all this stuff


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## Rusted B&B (Nov 6, 2020)

Just more progress - whether it's forward or backwards it's still a learning experience


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## MattsAwesomeStuff (Aug 10, 2017)

Ouch, rough man. (For those that didn't watch, he spent $1300 on 8 custom CNC'd swing arms, but forgot that there is a left and right side and the parts can't be clones, they have to be mirrored. So 4 of them will work, and he needs to order a mirrored set for the opposite side).

I get that you want to use up everything you paid for, and add more so you use 6 of them so there's only 2 "wasted", but... now instead of ordering 4 new mirrored ones, you have to order 6 new mirrored ones. This just directly adds to your mistake. You're buying 6 instead of 4. Even if you'll have 4 wasted, you'll still have minimized the cost of your error if you stick with 4 like you originally planned.

I'd say that since the design just needs to be mirrored, that perhaps the CNC shop would be willing to give you a deal, since the CAM and fixturing work should be fairly minimal on a mirrored part. Also, they may have some sympathy that you fucked up, and decide that unless they're booked 24/7, to run them for you at significant discount in their downtime.

Another thing too late to consider... aluminum never hits a fatigue limit. Unlike steel, it fatigues and degrades forever. It might not have been a good choice for a swingarm in suspension parts on something you want to use more than just as an occasional demo. It's carrying the weight of a tank and getting beat up and bashed around and taking the force of running the machine. It's definitely going to be stress cycled to failure, it's just a matter of, to what degree and how quickly.


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## Rusted B&B (Nov 6, 2020)

MattsAwesomeStuff said:


> Ouch, rough man. (For those that didn't watch, he spent $1300 on 8 custom CNC'd swing arms, but forgot that there is a left and right side and the parts can't be clones, they have to be mirrored. So 4 of them will work, and he needs to order a mirrored set for the opposite side).
> 
> I get that you want to use up everything you paid for, and add more so you use 6 of them so there's only 2 "wasted", but... now instead of ordering 4 new mirrored ones, you have to order 6 new mirrored ones. This just directly adds to your mistake. You're buying 6 instead of 4. Even if you'll have 4 wasted, you'll still have minimized the cost of your error if you stick with 4 like you originally planned.
> 
> ...


Yeah I talked with the shop and they are giving me a discount on the next time I order and whether I get 4 or 6 it will be the same price - once I hit a threshold on price it just caps instead of getting higher. I'm ok with the aluminum - it will last a very long time with it being so thick and with it being most likely powder coated it will protect it from the elements. Plus almost all swing arms - a arms and suspension parts are made from aluminum today. I have a 12 year old motorcycle with aluminum parts and still going strong.

Plus this isn't a daily driver or anything - more like a concept vehicle, which in a sense it is. I really just want to build a tank, and need a project to work on that satisfies the itch to work with my hands. Heck I've even seen a baja truck with really long swing arms out of cnc'ed aluminum. I really like pushing myself to do things I've never done before and somethings I get it right - sometimes not so much. Thanks a lot for the help and I will keep these ideas in my mind as I think about everything!


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## galderdi (Nov 17, 2015)

Sorry I know the conversation has moved on since discussing the steering using individual brakes. But I made this unit from two hydro handbrakes. It works very well. Each cylinder operates one of the back brakes. Pushing the lever forward turns right, pulling back turns left.


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## Rusted B&B (Nov 6, 2020)

galderdi said:


> Sorry I know the conversation has moved on since discussing the steering using individual brakes. But I made this unit from two hydro handbrakes. It works very well. Each cylinder operates one of the back brakes. Pushing the lever forward turns right, pulling back turns left.
> 
> 
> 
> View attachment 123221


That is very cool! See this is why I love the community - so many amazing ideas and smart people.


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## Rusted B&B (Nov 6, 2020)

Just more frame work and chilling out


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## Rusted B&B (Nov 6, 2020)

Just more and more fab work! Getting closer to the guts of this beast.


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## Rusted B&B (Nov 6, 2020)

I FINALLY found the pinout of the pedal but now I can't find the connector- go figure


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## Rusted B&B (Nov 6, 2020)

Soooooo - I have have spent many many hours trying to figure out my inverter and think I may have a dead unit  its very frustrating and annoying. I like 99.999999% sure my wiring is correct as I have gone over it 4 times. While there still might be something I don't see that's wrong, I don't think that's it. To the point that I have bought another wire harness and making a new one, taking a stupid amount of time building it.

first thing I did was apply voltage to everything 12-13v to the VCU and invertor where it's needed and 66V to the inverter


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## Rusted B&B (Nov 6, 2020)

Next thing I did was hook up the VCU to see what was going on

set the throttle









Set it to drive - I also check to see if I could switch to reverse and I could.









Then I check the info and tried to get it to spin and NOTHING!?!?!?!?!?!?


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## Rusted B&B (Nov 6, 2020)

At this point I have tried everything I can think of - I'm just getting nothing. I'm going to try and build the new wire harness and try that but I'm not sure thats going to help other then making thins much cleaner and less wires everywhere.


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